HomeMy WebLinkAbout022 Soils Investigation Report - Lot 12 1091 Stoneridge Drive • Bozeman, Montana • Phone (406) 587-1115 • Fax (406) 587-9768
www.chengineers.com • E-Mail: info@chengineers.com
September 10, 2021
Mountain High Homes
Attn: Dan Barnes
E-mail: dan@mountainhighhomes.net
RE: Soils Investigation Report – Lot 12, Block 2, Gallatin Park Subdivision; Bozeman,
Montana (210645)
Dear Dan,
C&H Engineering and Surveying Inc., (C&H Engineering) has conducted a subsurface soils
investigation for the above referenced property. The scope of services was to conduct a
subsurface soils investigation and provide a soils investigation report. The report documents the
site conditions, soil properties, and provides foundation design and general earthwork
recommendations.
Proposed Construction
It is understood that a commercial structure(s) is planned for construction. At the time of this
report detailed plans regarding the proposed structure(s) were not available.
It has been assumed that the foundation footings will not be subjected to unusual loading
conditions such as eccentric loads. If any of the foundation footings will be eccentrically loaded,
please contact this office so we can appropriately revise our allowable bearing capacity and
settlement estimates.
Subsurface Soil and Conditions
On May 13, 2021 a member of the staff of C&H Engineering visited the site to conduct a
subsurface soils investigation. The subsurface soils investigation consisted of examining four
exploratory test pit excavations. The exploratory test pits were excavated with a tracked
excavator provided by AX&T Dirtworks. The soil profiles revealed by the exploratory
excavations were logged and visually classified according to ASTM D 2488, which utilizes the
nomenclature of the Unified Soil Classification System (USCS).
The following paragraphs briefly summarize the subsurface soils and conditions observed in the
exploratory test pits excavated for the field investigation. The soil horizons are described as they
were encountered in the test pit excavations, starting with the horizon nearest the surface and
proceeding with each additional horizon encountered with depth.
SOILS INVESTIGATION REPORT
#210645 – LOT 12, BLOCK 2, GALLATIN PARK SUBDIVISION; BOZEMAN, MONTANA 2
The first soil horizon encountered in each exploratory excavation (except TP-4) was an Organic
Soil of Low Plasticity (OL); please note that 1.5 feet of organic undocumented fill was
encountered above the native organic layer in TP-4 only. This material was black in color, moist,
and very soft. This material was encountered to depths varying from 0.75 to 3.3 feet below
grounds surface (bgs). Organic soils are highly compressible and are not suitable for foundation
support. This material must be removed from beneath all foundation elements and in any area
that will receive flexible or rigid pavements.
Underlying the Organic Soil in each exploratory excavation was a Lean Clay with Sand (CL).
This material was present to depths varying from 4.3 feet bgs to 6.7 feet bgs. This material was
very moist and soft, suggesting groundwater is rising up within this material seasonally. This
material is moisture sensitive, highly compressible and must be removed from beneath all
foundation footings.
Underlying the Lean Clay in each exploratory excavation was a Poorly Graded Gravel with Sand
and Cobbles (GP), known locally as “pit-run” gravel. This material was dark brown in color,
very moist to saturated, medium dense and estimated to contain approximately 40 percent coarse
to fine grained sand, and approximately 60 percent rounded and subrounded gravels and cobbles.
This material was present to the end of each excavation, depths varying from 5.6 to 7.6 feet bgs.
Groundwater was encountered within this material in each exploratory excavation.
Based on the subsurface investigation, it is recommended that the excavation for the foundation
elements continue down to the Poorly Graded Gravel with Sand and Cobbles and structural fill
be used to achieve the desired bottom of footing elevation.
Groundwater
Groundwater was encountered at the same elevation as the Poorly Graded Gravel with Sand and
Cobbles in each exploratory excavation. Also, the Lean Clay with Sand soil encountered beneath
the organic soil was very soft and moist starting at a depth of approximately 2.5 to 3.0 feet bgs,
suggesting that groundwater is rising up to this level seasonally. Also, once the Lean Clay layer
is removed from above the Poorly Graded Gravel with Sand and Cobbles, the groundwater table
will likely be elevated in this area and may rise up higher than if the low permeability Lean Clay
was left in place. Because of this, a slab-on-grade with stem wall foundation is recommended for
any structure to be constructed on the subject property.
Please note that our subsurface investigation is not a detailed groundwater study, and
groundwater conditions may change dramatically due to conditions that are out of our control.
Our assessment of the groundwater conditions is based on the conditions observed within the
exploratory test pits on the day of the excavation, our general experience in the project area, and
any available literature regarding groundwater conditions in the vicinity of the subject property.
If more detailed knowledge of the seasonally high groundwater elevation across the subject
property is desired, it is recommended that groundwater monitoring wells be installed and
checked weekly from the early spring to late summer months.
SOILS INVESTIGATION REPORT
#210645 – LOT 12, BLOCK 2, GALLATIN PARK SUBDIVISION; BOZEMAN, MONTANA 3
Foundation Recommendations
Based on the subsurface soils encountered in the exploratory excavations, it is recommended that
a slab-on-grade with stem wall foundation be utilized. Basement and crawl space foundations are
not recommended due to seasonally high groundwater. Please find the following as general
recommendations for all foundation elements:
In order to keep the footing out of the active frost zone it is recommended that the bottom
of all footing elevations be a minimum of 48 inches below finished grade.
All foundation elements are to bear on compacted structural fill overlying the Poorly
Graded Gravel with Sand and Cobbles. All foundation footings shall be dimensioned for
an allowable bearing capacity of 2,500 pounds per square foot (psf).
It is recommended that typical strip footings for this structure have a minimum width of
16 inches and column footings should have a minimum width of 24 inches, provided the
soils allowable bearing capacity is not exceeded.
If construction takes place during the colder months of the year, the subgrade must be
protected from freezing. This may require the use of insulating blankets and/or ground
heaters.
Allowable Bearing Capacity & Settlement
The bearing capacity of a soil is defined as the ultimate pressure per unit area by the foundation
that can be supported by the soil in excess of the pressure caused by the surrounding soil at the
footing level. Bearing capacity is determined by the physical and chemical properties of the soil
located beneath the proposed structures footings.
It is recommended that the loads from the proposed structure be transmitted to properly placed
and compacted structural fill overlying the Poorly Graded Gravel with Sand and Cobbles. For
this scenario it is recommended that an allowable bearing capacity of 2,500 pounds per square
foot be used to dimension all foundation footings.
Settlement and differential settlement were estimated using conservative soil parameters and the
assumption that the foundation footings bear on properly placed and compacted structural fill
overlying the Poorly Graded Gravel with Sand and Cobbles. Based on conservative soil
parameter estimates, the bearing capacity recommended, and the assumption that all
recommendations made in this report will be properly implemented, it is expected that total and
differential settlement will be ½-inch or less. Structures of the type proposed can generally
tolerate movements of this magnitude, however, this movement should be checked by a
structural engineer to determine if it is acceptable.
SOILS INVESTIGATION REPORT
#210645 – LOT 12, BLOCK 2, GALLATIN PARK SUBDIVISION; BOZEMAN, MONTANA 4
Subgrade Preparation and Structural Fill
In general, the excavation for the foundation footings must be level and uniform and continue
down to the Poorly Graded Gravel with Sand and Cobbles. If any soft spots, undocumented fill
or boulders are encountered, they will need to be removed and backfilled with structural fill. The
excavation width must extend a minimum of one footing width from the outer edges of the
footings or to a distance equal to ½ the height of the required structural fill, whichever is greater.
For example, if 6 feet of structural fill is required, the excavation must extend out from the
footing a minimum distance of 3 feet. The purpose of this requirement is to keep the loads from
the structure fully contained within the structural fill.
Once the excavation is complete, the native subgrade shall be proof rolled with a large
compactor to an unyielding condition. Any areas that are found to be pumping or rutting shall be
sub-excavated and replaced with structural fill.
Structural fill is defined as all fill that will ultimately be subjected to structural loadings, such as
those imposed by footings, floor slabs, pavements, etc. Structural fill will need to be imported for
this project. Imported structural fill is recommended to be a well graded gravel with sand that
contains less than 15 percent of material that will pass a No. 200 sieve and that has a maximum
particle size of 3 inches. Also, the fraction of material passing the No. 40 sieve shall have a
liquid limit not exceeding 25 and a plasticity index not exceeding 6. The gravel and sand
particles also need to be made up of durable rock materials that will not degrade when
compacted; no shale or mudstone fragments should be present.
Structural fill must be placed in lifts no greater than 12 inches (uncompacted thickness) and be
uniformly compacted to a minimum of 97 percent of its maximum dry density, as determined by
ASTM D698. Typically, the structural fill must be moisture conditioned to within + 2 percent of
the materials optimum moisture content to achieve the required density. It is recommended that
the structural fill be compacted with a large vibrating smooth drum roller. Please note that if a
moisture-density relationship test (commonly referred to as a proctor) needs to be performed for
a proposed structural fill material to determine its maximum dry density and optimum moisture
content in accordance with ASTM D698, a sample of the material must be delivered to this
office a minimum of three full working days prior to beginning placement of the structural fill.
It is also acceptable to utilize a lift or two of ¾-inch washed rock to get up above the
groundwater elevation and then switch over to using 3-inch minus “pit-run” gravel as structural
fill. If ¾-inch washed rock is used as structural fill it needs to be compacted to an unyielding
condition with a large vibrating smooth drum roller.
At no time should surface water runoff be allowed to flow into and accumulate within the
excavation for the foundation elements. If necessary, a swale or berm should be temporarily
constructed to reroute all surface water runoff away from the excavation. Excavation should not
proceed during large precipitation events.
If any of the foundation footings are found to be located on a test pit, the area will need to be
excavated down to the full depth of the test pit and structural fill be placed and compacted in lifts
SOILS INVESTIGATION REPORT
#210645 – LOT 12, BLOCK 2, GALLATIN PARK SUBDIVISION; BOZEMAN, MONTANA 5
(as described in this report) to bring the area back up to the desired grade.
Foundation Wall Backfill
Approved backfill material should be placed and compacted between the foundation wall and the
edge of the excavation. The soils encountered during the field investigation, with the exception
of the Organic Soil and the undocumented fill, are suitable for use as foundation wall backfill
along the exterior of the foundation, provided they are not too moist. Structural fill is
recommended as foundation wall backfill in all areas that will support concrete slabs-on-grade or
other paving improvements. The backfill shall be placed in uniform lifts and be compacted to a
minimum of 95 percent of the material’s maximum dry density, as determined by ASTM D698.
The foundation wall backfill will need to be compacted with either walk behind compaction
equipment or hand operated compaction equipment in order to avoid damaging the foundation
walls. If walk behind compaction equipment is used, lifts should not exceed 8-inches (loose
thickness) and if hand operated compaction equipment is used lifts should not exceed 4-inches
(loose thickness).
Interior Slabs-on-Grade
In preparation for the interior slabs-on-grade, the excavation must continue down to the Poorly
Graded Gravel with Sand and Cobbles and structural fill be utilized to achieve the desired
bottom of slab elevation.
For all interior concrete slabs-on-grade, preventative measures must be taken to stop moisture
from migrating upwards through the slab. Moisture that migrates upwards through the concrete
slab can damage floor coverings such as carpet, hardwood and vinyl, in addition to causing
musty odors and mildew growth. Moisture barriers will need to be installed to prevent water
vapor migration and capillary rise through the concrete slab.
In order to prevent capillary rise through the concrete slab-on-grade it is recommended that 6
inches of ¾-inch washed rock (containing less than 10 percent fines) be placed and compacted
once the excavation for the slab is complete. The washed rock has large pore spaces between soil
particles and will act as a capillary break, preventing groundwater from migrating upwards
towards the bottom of the slab.
In order to prevent the upward migration of water vapor through the slab, it is recommended that
a 15-mil extruded polyolefin plastic that complies with ASTM E1745 (such as a Stego Wrap 15-
mil Vapor Barrier) be installed. The vapor barrier should be pulled up at the sides and secured to
the foundation wall or footing. Care must be taken during and after the installation of the vapor
barrier to avoid puncturing the material, and all joints are to be sealed per the manufacture’s
recommendations.
Once the excavation for the interior slab-on-grade is completed as described in the first
paragraph of this section, and the ¾ inch washed rock and moisture barriers have been properly
installed, it will be acceptable to form and cast the steel reinforced concrete slab. It is
SOILS INVESTIGATION REPORT
#210645 – LOT 12, BLOCK 2, GALLATIN PARK SUBDIVISION; BOZEMAN, MONTANA 6
recommended that interior concrete slabs-on-grade have a minimum thickness of 4 inches, and
the reinforcement shall be designed by a licensed structural engineer.
Exterior Slabs-on-Grade
For exterior areas to be paved with concrete slabs, it is recommended that, at a minimum, the
organic soil be removed. The native subgrade then needs to be compacted to a minimum of 95
percent of its maximum dry density, as determined by ASTM D698. Then for non-vehicular
traffic areas, a minimum of 6 inches of ¾-inch minus rock needs to be placed, and 4 inches of
4000 pounds per square inch (psi) concrete placed over the ¾-inch minus rock. For areas with
vehicular traffic, a minimum of 9 inches of ¾-inch minus rock should be placed, followed by 6
inches of 4000 psi concrete.
Exterior slabs that will be located adjacent to the foundation walls need to slope away from the
structure at a minimum grade of 2 percent and should not be physically connected to the
foundation walls. If they are connected, any movement of the exterior slab will be transmitted to
the foundation wall, which may result in damage to the structure.
Site Grading
Surface water should not be allowed to accumulate and infiltrate the soil near the foundation.
Proper site grading will ensure surface water runoff is directed away from the foundation. Please
find the following as general site grading recommendations:
Finished grade must slope away from the building a minimum of 5 percent within the
first 10 feet, in order to quickly drain ground surface and roof runoff away from the
foundation walls. Please note that in order to maintain this slope; it is imperative that any
backfill placed against the foundation walls be compacted properly. If the backfill is not
compacted properly, it will settle and positive drainage away from the structure will not
be maintained.
Permanent sprinkler heads for lawn care should be located a sufficient distance from the
structure to prevent water from draining toward the foundation or saturating the soils
adjacent to the foundation.
Rain gutter down spouts are to be placed in such a manner that surface water runoff
drains away from the structure.
All roads, walkways, and architectural land features must properly drain away from all
structures. Special attention should be made during the design of these features to not
create any drainage obstructions that may direct water towards or trap water near the
foundation.
SOILS INVESTIGATION REPORT
#210645 – LOT 12, BLOCK 2, GALLATIN PARK SUBDIVISION; BOZEMAN, MONTANA 7
Asphalt Paving Improvements
For areas to be paved with asphalt, it is recommended that, as a minimum, the topsoil and any
organics be removed. The native subgrade then needs to be compacted at ± 2 percent of its
optimum moisture content to 95 percent of its maximum dry density. Following compaction of
the native subgrade, a layer of geotextile (such as a Mirafi 160N) shall be installed. Next a 12-
inch layer of compacted 6-inch minus gravel needs to be placed, followed by a 6-inch layer of
compacted 1-inch minus road mix. Both gravel courses must be compacted at ± 2 percent of their
optimum moisture content to 95 percent of their maximum dry density, as determined by ASTM
D698. A 3-inch-thick layer of asphalt pavement can then be placed and compacted over this
cross-section.
Construction Administration
The foundation is a vital element of a structure; it transfers all of the structures dead and live
loads to the native soil. It is imperative that the recommendations made in this report are
properly adhered to. A representative from C&H Engineering should observe the construction of
any foundation or drainage elements recommended in this report. The recommendations made in
this report are contingent upon our involvement. If the soils encountered during the excavation
differ than those described in this report or any unusual conditions are encountered, our office
should be contacted immediately to examine the conditions, re-evaluate our recommendations
and provide a written response.
If construction and site grading take place during cold weather, it is recommended that approved
winter construction practices be observed. All snow and ice shall be removed from cut and fill
areas prior to site grading taking place. No fill should be placed on soils that are frozen or
contain frozen material. No frozen soils can be used as fill under any circumstances.
Additionally, Concrete should not be placed on frozen soils and should meet the temperature
requirements of ASTM C 94. Any concrete placed during cold weather conditions shall be
protected from freezing until the necessary compressive strength has been attained. Once the
footings are placed, frost shall not be permitted to extend below the foundation footings, as this
could heave and crack the foundation footings and/or foundation walls.
It is the responsibility of the contractor to provide a safe working environment with regards to
excavations on the site. All excavations should be sloped or shored in the interest of safety and in
accordance with local and federal regulations, including the excavation and trench safety
standards provided by the Occupational Safety and Health Administration (OSHA).
Report Limitations
The recommendations made in this report are based on limited information obtained from the
exploratory test pit excavated on the subject property. It is not uncommon for variations in the
subsurface conditions to occur, the nature and extent of which do not become evident until
additional exploration or construction is conducted. The variations may result in additional
construction costs, and it is suggested that a contingency be provided for this purpose.
OL
CL
GP
0.8
4.3
5.6
0 TO 0.75 FEET: ORGANIC SOIL; (OL); black; moist; low plasticity; very soft.
0.75 TO 4.3 FEET: LEAN CLAY WITH SAND; (CL); tan; moist to very moist; medium
plasticity; soft to very soft.
4.3 TO 5.6 FEET: POORLY GRADED GRAVEL WITH SAND AND COBBLES; (GP); dark
brown; moist to saturated; non plastic plasticity; dense.
Bottom of test pit at 5.6 feet.
NOTES
GROUND ELEVATION
LOGGED BY Michael J. Welch, P.E.
EXCAVATION METHOD Tracked Excavator
EXCAVATION CONTRACTOR AX&T Dirtworks GROUND WATER LEVELS:
DATE STARTED 5/13/21 COMPLETED 5/13/21
AT TIME OF EXCAVATION 5.60 ft
AFTER EXCAVATION ---
AT END OF EXCAVATION ---DEPTH(ft)0.0
2.5
5.0 SAMPLE TYPENUMBERPAGE 1 OF 1
TEST PIT NUMBER TP1
PROJECT NUMBER 210645
CLIENT Mountain High Homes, Inc.
PROJECT LOCATION Lot 12, Gallatin Park Subdivision
PROJECT NAME Soils Investigation
GENERAL BH / TP / WELL - GINT STD US.GDT - 9/9/21 13:56 - G:\C&H\21\210645S\TEST PIT LOGS (210645).GPJU.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION
OL
CL
GP
1.2
5.5
6.3
0 TO 1.2 FEET: ORGANIC SOIL; (OL); black; moist; low plasticity; very soft.
1.2 TO 5.5 FEET: LEAN CLAY WITH SAND; (CL); tan; moist to very moist; mediumplasticity; soft to very soft.
5.5 TO 6.3 FEET: POORLY GRADED GRAVEL WITH SAND AND COBBLES; (GP); dark
brown; moist to saturated; non plastic plasticity; dense.
Bottom of test pit at 6.3 feet.
NOTES
GROUND ELEVATION
LOGGED BY Michael J. Welch, P.E.
EXCAVATION METHOD Tracked Excavator
EXCAVATION CONTRACTOR AX&T Dirtworks GROUND WATER LEVELS:
DATE STARTED 5/13/21 COMPLETED 5/13/21
AT TIME OF EXCAVATION 6.30 ft
AFTER EXCAVATION ---
AT END OF EXCAVATION ---DEPTH(ft)0.0
2.5
5.0 SAMPLE TYPENUMBERPAGE 1 OF 1
TEST PIT NUMBER TP2
PROJECT NUMBER 210645
CLIENT Mountain High Homes, Inc.
PROJECT LOCATION Lot 12, Gallatin Park Subdivision
PROJECT NAME Soils Investigation
GENERAL BH / TP / WELL - GINT STD US.GDT - 9/9/21 13:56 - G:\C&H\21\210645S\TEST PIT LOGS (210645).GPJU.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION
OL
CL
GP
1.3
5.5
6.3
0 TO 1.3 FEET: ORGANIC SOIL; (OL); black; moist; low plasticity; very soft.
1.3 TO 5.5 FEET: LEAN CLAY WITH SAND; (CL); tan; moist to very moist; medium
plasticity; soft to very soft.
5.5 TO 6.3 FEET: POORLY GRADED GRAVEL WITH SAND AND COBBLES; (GP); dark
brown; moist to saturated; non plastic plasticity; dense.
Bottom of test pit at 6.3 feet.
NOTES
GROUND ELEVATION
LOGGED BY Michael J. Welch, P.E.
EXCAVATION METHOD Tracked Excavator
EXCAVATION CONTRACTOR AX&T Dirtworks GROUND WATER LEVELS:
DATE STARTED 5/13/21 COMPLETED 5/13/21
AT TIME OF EXCAVATION 6.30 ft
AFTER EXCAVATION ---
AT END OF EXCAVATION ---DEPTH(ft)0.0
2.5
5.0 SAMPLE TYPENUMBERPAGE 1 OF 1
TEST PIT NUMBER TP3
PROJECT NUMBER 210645
CLIENT Mountain High Homes, Inc.
PROJECT LOCATION Lot 12, Gallatin Park Subdivision
PROJECT NAME Soils Investigation
GENERAL BH / TP / WELL - GINT STD US.GDT - 9/9/21 13:56 - G:\C&H\21\210645S\TEST PIT LOGS (210645).GPJU.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION
OL
OL
CL
GP
1.5
3.3
6.7
7.6
0 TO 1.5 FEET: UNDOCUMENTED FILL; (OL); black; dry to moist; low plasticity; loose.
1.5 TO 3.3 FEET: ORGANIC SOIL; (OL); black; moist; low plasticity; very soft.
3.3 TO 6.7 FEET: LEAN CLAY WITH SAND; (CL); tan; moist to very moist; mediumplasticity; soft to very soft.
6.7 TO 7.6 FEET: POORLY GRADED GRAVEL WITH SAND AND COBBLES; (GP); dark
brown; moist to saturated; non plastic plasticity; dense.
Bottom of test pit at 7.6 feet.
NOTES
GROUND ELEVATION
LOGGED BY Michael J. Welch, P.E.
EXCAVATION METHOD Tracked Excavator
EXCAVATION CONTRACTOR AX&T Dirtworks GROUND WATER LEVELS:
DATE STARTED 5/13/21 COMPLETED 5/13/21
AT TIME OF EXCAVATION 7.60 ft
AFTER EXCAVATION ---
AT END OF EXCAVATION ---DEPTH(ft)0.0
2.5
5.0
7.5 SAMPLE TYPENUMBERPAGE 1 OF 1
TEST PIT NUMBER TP4
PROJECT NUMBER 210645
CLIENT Mountain High Homes, Inc.
PROJECT LOCATION Lot 12, Gallatin Park Subdivision
PROJECT NAME Soils Investigation
GENERAL BH / TP / WELL - GINT STD US.GDT - 9/9/21 13:56 - G:\C&H\21\210645S\TEST PIT LOGS (210645).GPJU.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION