HomeMy WebLinkAboutAppendix F Stormwater Drainage Report
COTTON WOO D & IDA MIXED USED DEV ELOPMENT
LOT S 5-28 , BLOCK 105 OF NORTHERN PACIFIC ADD ITION
COMPREHENSIVE DRAINAGE REPORT
BOZEMAN , MONTANA
CERTIFICATION
I hereby state that this Final Drainage Report has been prepared by me or under my supervision and
meets the standard of care and expertise which is usual and customary in this community of
professional engineers. The analysis has been prepared utilizing procedures and practices specified by
the City of Billings and within the standard accepted practices.
____________________________________________ ___________________________
Mike Russell, P.E. Date
4/18/2019
April 18, 2019
Project No. 18061.02
STORMWATER MANAGEMENT DESIGN REPORT
FOR
COTTONWOOD & IDA MIXED USE DEVELOPMENT
BOZEMAN, MONTANA
OVERVIEW NARRATIVE
The purpose of this drainage plan is to quantify storm drainage improvements required for the
Cottonwood & Ida Mixed Use Development. The site is located bounded by the future Aspen Street
to the north, Ida Avenue to the east, Cottonwood Street to the south, and existing businesses
directly adjacent to the west. The site, which occupies the majority of the block described above, will
consist of five new buildings along with the renovation of one existing building, as well as a partial
sub-surface parking structure in the northern portion of the site. The site totals approximately 2.07
acres and has historically had a commercial use with various on-site improvements in hardscaped
surfaces, paving, concrete, and rooftop extant throughout the site. The proposed project will
disturb or otherwise improve the entirety of the 2.07 acres with the nominal exception of the
existing building which will remain. Additional off-site infrastructure improvements will be made in
conjunction with this proposed project but those improvements are beyond the scope of this storm
drainage report.
Generally, the stormwater runoff impacts within the project’s private property limits will be
mitigated through a series of on-site subsurface drainage facilities which will be discharged into the
(future) storm drain infrastructure within the Aspen Street right-of-way at an allowable controlled
rate.
This report presents a summary of calculations performed to quantify the stormwater runoff from
the improved site. All design criteria and calculations are in accordance with The City of Bozeman
Design Standards and Specifications Policy , dated March 2004. The site stormwater improvements have
been designed with the intent to meet the current City of Bozeman drainage regulations for the
entire site to the extent feasible.
Specific site information and criteria are described below:
P:06020.04_C&I_CDP_041819 2 (04/18/19) JAZ
1. Development Location
a. Address: The current physical addresses for the proposed building is 720 North Ida
Avenue, Bozeman, MT 59715, respectively. The new development has not been
readdressed yet.
b. Legal Description: The site is located on Lots 5-28, Block 105 of the Northern
Pacific Addition, Bozeman, MT 59715
2. Areas (AC)
c. Total Disturbed Area: The development will consist of constructing the utilities
and surface improvements on 2.07 acres, or 90,169 square feet. To be conservative,
the existing site will be considered greenfield for pre-development.
d. Existing Impervious Area: Based on the parameters listed above, the existing site
exhibits the following qualities (again, assuming greenfield conditions for pre-
development):
Impervious Area (Gravel) – 0.012 acres
Impervious Area (Rooftop) – 0.349 acres
Impervious Area (Concrete) – 0.469 acres
Pervious Area (Grass, Open Field) – 1.177 acres
Impervious Area (Asphalt) – 0.063 acres
Total area = ~2.07 acres
e. Post-Development Impervious Area: As a result of the new storage lot
development, the site will exhibit the following qualities:
Impervious Area (Gravel) – 0 acres
Impervious Area (Rooftop) – 0.933 acres
Impervious Area (Concrete) – 0.908 acres
Pervious Area (Landscaping) – 0.092 acres
Impervious Area (Asphalt) – 0.138 acres
Total area = ~2.07 acres
3. Type of Development
The proposed Cottonwood and Ida site includes 5 new building with an underground
parking garage, curb and gutter, concrete flatwork, storm drain facilities, utilities, and
landscaping. The stormwater system will consist of an underground Stormtech chamber
storage system (or approved equivalent product from other vendor), and the chamber
system will be connected via a series of pipes and area inlets. Stormwater runoff from
Buildings 6, 1, and 2 along with additional runoff between those three buildings will be
captured via roof drain systems and area inlets that are connected into the podium storm
drain system. The podium storm drain system will ultimately be routed to one or two
P:06020.04_C&I_CDP_041819 3 (04/18/19) JAZ
separate locations where they will be picked up and conveyed to the chamber storage system
via the storm drain system found external to the podium.
4. Off-site Discharge Point
There will be an off-site discharge point for this site through a 15-inch pipe that is connected
to the City storm drain system in Aspen Street, that will be newly constructed along with the
off-site infrastructure improvements. Discharge will be restricted to the 2-year pre-developed
rate of 0.17 ft 3/second by a 1-inch circular orifice.
5. Hydrologic Criteria
Description of Runoff Method Used: Because the site is less than five (5) acres, the
Rational Method was used to estimate the total direct runoff of the site. The stormwater
detention facilities for this project are sized to contain the water quality storm and the 10-
year storm event.
CALCULATIONS
6. Hydrology Calculations
As mentioned above, the Rational Method was used to determine the runoff volume for the
site. All calculations have been provided in the appendices of this report and are referenced
within the Storm Drain plan sheet for convenience of review.
7. Culvert and Pipe System Capacities and Outlet Velocities
All on-site conveyance pipes are designed to handle the flow rates expected from the
contributing area based on a 25-year design storm.
8. Ditch Capacities and Velocities
No new ditches are proposed for this site. No existing ditches currently exist on-site.
9. Required BMP’s Capacities, Flow Rates, and Operating Levels
The stormwater management facilities for this project consist of an underground detention
facility in the form of a chamber system, and storm drain area/curb inlets. The stormwater
system on site was designed using the online ADS Stormtech Design Tool. The detention
volume determined by the Rational Method was used to ensure that the length and width of
the design tool was larger than the required volume from the spreadsheet. The required
storage for the site based on a 10-year, 2-hour storm event is 4,700 ft 3, and the chamber
system was design with a capacity of 7,000 ft3 so sufficient storage is provided on site. The
rational method was used to calculate stormwater quantities, so the storage provided is
conservative and meets the City requirements. The chamber system allows for infiltration of
the stormwater, but this was not considered in the volume calculations.
P:06020.04_C&I_CDP_041819 4 (04/18/19) JAZ
An isolation row is provided in the chamber system to collect and confine sediment and
provides an access for the maintenance and removal of said sediments from the storm drain
system. This isolation row acts as water quality treatment for the first 0.5-inch of rainfall
from a 24-hour storm.
The following presents the design for the 10-year storm for the Site:
Water Quantity Storage Required = 4,700 CF
Water Quantity Storage Provided = 7,000 CF
The following presents the design for the stormwater storage drawdown time:
The chamber system will discharge via the 2.25-inch orifice at a rate of 1.34 ft 3/second.
Total Drawdown Time = 7,000CF / 0.17CFS / 60MIN/HR / 60S/MIN = 11.44HR
The chamber system will drain in less than the required 48 hours.
10. Geotechnical Report
The geotechnical report has been included in the appendices of this report.
APPENDICES
1. Hydrology Calculations
2. Geotechnical Report
3. Floodplain Maps
There are no known flood plains in this area.
4. Topographic Map of Pre-Developed and Finished Grade Contours at 2-Foot Max
Intervals
Topographic intervals are shown on the attached site drawings.
5. Drainage Plan
The drainage plan with required information is included in the attached plan set.
6. Construction Stormwater Pollution and Prevention Plan and Permit
The Stormwater Pollution and Prevention Plan and Permit (SWPPP) and Notice of Intent
(NOI) shall be submitted to the City of Bozeman and the Montana Department of
Environment Quality, by the Contractor prior to construction activities, for review.
Project: Cottonwood Ida Mixed Use Development
Project #: 0604.02
Date: 1/9/2019
Design Storm Frequency =10 years
Discharge Rate, d =0.00 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
Value
A A/(43560 ft2/acre)C Cf C x Cf C' C' x A
(ft2)(Acres)=(C x Cf) < or = 1 (Acres)
0 0.000 0.7 1 0.70 0.70 0.000
0 0.000 0.95 1 0.95 0.95 0.000
0 0.000 0.95 1 0.95 0.95 0.000
90169 2.070 0.2 1 0.20 0.20 0.414
0 0.000 0.95 1 0.95 0.95 0.000
90169 2.07 0.414
Weighted Runoff Coefficient, Cwd SCjAj
SAj
Cwd x Cf x SAj =0.41
Where Cj is the adjusted runoff coefficient for surface type j
and Aj is the area of surface type j
Rainfall Rainfall Peak Flow
Duration, t Intensity, i = Cwd x SAj x i
(min) (in/hr)(ft3/s)
1 9.16 3.79
5 3.22 1.33
10 2.05 0.85
15 1.58 0.65
20 1.31 0.54
25 1.13 0.47
30 1.00 0.42
35 0.91 0.38
40 0.83 0.34
45 0.77 0.32
50 0.72 0.30
55 0.68 0.28
60 0.64 0.26
75 0.55 0.23
90 0.49 0.20
105 0.44 0.18
120 0.41 0.17
150 0.35 0.15
180 0.31 0.13
360 0.20 0.08
720 0.13 0.05
1440 0.08
1,215.75 ft3 0.17 (ft3/s)
2276.13 0.00 2276.13
2901.06 0.00 2901.06
1401.12 0.00 1401.12
1785.81 0.00 1785.81
1215.75 0.00 1215.75
1314.50 0.00 1314.50
1099.30 0.00 1099.30
1160.24 0.00 1160.24
953.86 0.00 953.86
1031.34 0.00 1031.34
894.89 0.00 894.89
925.25 0.00 925.25
827.66 0.00 827.66
862.49 0.00 862.49
748.38 0.00 748.38
789.87 0.00 789.87
649.37 0.00 649.37
702.12 0.00 702.12
509.48 0.00 509.48
587.17 0.00 587.17
227.58 0.00 227.58
399.73 0.00 399.73
= Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
(ft3) (ft3) (ft3)
= 0.2000 Cwd x Cf =0.20
Runoff Volume Discharge Volume Site Detention
=
Rooftop
Concrete
Open Land (assumed greenfield)
Asphalt
Totals
Gravel
RATIONAL METHOD FOR RUNOFF CALCULATIONS
Pre-Development Runoff Volume (for on-site drainage)
Surface Type
=
Project: Cottonwood Ida Mixed Use Development
Project #: 0604.02
Date: 1/9/2019
Design Storm Frequency =10 years
Allowable Discharge Rate, d =0.17 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
Value
A A/(43560 ft2/acre)C Cf C x Cf C' C' x A
(ft2)(Acres)=(C x Cf) < or = 1 (Acres)
0 0.000 0.7 1 0.70 0.70 0.000
39541 0.933 0.95 1 0.95 0.95 0.886
39541 0.908 0.95 1 0.95 0.95 0.862
4000 0.092 0.25 1 0.25 0.25 0.023
6000 0.138 0.95 1 0.95 0.95 0.131
89082 2.0700 1.9022
Weighted Runoff Coefficient, Cwd SCjAj
SAj
Cwd x Cf x SAj =1.90
Where Cj is the adjusted runoff coefficient for surface type j
and Aj is the area of surface type j
Rainfall Rainfall Peak Flow
Duration, t Intensity, i = Cwd x SAj x i
(min) (in/hr)(ft3/s)
1 9.16 17.43
5 3.22 6.12
10 2.05 3.90
15 1.58 3.00
20 1.31 2.49
25 1.13 2.15
30 1.00 1.91
35 0.91 1.73
40 0.83 1.58
45 0.77 1.47
50 0.72 1.37
55 0.68 1.29
60 0.64 1.22
75 0.55 1.05
90 0.49 0.94
105 0.44 0.85
120 0.41 0.78
150 0.35 0.67
180 0.31 0.60
360 0.20 0.38
720 0.13 0.24
1440 0.08 0.15
4,614.15 ft3 6.12 (ft3/s)
10458.20 7294.48 3163.71
13329.61 14588.97 -----
6437.78 1823.62 4614.15
8205.34 3647.24 4558.09
5586.04 1215.75 4370.29
6039.80 1519.68 4520.11
5050.98 911.81 4139.17
5330.98 1063.78 4267.20
4382.72 607.87 3774.84
4738.73 759.84 3978.89
4111.78 506.56 3605.22
4251.26 557.22 3694.04
3802.87 405.25 3397.62
3962.92 455.91 3507.01
3438.61 303.94 3134.67
3629.23 354.59 3274.64
2983.67 202.62 2781.05
3226.04 253.28 2972.76
2340.94 101.31 2239.63
2697.88 151.97 2545.91
1045.66 10.13 1035.53
1836.67 50.66 1786.01
= Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
(ft3) (ft3) (ft3)
= 0.9189 Cwd x Cf =0.92
Runoff Volume Discharge Volume Site Detention
=
Rooftop
Concrete
Grass, Landscaping, Field
Asphalt
Totals
Gravel
RATIONAL METHOD FOR RUNOFF CALCULATIONS
Post-Development Increase in Impervious Cover (for on-site improvements)
Surface Type
=
TABLE I-1: Runoff Coefficients for Use in the Rational Method
LAND USE RUNOFF COEFFICIENTS, C
Open Land 0.2
Low to Medium Density Residential 0.35
Dense Residential 0.5
Commercial Neighborhood 0.6
Commercial Downtown 0.8
Industrial 0.8
Design Standards and Specifications Policy
City of Bozeman, March 2004 as Amended
RAINFALL INTENSITY-DURATION CURVES (Figures I-2, I-3)
Time 2 5 10 25 50 100
(min)(in/hr)(in/hr)(in/hr)(in/hr)(in/hr)(in/hr)
1 4.20 7.15 9.16 10.72 13.72 15.69
5 1.60 2.55 3.22 3.83 4.74 5.34
10 1.05 1.64 2.05 2.46 3.00 3.35
15 0.83 1.26 1.58 1.89 2.30 2.56
20 0.70 1.05 1.31 1.58 1.90 2.11
25 0.61 0.91 1.13 1.37 1.64 1.82
30 0.55 0.81 1.00 1.22 1.45 1.61
35 0.50 0.73 0.91 1.10 1.31 1.45
40 0.46 0.67 0.83 1.01 1.20 1.33
45 0.43 0.63 0.77 0.94 1.11 1.22
50 0.40 0.58 0.72 0.88 1.04 1.14
55 0.38 0.55 0.68 0.82 0.97 1.07
60 0.36 0.52 0.64 0.78 0.92 1.01
75 0.31 0.45 0.55 0.68 0.79 0.87
90 0.28 0.40 0.49 0.60 0.70 0.77
105 0.26 0.36 0.44 0.55 0.64 0.69
120 0.24 0.33 0.41 0.50 0.58 0.63
150 0.21 0.29 0.35 0.43 0.50 0.55
180 0.19 0.26 0.31 0.39 0.45 0.48
360 0.12 0.17 0.20 0.25 0.28 0.30
720 0.08 0.11 0.13 0.16 0.18 0.19
1440 0.05 0.07 0.08 0.10 0.11 0.12
Storm Recurrence Interval
Design Standards and Specifications Policy
City of Bozeman, March 2004 as Amended
Zoning District/Design Storm Requirement
Zoning Type
Design Rainfall
Frequency
Open Land 2-year
Residential 10-year
Commercial 10-year
(p. 28, Table I-3)
STORMWATER MANAGEMENT MANUAL
TABLE 2-5 FREQUENCY FACTORS FOR THE RATIONAL FORMULA
Recurrence Interval Adjustment Factor
(Years)Cf
2 1.00
5 1.00
10 1.00
25 1.10
50 1.20
100 1.25
* C X Cf should not exceed 1.0
i
TABLE OF CONTENTS
INTRODUCTION ............................................................................................................................................. 1
EXECUTIVE SUMMARY................................................................................................................................... 1
SITE LOCATION AND DESCRIPTION ............................................................................................................... 3
PROPOSED IMPROVEMENTS ......................................................................................................................... 3
GEOLOGY ....................................................................................................................................................... 4
AREA SOILS INFORMATION ........................................................................................................................... 5
EXPLORATIONS, TESTING, AND SUBSURFACE CONDITIONS ......................................................................... 5
Subsurface Explorations ............................................................................................................................ 5
Laboratory Testing ..................................................................................................................................... 6
Soil Conditions ........................................................................................................................................... 6
Groundwater Conditions ........................................................................................................................... 8
GEOTECHNICAL ISSUES ................................................................................................................................ 10
GENERAL CONSTRUCTION RECOMMENDATIONS ....................................................................................... 11
Re-Excavation of Test Pits ........................................................................................................................11
Sediment Control .....................................................................................................................................11
Topsoil Stripping and Re-Use ...................................................................................................................11
Groundwater Dewatering ........................................................................................................................ 11
OSHA Standards and Excavation Shoring ................................................................................................12
Excavation and Re-Use of On-Site Soils ...................................................................................................12
STRUCTURAL DESIGN PARAMETERS ........................................................................................................... 13
Seismic Design Factors .............................................................................................................................13
Foundation Bearing Pressure ..................................................................................................................13
Lateral Earth Pressures ............................................................................................................................13
Subgrade Reaction Modulus .................................................................................................................... 14
FOUNDATION AND EARTHWORK RECOMMENDATIONS ............................................................................ 14
General ....................................................................................................................................................14
Foundation Design ................................................................................................................................... 15
Foundation Excavation - Parking Garage ................................................................................................. 15
Foundation Excavation - Building 3 (Southeast Side) .............................................................................. 15
Foundation Excavation - Building 4 (South Side) ..................................................................................... 15
Standard Shallow Footings (Conventional Footings) ...............................................................................16
Foundation Backfill .................................................................................................................................. 17
Interior Slabs (Parking Garage and At-Grade Slabs) ................................................................................ 18
Exterior Slabs (Sidewalks and Traffic Slabs) ............................................................................................. 18
ii
TABLE OF CONTENTS (cont.)
SUBSURFACE DRAINAGE RECOMMENDATIONS.......................................................................................... 19
Subsurface Drainage (Parking Garage) .................................................................................................... 19
Subsurface Drainage (At-Grade Slabs) .....................................................................................................20
MOISTURE PROTECTION RECOMMENDATIONS .......................................................................................... 20
Moisture Protection (Parking Garage) ..................................................................................................... 20
Moisture Protection (At-Grade Slabs) .....................................................................................................20
SURFACE DRAINAGE RECOMMENDATIONS ................................................................................................ 21
FOUNDATION-RELATED FILL MATERIAL RECOMMENDATIONS .................................................................. 21
Excavated Foundation Soils ..................................................................................................................... 21
Sandy (pitrun) Gravel ............................................................................................................................... 22
Crushed (road mix) Gravel .......................................................................................................................22
Clean Crushed Rock ................................................................................................................................. 22
Fill Placement and Compaction ............................................................................................................... 22
UNDERGROUND UTILITY RECOMMENDATIONS ......................................................................................... 23
PAVEMENT SECTION RECOMMENDATIONS ................................................................................................ 23
Construction Notes ..................................................................................................................................28
Pavement Section Materials, Placement, and Compaction .................................................................... 28
COLD/WINTER WEATHER CONSTRUCTION ................................................................................................. 29
CONSTRUCTION INSPECTION ...................................................................................................................... 29
PRODUCTS ................................................................................................................................................... 29
LIMITATIONS ............................................................................................................................................... 30
REFERENCES ................................................................................................................................................ 31
iii
TABLE OF CONTENTS (cont.)
SUPPLEMENTAL INFORMATION
List Of Tables
Table 1 – Summary of Soil Conditions in Test Pits 1 – 5
Table 2 – Summary of Soil Conditions in Boreholes 1 – 7
Table 3 – Summary of Groundwater Conditions in Test Pits 1 – 5
Table 4 – Summary of Groundwater Conditions in Boreholes 1 – 7
Table 5 – Summary of 2018 Seasonal High Groundwater Measurements in MW-1 – MW-5
Table 6 – Compaction Recommendations (Application vs. Percent Compaction)
Table 7 – Pavement Design – E. Aspen St. (New) – Option 1 – Stable SG
Table 8 – Pavement Design – N. Ida Ave. (Reconstruction) – Option 1 – Stable SG
Table 9 – Alternative Pavement Design – E. Aspen St. (New) – Option 2 – Stable SG
Table 10 – Alternative Pavement Design – N. Ida Ave. (Reconstruction) – Option 2 – Stable SG
Table 11 – Pavement Design – E. Cottonwood St. (Utility Trench) – Option 1 – Stable SG
Table 12 – Pavement Design – N. Wallace Ave. (Utility Trench) – Option 1 – Stable SG
Table 13 – Pavement Design – E. Cottonwood St. (Parking Stalls) – Option 1 – Stable SG
Table 14 – Pavement Design – Front St. (Road & Parking Stalls) – Option 1 – Stable SG
Table 15 – Pavement Design – W. Side Service Drive (New) – Option 1 – Stable SG
Table 16 – Pavement Design – E. Aspen St. – Gravel Road (New) – Option 1 – Stable SG
Table 17 – Product Reference Guide
List Of Figures
Figure 1 – Vicinity Map
Figure 2 – Geology Map
Figure 3 – BHs and TPs w/ Native Gravel Depth
Figure 4 – MWs w/ 2018 High Groundwater
Figure 5 – Foundation Detail – Parking Garage
Figure 6 – Foundation Detail – At-Grade Slab (Mass Over-Excavation)
Figure 7 – Foundation Detail – At-Grade Slab (Footing Over-Excavation)
List Of Appendices
Appendix A – On-Site Exploration Logs And Photos
Appendix B – Nearby Soils Information
Appendix C – Groundwater Monitoring Data
Appendix D – Asphalt Pavement Section Design
Appendix E – Products
Appendix F – Limitations Of Your Geotechnical Report
Allied Engineering Services, Inc. Page 1
INTRODUCTION
This report presents our geotechnical assessment for the proposed site of the Cottonwood + Ida Mixed-
Use Development on the northeast side of Bozeman, MT. This will be a multi-building, infill project that
will re-develop about two acres on the northwest corner of E. Cottonwood Street and N. Ida Avenue.
The geotechnical information contained herein is based on an investigation and analysis of the site’s
subsurface conditions, knowledge of the underlying geology, and our previous geotechnical engineering
experience in the Bozeman area. The purpose of this report is to inform all associated parties of the
site’s soil and groundwater conditions and any potential geotechnical issues or concerns that we
identify; and to provide recommendations that pertain to site earthwork, structural design, foundations,
slabs, walls, subsurface drainage, surface drainage, moisture protection, foundation fill materials, under-
ground utilities, and asphalt pavements for streets, parking stalls, and the west side service drive. We
believe our recommendations are reasonable and prudent; and therefore they should be considered
and implemented during the planning, design, and construction phases of this site development project.
EXECUTIVE SUMMARY
Our investigation of the subject property has included the digging of five test pits to a depth of 13 to 14
feet, the installation of groundwater monitoring wells, the drilling of seven boreholes to a depth of 30 to
35 feet, and the monitoring of groundwater across the site during the spring and early summer of 2018.
By far, the biggest potential geotechnical concern at the site is the height that seasonal high ground-
water rises and its possible impacts on the underground parking garage that will underlie the buildings
on the north side of the site. As currently designed, the deepest part of the garage will be about 2.0 feet
above the highest groundwater that was measured in 2018, which was a good year for monitoring due
to the above-average snowpack levels. Since 2019 is lining up to be another good year for monitoring, it
is recommended that we do some more monitoring during the upcoming spring. The purpose of this is
to see if we obtain similar data and provide more confidence that the garage is set at a shallow enough
elevation to minimize the risk of any future groundwater-related problems.
The site is underlain by clean, alluvial sandy gravel that begins at a depth of 4.0 to 4.5 feet. The gravel
deposit extends to depths of 28 to >30 feet before overlying Tertiary-aged bedrock. Overlying the gravel
is about 3.0 to 3.5 feet of stiff silt/clay that is interbedded with multiple, thin layers of black, organic
topsoil. In the unimproved area of the site (south half), the property is covered by 0.5 to 1.0-foot of
topsoil. The north half is covered by buildings, concrete, asphalt, and about a foot of gravelly fill. The
highest groundwater levels recorded in 2018 ranged from 8.0 to 9.0 feet below existing grades.
Cottonwood + Ida Mixed Use Development
E. Cottonwood St. / N. Ida Ave. – Bozeman, MT
Project: 18-054
March 15, 2019
Allied Engineering Services, Inc. Page 2
This project involves construction of five, new, three to four-story buildings along with the renovation of
the small, existing building in the southwest corner of the site. The three, northern buildings will be
built on top of a partially buried parking garage, while the two buildings on the south and southeast
sides will be underlain by at-grade slabs. The clean sandy gravel that underlies the site at depths of 4.0
to 4.5 feet will provide suitable bearing for the new structures and is defined as the “target” bearing
material for all footings. Due to the northward sloping site topography, the depth of the parking garage
will range from about 4.0 feet on the north to 6.0 feet deep on the south. As a result, the bottom of the
excavation should reach “target” gravels in most areas; thereby, the need for additional over-excavation
should be minimal. The two buildings on the south side of the site contain numerous interior footings.
Due to complexity of the foundation plans, it may be best to simply mass over-excavate the foundation
footprint areas down to “target” gravel and build back up to footing and slab grades with structural fill.
The only other option is to over-excavate all footing areas on an individual basis, which will be time
consuming. The benefits of mass over-excavation include speed and efficiency of foundation earthwork
and the generation of on-site soils that can then be used for embankment fill in other site areas.
The slab elevation of the parking garage has been set above the shallowest groundwater levels that
were measured in 2018. The big question is how high can water rise during future years. The 2018 data
should be pretty representative given the amount of snow last year; however, this is not a guarantee of
what could happen in other years. For this reason, we recommend that either subsurface drainage or
moisture protection provisions be incorporated into garage construction. One approach is to underlay
the garage with a subsurface drainage system. The issue with this is that there is no easy place to
discharge any groundwater and it would require a sump chamber with pumps. Another option would be
to water-proof the underside of the slab and the garage walls to prevent water from getting into the
garage if it ever rose above the slab elevation. If water-proofing is selected, the slab will need to be
structurally designed to resist buoyancy uplift forces on the bottom of the slab.
A unique element of this project will be the installation of a large, subsurface storm drain chamber
system on the west side of the site under the emergency access drive. This system will accept all run-off
from the site, temporarily store it, and allow it to slowly infiltrate into the subsurface soils. Our main
recommendation for this system is that a direct hydraulic connection be made between it and the native
sandy gravels. This can be done by setting the chambers on the native gravels or by bearing them on a
section of clean crushed rock that in turn bears on the native gravels. By doing so, all silt/clay will be
removed under the system and the chambers will drain more freely/quickly. Also, this should reduce
the likelihood of hydraulic loading against the foundation walls on the west side of the parking garage.
This project will trigger the need for underground utility improvements in the adjacent streets. In order
to minimize trench settlement issues in existing paved streets, we recommend that all water and sewer
trenches be backfilled with on-site or imported sandy gravel. This will require removal and replacement
of the near surface silt/clay soils. All native gravels can be re-used for backfill.
Several streets will be upgraded and/or constructed as part of this project. In addition, new street-side
parking stalls will be added along Cottonwood Street and Front Street. Due to the extensive under-
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ground utility work, large sections of existing streets will be tore up and need to be re-surfaced. As part
of this report, we have provided several pavement sections depending on location (street, utility trench,
parking stalls, and the west side service drive). For the Aspen and Ida Street improvements, two options
are presented. Option 1 consists of a thicker sub-base gravel section over normal woven fabric whereas
Option 2 includes a little thinner sub-base section over higher strength geosynthetic. For Option 2, the
fabric cost will be higher, but the benefit is shallower excavation and less gravel needed.
SITE LOCATION AND DESCRIPTION
The project site is bounded on the south by E. Cottonwood St., on the east by N. Ida Ave., on the north
by the future extension of E. Aspen St., and on west by several existing buildings that line the east side
of N. Wallace Ave. The subject property will encompasses approximately two acres and is comprised of
Lots 5 through 28 of Block 105 of the Northern Pacific Addition. Its legal description is the SW1/4, SE1/4
of Section 6, T2S, R6E, Gallatin County and its latitude and longitudinal coordinates (near center of site)
are 45.687160° and -111.027222°. See Figures 1, 3, and 4 for aerial images that show the site location
and existing conditions.
The square-shaped site generally slopes to the north/northeast at grades of one to two percent, similar
to most other areas around Bozeman. There is about five feet of vertical drop across the property with
a high elevation of 4776 feet near the southwest corner and a low of 4771 feet at the northeast corner.
The south half of the site is largely undeveloped, except for a small old building in the southwest corner.
Most recently, this area was used for equipment and materials staging during the construction of the
Block 106 building project on the south side of E. Cottonwood St. The majority of the north half is
covered by concrete or asphalt surfacing and contains three old, single story, metal buildings. We
expect most, if not all, of the existing buildings on the site are underlain by slab-on-grade foundations.
PROPOSED IMPROVEMENTS
In order to make room for the new improvements, all existing buildings on the north side of the site will
be demolished and removed. The small building in the southwest corner will be saved, renovated, and
incorporated into the new project. The property will be cleared of all foreign and random debris as well
as all existing concrete and asphalt areas.
Based on a review of the 100% design development drawings, which were issued on January 21, 2019,
the project will be a high density development that consists of five, new, three to four-story buildings
along with the existing building in the southwest corner. Most of the buildings will be used for multi-
family residential housing, while the northwestern-most building will provide for office and commercial
space. All of the buildings will be interconnected by sidewalks and have large areas of concrete-covered,
outdoor living and gathering places (patios and courtyards).
The most interesting feature of this project will be a large, partially-buried, underground parking garage
that essentially takes up the entire north half of the site. The three, northern buildings (Buildings 6, 1,
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and 2 from west to east across the site) will largely be constructed on top of the garage. The north and
south portions of some of these buildings will extend beyond the garage foundation footprint area and
bear on separate footings. As currently designed, the garage will be 11 feet in height from the below-
grade slab elevation of 4768 feet up to the top of the roof (podium elevation of 4779 feet). In the north
half of the site, the existing topography ranges from 4774 feet near the southwest corner of the garage
to 4772 feet near the northeast corner. This means the depth of the garage will generally range from
4.0 to 6.0 feet below existing grades in the north to south direction. The foundation for the garage will
consist of perimeter footings/walls as well as many interior spread footings for the support of the roof
and the three, overlying buildings.
Two, new buildings will be located in the southeast corner (Building 3) and the south side (Building 4) of
the site. Both of these buildings will be underlain by at-grade slabs and supported on a shallow,
conventional foundation consisting of perimeter footings and walls and interior and exterior footings.
Based on the structural drawings in the DD set, it appears that the foundation plan for each building is
complex and contains many interior, strip and spread footings. The proposed finished floor elevation for
Building 3 will be 4775 feet, which is between 0.0 and 2.0 feet above existing site grades. Building 4 will
be set higher at a floor elevation of 4777.75 feet, which is 3.0 to 4.0 feet above existing grades.
This development project will trigger several road improvements and upgrades around the site. A new
section of E. Aspen Street will be constructed along the north side of the property, while the portion of
N. Ida Avenue (along east side of site) from E. Cottonwood Street to Front Street will be widened and re-
constructed. On-street parking stalls will be added on the north side of E. Cottonwood Street as well as
along a short segment of Front Street. Large areas along E. Cottonwood Street and the intersection at
N. Wallace Avenue will be tore up for underground utility installation and will need to be re-surfaced.
Finally, a service drive for emergency vehicle access will be constructed along the west side of the site.
With the exception of the portion of Aspen from Ida to Front (which will be gravel surfaced), all other
streets, parking stalls, and access drives will be paved.
There is one other element of this project that is a little unique. Due to the high density of the buildings
and the fact that most other site areas are covered by exterior concrete, there is no space for on-site
retention/detention ponds for stormwater drainage. In order to address this item, a large, subsurface
storm drain chamber system is planned under the west side service drive. All stormwater drainage from
the site and building roofs will be routed to this buried structure for subsurface storage and subsequent
infiltration into the underlying soils.
GEOLOGY
According to a geology map for the Bozeman area, an excerpt of which is attached as Figure 2, the
mapped geology throughout most of the northeast side of the city consists of Quaternary-aged, alluvial
and fluvial deposits (Qal) from the Bozeman Creek and E. Gallatin River drainages. Based on previous
geotechnical experience, the dominate material within this formation is shallow cobbly, sandy gravel
that typically begins at a depth of three to five feet. The gravels are overlain by an intermediate layer of
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silt/clay and capped by a thin layer of organic topsoil. In this part of Bozeman, the gravels are expected
to extend to a depth of 25 to 40 feet before overlying consolidated beds of Tertiary-aged gravels, sands,
silts, and clays, which are generally and locally considered to be “bedrock”.
Note: As expected, we found the project site to be underlain by shallow sandy gravels beginning at
depths of 4.0 to 4.5 feet. These alluvial materials were consistent throughout their depth and extended
to the bottom of most of our boreholes at about 30 feet. In one our boreholes (BH-2), we encountered
the Tertiary bedrock sediments that underlie the alluvial gravels at a depth of 28 feet. Based on this,
there is a good chance the geologic contact between the gravels and the Tertiary bedrock is around the
30 to 35-foot depth throughout the site. See the following report sections for more detailed description
of the subsurface conditions.
AREA SOILS INFORMATION
In 2005, we performed the soils investigation for the two properties to the south of the site along the
south side of E. Cottonwood St. The eastern property is home to the Mill Lofts building, while the
western property is where the Block 106 building project was recently completed. As part of our work,
we drilled five, deep borings and dug four, shallow test pits. The locations of these explorations as well
as the logs are attached in Appendix B. In general, we encountered dense to very dense, clean sandy
gravel beginning at depths of 3.0 to 4.0 feet. The sandy gravel formation extended to the bottom of the
30-foot boreholes.
EXPLORATIONS, TESTING, AND SUBSURFACE CONDITIONS
Subsurface Explorations
Subsurface conditions were investigated across the site in two phases under the direction of Lee Evans,
a professional geotechnical engineer with Allied Engineering. On April 24, 2018, we dug five test pits
(TP-1 through TP-5). This was followed up on February 13 and 14, 2019 with seven deeper boreholes
(BH-1 through BH-7). The purpose of the test pits was to observe the shallow soil conditions and install
groundwater monitoring wells, while the boreholes allowed for better evaluation of the thickness and
in-place density of underlying alluvial sandy gravel formation.
For Phase 1, the test pits were dug with a sub-contract excavator provided by Townsend Backhoe. All
pits extended to a depth of 13 to 14 feet. For future groundwater monitoring purposes, PVC wells were
installed in each of the five pits. In a corresponding manner, these wells were labeled as MW-1 (in TP-1)
through MW-5 (in TP-5). For the Phase 2 work, the borehole drilling was completed with a hollow stem
auger rig provided by O’Keefe Drilling. Most boreholes were terminated around the 30-foot depth with
BH-2 going a little deeper to about 35 feet. Following the fieldwork, all explorations were fully back-
filled, cleaned up to the best extent possible, and labeled with identifying stakes. The three boreholes in
the existing asphalt and concrete areas were capped with like materials.
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See Figures 3 and 4 for maps showing the approximate test pit and borehole locations. The base map
for each figure is an aerial photo of the current site conditions. In addition to the exploration locations,
the depths to native sandy gravel are presented on Figure 3 and the depths of the 2018 seasonal high
groundwater (that were monitored in the wells) are shown on Figure 4. These figures allow for an easy
understanding of the depths and variations to gravel and groundwater across the site.
During the explorations, soil and groundwater conditions were visually characterized, measured, and
logged. The relative density of the underlying soils was estimated based on ease/difficulty of digging
and drilling, sidewall stability of the completed test pit excavation, rate of auger advancement, and
standard penetration tests (blow counts) at 2.0 to 3.0-foot intervals. Our borehole and test pit logs are
included in Appendix A. Each of the logs provides pertinent field information, such as soil depths,
thicknesses, and descriptions, groundwater depths (at the time of the exploration), relative density data,
soil sample information, and a sketch of the soil stratigraphy. Please be aware the detail shown on the
logs cannot be accurately summarized in a paragraph; therefore, it is very important to review the logs
in conjunction with this report.
To better illustrate the near-surface on-site soils, two photos from TP-1 through TP-5 are also provided.
The first photo of each set shows the sidewall of the excavation, while the latter photo is of the
excavated spoil pile. All photos have been marked up to call out the soil layers and materials that are
described on the logs as well as identifying characteristics.
Note: Please be aware that no compaction of test pit backfill soils was done; therefore, these areas will
be susceptible to future settlement. As discussed in a later section of the report, all old test pit locations
should be re-excavated to their original depth and properly backfilled and compacted if they will under-
lie any of the site improvements, including building footprints, exterior footings and slabs, underground
utilities, and other hardscape and landscape areas.
Laboratory Testing
During the test pits, no soil samples were collected. In our opinion, the site’s shallow gravelly conditions
did not warrant much for testing. During borehole drilling, several samples were obtained from each of
the holes. All samples above the groundwater table were tested for natural moisture content. Our test
results are included on the borehole logs in Appendix A.
Note: Assuming the on-site, non-organic soils will be re-used for site fill and foundation wall backfill, we
recommend representative samples be collected during construction and tested for standard proctors.
This information will be beneficial for compaction testing.
Soil Conditions
Based on our “peppering” of test pits and boreholes across the site, the entire property is underlain by
shallow, clean, cobbly, sandy gravels beginning at depths of 4.0 to 4.5 feet. These gravelly materials
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resemble good pitrun gravel and contain abundant 4” to 6” gravels and scattered 8” to 10” cobbles. The
gravels extended to the bottom our 13 to 14 feet test pits and to about the 30-foot depth in most of the
boreholes. The only exception was found in BH-2 where the alluvial gravels overlaid Tertiary bedrock
beginning at the 28-foot depth. Based on blow counts being greater than 30 blows/foot (in most bore-
holes and at most SPT sample depths), the gravels are generally in a dense to very dense condition. For
whatever reason, the gravels in BH-2 were a little less dense (medium dense to dense). See Figure 3 for
the gravel depth variation across the site.
Overlying the sandy gravel is about 3.0 to 3.5 feet of silt/clay, which is interbedded with multiple, thin
layers of black topsoil. The upper silt/clay is darker brown and stiff. With increasing depth, the silt/clay
is more brown to tan and moister (and consequently a little less stiff). Near the bottom of the silt/clay
layer there are some scattered gravels. This transitional zone does not constitute clean sandy gravel.
Much of the site is blanketed by about 0.5 to 1.0-foot of topsoil. In the developed northern half of the
site, the existing concrete and asphalt surfacing is underlain by approximately one foot of gravelly fill. In
some areas, the fill was more of a silty, sandy gravel, while in others it was a clayey gravel random fill.
See the attached test pit and borehole logs in Appendix A for the detailed soil conditions.
Provided in Table 1 and 2 is a summary of the soil conditions observed in the five test pits and seven
boreholes. The material descriptions and soil depths in the tables match the data shown on the logs.
Table 1. Summary of Soil Conditions in Test Pits 1 – 5
TP
#
TP
LOCATION TOPSOIL RANDOM
FILL
NATIVE
SILT/CLAY
(DK BROWN)
TOPSOIL
(BURIED LAYER)
NATIVE
SILT/CLAY
(BROWN)
NATIVE
SANDY
GRAVEL
1 SW Corner 0.0’ - 0.8’ -------- 0.8’ - 2.0’ 2.0’ - 2.5’ 2.5’ - 4.0’ 4.0’ - 13.0’
2 SE Corner 0.0’ - 0.5’ -------- 0.5’ - 1.0’
1.5’ - 2.0’
1.0’ - 1.5’
2.0’ - 2.5’ 2.5’ - 4.0’ 4.0’ - 13.0’
3 Center 0.0’ - 0.8’ -------- 0.8’ - 2.0’ 2.0’ - 2.7’ 2.7’ - 4.3’ 4.3’ - 13.3’
4 NW Corner 0.0’ - 0.5’ 0.5’ - 1.0’ 1.5’ - 2.7’ 1.0’ - 1.5’
2.7’ - 3.0’ 3.0’ - 4.5’ 4.5’ - 13.5’
5 NE Corner 0.0’ - 0.5’ 0.5’ - 1.0’ 1.5’ - 3.0’ 1.0’ - 1.5’ 3.0’ - 4.0’ 4.0’ - 14.0’
Notes: 1) All soil measurements are depths below existing ground. 2) The random fill in TP-4 and TP-5 ranged from a sandy silt w/ intermixed gravel to more of a silty, sandy gravel. 3) The native silt/clay is an unsuitable bearing material and shall be removed from under all footing locations.
4) The “target” bearing material for all foundation elements is the dense, native sandy gravel starting at 4.0’ to 4.5’.
5) PVC monitoring wells were installed in TP-1 through TP-5 for future groundwater monitoring purposes.
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Table 2. Summary of Soil Conditions in Boreholes 1 – 7
BH
# BH LOCATION
ASPHT.
OR CONC.
SURFACE
GRVL. OR
RANDOM
FILL
TOPSOIL
NATIVE
SILT/CLAY
(UNDIFF.)
NATIVE
SANDY
GRAVEL
TERTIARY
BEDROCK
1 S1/2 of Site, SW Side -------- -------- 0.0’ - 0.5’ 0.5’ - 4.0’ 4.0’ - 30.5’ --------
2 S1/2 of Site, Central -------- -------- 0.0’ - 0.5’ 0.5’ - 4.5’ 4.5’ - 28.0’ 28.0’ - 35.2’
3 S1/2 of Site, SE Side -------- -------- 0.0’ - 0.5’ 0.5’ - 4.0’ 4.0’ - 29.8’ --------
4 N1/2 of Site, SW Side -------- 0.0’ - 1.0’ -------- 1.0’ - 4.0’ 4.0’ - 29.9’ --------
5 N1/2 of Site, SE Side 0.0 - 0.33’ 0.33’ - 1.5’ -------- 1.5’ - 4.0’ 4.0’ - 29.2’ --------
6 N1/2 of Site, NW Side 0.0’ - 0.5’ 0.5’ - 1.5’ -------- 1.5’ - 4.5’ 4.5’ - 29.8’ --------
7 N1/2 of Site, NE Side 0.0’ - 0.2’ 0.2’ - 2.0’ -------- 2.0’ - 4.0’ 4.0’ - 29.8’ --------
Notes: 1) All soil measurements are depths below existing ground. 2) The fill in BH-4, BH-5, and BH-6 appeared to be silty, sandy gravel. 3) In contrast, the fill in BH-7 was a brown to black, clayey gravel with wood fragments. 4) Similar to the test pits, the native silt/clay contains multiple layers of interbedded, black topsoil. 5) Since it was impossible to measure the topsoil layers in the BHs, the silt/clay layer is noted as “undifferentiated”. 6) The native silt/clay is an unsuitable bearing material and shall be removed from under all footing locations.
7) The “target” bearing material for all foundation elements is the dense, native sandy gravel starting at 4.0’ to 4.5’.
Groundwater Conditions
Based on our test pits (which were dug in April 2018), our boreholes (which were drilled in February
2019), and our 2018 groundwater monitoring data, it appears that the site is underlain by a relatively
deep groundwater table (>9 feet) during most of the year. During a short period in the spring of 2018,
groundwater rose inside of 9 feet and got as high as about 8 feet in one of the monitoring wells. See
Table 3 and 4 for a summary of our groundwater observations in the test pits and boreholes, Table 5 for
the seasonal high measurements in the monitoring wells, and our 2018 monitoring data in Appendix C.
Table 3. Summary of Groundwater Conditions in Test Pits 1 – 5
TP # TP
LOCATION
GROUNDWATER
DEPTH
DATE OF
MEASUREMENT
1 SW Corner 9.0’ 4/24/18
2 SE Corner 10.0’ 4/24/18
3 Center 9.25’ 4/24/18
4 NW Corner 9.0’ 4/24/18
5 NE Corner 9.33’ 4/24/18
Notes: 1) All groundwater measurements are depths below existing ground.
2) PVC monitoring wells were installed in TP-1 through TP-5.
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Table 4. Summary of Groundwater Conditions in Boreholes 1 – 7
BH # BH
LOCATION
GROUNDWATER
DEPTH
DATE OF
MEASUREMENT
1 S1/2 of Site, SW Side 13.1’ 2/13/19
2 S1/2 of Site, Central 13.6’ 2/13/19
3 S1/2 of Site, SE Side 15.0’ 2/13/19
4 N1/2 of Site, SW Side 13.3’ 2/14/19
5 N1/2 of Site, SE Side 14.0’ 2/14/19
6 N1/2 of Site, NW Side 13.7’ 2/14/19
7 N1/2 of Site, NE Side 14.6’ 2/13/19
Notes: 1) All groundwater measurements are depths below existing ground.
From the date of our test pits and the installation of the monitoring wells, we monitored groundwater
levels at the site from the end of April 2018 up through July 31, 2018. The highest measurements that
we recorded were around the 8.0 to 9.0-foot depths with the shallowest depth being 7.8 feet in MW-3.
Due to the extensive snowpack in the 2018, this was a good year to monitor groundwater levels across
the Bozeman area and greater Gallatin Valley; thus the data should be pretty representative of normal
seasonal high groundwater elevations. See Figure 4 for the seasonal high groundwater depth variation
across the site. Provided in Table 5 is a summary of the highest water depths that were recorded during
our 2018 monitoring work.
Table 5. Summary of 2018 Seasonal High Groundwater Measurements in MW-1 – MW-5
MW # MW
LOCATION
WELL DEPTH
(BELOW EG)
CASING HEIGHT
(ABOVE EG)
SHALLOWEST
GW DEPTH
DATE OF
MEASUREMENT
1 SW Corner 13.0’ 31” 7.98’ 5/15/18
2 SE Corner 13.0’ 36” 8.52’ 4/30/18
3 Center 13.3’ 27” 7.77’ 4/30/18
4 NW Corner 13.5’ 28” 8.46’ 4/30/18
5 NE Corner 14.0’ 22” 8.82’ 4/30/18
Notes: 1) All groundwater measurements are depths below existing ground.
2) PVC monitoring wells were installed in TP-1 through TP-5 and named as MW-1 through MW-5.
3) EG = existing ground.
Groundwater elevations in the Bozeman area fluctuate on a seasonal basis. They are typically at their
lowest in the latter part of the year, but rise to the shallowest depths during the spring (April, May, or
June) as a result of recharge from the melting mountain snowpack, spring precipitation, and agricultural
irrigation. Since our 2018 groundwater monitoring started on April 24, our three month long data set
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should contain the highest water levels of last year. There is an off chance that groundwater actually
peaked earlier at some point before April 24. Even if it did, we do not expect it to be too much different
from the highest levels that we recorded.
Note: Due to the abundance of snow around Bozeman in the winter 2019, this spring is shaping up to
be another good year for groundwater monitoring. In order to confirm last year’s monitoring data and
also to see if water levels rise higher in 2019, we recommend that additional groundwater monitoring
be undertaken beginning in late March 2019. Since the monitoring wells are in-place, it will be very easy
to collect more data. The intent of this work is to hopefully show that groundwater depths do not reach
the bottom of the parking garage slab elevation during two consecutive pretty wet years.
GEOTECHNICAL ISSUES
Given the soil conditions, the site has no issues regarding foundation earthwork and foundation bearing.
The on-site silt/clay should be readily re-usable for exterior foundation wall backfill and other site fill
around the buildings. Provided the surface topsoil layer, which is most heavily organic, is stripped, the
thin, interbedded topsoil layers that are buried in the silt/clay profile do not present any problem. They
will simply be mixed in and distributed during excavation. The clean, sandy gravel that underlies the site
at 4.0 to 4.5 feet is the “target” bearing material for all footings.
Due the relatively deep groundwater table, we do not expect any issues with soft subgrades during
street construction. The silt/clay subgrade soils will likely be in a moist condition immediately upon
excavation, but should dry to a stiff and hard condition in limited time.
The biggest potential risk at the site is the depth of the partially buried parking garage and possible
impacts that are caused by seasonal high groundwater. Right now, the depth of the garage is set at 4.0
to 6.0 feet below existing grades, which is about 2.0 feet above the shallowest groundwater (8.0 feet)
that was measured in 2018. We do not recommend deepening the garage any more than this during
the final design. We believe the 2.0-foot buffer should be a maintained at a minimum. The reason
being is that high groundwater in future years could be higher than that which was recorded in 2018.
Another issue at the site is the lack of a suitable location to discharge groundwater from an underslab
collection system under the parking garage. A subsurface drainage system such that this would be a
good idea and provide for a safety element in the event that high groundwater reached the bottom of
the slab elevation. However, not only is there no location on the property to discharge the water, but
the depth of the garage would require a sump chamber with pumps to lift the water to the ground
surface. If a sub-drain system is installed, it would need to be discharged to the street and to a location
that would not negatively affect any neighboring properties.
In lieu of a sub-drain system, another option is to water-proof the garage. If this is done, the garage
floor will need to be designed to withstand some buoyant forces (especially in the deeper south half of
the garage). Otherwise, any trapped groundwater pressure under the slab may want to lift and crack it.
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GENERAL CONSTRUCTION RECOMMENDATIONS
Re-Excavation of Test Pits
We expect that most, if not all, of our five test pits will be encroached upon during site development
and building construction. All five of the pits were backfilled with monitoring wells; thus, their locations
will be easy to find. During backfilling, the pits were not compacted (other than some periodic tamping
with the excavator bucket); and as a result, they will undergo significant soil settlement over time. If any
site improvements, including building foundations, interior and exterior concrete slabs, underground
utilities, and asphalt areas, will overlie any of the test pits, we recommend they be re-excavated back
down to their original depth and properly backfilled and compacted with suitable material. All test pits
were dug to depths of 13 to 14 feet.
Sediment Control
Prior to beginning any earthwork construction at the site, adequate sediment control measures must be
in place in order to prevent disturbed soils/sediment from being carried down slope and off the site via
surface water runoff. According to Montana State Law, all surface waters must be fully protected from
the introduction of sediment by construction-related activities. Sediment protection barriers will need
to be placed along/around all established drainages, waterways, ponds, wetlands, stormwater inlets,
and in curb/gutter, etc. that lie within/adjacent to the site. In addition to protecting these items, we
believe that it is a responsible practice to install a continuous barrier along the down slope side of the
construction limits, especially on sloping sites. If material stockpiles will be located close to waterways
and wetlands, sediment barriers should be installed around these areas well. In general, establishing
and maintaining proper sediment control usually takes a “minimal level of effort”, and on large-sized
projects, is a State requirement. By doing this, disturbed soils are kept as close to the “source area” as
possible and they are restricted from being washed further down slope and potentially off the property.
Topsoil Stripping and Re-Use
Throughout the south half of the site, the ground surface is blanketed by 0.5 to 1.0-foot of topsoil in
most locations. Under existing concrete and asphalt pavements in the north half, no topsoil was found.
As a general rule, all topsoil must be stripped throughout the building footprint, under exterior concrete
and asphalt areas, and in other site areas that will be filled with embankment to raise site grades. Final
site grading (in landscape areas) and the reclamation of disturbed construction areas are the only
recommended uses of this material.
Groundwater Dewatering
The maximum depth for foundation excavation should be 4.0 to 6.0 feet (based on the 4.0-foot gravel
depth and the 6.0-foot depth of the garage on the south side). As a result, we are not expecting there
will be a need for groundwater dewatering during foundation earthwork. Also, the shallow excavation
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for road building will not require any dewatering. Depending on the time of year and the depth of the
utilities, some dewatering may be needed for water and sewer installations.
OSHA Standards and Excavation Shoring
Based on the depth to native sandy gravel in the proposed building area, the foundation excavation will
likely only be on the order of 4.0 to 6.0 feet deep. This shallow excavation will not require any sort of
shoring. Instead, the excavation can be enlarged as needed and the sidewalls sloped as required by the
OSHA standards for excavations deeper than 4.0 feet. Per OSHA, the native silt/clay would classify as a
Type A soil and the native sandy gravel would be a Type C soil. The allowable sidewall slopes in these
soils when deeper than 4.0 feet and properly benched is 3/4:1 and 1.5:1, respectively.
Excavation and Re-Use of On-Site Soils
All on-site soils and existing building materials (asphalt, concrete, gravel bases) can be re-used as part of
the re-development project. We do not expect any issues with cut and fill, particularly wet soils, soft
subgrades, or compaction issues. During site demolition and excavation, if any site soils are found that
are contaminated with foreign or construction debris, they shall be removed from the site and properly
disposed of. Provided below are the allowable re-uses of the on-site materials:
• Topsoil materials shall only be used for final site grading in landscape areas. The most heavily
organic soil is the surface topsoil layer in the south half of the site. There is no reason to try and
isolate and strip the layers of buried topsoil that are sandwiched in the native silt/clay. These
layers are not very organic and can be intermixed in the silt/clay during excavation.
• Existing concrete and asphalt surfacing can be salvaged and stockpiled. Provided the materials
are crushed to a 6-inch maximum aggregate size, they can be blended with other clean gravel
and re-used as part of the sub-base section under streets. The recycled materials shall be mixed
in at a rate of <50% (with >50% gravel).
• Any gravelly material that is found under the existing buildings, concrete, or asphalt areas can
be salvaged and re-used as site fill. If the gravel is clean and meets MPWSS specifications, it can
be re-used as part of the sub-base section under streets.
• Native silt/clay that has a moisture content conducive for proper compaction can be re-used for
foundation exterior wall backfill or site fill. This can include any silt/clay that contains the inter-
bedded, buried topsoil layers. During excavation, these soils should be thoroughly mixed.
• Native sandy gravel can be re-used as foundation wall backfill, site fill, or as part of the sub-base
component of the new pavement sections. If it will be used for backfill or sub-base, all rocks
larger than about six inches should be removed. Due to rockiness of the gravel, we do not
recommend that any of it be used as granular structural fill under footings and interior slabs.
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STRUCTURAL DESIGN PARAMETERS
Seismic Design Factors
A main requirement of the Structural Engineer’s seismic analysis will be a determination of the site class.
Based on our on-site explorations and knowledge of the underlying geology, the site class for the project
site will be Site Class D (as per criteria presented in the 2012 IBC). This site class designation is valid as
long as our foundation recommendations are followed.
To obtain site-specific seismic loading and response spectrum parameters, a web-based application from
the USGS Earthquake Hazards Program can be used. The link to their web page is as follows:
https://earthquake.usgs.gov/hazards/designmaps/usdesign.php. Upon entering the program, the user
needs to enter the design code reference document, site soil classification, risk category, site latitude,
and site longitude.
Foundation Bearing Pressure
As long as our shallow foundation support recommendations are followed, the allowable bearing
pressure for all perimeter, interior, and exterior footings and any other foundation component is 4,500
pounds per square foot (psf). Allowable bearing pressures from transient loading (due to wind or
seismic forces) may be increased by 50 percent. We estimate that the above-referenced bearing
pressure will result in total settlements of one inch or less, with only minor differential settlements.
Note: In most boreholes, the SPT data in the native sandy gravel was well in excess of 30 blows/foot
and in many sample locations was over 50 blow/foot. This correlates to a dense to very dense gravel
condition. As a result, a higher bearing capacity of 4,500 psf is suitable for this site.
Lateral Earth Pressures
All foundation walls that will be fixed at the top prior to the placement of backfill should be designed for
an “at rest” equivalent fluid pressure of 60 pounds per cubic foot (pcf). Cantilevered retaining walls
may be designed for a lower, “active” equivalent fluid pressure of 45 pcf, provided either some slight
outward rotation of the wall is acceptable upon backfilling or the wall is constructed in such a way that
accommodates the expected rotation. These “at rest” and “active” design values are only applicable for
walls that will have backfill slopes of less than ten percent; and which will not be externally loaded by
surface pressures applied above and/or behind the wall.
Lateral forces from wind, earthquakes, and earth pressures on the opposite side of the structure will be
resisted by passive earth pressure against the buried portion of the foundation wall and by friction at
the bottom of the footing. Passive earth pressures in compacted, fine-grained backfill (silt/clay) should
be assumed to have an equivalent fluid pressure of 280 pcf; while a coefficient of friction of 0.5 is
estimated between cast-in-place concrete and the “target” native sandy gravel (or granular structural fill
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that is required to build up to footing grades). Actual footing loads (not factored or allowable loads)
should be used for calculating frictional resistance to sliding along the base of the footing. Please be
aware that the friction coefficient has no built-in factor of safety; therefore, an appropriate safety factor
should be selected and used in all subsequent calculations for each load case.
The above-referenced, equivalent fluid pressures (for at rest, active, and passive conditions) assume
that the wall will be backfilled with a suitable material that is compacted to an unyielding condition and
it will lie above the groundwater table and/or be well drained; thereby, preventing the backfill from
becoming saturated and the wall from experiencing hydrostatic pressure. Each of these design
pressures is for static conditions and will need to be factored accordingly to represent seismic loading.
We recommend that we be retained to evaluate lateral earth pressures for geometries and/or loading
conditions that do not meet the previously mentioned criteria.
Subgrade Reaction Modulus
As long as our interior slab support recommendations are followed (as presented later in the report),
the subgrade reaction modulus (k) can be assumed to be 200 pounds/cubic inch (pci). This is a modified
design value that uses the subgrade reaction modulus (k) of the native silt/cay and factors it (increases
it) based on a minimum section thickness of imported gravel to be placed under the slab. This design
value assumes the slab will be underlain by at least 18 inches of compacted, granular structural fill
(which can include a portion of the thickness being in-place, native sandy gravel such as will be the case
under the parking garage).
FOUNDATION AND EARTHWORK RECOMMENDATIONS
General
Three detailed illustrations of our foundation earthwork and drainage recommendations are included as
Figures 5, 6, and 7. Please refer to these exhibits during the review of this report since they show a
cross sectional view of our geotechnical recommendations. Provided below is a summary of the figures.
• Figure 5: This foundation detail is for the Parking Garage. This figure shows mass excavation
down to footing grades and the native sandy gravel. It also shows the options for subsurface
drainage and moisture protection to better protect the garage from high groundwater.
• Figure 6: This foundation detail is for Buildings 3 and 4 and shows the At-Grade Slab (Mass
Over-Excavation) option where the entire foundation footprint area is mass excavated down to
native sandy gravel and built back up to footing and slab grades with granular structural fill.
• Figure 7: This foundation detail is for Buildings 3 and 4 and shows the At-Grade Slab (Footing
Over-Excavation) option where only the footings are over-excavated down to native gravel and
built back up with granular structural fill. It also shows the minimum gravel section under slabs.
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Foundation Design
The shallow gravel conditions readily allow for use of a conventional foundation consisting of footings
and at-grade slabs. This site does not require a deep foundation or ground improvement system.
Note: Portions of some of the buildings that will be constructed on top of the parking garage will extend
outside of the foundation footprint area of the garage and bear on separate footings. To prevent lateral
loading of the garage walls by these foundation loads, it is recommended that footing elevation match
the parking garage footings (or that the walls be designed to handle these lateral loads).
Foundation Excavation – Parking Garage
As currently designed, the bottom slab elevation of the parking garage is set at 4768 feet. Due to the
site’s sloping topography, this means that the slab grade will about 4.0 feet below existing grades on the
north side of the structure and 6.0 feet below existing grade on the south side. The entire parking
garage area will be mass excavated down to perimeter and interior footing grades in a large excavation
that encompasses the footprint area. Based on the excavation depth, we expect that the native sandy
gravel will be encountered at the bottom of the excavation in most areas. There should be limited need
for further over-excavation under footings (down to “target” gravel) and subsequent replacement with
granular structural fill.
Foundation Excavation – Building 3 (Southeast Side)
As currently designed, the proposed finished floor elevation for Building 3 is set at 4775 feet, which is
between 0.0 and 2.0 feet above existing site grades. According to the structural drawings, this building
is littered with many interior footings. Due to the layout of the interior footings, the best foundation
excavation option will likely be mass over-excavation of the footprint area down to “target” gravel and
replacement with granular structural fill back up to footing and slab grades. This approach results in
more excavation and structural fill, but is often way faster and more efficient than “chasing” all footings
on an individual basis down to “target” gravel.
Foundation Excavation – Building 4 (South Side)
As currently designed, the proposed finished floor elevation for Building 4 is set at 4777.75 feet, which is
between 3.0 and 4.0 feet above existing site grades. According to the structural drawings, this building
contains many interior footings as well. Similar to Building 3, the best foundation excavation option will
likely be mass over-excavation of the footprint area down to “target” gravel and replacement with
granular structural fill back up to footing and slab grades. For this building, this will require a larger
amount of gravel import to build back up to interior footing and slab grades. Our thinking is that if site
fill needs to be hauled into the site anyway, it would be better to place the good gravel under the
buildings and make foundation earthwork easier rather than importing random fill for placement around
the buildings. Then the on-site material from the mass excavations could be simply used for the site fill.
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Standard Shallow Foundation (Conventional Footings)
• The “target” foundation bearing material for all footings is the “clean”, native sandy gravel that
was encountered at typical depths of 4.0 to 4.5 feet across the site. The “target” gravel is
identifiable based on its brown color, clean sandy composition, and presence of abundant large
and rounded gravels and cobbles.
• All perimeter, interior, and exterior footings must bear directly on the native sandy gravel or on
granular structural fill than in turn bears on this “target” material. All footing locations must be
dug down to and make contact with the good, clean sandy gravel. All overlying materials are
unsuitable for bearing and must be removed from under footings.
• Given the shallow gravel depth, we expect the parking garage footings will readily bear within
the “target” gravel with limited need for over-excavation and replacement with granular
structural fill. On the other hand for Buildings 3 and 4, perimeter footings and interior footings
(that are poured directly under the slab) will need to be over-excavated in order to ensure the
structural fill lies upon the “target” gravel.
• As discussed in the preceding report section, there are two options for foundation excavation.
In many instances, mass over-excavation of the entire foundation footprint area (down to
“target” gravel) and placement of a compacted, gravel building pad (back up to interior footing
and slab grades) makes the most sense. For exterior footings that are located well away from
the foundation wall, these elements can be excavated on an individual basis.
• There are several possible issues with over-excavating under interior footings, especially those
that are numerous and closely spaced and those that will bear on thick sections of granular
structural fill. First, the excavation needs to be precise (such that the footing will be centered)
and there may not be much unexcavated material left in the footprint area once all the footings
are excavated. Second, the width of the excavation is dependent the thickness of the structural
fill. For thick fills, this results in wide excavations. For situations like this, it is often better to
mass over-excavate the footprint area rather than monkeying around with footing excavation.
• In areas where granular structural fill is required to build back from native gravel up to footing
grade, the minimum width of compacted structural fill beyond the outside edge of the footing is
dependent on the thickness of structural fill under the footing. The minimum width is defined
as one-half the fill thickness. As an example, where fill thickness is 2.0 feet, the minimum width
beyond the edge of footing is 1.0 foot (on all sides of the footing). If the fill thickness is 8.0 feet
(like under interior footings), the minimum width would be 4.0 feet (on all sides of the footing).
• The granular structural fill section should be centered under all perimeter, interior, and exterior
footings and extend a minimum width (dependent on the fill thickness under footing) beyond
the outside edge of footings in all directions.
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• For mass excavation, all nearby exterior footings should be encapsulated by the excavation
limits where possible and it makes economic sense. At a minimum, the width of the excavation
(beyond edge of footing) must satisfy the requirements for structural fill thickness (see above).
Typically, mass excavations are dug about 5.0 feet beyond footings for more working space.
• Use a smooth foundation bucket to prevent any unnecessary disturbance to the native sandy
gravel subgrade surface. Prior to forming up the footings or placing granular structural fill under
the footing locations, the excavated gravel subgrade surface shall be vibratory re-compacted to
a dense and unyielding condition. Wherever possible, a large, smooth drum roller should be
used for gravel subgrade compaction.
• Granular structural fill can consist of imported 4”-minus sandy (pitrun) gravel or 1.5”-minus
crushed (roadmix) gravel. See a later report section for additional material specifications.
• We do not recommend re-using the native gravels for granular structural fill under foundation
elements due to their rocky composition and abundance of gravels/cobbles over four inches.
Materials with large rocks are hard to spread without causing aggregate segregation and hard to
adequately compact with smaller equipment.
• The granular structural fill section should be placed in multiple lifts (depending on thickness of
fill required and the size of the roller used) with each lift being vibratory compacted to a dense
and unyielding condition. See a later report section for additional compaction specifications. As
stated above, a large smooth drum roller should be used wherever possible. Small, walk-behind
sheepsfoot rollers and hand-held, jumping jack compactors should be used along edges and in
corners of the excavation.
• In areas where granular structural fill is placed under footings, it is important that the entire
minimum width of structural fill be well compacted. To minimize the possibility of inadequate
compaction along the sidewalls of the excavation (where it is tougher to compact due to space
constraints), the excavation width should be enlarged in excess of the minimum structural fill
width. By doing so, there is a little more excavation and structural fill used, but the minimum
width of structural fill under footings can be properly compacted with better assurance.
• The minimum depth of cover for frost protection of perimeter and exterior footings is four feet
(unless they are frost protected according to IBC standards). This dimension is measured from
bottom of footing up to the final grade of the ground surface.
Foundation Backfill
• Exterior foundation wall backfill can consist of any on-site soil, provided it is not organic or too
rocky, and has a moisture content that will allow for proper compaction. We recommend that
cobbles larger than about six inches be kept away from the foundation walls to prevent point
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loading the walls and possibly causing damage. Given the large cobbles in the native gravel,
only select material should be used for wall backfill. In landscape areas, topsoil should be placed
as backfill in the uppermost four to six inches of finished grade.
• Interior foundation wall backfill under slabs should be limited to high quality, granular structural
fill, such as imported 4”-minus sandy (pitrun) gravel or 1.5”-minus crushed (roadmix) gravel.
This material is easy to compact in tight and confined areas and does not have the settlement
potential that a silt/clay or cobbly soil has. See a later report section for additional material
specifications.
• All wall backfill materials should be placed in thin, level lifts and be vibratory compacted with a
walk-behind, sheepsfoot roller and jumping jack compactor to a dense and unyielding condition.
Pay particular attention to proper compaction under interior and exterior slabs.
Interior Slabs (Parking Garage and At-Grade Slabs)
• All organic topsoil must be stripped from under slabs.
• Under the parking garage slab, compacted clean crushed rock shall be used to infill around the
footings and build up to bottom of slab grade. This material is not only easy to place/compact,
but it will provide a free-draining drainage layer under the slab.
• At a minimum, at-grade slabs should be underlain by a 6-inch layer of compacted, clean crushed
rock that is supported on a 12-inch layer of compacted granular structural fill, which in turn
bears on a re-compacted native subgrade or embankment fill. The structural fill materials can
consist of import 4”-minus sandy (pitrun) gravel or 1.5”-minus crushed (roadmix) gravel. The
purpose for the minimum 18-inch gravel/crushed rock section is to create a stable working
platform and also to provide for a high strength section for uniform slab support.
• Prior to any fill placement, the subgrade soils should be re-compacted to a dense and unyielding
condition. A large roller should be used wherever possible.
Exterior Slabs (Sidewalks and Traffic Slabs)
• All organic topsoil must be stripped from under slabs.
• To limit frost heaving and settlement potential under sidewalk slabs located next to foundation
walls, we recommend these slabs bear on granular structural fill than in turn is supported on the
native gravels (similar to footing recommendations). By enlarging the foundation excavation, all
fine-grained soils will be removed from under slabs. A good material for use as structural fill
under exterior slabs is a thick section of compacted, clean crushed rock. This material is easy to
compact (in lifts) and is free-draining.
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• For sidewalk slabs that are located away from the foundation wall, they can be supported on
non-granular native soils or embankment fill. To minimize movement of these slabs during the
winter months, consideration should be given to bearing them on at least 12 inches of granular
structural fill.
• Standard sidewalks should be 4 inches thick and underlain by a minimum of 4 inches of clean
crushed rock that in turn is placed on re-compacted native subgrade soils or embankment fill.
• Traffic slabs shall be composed of 6 inches of reinforced concrete. We recommend a minimum
12-inch thick gravel section under these slabs that is comprised of 6 inches of 1.5”-minus base
course gravel and 6 inches of 6”-minus sub-base gravel.
SUBSURFACE DRAINAGE RECOMMENDATIONS
Subsurface Drainage (Parking Garage)
• The biggest potential risk at the site is seasonal high groundwater that was to reach the garage
floor elevation. The best way to reduce or eliminate this risk is to shallow the garage floor depth
(below existing site grades) as much as the site grading will allow. Right now, the deepest part
of the garage is about 2.0 feet above the 2018 seasonal high groundwater elevation. Obviously,
there is a chance that water could rise higher during future years.
• One option to provide some groundwater protection under and around the garage is to install a
sub-drain system (under the slab in the clean crushed rock layer) and a perimeter footing drain
around the outside. Normally, this is an easy solution. At this site, it is a little more complex for
a couple of reasons. First, the depth of the drain system would require a sump chamber and
pump(s) to lift the water to the ground surface since gravity discharge will not work. Second,
there is no easy place to discharge the water. Due to the high density of the development,
there is no on-site location and the storm drain chamber system is obviously not suitable (as this
would just recharge the ground water table next to the garage). Really, the only location for
discharge is in the street on the north side of the site. A concern with this is if the pumps need
to turn on and run for a period of time where is the water going to go and what downstream
properties could it impact. This would need to be analyzed by the Civil Engineer.
• The sub-drain system shall consist of an interconnected network of 4-inch, slotted or perforated,
PE or PVC piping that snakes through the clean crushed rock layer under the slab. The piping
shall hydraulically connect to the perimeter footing drain and be routed to the sump chamber.
• The exterior portion of the sub-drain system shall consist of a standard, 4-inch footing drain that
encircles the foundation footprint area. The piping shall be placed at footing grade, be well
bedded in clean crushed rock, and wrapped in light-weight, 4 oz. non-woven filter fabric. The
footing drain shall be connected with the underslab drain in a minimum of four locations.
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Subsurface Drainage (At-Grade Slabs)
• Provided Buildings 3 and 4 will be underlain by an at-grade slab that is set at or above finished
grades, there is no reason for any subsurface drainage improvements, such as footing drains.
MOISTURE PROTECTION RECOMMENDATIONS
Moisture Protection (Parking Garage)
• No vapor barrier is required under the parking garage slab. Similar to residential garages with
housing areas above, the parking garage will be temporarily or permanently open to the outside
air at the garage entry location. This should vent the space enough and prevent the buildup of
moisture in the garage.
• At a minimum, some consideration should be given to installing a water stop seal around the
perimeter interface between the top of the footing and the bottom of the foundation wall. This
would prevent the seepage of groundwater into the garage space along the top of the footing.
One of the biggest areas of risk is along the west wall of the garage adjacent to the subsurface
storm drain chamber system. At this location, the groundwater table elevation could be in a
mounded condition during a heavy run-off event. If water rose above the top of the footing,
this seal should cut it off from seeping into the garage.
• In lieu of installing a subsurface drain system under and around the garage, another option is
water-proofing the underside of the slab and outside walls of the garage. This could be done
with a liner/membrane or even an additive in the concrete mix. A possible structural issue with
this option is groundwater buoyancy forces on the bottom of the slab (in the event water was to
rise to this elevation). In order to prevent the potential for slab lifting and/or cracking, these
additional forces would need to be considered in the structural design of the slab.
• At a minimum (regardless if a sub-drain system is installed or not), the foundation walls shall be
damp-proofed with a commercial product meeting the building code. This is probably of most
important in the areas adjacent to and near the subsurface storm drain chamber system for the
same reasons as discussed above for the perimeter water stop seal.
Moisture Protection (At-Grade Slabs)
• A heavy duty vapor barrier shall underlie the entire floor area of the interior slab and be placed
on top of the clean crushed rock layer (directly below the slab). The purpose of the barrier is to
minimize the upward migration of water vapor into the building. The vapor barrier that we
recommend is a Stego 15-mil vapor barrier (which has a water vapor transmission rate of 0.006
or less as established by ASTM E 96). This product is available from MaCon Supply in Bozeman
and a specification sheet is included in Appendix E. All seams, joints, and pipe penetrations in
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the vapor barrier shall be sealed with Stego wrap polyethylene tape. Also, the vapor barrier
should be secured and sealed along the perimeter foundation walls.
• Foundation walls shall be damp-proofed as required by the building code.
SURFACE DRAINAGE RECOMMENDATIONS
Final site grading next to the building must establish and promote positive surface water drainage away
from the foundation footprint in all directions. Absolutely no water should be allowed to accumulate
against or flow along any exposed wall (and thereby soak into the foundation wall backfill). Concrete or
asphalt surfacing that abut the foundation should be designed with a minimum grade of two percent;
while adjacent landscaped areas should have a slope of at least five percent within ten feet of the wall.
Steeper side slopes than five percent (in landscape areas) are encouraged wherever possible. By doing
this, any minor settlements in the foundation backfill should not negatively affect the positive drainage
away from the building. To further reduce the potential for moisture infiltration along foundation walls,
backfill materials should be placed in thin lifts and be well compacted, and in landscaped areas, they
should be capped by four to six inches of low permeable topsoil. With the exception of the locations
that will be surfaced by concrete or asphalt, finished grades (next to foundation walls) should be set no
less than six inches below the top of the interior concrete slab or below the bottom of the sill plate for
framed floor applications.
Note: We recommend that the subsurface storm drain chamber system on the west side of the site be
hydraulically connect to the clean, sandy gravel that underlies the property at depths of 4.0 to 4.5 feet.
This can be accomplished by either bearing the chambers directly on the native gravel or on a section of
clean crushed rock that in turn bears on the gravel. Depending on the chamber elevation relative to the
top of the gravels, this may require some over-excavation and crushed rock replacement. The idea here
is to remove all silt/clay from under the system. This will allow to free and rapid infiltration down into
the native gravels. This should also minimize the likelihood for groundwater mounding on the west side
of the parking garage wall (which could rise up above the garage floor elevation).
FOUNDATION-RELATED FILL MATERIAL RECOMMENDATIONS
Provided below are specifications for the fill materials that are recommended for use during foundation
earthwork construction. These include on-site excavated soils, sandy (pitrun) gravel, crushed (road mix)
gravel, and clean crushed rock. Fill placement and compaction criteria follow the specifications.
Excavated Foundation Soils
The soils that will be excavated during foundation earthwork will include existing pavement/concrete
surfacing materials, gravel/random fill, topsoil, silt/clay, and sandy gravel. Please refer to the attached
borehole and test pit logs for more details. The acceptable re-uses of excavated soils are detailed in an
earlier section of the report that is entitled “Excavation and Re-Use of On-Site Soils”.
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Sandy (pitrun) Gravel
Sandy (pitrun) gravel is a granular structural fill alternative for placement under footings and slabs and
behind walls. This material shall be a non-plastic, well-graded, mixture of clean, sand and gravel with
100 percent of its gravels/cobbles passing a four-inch screen and between 2 and 10 percent of its
silt/clay particles (by weight) finer than the No. 200 sieve. It should meet all material and gradation
specifications as presented in Section 02234 of the Montana Public Works Standard Specifications
(MPWSS) for 4”-minus, uncrushed, sub-base course gravel.
Crushed (road mix) Gravel
Crushed (road mix) gravel is a granular structural fill alternative for placement under footings and slabs
and behind walls. This material shall be a non-plastic, well-graded, mixture of clean, sand and gravel
that is processed (crushed) such that 100 percent of its rock fragments pass a 1-1/2-inch screen and
between 0 and 8 percent of its silt/clay particles (by weight) are finer than the No. 200 sieve. It should
meet all material and gradation specifications as presented in Section 02235 of the MPWSS for 1-1/2”-
minus, crushed, base course gravel.
Clean Crushed Rock
The primary uses for crushed rock include placement under concrete slabs and behind foundation and
retaining walls for drainage-related purposes. The crushed rock shall consist of a clean assortment of
angular rock fragments with 100 percent passing a one-inch screen and less than 1 percent (by weight)
finer than the No. 100 sieve. This aggregate product needs to be manufactured by a crushing process
and over 50 percent of its particles must have fractured faces. It is not acceptable to use rock that
contains abundant spherical particles for foundation-related applications.
Fill Placement and Compaction
All fill materials should be placed in uniform, horizontal lifts and compacted to an unyielding condition.
This includes clean crushed rock, which can be readily compacted by vibratory means. In general, the
maximum “loose lift thickness” for fill materials (prior to compaction) should be limited to 12 inches for
large, self-propelled rollers, 6 inches for remote-controlled, dual drum rollers and walk-behind, jumping
jack compactors, and 4 inches for walk-behind vibratory plate compactors. The moisture content of any
material to be compacted should be within approximately two percent (+/-) of its optimum value for
maximum compaction.
Special attention must be paid to the proper compaction of structural fill materials along the edges and
in the corners of the foundation excavation. These areas are usually “tight and confined” and, as a
result, cannot be adequately compacted with large equipment. For compaction of these areas, smaller
hand-held or walk-behind compactors will need to be used. The only other alternative is to open up the
size of the excavations a little wider in order to permit the use of larger rollers.
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Provided in Table 6 (on the following page) are compaction recommendations for general foundation
applications. These are presented as a percentage of the maximum dry density of the fill material as
defined in ASTM D-698.
Table 6. Compaction Recommendations (Application vs. Percent Compaction)
APPLICATION % COMPACTION
Granular Structural Fill Under Footings and Interior Slabs: 97
Embankment Fill Under Interior Slabs: 97
Embankment Fill Under Exterior Slabs: 95
Backfill Behind Foundation and Retaining Walls: 95
Clean Crushed Rock Under Slabs and Behind Walls: N/A (Vibration Required)
Site Fill Around Building and Under Concrete and Pavement Areas: 95
UNDERGROUND UTILITY RECOMMENDATIONS
Given the shallow gravel conditions, we do not expect any issues with the utility installation. All utilities
should be designed and constructed in accordance with City of Bozeman (COB) standards, Montana
Public Works (MPW) specifications, and COB modifications to the MPW specifications. Probably the
biggest thing to keep in mind is that the native gravels contain abundant and large gravels and cobbles.
In order to adequately protect the piping during the installation and backfill (from point loading caused
by large rocks), we recommend that all pipes be well bedded with crushed rock both below and above
the pipes. Also, rocks larger than about six inches should be removed from the first lift of trench backfill.
Only backfill that is relatively dry should be used such that proper compaction can be achieved. Trench
backfill is typically re-compacted to 95% of the standard proctor density.
Note: Large sections of existing paved streets will be tore up for new utility installations. To prevent
poor compaction and possible trench settlement issues, we recommend that all trenches in the existing
city streets be fully backfilled with sandy gravel. This can include a combination of native gravels as well
as imported gravel. Based on the depth of the native gravel and our pavement section recommendation
for trench re-surfacing, this will not amount to a very large quantity of imported trench backfill. Besides
the minimizing of trench settlement potential, the sole use of gravel backfill will eliminate the need for
any geotextile separation fabric at the bottom of the pavement section materials.
PAVEMENT SECTION RECOMMENDATIONS
Several pavement sections have been developed for the different aspects of this project. All assume
stable silt/clay subgrade conditions that are dry, hard, and can be compacted. If soft subgrade soils are
found (which we do not expect will be the case), they will first need to be opened up, scarified, and
dried. See Appendix D for our pavement design calculations and Tables 7 through 16 for the pavement
design sections. A summary of the different sections is provided below.
Cottonwood + Ida Mixed Use Development
E. Cottonwood St. / N. Ida Ave. – Bozeman, MT
Project: 18-054
March 15, 2019
Allied Engineering Services, Inc. Page 24
• E. Aspen Street (New): See Table 7. This is for the new paved section of Aspen from Wallace to
Ida. It presents Option 1, which includes a thicker section of sub-base and normal woven fabric.
This section is designed for 150,000 ESALs.
• N. Ida Avenue (Reconstruction): See Table 8. This is for the widened and reconstructed section
of Ida from Cottonwood to Front. It presents Option 1, which includes a thicker section of sub-
base and normal woven fabric. This section is designed for 150,000 ESALs.
• E. Aspen Street (New): See Table 9. This is for the new paved section of Aspen from Wallace to
Ida. It presents Option 2, which is an alternative section that includes a little thinner section of
sub-base and special, high strength geosynthetic. Although the geosynthetic is more expensive,
the excavation depth is less (which is good in areas of existing utilities) and the quantity of sub-
base is reduced. According to Mirafi software, this reinforced section is good for 450,000 ESALs.
• N. Ida Avenue (Reconstruction): See Table 10. This is for the widened and reconstructed section
of Ida from Cottonwood to Front. It presents Option 2, which is an alternative section that
includes a little thinner section of sub-base and special, high strength geosynthetic. Although
the geosynthetic is more expensive, the excavation depth is less (which is good in areas of
existing utilities) and the quantity of sub-base is reduced. According to Mirafi software, this
reinforced section is good for 450,000 ESALs.
• E. Cottonwood Street (Utility Trench): See Table 11. This is for the re-surfacing of utility trench
excavations in Cottonwood. If the trenches are fully backfilled with gravel (as recommended)
meaning the soils at subgrade elevation will be gravel, then the separation fabric at the bottom
of the pavement section can be eliminated. This section is designed for 150,000 ESALs.
• N. Wallace Avenue (Utility Trench): See Table 12. This is for the re-surfacing of utility trench
excavations in Wallace. If the trenches are fully backfilled with gravel (as recommended)
meaning the soils at subgrade elevation will be gravel, then the separation fabric at the bottom
of the pavement section can be eliminated. This section is designed for 150,000 ESALs.
• E. Cottonwood Street (Parking Stalls): See Table 13. This is for the new parking stalls on the
north side of Cottonwood. This section is designed for 50,000 ESALs.
• Front Street (Road and Parking Stalls): See Table 14. This is for the new parking stalls on the
west side of Front as well as the re-surfacing of Front. This section is designed for 50,000 ESALs.
• West Side Service Drive (New): See Table 15. This is for the new emergency vehicle access on
the west side of the site. This section is designed for 50,000 ESALs.
• E. Aspen Street – Gravel Portion to East of Ida (New): See Table 16. This is for re-surfacing of
the gravel portion of Aspen from Ida to Front. This section is designed for 10,000 ESALs.
Cottonwood + Ida Mixed Use Development
E. Cottonwood St. / N. Ida Ave. – Bozeman, MT
Project: 18-054
March 15, 2019
Allied Engineering Services, Inc. Page 25
Table 7. Pavement Section Design – E. Aspen St. (New) – Option 1 – Stable Subgrade
COMPONENT COMPACTED THICKNESS (IN)
Asphalt Concrete: 3
Base Course – 1.5”-Minus Crushed (road mix) Gravel: 6
Sub-Base Course – 6”-Minus Uncrushed Sandy (pitrun) Gravel: 15
315 lb. Woven Geotextile Fabric (Mirafi 600X or Approved Equal): Yes (for silt/clay subgrade)
Stable Subgrade Soils (Less Topsoil): Compacted to 95%
TOTAL SECTION THICKNESS: 24
Notes: 1) Option 1 is applicable for stable subgrade situations. We expect stable subgrade soils in all areas of the site.
2) Subgrade soils should be re-compacted and proof-rolled to confirm stability.
3) If subgrade ruts and deflects when proof-rolled with loaded truck, then the subgrade is unstable.
4) If unstable conditions exist, either the subgrade will need to be dried or the sub-base gravel section thickened.
5) Separation fabric is recommended for all silt/clay and dirty gravel subgrade conditions.
6) If areas of the subgrade consist of clean sandy gravel, no separation fabric is necessary at these locations.
Table 8. Pavement Section Design – N. Ida Ave. (Reconstruction) – Option 1 – Stable Subgrade
COMPONENT COMPACTED THICKNESS (IN)
Asphalt Concrete: 3
Base Course – 1.5”-Minus Crushed (road mix) Gravel: 6
Sub-Base Course – 6”-Minus Uncrushed Sandy (pitrun) Gravel: 15
315 lb. Woven Geotextile Fabric (Mirafi 600X or Approved Equal): Yes (for silt/clay subgrade)
Stable Subgrade Soils (Less Topsoil): Compacted to 95%
TOTAL SECTION THICKNESS: 24
Notes: 1) See Table 7 notes. These all apply to this section as well.
Table 9. Alt. Pavement Section Design – E. Aspen St. (New) – Option 2 – Stable Subgrade
COMPONENT COMPACTED THICKNESS (IN)
Asphalt Concrete: 3
Base Course – 1.5”-Minus Crushed (road mix) Gravel: 6
Sub-Base Course – 6”-Minus Uncrushed Sandy (pitrun) Gravel: 12
Mirafi RS580i High Strength Geosynthetic (No Approved Equal): Yes (for all subgrade soils)
Stable Subgrade Soils (Less Topsoil): Compacted to 95%
TOTAL SECTION THICKNESS: 21
Notes: 1) See Table 7 notes. These all apply to this section as well.
Cottonwood + Ida Mixed Use Development
E. Cottonwood St. / N. Ida Ave. – Bozeman, MT
Project: 18-054
March 15, 2019
Allied Engineering Services, Inc. Page 26
Table 10. Alt. Pavement Section Design – N. Ida Ave. (Reconstruction) – Option 2 – Stable Subgrade
COMPONENT COMPACTED THICKNESS (IN)
Asphalt Concrete: 3
Base Course – 1.5”-Minus Crushed (road mix) Gravel: 6
Sub-Base Course – 6”-Minus Uncrushed Sandy (pitrun) Gravel: 12
Mirafi RS580i High Strength Geosynthetic (No Approved Equal): Yes (for all subgrade soils)
Stable Subgrade Soils (Less Topsoil): Compacted to 95%
TOTAL SECTION THICKNESS: 21
Notes: 1) See Table 7 notes. These all apply to this section as well.
Table 11. Pavement Section Design – E. Cottonwood St. (Util. Trench) – Option 1 – Stable Subgrade
COMPONENT COMPACTED THICKNESS (IN)
Asphalt Concrete: 3
Base Course – 1.5”-Minus Crushed (road mix) Gravel: 6
Sub-Base Course – 6”-Minus Uncrushed Sandy (pitrun) Gravel: 15
315 lb. Woven Geotextile Fabric (Mirafi 600X or Approved Equal): Yes (for silt/clay subgrade)
Stable Subgrade Soils (Less Topsoil): Compacted to 95%
TOTAL SECTION THICKNESS: 24
Notes: 1) See Table 7 notes. These all apply to this section as well.
Table 12. Pavement Section Design – N. Wallace Ave. (Utility Trench) – Option 1 – Stable Subgrade
COMPONENT COMPACTED THICKNESS (IN)
Asphalt Concrete: 3
Base Course – 1.5”-Minus Crushed (road mix) Gravel: 6
Sub-Base Course – 6”-Minus Uncrushed Sandy (pitrun) Gravel: 15
315 lb. Woven Geotextile Fabric (Mirafi 600X or Approved Equal): Yes (for silt/clay subgrade)
Stable Subgrade Soils (Less Topsoil): Compacted to 95%
TOTAL SECTION THICKNESS: 24
Notes: 1) See Table 7 notes. These all apply to this section as well.
Cottonwood + Ida Mixed Use Development
E. Cottonwood St. / N. Ida Ave. – Bozeman, MT
Project: 18-054
March 15, 2019
Allied Engineering Services, Inc. Page 27
Table 13. Pavement Section Design – E. Cottonwood St. (Park. Stalls) – Option 1 – Stable Subgrade
COMPONENT COMPACTED THICKNESS (IN)
Asphalt Concrete: 3
Base Course – 1.5”-Minus Crushed (road mix) Gravel: 6
Sub-Base Course – 6”-Minus Uncrushed Sandy (pitrun) Gravel: 9
315 lb. Woven Geotextile Fabric (Mirafi 600X or Approved Equal): Yes (for silt/clay subgrade)
Stable Subgrade Soils (Less Topsoil): Compacted to 95%
TOTAL SECTION THICKNESS: 18
Notes: 1) See Table 7 notes. These all apply to this section as well.
Table 14. Pavement Section Design – Front St. (Road/Parking Stalls) – Option 1 – Stable Subgrade
COMPONENT COMPACTED THICKNESS (IN)
Asphalt Concrete: 3
Base Course – 1.5”-Minus Crushed (road mix) Gravel: 6
Sub-Base Course – 6”-Minus Uncrushed Sandy (pitrun) Gravel: 9
315 lb. Woven Geotextile Fabric (Mirafi 600X or Approved Equal): Yes (for silt/clay subgrade)
Stable Subgrade Soils (Less Topsoil): Compacted to 95%
TOTAL SECTION THICKNESS: 18
Notes: 1) See Table 7 notes. These all apply to this section as well.
Table 15. Pavement Section Design – W. Side Service Drive (New) – Option 1 – Stable Subgrade
COMPONENT COMPACTED THICKNESS (IN)
Asphalt Concrete: 3
Base Course – 1.5”-Minus Crushed (road mix) Gravel: 6
Sub-Base Course – 6”-Minus Uncrushed Sandy (pitrun) Gravel: 9
315 lb. Woven Geotextile Fabric (Mirafi 600X or Approved Equal): Yes (for silt/clay subgrade)
Stable Subgrade Soils (Less Topsoil): Compacted to 95%
TOTAL SECTION THICKNESS: 18
Notes: 1) See Table 7 notes. These all apply to this section as well.
Cottonwood + Ida Mixed Use Development
E. Cottonwood St. / N. Ida Ave. – Bozeman, MT
Project: 18-054
March 15, 2019
Allied Engineering Services, Inc. Page 28
Table 16. Pavement Section Design – E. Aspen St. – Grvl. Road (New) – Option 1 – Stable Subgrade
COMPONENT COMPACTED THICKNESS (IN)
Asphalt Concrete: 0
Base Course – 1.5”-Minus Crushed (road mix) Gravel: 6
Sub-Base Course – 6”-Minus Uncrushed Sandy (pitrun) Gravel: 12
315 lb. Woven Geotextile Fabric (Mirafi 600X or Approved Equal): Yes (for silt/clay subgrade)
Stable Subgrade Soils (Less Topsoil): Compacted to 95%
TOTAL SECTION THICKNESS: 18
Notes: 1) See Table 7 notes. These all apply to this section as well.
Construction Notes
• Subgrade soils can consist of any non-organic soil, including silt/clay, sandy gravel, or a mix of
both. During our explorations, all near surface soils were in a stiff and dry condition. As a result,
we are expecting stable subgrade conditions throughout the site.
• If subgrade soils are wet during construction due to either high groundwater or precipitation,
they will need to be scarified, opened up, turned over, and allowed to dry out. If the moisture
content can be reduced enough, the in-place soils can be re-stabilized. The subgrade soils shall
be re-compacted and proof-rolled to verify that adequate conditions exist.
• If subgrade soils are highly unstable and cannot be corrected by scarification and drying, then
modifications to the design pavement section will be necessary. The options include thickening
the sub-base gravel section, substituting the woven fabric with a stronger geosynthetic fabric or
geogrid, or a combination of both.
• Any clean, sandy gravel that is separated and salvaged during foundation excavation or other
site earthwork can be re-used as part of the sub-base gravel section of the road improvements.
All rocks larger than about 6 inches shall be removed (such that the material gradation is similar
to an imported sub-base material).
• As discussed earlier in the report, the existing concrete and pavement surfacing materials can be
processed, stripped, salvaged, and re-used as part of the sub-base section under roads as well.
The materials shall be crushed to a 6”-minus aggregate size and be thoroughly blended/mixed
with gravel at a ratio of <50% recycled products to >50% gravel.
Pavement Section Materials, Placement, and Compaction
The sub-base and base course materials that comprise the granular parts of the pavement section shall
consist of 6-inch minus uncrushed sandy (pitrun) gravel and 1-1/2-inch minus crushed (road mix) gravel,
Cottonwood + Ida Mixed Use Development
E. Cottonwood St. / N. Ida Ave. – Bozeman, MT
Project: 18-054
March 15, 2019
Allied Engineering Services, Inc. Page 29
respectively. Both of these gravel courses shall meet the material and gradation specifications as
presented in MPWSS, Sections 02234 and 02235. Under normal circumstances, the gravel products shall
be placed in loose lifts not exceeding 12 inches in thickness (depending on size of the compactor) and
compacted to at least 95 percent of the maximum dry density as defined in ASTM D-698. However, if
subgrade soils are found to be overly moist, soft, and unstable; then the initial lift of the sub-base gravel
section should be thickened to prevent damaging and tearing the geotextile fabric with the construction
equipment. Asphalt concrete pavement shall meet the specifications in MPWSS Section 02510; and be
compacted to 93 percent (min.) of the Rice mix density.
COLD/WINTER WEATHER CONSTRUCTION
If foundation construction will occur during the cold/winter weather season, the Contractor shall take all
necessary precautions to prevent the earthwork from freezing and/or from being contaminated with
intermixed snow. Exposed subgrade and fill material surfaces (under footings, slabs, and walls) should
be adequately covered on a nightly basis with concrete insulation blankets to prevent frost penetration
and to protect them from snow accumulation. All soils that are used for fill under or around foundation
components should be relatively dry, be free of snow and frozen clods, and must not be placed when it
is snowing heavily and/or sticking to the ground. Absolutely no fill materials (or the pouring of footings)
should be placed over layers of snow or on frozen soils, which may be in a “frost-heaved condition”.
When earthwork will proceed during the non-optimal times of the year, we recommend that it be
performed in an expeditious manner; thereby, minimizing the time that the foundation excavation is left
open and exposed to the elements. In addition, positive surface drainage should be established away
from the excavation in order to prevent the entry of surface water runoff and the saturation of the
foundation soils. Please understand that carelessness with respect to the above-referenced items can
potentially lead to foundation settlement problems in the spring when the frost thaws and/or the snow
melts. Cold weather concrete practices/methods should be implemented when the conditions dictate.
CONSTRUCTION INSPECTION
If Allied Engineering will be required to verify that site development proceeded in accordance with the
geotechnical recommendations, we must be retained for inspection and oversight during the foundation
earthwork.
PRODUCTS
Provided in Table 17 (on the following page) is a reference guide for all products (other than foundation-
related fill material) that have been recommended within this report. Listed below is the name of the
product, its intended use, and where it can be obtained. The manufacturer specification sheet for each
of these products is included in Appendix E. These specified products or “approved equals” are available
at either MaCon Supply in Bozeman/Four Corners, MT, Core & Main (formerly HD Supply Waterworks)
in Belgrade, MT, HD Fowler in Belgrade, MT, or Brock White in Bozeman, MT.
Cottonwood + Ida Mixed Use Development
E. Cottonwood St. / N. Ida Ave. – Bozeman, MT
Project: 18-054
March 15, 2019
Allied Engineering Services, Inc. Page 31
REFERENCES
1. International Code Council, 2012, “International Building Code”.
2. Montana Contractors’ Association, April 2010, “Montana Public Works Standard Specifications”,
Sixth Edition.
3. Slagle, Steven E., May 1995, “Geohydrologic Conditions and Land Use in the Gallatin Valley,
Southwestern Montana, 1992-93”, U.S. Department of the Interior, U.S. Geological Survey.
P:\Projects\2018\18-054 Cottonwood + Ida - Geotech\Design\Geotech\Report 2 - Final Report\Text\18-054 geotechrpt.03.15.19.doc
LIST OF FIGURES
FFiigguurree 11 –– VViicciinniittyy MMaapp
FFiigguurree 22 –– GGeeoollooggyy MMaapp
FFiigguurree 33 –– BBHHss aanndd TTPPss ww// NNaattiivvee GGrraavveell DDeepptthh
FFiigguurree 44 –– MMWWss ww// 22001188 HHiigghh GGrroouunnddwwaatteerr
FFiigguurree 55 –– FFoouunnddaattiioonn DDeettaaiill –– PPaarrkkiinngg GGaarraaggee
FFiigguurree 66 –– FFoouunnddaattiioonn DDeettaaiill –– AAtt--GGrraaddee SSllaabb ((MMaassss EExxcc..))
FFiigguurree 77 –– FFoouunnddaattiioonn DDeettaaiill –– AAtt--GGrraaddee SSllaabb ((FFoooottiinngg EExxcc..))
FIGURECivil Engineering
Geotechnical Engineering
Land Surveying
32 DISCOVERY DRIVE . BOZEMAN, MT 59718
PHONE (406) 582-0221 . FAX (406) 582-5770
www.alliedengineering.com
COTTONWOOD + IDA DEVELOPMENT
BHs & TPs w/ NATIVE GRAVEL DEPTH
BOZEMAN, MONTANA
3
N
TP-1
LEGEND
BOREHOLE LOCATION
(APPROXIMATE)
E COTTONWOOD ST
N
W
A
L
L
A
C
E
A
V
E
TP-2
TP-3
TP-4 TP-5
N
I
D
A
A
V
E
E ASPEN ST
TEST PIT LOCATION
(APPROXIMATE)
BH-6
BH-7
BH-4 BH-5
BH-1
BH-2
BH-3
4.5'
4.0'
4.0'
4.0'
4.5'
4.0'4.0'
4.5'4.0'
4.3'
4.0'
4.0'
BH-1
4.0'
TP-1
4.0'
FIGURECivil Engineering
Geotechnical Engineering
Land Surveying
32 DISCOVERY DRIVE . BOZEMAN, MT 59718
PHONE (406) 582-0221 . FAX (406) 582-5770
www.alliedengineering.com
COTTONWOOD + IDA DEVELOPMENT
MWs w/ 2018 HIGH GROUNDWATER
BOZEMAN, MONTANA
4
N
TP-1
LEGEND
BOREHOLE LOCATION
(APPROXIMATE)
E COTTONWOOD ST
N
W
A
L
L
A
C
E
A
V
E
TP-2
TP-3
TP-4 TP-5
N
I
D
A
A
V
E
E ASPEN ST
TEST PIT LOCATION
(APPROXIMATE)
BH-6
BH-7
BH-4 BH-5
BH-1
BH-2
BH-3
8.5'8.8'
7.8'
8.0'
8.5'
BH-1
TP-1
8.0'
LIST OF APPENDICES
AAppppeennddiixx AA –– OOnn--SSiittee EExxpplloorraattiioonn LLooggss AAnndd PPhhoottooss
AAppppeennddiixx BB –– NNeeaarrbbyy SSooiillss IInnffoorrmmaattiioonn
AAppppeennddiixx CC –– GGrroouunnddwwaatteerr MMoonniittoorriinngg DDaattaa
AAppppeennddiixx DD –– AAsspphhaalltt PPaavveemmeenntt SSeeccttiioonn DDeessiiggnn
AAppppeennddiixx EE –– PPrroodduuccttss
AAppppeennddiixx FF –– LLiimmiittaattiioonnss OOff YYoouurr GGeeootteecchhnniiccaall RReeppoorrtt
APPENDIX A
OOnn--SSiittee EExxpplloorraattiioonn LLooggss AAnndd PPhhoottooss
EExxppllaannaattiioonn ooff SSooiill CCllaassssiiffiiccaattiioonn NNoommeennccllaattuurree
77 BBoorreehhoollee LLooggss ((BBHH--11,, BBHH--22,,……..tthhrroouugghh BBHH--77))
55 TTeesstt PPiitt LLooggss ((TTPP--11,, TTPP--22,,……..tthhrroouugghh TTPP--55))
1100 TTeesstt PPiitt PPhhoottooss ((EExxccaavvaattiioonn SSiiddeewwaallllss aanndd SSppooiill PPiilleess))
APPENDIX B
NNeeaarrbbyy SSooiillss IInnffoorrmmaattiioonn
EExxpplloorraattiioonn MMaapp ffoorr AArreeaa ttoo SSoouutthh ooff PPrroojjeecctt SSiittee
55 BBoorreehhoollee LLooggss ((BBHH--11,, BBHH--22,,……..tthhrroouugghh BBHH--55))
44 TTeesstt PPiitt LLooggss ((TTPP--11,, TTPP--22,,……..tthhrroouugghh TTPP--44))
APPENDIX C
GGrroouunnddwwaatteerr MMoonniittoorriinngg DDaattaa
22001188 SSeeaassoonnaall HHiigghh DDaattaa ((MMWW--11 tthhrroouugghh MMWW--55))
Groundwater Monitoring Data: Summary of Wells
Project Name: Cottonwood + Ida
Project Number: 18-054
Location: See Maps
Date Installed: 4/24/2018
Installed By: AESI
NOTES:
1) MW-1 through MW-5 were installed during test pit explorations on 04/24/2018.
2) MW-1 was installed in TP-1, located at SW corner of property.
3) MW-2 was installed in TP-2, located at SE corner of property.
4) MW-3 was installed in TP-3, located near center of property.
5) MW-4 was installed in TP-4, located at NW corner of property.
6) MW-5 was installed in TP-5, located at NE corner of property.
7) Highest water measurement to date in each well:
MW-1 MW-2 MW-3 MW-4 MW-5
Date Time Depth to GW Depth to GW Depth to GW Depth to GW Depth to GW
below EG below EG below EG below EG below EG
(feet) (feet) (feet) (feet) (feet)
4/24/2018 NA 9.00 10.00 9.25 9.00 9.33
4/30/2018 8:45 AM 8.03 8.52 7.77 8.46 8.82
5/7/2018 4:45 PM 8.06 8.68 7.90 8.62 9.01
5/15/2018 8:15 AM 7.98 8.65 7.86 8.56 9.05
5/22/2018 8:15 AM 8.17 8.82 8.06 8.78 9.26
5/29/2018 8:00 AM 8.14 8.79 8.03 8.74 9.26
6/5/2018 8:15 AM 8.10 8.72 7.98 8.74 9.23
6/12/2018 8:00 AM 8.45 9.05 8.32 9.07 9.56
6/19/2018 3:15 PM 8.31 8.96 8.21 8.95 9.35
6/26/2018 8:15 AM 8.52 9.08 8.38 9.13 9.59
7/3/2018 3:45 PM 8.50 9.04 8.35 9.10 9.52
7/9/2018 8:00 AM 8.83 9.38 8.68 9.45 9.86
7/16/2018 2:00 PM 9.17 9.69 9.02 9.79 10.18
7/24/2018 11:25 AM 9.54 10.03 9.36 10.06 10.48
7/31/2018 11:30 AM 9.89 10.34 9.67 10.37 10.76
32 Discovery Drive
Bozeman, MT 59718Phone (406) 582-0221
Fax (406) 582-5770
Groundwater Monitoring Data: Page 1 of 1
APPENDIX D
AAsspphhaalltt PPaavveemmeenntt SSeeccttiioonn DDeessiiggnn
AAssppeenn SSttrreeeett ((NNeeww))
IIddaa AAvveennuuee ((RReeccoonnssttrruuccttiioonn))
EExxppllaannaattiioonn ooff DDeessiiggnn IInnppuutt PPaarraammeetteerrss ((AAssppeenn aanndd IIddaa))
AAlltteerrnnaattiivvee PPaavveemmeenntt SSeeccttiioonn ((AAssppeenn aanndd IIddaa))
CCoottttoonnwwoooodd SSttrreeeett ((UUttiilliittyy TTrreenncchh))
WWaallllaaccee AAvveennuuee ((UUttiilliittyy TTrreenncchh))
CCoottttoonnwwoooodd SSttrreeeett ((PPaarrkkiinngg SSttaallllss))
FFrroonntt SSttrreeeett ((RRooaadd aanndd PPaarrkkiinngg SSttaallllss))
WWeesstt SSiiddee SSeerrvviiccee DDrriivvee ((NNeeww))
AAssppeenn SSttrreeeett –– GGrraavveell PPoorrttiioonn ttoo EEaasstt ooff IIddaa ((NNeeww))
Pavement Section Design: Page 1 of 1
PAVEMENT DESIGN - Aspen St. (New) - Option 1
(Note: The Option 1 design requires stable subgrade (ie. dry, hard, compacted, no rutting/deflection).
Project: Cottonwood + Ida Mixed-Use Development - Bozeman, MT
Project Number: 18-054
Date: March 6, 2019
Prepared By: Lee Evans
Important Notes:
1) A traffic loading of 150,000 ESALs is conservative for local city streets in Bozeman.
2) Subgrade soils will consist of sandy silt/sandy lean clay having a soaked CBR of 2.0 to 3.0.
DESIGN INPUT PARAMETERS
ESALs (total)150,000
Subgrade CBR, (%)2.5
Subgrade Resilient Modulus, MR (psi)3,750
Reliability, R (%)90
Standard Normal Deviate, ZR -1.282
Overall Standard Deviation, So 0.45
Initial Serviceability, po 4.2
Terminal Serviceability, pt 2.0
Design Serviceability Loss, (PSI)2.2
5.17609 = left side
Required Structural Number, RSN 3.20 5.1927 = right side
(Manipulate RSN such that the left and right side of equation match.)
Asphalt Concrete Layer Coefficient, a1 0.41
Base Course Layer Structural Coefficient, a2 0.14
Base Course Layer Drainage Coefficient, m2 0.90
Sub-Base Course Layer Structural Coefficient, a3 0.09
Sub-Base Course Layer Drainage Coefficient, m3 0.90
DESIGN PAVEMENT SECTION
Asphalt Concrete Thickness, D1 (in)3.0
Granular Base Course Thickness, D2 (in)6.0
Granular Sub-Base Course Thickness, D3 (in)15.0
Calculated Structural Number, CSN 3.20
(Manipulate layer thicknesses such that CSN matches or exceeds RSN.)
DESIGN EQUATION
Pavement Section Design: Page 1 of 1
PAVEMENT DESIGN - Ida Ave. (Reconstruction) - Option 1
(Note: The Option 1 design requires stable subgrade (ie. dry, hard, compacted, no rutting/deflection).
Project: Cottonwood + Ida Mixed-Use Development - Bozeman, MT
Project Number: 18-054
Date: March 6, 2019
Prepared By: Lee Evans
Important Notes:
1) A traffic loading of 150,000 ESALs is conservative for local city streets in Bozeman.
2) Subgrade soils will consist of sandy silt/sandy lean clay having a soaked CBR of 2.0 to 3.0.
DESIGN INPUT PARAMETERS
ESALs (total)150,000
Subgrade CBR, (%)2.5
Subgrade Resilient Modulus, MR (psi)3,750
Reliability, R (%)90
Standard Normal Deviate, ZR -1.282
Overall Standard Deviation, So 0.45
Initial Serviceability, po 4.2
Terminal Serviceability, pt 2.0
Design Serviceability Loss, (PSI)2.2
5.17609 = left side
Required Structural Number, RSN 3.20 5.1927 = right side
(Manipulate RSN such that the left and right side of equation match.)
Asphalt Concrete Layer Coefficient, a1 0.41
Base Course Layer Structural Coefficient, a2 0.14
Base Course Layer Drainage Coefficient, m2 0.90
Sub-Base Course Layer Structural Coefficient, a3 0.09
Sub-Base Course Layer Drainage Coefficient, m3 0.90
DESIGN PAVEMENT SECTION
Asphalt Concrete Thickness, D1 (in)3.0
Granular Base Course Thickness, D2 (in)6.0
Granular Sub-Base Course Thickness, D3 (in)15.0
Calculated Structural Number, CSN 3.20
(Manipulate layer thicknesses such that CSN matches or exceeds RSN.)
DESIGN EQUATION
Explanation of Design Input Parameters: Page 1 of 3
PAVEMENT SECTION DESIGN - Local City Streets
(EXPLANATION OF DESIGN INPUT PARAMETERS)
Design Life (yr): 20
ESALs (total) – Local City Streets: 150,000
Soaked Subgrade CBR, (%): 2.5
Subgrade Resilient Modulus, MR (psi): 3,750
Reliability, R (%): 90
Standard Normal Deviate, ZR: -1.282
Overall Standard Deviation, So: 0.45
Initial Serviceability, po: 4.2
Terminal Serviceability, pt: 2.0
Design Serviceability Loss, (PSI) 2.2
Asphalt Concrete Layer Coefficient, a1: 0.41
Base Course Layer Structural Coefficient, a2: 0.14
Base Course Layer Drainage Coefficient, m2: 0.90
Sub-Base Course Layer Structural Coefficient, a3: 0.09
Sub-Base Course Layer Drainage Coefficient, m3: 0.90
Design Life: A design life of 20 years is typical for new asphalt projects in Bozeman,
including city streets and alleys as well as private facilities.
ESALs (total) – Local City Streets: According to Table 18.12 in Reference 1, the
estimated design Equivalent 18,000-lb Single Axle Load (ESAL) value for roadways
subjected to light vehicle and medium truck traffic ranges from 10,000 to 1,000,000.
The Cottonwood + Ida Mixed-Use Development project will include new construction
and re-construction of two main roads. These include Aspen Street and Ida Avenue,
both of which are classified as local city streets in the 2017 Bozeman Transportation
Master Plan. Other adjacent roads will be impacted by utility construction (Wallace Ave.
and Cottonwood St.) and by the addition of parking stalls (Front St. and Cottonwood
St.). All of these roadways will primarily carry lighter-weight vehicles (cars, SUVs, pick-
up trucks, etc), but will also be impacted by school buses, garbage trucks, and delivery
trucks (due to the industrial uses in the general project area). The lighter vehicles are
classified as Class 1, 2, and 3 and have equivalent ESAL values of 0.001 to 0.007 per trip;
while the heavier buses and trucks range from Class 4 to 9 and have equivalent ESAL
values of 0.257 to 1.462 per trip. We recommend erring on the conservative side for
local city streets and alleys and assume a value of 150,000 for the anticipated ESALs
over a 20-year design life. We believe this is a reasonable assumption for this re-
development project.
Explanation of Design Input Parameters: Page 2 of 3
Soaked Subgrade CBR: In April 2018 and February 2019, AESI dug 5 test pits and drilled
7 boreholes across the project site. In general, the site’s soil conditions consist of about
6 to 12 inches of topsoil overlying silt/clay down to a depth of 4.0 to 4.5 feet. Beginning
at this depth is the regional deposit of alluvial sandy gravel that underlies the Bozeman
area. We expect that all pavement areas will be supported on silt/clay subgrade soils.
For this reason, we have designed the new asphalt pavement improvements based on
“fine-grained, subgrade support conditions”. Over the past years, we have conducted
CBR tests on several samples of the Bozeman-area silt/clay soils. Typically, soaked CBRs
for these soils ranged from 2.0 to 3.0%. Based on these test results, we selected a
design soaked CBR value of 2.5%.
Subgrade Resilient Modulus: For fine-grained soils with a CBR of 10.0 or less, an
accepted correlation between CBR and resilient modulus is MR = 1500 x CBR. Based on
this equation, the design resilient modulus value shall be 3,750 psi.
Reliability: According to Table 2.2 in Reference 2, the recommended reliability level for
local streets in urban settings ranges from 50 to 80 percent, while reliability levels for
collector and principal arterial streets are recommended to be 80 to 95 percent and 80
to 99 percent, respectively. To provide for a greater factor of safety, we chose a design
reliability level of 90 percent for all streets, regardless of functional classification.
Standard Normal Deviate: According to Table 4.1 in Reference 2, a 90 percent reliability
value corresponds to a standard normal deviate of –1.282.
Overall Standard Deviation: According to Sections 2.1.3 and 4.3 in Reference 2, a
design value of 0.45 is recommended for flexible pavements.
Initial Serviceability: According to Section 2.2.1 in Reference 2, a design value of 4.2 is
recommended for flexible pavements.
Terminal Serviceability: According to Section 2.2.1 in Reference 2, a design value of 2.0
is suggested for roads that will be subjected to small traffic volumes; while a value of 2.5
or higher should be used when designing major highways. We selected a terminal
serviceability of 2.0.
Design Serviceability Loss: This is the difference between the initial and terminal
serviceability. Therefore, the design value shall be 2.2.
Asphalt Concrete Layer Coefficient: According to the table with the revised surfacing
structural coefficients in Reference 4, a design value of 0.41 is recommended for all
asphalt plant mix grades. This value replaces the 0.33 asphalt coefficient that was
provided in Table 3-2 of Reference 3.
Explanation of Design Input Parameters: Page 3 of 3
Base Course Layer Structural Coefficient: According to the table with the revised
surfacing structural coefficients in Reference 4, a design value of 0.14 is recommended
for new 1.5”-minus, crushed base course gravel. This value replaces the 0.12 crushed
gravel coefficient that was provided in Table 3-2 of Reference 3.
Base Course Layer Drainage Coefficient: According to Table 2.4 in Reference 2, a
coefficient of 0.80 to 1.00 should be used when fair to good drainage is anticipated
within the pavement structure. We assume good drainage for this project (ie. 1.00);
however, in order to be more conservative, a value of 0.90 was selected for the design.
Sub-Base Course Layer Structural Coefficient: We assume that imported, 6”-minus,
uncrushed sandy (pitrun) gravel will be placed for the sub-base section of the roads.
This is the standard product used in the Bozeman area for sub-base. According to
pavement design charts for gravelly soils, we estimated that 6”-minus pitrun will have a
CBR of between 15.0 and 20.0%, which correlates to a structural coefficient of 0.09.
Sub-Base Course Layer Drainage Coefficient: The drainage coefficients for sub-base
and base course layers are typically the same; therefore, we selected a value of 0.90 for
the design. See the base course layer drainage coefficient section for an explanation.
Reference List
1) Traffic and Highway Engineering; Nicholas J. Garber and Lester A. Hoel; 1988.
2) Design of Pavement Structures; AASHTO; 1993.
3) Pavement Design Manual; Montana Department of Transportation; 1991.
4) Pavement Design Memo; Montana Department of Transportation; May 11, 2006.
5) Geotechnical Manual; Montana Department of Transportation; July 2008.
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Pavement Section Design: Page 1 of 1
PAVEMENT DESIGN - Cottonwood St. (Utility Trench) - Opt. 1
(Note: The Option 1 design requires stable subgrade (ie. dry, hard, compacted, no rutting/deflection).
Project: Cottonwood + Ida Mixed-Use Development - Bozeman, MT
Project Number: 18-054
Date: March 6, 2019
Prepared By: Lee Evans
Important Notes:
1) A traffic loading of 150,000 ESALs is conservative for local city streets in Bozeman.
2) Subgrade soils will consist of sandy silt/sandy lean clay having a soaked CBR of 2.0 to 3.0.
DESIGN INPUT PARAMETERS
ESALs (total)150,000
Subgrade CBR, (%)2.5
Subgrade Resilient Modulus, MR (psi)3,750
Reliability, R (%)90
Standard Normal Deviate, ZR -1.282
Overall Standard Deviation, So 0.45
Initial Serviceability, po 4.2
Terminal Serviceability, pt 2.0
Design Serviceability Loss, (PSI)2.2
5.17609 = left side
Required Structural Number, RSN 3.20 5.1927 = right side
(Manipulate RSN such that the left and right side of equation match.)
Asphalt Concrete Layer Coefficient, a1 0.41
Base Course Layer Structural Coefficient, a2 0.14
Base Course Layer Drainage Coefficient, m2 0.90
Sub-Base Course Layer Structural Coefficient, a3 0.09
Sub-Base Course Layer Drainage Coefficient, m3 0.90
DESIGN PAVEMENT SECTION
Asphalt Concrete Thickness, D1 (in)3.0
Granular Base Course Thickness, D2 (in)6.0
Granular Sub-Base Course Thickness, D3 (in)15.0
Calculated Structural Number, CSN 3.20
(Manipulate layer thicknesses such that CSN matches or exceeds RSN.)
DESIGN EQUATION
Pavement Section Design: Page 1 of 1
PAVEMENT DESIGN - Wallace Ave. (Utility Trench) - Opt. 1
(Note: The Option 1 design requires stable subgrade (ie. dry, hard, compacted, no rutting/deflection).
Project: Cottonwood + Ida Mixed-Use Development - Bozeman, MT
Project Number: 18-054
Date: March 6, 2019
Prepared By: Lee Evans
Important Notes:
1) A traffic loading of 150,000 ESALs is conservative for local city streets in Bozeman.
2) Subgrade soils will consist of sandy silt/sandy lean clay having a soaked CBR of 2.0 to 3.0.
DESIGN INPUT PARAMETERS
ESALs (total)150,000
Subgrade CBR, (%)2.5
Subgrade Resilient Modulus, MR (psi)3,750
Reliability, R (%)90
Standard Normal Deviate, ZR -1.282
Overall Standard Deviation, So 0.45
Initial Serviceability, po 4.2
Terminal Serviceability, pt 2.0
Design Serviceability Loss, (PSI)2.2
5.17609 = left side
Required Structural Number, RSN 3.20 5.1927 = right side
(Manipulate RSN such that the left and right side of equation match.)
Asphalt Concrete Layer Coefficient, a1 0.41
Base Course Layer Structural Coefficient, a2 0.14
Base Course Layer Drainage Coefficient, m2 0.90
Sub-Base Course Layer Structural Coefficient, a3 0.09
Sub-Base Course Layer Drainage Coefficient, m3 0.90
DESIGN PAVEMENT SECTION
Asphalt Concrete Thickness, D1 (in)3.0
Granular Base Course Thickness, D2 (in)6.0
Granular Sub-Base Course Thickness, D3 (in)15.0
Calculated Structural Number, CSN 3.20
(Manipulate layer thicknesses such that CSN matches or exceeds RSN.)
DESIGN EQUATION
Pavement Section Design: Page 1 of 1
PAVEMENT DESIGN - Cottonwood St. (Parking Stalls) - Opt. 1
(Note: The Option 1 design requires stable subgrade (ie. dry, hard, compacted, no rutting/deflection).
Project: Cottonwood + Ida Mixed-Use Development - Bozeman, MT
Project Number: 18-054
Date: March 6, 2019
Prepared By: Lee Evans
Important Notes:
1) A traffic loading of 50,000 ESALs is conservative for street-side parking stalls.
2) Subgrade soils will consist of sandy silt/sandy lean clay having a soaked CBR of 2.0 to 3.0.
DESIGN INPUT PARAMETERS
ESALs (total)50,000
Subgrade CBR, (%)2.5
Subgrade Resilient Modulus, MR (psi)3,750
Reliability, R (%)90
Standard Normal Deviate, ZR -1.282
Overall Standard Deviation, So 0.45
Initial Serviceability, po 4.2
Terminal Serviceability, pt 2.0
Design Serviceability Loss, (PSI)2.2
4.69897 = left side
Required Structural Number, RSN 2.72 4.7294 = right side
(Manipulate RSN such that the left and right side of equation match.)
Asphalt Concrete Layer Coefficient, a1 0.41
Base Course Layer Structural Coefficient, a2 0.14
Base Course Layer Drainage Coefficient, m2 0.90
Sub-Base Course Layer Structural Coefficient, a3 0.09
Sub-Base Course Layer Drainage Coefficient, m3 0.90
DESIGN PAVEMENT SECTION
Asphalt Concrete Thickness, D1 (in)3.0
Granular Base Course Thickness, D2 (in)6.0
Granular Sub-Base Course Thickness, D3 (in)9.0
Calculated Structural Number, CSN 2.72
(Manipulate layer thicknesses such that CSN matches or exceeds RSN.)
DESIGN EQUATION
Pavement Section Design: Page 1 of 1
PAVEMENT DESIGN - Front St. (Road & Parking Stalls) - Opt. 1
(Note: The Option 1 design requires stable subgrade (ie. dry, hard, compacted, no rutting/deflection).
Project: Cottonwood + Ida Mixed-Use Development - Bozeman, MT
Project Number: 18-054
Date: March 6, 2019
Prepared By: Lee Evans
Important Notes:
1) A traffic loading of 50,000 ESALs is conservative for street-side parking stalls.
2) Subgrade soils will consist of sandy silt/sandy lean clay having a soaked CBR of 2.0 to 3.0.
DESIGN INPUT PARAMETERS
ESALs (total)50,000
Subgrade CBR, (%)2.5
Subgrade Resilient Modulus, MR (psi)3,750
Reliability, R (%)90
Standard Normal Deviate, ZR -1.282
Overall Standard Deviation, So 0.45
Initial Serviceability, po 4.2
Terminal Serviceability, pt 2.0
Design Serviceability Loss, (PSI)2.2
4.69897 = left side
Required Structural Number, RSN 2.72 4.7294 = right side
(Manipulate RSN such that the left and right side of equation match.)
Asphalt Concrete Layer Coefficient, a1 0.41
Base Course Layer Structural Coefficient, a2 0.14
Base Course Layer Drainage Coefficient, m2 0.90
Sub-Base Course Layer Structural Coefficient, a3 0.09
Sub-Base Course Layer Drainage Coefficient, m3 0.90
DESIGN PAVEMENT SECTION
Asphalt Concrete Thickness, D1 (in)3.0
Granular Base Course Thickness, D2 (in)6.0
Granular Sub-Base Course Thickness, D3 (in)9.0
Calculated Structural Number, CSN 2.72
(Manipulate layer thicknesses such that CSN matches or exceeds RSN.)
DESIGN EQUATION
Pavement Section Design: Page 1 of 1
PAVEMENT DESIGN - W. Side Service Drive (New) - Option 1
(Note: The Option 1 design requires stable subgrade (ie. dry, hard, compacted, no rutting/deflection).
Project: Cottonwood + Ida Mixed-Use Development - Bozeman, MT
Project Number: 18-054
Date: March 6, 2019
Prepared By: Lee Evans
Important Notes:
1) A traffic loading of 50,000 ESALs is conservative for low volume alleys.
2) Subgrade soils will consist of sandy silt/sandy lean clay having a soaked CBR of 2.0 to 3.0.
DESIGN INPUT PARAMETERS
ESALs (total)50,000
Subgrade CBR, (%)2.5
Subgrade Resilient Modulus, MR (psi)3,750
Reliability, R (%)90
Standard Normal Deviate, ZR -1.282
Overall Standard Deviation, So 0.45
Initial Serviceability, po 4.2
Terminal Serviceability, pt 2.0
Design Serviceability Loss, (PSI)2.2
4.69897 = left side
Required Structural Number, RSN 2.72 4.7294 = right side
(Manipulate RSN such that the left and right side of equation match.)
Asphalt Concrete Layer Coefficient, a1 0.41
Base Course Layer Structural Coefficient, a2 0.14
Base Course Layer Drainage Coefficient, m2 0.90
Sub-Base Course Layer Structural Coefficient, a3 0.09
Sub-Base Course Layer Drainage Coefficient, m3 0.90
DESIGN PAVEMENT SECTION
Asphalt Concrete Thickness, D1 (in)3.0
Granular Base Course Thickness, D2 (in)6.0
Granular Sub-Base Course Thickness, D3 (in)9.0
Calculated Structural Number, CSN 2.72
(Manipulate layer thicknesses such that CSN matches or exceeds RSN.)
DESIGN EQUATION
Pavement Section Design: Page 1 of 1
PAVEMENT DESIGN - Aspen St. - Grvl Portion (New) - Opt. 1
(Note: The Option 1 design requires stable subgrade (ie. dry, hard, compacted, no rutting/deflection).
Project: Cottonwood + Ida Mixed-Use Development - Bozeman, MT
Project Number: 18-054
Date: March 6, 2019
Prepared By: Lee Evans
Important Notes:
1) A traffic loading of 10,000 ESALs is conservative for a gravel-surfaced, local road.
2) Subgrade soils will consist of sandy silt/sandy lean clay having a soaked CBR of 2.0 to 3.0.
DESIGN INPUT PARAMETERS
ESALs (total)10,000
Subgrade CBR, (%)2.5
Subgrade Resilient Modulus, MR (psi)3,750
Reliability, R (%)50
Standard Normal Deviate, ZR 0
Overall Standard Deviation, So 0.45
Initial Serviceability, po 4.2
Terminal Serviceability, pt 2.0
Design Serviceability Loss, (PSI)2.2
4 = left side
Required Structural Number, RSN 1.73 4.0903 = right side
(Manipulate RSN such that the left and right side of equation match.)
Asphalt Concrete Layer Coefficient, a1 0.41
Base Course Layer Structural Coefficient, a2 0.14
Base Course Layer Drainage Coefficient, m2 0.90
Sub-Base Course Layer Structural Coefficient, a3 0.09
Sub-Base Course Layer Drainage Coefficient, m3 0.90
DESIGN PAVEMENT SECTION
Asphalt Concrete Thickness, D1 (in)0.0
Granular Base Course Thickness, D2 (in)6.0
Granular Sub-Base Course Thickness, D3 (in)12.0
Calculated Structural Number, CSN 1.73
(Manipulate layer thicknesses such that CSN matches or exceeds RSN.)
DESIGN EQUATION
APPENDIX E
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LIMITATIONS OF YOUR GEOTECHNICAL REPORT
GEOTECHNICAL REPORTS ARE PROJECT AND CLIENT SPECIFIC
Geotechnical investigations, analyses, and recommendations are project and client specific. Each project
and each client have individual criterion for risk, purpose, and cost of evaluation that are considered in the
development of scope of geotechnical investigations, analyses and recommendations. For example, slight
changes to building types or use may alter the applicability of a particular foundation type, as can a
particular client’s aversion or acceptance of risk. Also, additional risk is often created by scope-of-
service limitations imposed by the client and a report prepared for a particular client (say a construction
contractor) may not be applicable or adequate for another client (say an architect, owner, or developer for
example), and vice-versa. No one should apply a geotechnical report for any purpose other than that
originally contemplated without first conferring with the consulting geotechnical engineer. Geotechnical
reports should be made available to contractors and professionals for information on factual data only and
not as a warranty of subsurface conditions, such as those interpreted in the exploration logs and discussed
in the report.
GEOTECHNICAL CONDITIONS CAN CHANGE
Geotechnical conditions may be affected as a result of natural processes or human activity. Geotechnical
reports are based on conditions that existed at the time of subsurface exploration. Construction operations
such as cuts, fills, or drains in the vicinity of the site and natural events such as floods, earthquakes, or
groundwater fluctuations may affect subsurface conditions and, thus, the continuing adequacy of a
geotechnical report.
GEOTECHNICAL ENGINEERING IS NOT AN EXACT SCIENCE
The site exploration and sampling process interprets subsurface conditions using drill action, soil
sampling, resistance to excavation, and other subjective observations at discrete points on the surface and
in the subsurface. The data is then interpreted by the engineer, who applies professional judgment to
render an opinion about over-all subsurface conditions. Actual conditions in areas not sampled or
observed may differ from those predicted in your report. Retaining your consultant to advise you during
the design process, review plans and specifications, and then to observe subsurface construction
operations can minimize the risks associated with the uncertainties associated with such interpretations.
The conclusions described in your geotechnical report are preliminary because they must be based on the
assumption that conditions revealed through selective exploration and sampling are indicative of actual
Allied Engineering Services, Inc. Page 2
conditions throughout a site. A more complete view of subsurface conditions is often revealed during
earthwork; therefore, you should retain your consultant to observe earthwork to confirm conditions and/or
to provide revised recommendations if necessary. Allied Engineering cannot assume responsibility or
liability for the adequacy of the report’s recommendations if another party is retained to observe
construction.
EXPLORATIONS LOGS SHOULD NOT BE SEPARATED FROM THE REPORT Final explorations logs developed by the consultant are based upon interpretation of field logs (assembled
by site personnel), field test results, and laboratory and/or office evaluation of field samples and data.
Only final exploration logs and data are customarily included in geotechnical reports. These final logs
should not be redrawn for inclusion in Architectural or other design drawings, because drafters may
commit errors or omissions in the transfer process.
To reduce the likelihood of exploration log misinterpretation, contractors should be given ready access to
the complete geotechnical report and should be advised of its limitations and purpose. While a contractor
may gain important knowledge from a report prepared for another party, the contractor should discuss the
report with Allied Engineering and perform the additional or alternative work believed necessary to
obtain the data specifically appropriate for construction cost estimating purposes.
OWNERSHIP OF RISK AND STANDARD OF CARE
Because geotechnical engineering is much less exact than other design disciplines, there is more risk
associated with geotechnical parameters than with most other design issues. Given the hidden and
variable character of natural soils and geologic hazards, this risk is impossible to eliminate with any
amount of study and exploration. Appropriate geotechnical exploration, analysis, and recommendations
can identify and lesson these risks. However, assuming an appropriate geotechnical evaluation, the
remaining risk of unknown soil conditions and other geo-hazards typically belongs to the owner of a
project unless specifically transferred to another party such as a contractor, insurance company, or
engineer. The geotechnical engineer’s duty is to provide professional services in accordance with their
stated scope and consistent with the standard of practice at the present time and in the subject geographic
area. It is not to provide insurance against geo-hazards or unanticipated soil conditions.
The conclusions and recommendations expressed in this report are opinions based our professional
judgment and the project parameters as relayed by the client. The conclusions and recommendations
assume that site conditions are not substantially different than those exposed by the explorations. If
during construction, subsurface conditions different from those encountered in the explorations are
observed or appear to be present, Allied Engineering should be advised at once such that we may review
those conditions and reconsider our recommendations where necessary.
RETENTION OF SOIL SAMPLES
Allied Engineering will typically retain soil samples for one month after issuing the geotechnical report.
If you would like to hold the samples for a longer period of time, you should make specific arrangements
to have the samples held longer or arrange to take charge of the samples yourself.