HomeMy WebLinkAbout023 Geology, Soils, and SlopesGran Cielo Subdivision
Phase 3
Preliminary Plat
Application
23 - Geology, Soils, and Slopes
City of Bozeman Staff has approved a waiver for this section during the pre-application
process. See the included Geotech Report Gran Cielo Subdivision, Block 14, Phase 4, and
the 2007 HKM geotechnical report.
23 – Geology, Soils, and Slopes
Geotechnical Summary
Final Geotechnical Report
Blk. 14, Ph. IV, Gran Cielo Sub. – Bozeman, MT
Project: 18-130.08
January 26, 2023
Allied Engineering Services, Inc. Page 2
SITE LOCATION AND EXISTING CONDITIONS
The project site is located on the northeast side of the existing Gran Cielo Subdivision. See Figure 1 for
the site location. The project area is undeveloped and is currently being used for construction staging
and storage.
PROPOSED PROJECT
The proposed residential/multi-family project will include the construction of four, four-story, buildings
and a large, asphalt parking lot in between the buildings. All the buildings will be supported on standard
shallow foundations (perimeter footings/frost walls and interior footings) and be underlain by at-grade
slabs. No off-site improvements will be built as part of the project. All adjacent streets are already in-
place with city water and sewer mains. See Figure 2 for a concept site plan.
As we understand it, some of the asphalt parking lot areas may be covered by covered canopies. The
canopy structures will bear on standard footings/columns. The stormwater drainage from the parking
lot areas will be graded/routed to the existing detention pond area in the northwest corner of the site.
Other site improvements will include building services (ie. water service, fire service, and sewer service)
as well as a short, looped water main extension in the parking lot.
The above description of the proposed project is based on previous correspondence with the Architect
and Civil Engineer, along with a review of the concept site/civil plans for the project.
PROJECT ASSUMPTIONS
Provided below are some project assumptions:
• Prior to the Gran Cielo Subdivision development work, the groundwater depths in the project
area were higher, especially in the spring during seasonal high water. This is based on 2017-
2018 groundwater monitoring data compared to current data from 2022 that was collected on
some of the neighboring properties to the east and south. Most likely, the groundwater table is
below the top of the “target” sandy gravel during most of the year. As a result, there is little
chance that groundwater will impact foundation excavation/earthwork and the deeper ground-
water conditions should lead to better/firmer subgrade soils for parking lot construction.
• If groundwater is found to be above the top of the sandy gravel during foundation excavation,
we recommend dewatering and the possible need for an initial layer of fabric-covered, clean,
crushed rock to get above the wetness. Both of these recommendations are detailed herein.
• We expect stable subgrade conditions during parking lot construction. If some of the soils are
overly moist, some drying may be required. We have provided a 24-inch thick pavement section
design for stable subgrade conditions. If needed, a thicker section is included for soft subgrade.
Final Geotechnical Report
Blk. 14, Ph. IV, Gran Cielo Sub. – Bozeman, MT
Project: 18-130.08
January 26, 2023
Allied Engineering Services, Inc. Page 3
SUMMARY OF SITE CONDITIONS
Provided below is a summary of the site conditions:
• The project site and surrounding areas are underlain by shallow, native sandy gravel beginning
at depths of 2.0 to 4.0 feet. The gravels extend for 10’s of feet and are the “target” foundation
bearing material for all footings.
• The native gravels are overlain by silt/clay and about 9 to 12 inches of organic topsoil. We
expect the silt/clay will be in a moist, but stable condition for asphalt pavement construction.
• Prior to the development of the Gran Cielo Subdivision, seasonal high groundwater levels in the
general area rose to depths of 1.0 to 2.0 feet. Based on some groundwater monitoring that was
conducted by AESI in the spring of 2022 on the neighboring Bennett property (to the southeast
of the Block 14, Phase IV area), the high water levels were significantly lower in 2022 and rose to
depths of 4.5 to 5.0 feet. Based on this limited data, it appears that post-development, ground-
water levels are now lower as a result of “better drainage” around the underground utilities.
SUMMARY OF GEOTECHNICAL ISSUES
We do not expect any major issues at the site. Below are some potential issues and a summary of either
why they are not issues or how they should be dealt with during construction:
• High Groundwater: Since the buildings will be underlain by at-grade slabs, groundwater will not
be an issue following foundation construction as well as long-term. Depending on the time of
year, groundwater dewatering may be required during foundation excavation and underground
utility installation. If the bottom of the foundation excavation is wet or contains groundwater,
the first lift of building pad structural fill must consist of fabric-covered, clean crushed rock.
• Soft Subgrade: We expect that the near surface, silt/clay will be in a moist, but stable condition
during asphalt parking lot construction. If it is a little too moist and soft, it may need to be
allowed to air dry or be scarified. Assuming stable conditions, we have provided a 24-inch
design pavement section thickness (see below). If highly unstable/soft conditions are found to
exist, we have provided a thicker pavement section option (33 inches thick) that incorporates a
layer of Tensar TX-190L geogrid reinforcement for subgrade stabilization.
SUMMARY OF RECOMMENDATIONS
Provided below is a summary of the building and parking lot recommendations for the project:
• The design soils bearing pressure for this project is 3,000 psf. This assumes that the buildings
will be mass over-excavated down to native gravel per our recommendations.
Final Geotechnical Report
Blk. 14, Ph. IV, Gran Cielo Sub. – Bozeman, MT
Project: 18-130.08
January 26, 2023
Allied Engineering Services, Inc. Page 4
• The on-site soils are not corrosive to concrete. As a result, normal cement can be used for the
foundation concrete.
• All buildings shall be underlain by at-grade slabs (slab-on-grade) and be supported on shallow,
conventional foundations consisting of perimeter footings/foundation walls and a dense array of
interior, strip and spread footings. The buildings will not contain any crawl space areas.
• The entire foundation footprint area of all buildings shall be mass over-excavated down to the
native “target” sandy gravel (in a large, “bathtub” excavation) and a building pad section of
granular structural fill shall be placed to build up to footing and interior slab grades. All footings
must bear on native gravel or on structural fill that in turn is supported on the native gravel.
• For the canopy structures in the parking lot area, all footings shall be individually excavated and
bear on native sandy gravel or on granular structural fill that in turn is supported on the gravel.
• The recommended granular structural fill material is import, 3”-minus sandy gravel.
• All interior foundation wall backfill (under interior slabs) must consist of granular structural fill.
For exterior wall backfill, native non-organic soils are be used.
• The interior slab of the building shall be underlain by a minimum of 6 inches of 1”-minus clean,
crushed rock that in turn bears on the thick section of building pad granular structural fill, which
overlies “target” sandy gravel throughout the bottom of the mass over-excavation area.
• The moisture protection provisions for the buildings shall include a 15-mil, heavy duty, vapor
barrier under the interior slab and damp-proofing of the foundation walls per the IBC. Due to
the slab-on-grade foundation configuration, no footing drains are required. Any elevator pits
shall be underlain by a vapor barrier, be water-proofed per IBC, and contain a sump chamber.
• The typical city standard under exterior concrete slabs is 3 inches (min.) of clean, crushed rock.
We recommend thickening this crushed rock layer to 6 to 12 inches (depending on the location
of the slab relative to the building) in order to improve the subgrade support and reduce the risk
of frost heaving. For driveway/vehicle slabs, our recommendation for the slab support section is
6 inches of crushed rock and 12 inches of sub-base gravel over fabric-covered subgrade.
• In 2019, AESI performed a soil corrosivity analysis for the Gran Cielo Subdivision to determine
what requirements would be required for the corrosion protection of ductile iron water mains,
water services, and fire services. As part of this work, we tested four samples of the shallow,
sandy gravel soils. Based on the testing, none of the subdivision soils are highly corrosive and
the use of special, zinc-coated DIP pipe is not needed. Due to the test results and the shallow
gravel depths, polyethylene encasement is also not needed around water mains, water services,
and fire services (since all piping will be installed and surrounded by the native sandy gravel).
Final Geotechnical Report
Blk. 14, Ph. IV, Gran Cielo Sub. – Bozeman, MT
Project: 18-130.08
January 26, 2023
Allied Engineering Services, Inc. Page 5
• One of the major benefits of the building pad granular structural fill section is that all of the sub-
slab plumbing trenches and excavation under the slab area will be in the 3”-minus gravel section
materials. For plumbing trench backfill (above the pipe bedding), either the granular structural
fill can be re-used (which will require placement in thin lifts and compaction) or 1”-minus, clean,
crushed rock can be used (which is easier to place and compact in tight/confined areas). It is our
recommendation that if crushed rock is used for trench backfill, it should be placed in lifts and
be vibratory compacted. The use of crushed rock is viewed as a construction expediate to the
Contractor and we do not believe a change order is warranted if the Contractor elects to use
crushed rock in lieu of the excavated, 3”-minus sandy gravel.
• We expect stable parking lot subgrade conditions in most (if not all) areas of the site. Where the
subgrade soils are overly moist and softer, some level of subgrade drying and scarification may
be needed. The design pavement section we recommend for stable subgrade conditions is:
o 3” Asphalt
o 6” Base Gravel
o 15” Sub-Base Gravel
o 315 lb. Woven Geotextile Fabric
o Stable Subgrade (Dry, Hard, and Compacted)
24” Total Section Thickness
• If some areas of the parking lot subgrade are too wet and soft to adequately dry out, then a
thicker pavement section option with geogrid reinforcement may be needed. The section that is
provided below is for unstable subgrade conditions: (Note: Most likely, this thicker pavement
section recommendation will not be needed during construction.)
o 3” Asphalt
o 6” Base Gravel
o 24” Sub-Base Gravel
o Tensar TX-190L Geogrid
o 8 oz. Non-Woven Geotextile Fabric
o Soft Subgrade (Smooth and Rut-Free)
33” Total Section Thickness
EXPLORATIONS, TESTING, AND SUBSURFACE CONDITIONS
Subsurface Explorations
No on-site test pits were conducted by AESI. All test pit work within the boundaries of the Gran Cielo
Subdivision property were performed by HKM during their 2007 geotechnical investigation. See Figure 3
for a map showing all of HKM’s test pits.
Final Geotechnical Report
Blk. 14, Ph. IV, Gran Cielo Sub. – Bozeman, MT
Project: 18-130.08
January 26, 2023
Allied Engineering Services, Inc. Page 6
Over the years, AESI has dug test pits on many of the nearby properties, located to the west, east, and
south. See Figure 1 for a map showing all of AESI’s area test pits. In addition to our nearby test pits, we
have witnessed/inspected all of the foundation earthwork in the Gran Cielo Subdivision up to this point.
As a result, we are very familiar with the soil conditions.
Laboratory Testing
No laboratory testing was conducted as part of this project.
Note: As stated previously, AESI dug test pits and sampled/tested the Gran Cielo Subdivision soils as
part of our subdivision-wide, soil corrosivity analysis in 2019.
Soil Conditions
The soil conditions throughout the Gran Cielo Subdivision area consist of about 9 to 12 inches of organic
topsoil overlying a thin layer of sandy silt to sandy lean clay. In most locations, the silt/clay is slightly
moist to moist and stiff to very stiff. Beginning at depths of 2.0 to 4.0 feet is the “clean” sandy gravel
with scattered cobbles. The gravelly soils extend for 10’s of feet below ground surface and are defined
as the “target” foundation bearing material for all footings.
Groundwater Conditions
Groundwater depths are assumed to range from 3.0 to 8.0 feet, depending on the location and the time
of year. Most likely, groundwater levels stay below the top of the sandy gravel during much of the year.
In some areas, seasonal high groundwater may rise to near or above the top of the gravels in the spring.
GEOTECHNICAL ISSUES
Given the site’s soil and groundwater conditions and the fact that the buildings will be underlain by at-
grade slabs, this project has limited geotechnical issues.
The only two, potential issues that we can foresee include: 1) high groundwater during foundation
earthwork and 2) soft subgrade during parking lot construction. Each of these items is further described
below.
• High Groundwater During Foundation Excavation: There is a chance that groundwater will be
near or above the top of the “target” sandy gravel during mass foundation over-excavation. If
this is the situation, we first recommend that the excavation area be dewatered to below the
top of the gravel. If some areas of the excavation contain wet gravel subgrade soils or shallow,
standing groundwater, the first lift of granular structural fill must consist of fabric-covered, 1”-
minus, clean, crushed rock (to get above the wetness before placing granular structural fill).
Final Geotechnical Report
Blk. 14, Ph. IV, Gran Cielo Sub. – Bozeman, MT
Project: 18-130.08
January 26, 2023
Allied Engineering Services, Inc. Page 7
• Soft Subgrade During Parking Lot Construction: All of the subgrade soils under the parking lots
will consist of native, non-organic silt/clay (following topsoil stripping). We expect slightly moist
to moist and stiff to very stiff conditions in most (if not all) areas. If subgrade soils are overly
moist and on the softer side, some level of drying and scarification may be required by the
Earthwork Contractor to improve the stability of the subgrade soils. This work will take time and
effort. If this condition occurs, it will be a requirement that the subgrade first try and be dried
out. If the weather does not cooperate or if the soils are just too wet and soft, then the thicker,
geogrid-reinforced pavement section option may need to be used in some areas of the site. We
do expect the use of the thicker section will be widespread and it will likely not be needed at all.
GENERAL CONSTRUCTION RECOMMENDATIONS
Topsoil Stripping and Re-Use
The site is blanketed by approximately 9 to 12 inches of black to dark brown, organic topsoil. All topsoil
must be completely removed from within the building foundation footprint areas and from under all
exterior concrete slab and asphalt pavement areas. The final site grading (in landscape areas) and the
reclamation of disturbed construction areas are the only recommended uses of this material.
Groundwater Dewatering
Depending on the time of year, groundwater dewatering may be required for foundation excavation and
water and sewer installations. If groundwater dewatering is needed, we recommend the installation of
standard wellpoints/dewatering wells (which most utility contractors use) that lower the groundwater
table well below the bottom of the excavation.
Subgrade Scarification and Drying
Depending on the time of year and the subgrade elevations (ie. cut depth), some areas of the parking lot
subgrade soils may need to be dried and scarified. This will take time, effort, and good weather. Most
likely, most of the subgrade soils will be slightly moist to moist and stiff to very stiff and not be an issue.
Excavation and Re-Use of On-Site Soils
The soils that will be excavated during foundation earthwork and site development will include topsoil,
silt/clay, and sandy gravel. Provided below are the allowable re-uses of the on-site materials:
• Organic topsoil materials shall only be used for final site grading in landscape areas.
• The only allowable uses for native silt/clay are for site grading, embankment fill under parking
lot areas, and exterior foundation wall backfill. Only the driest silt/clay that can be compacted
to project specifications shall be re-used for wall backfill. As discussed in a later backfill section
Final Geotechnical Report
Blk. 14, Ph. IV, Gran Cielo Sub. – Bozeman, MT
Project: 18-130.08
January 26, 2023
Allied Engineering Services, Inc. Page 8
of the report, we are recommending a thicker gravel/crushed rock section under exterior slabs
that abut the foundation walls and lie in front of doorways and underlie patios/porches/decks.
• For interior foundation wall backfill (under interior slabs), we recommend the exclusive use of
imported, granular structural fill (3”-minus sandy gravel). No on-site soils shall be used for
interior backfill.
• The only locations where native sandy gravels will likely be encountered is at the bottom of the
foundation excavation and in the utility trench excavations.
STRUCTURAL DESIGN PARAMETERS AND CONSIDERATIONS
Foundation Design
All buildings will be underlain by an at-grade slab (slab-on-grade) with perimeter footings/frost walls as
well as an array of interior footings (throughout the building area). No crawl space areas are planned.
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 2021 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/. Upon entering this page, there are links to three third-
party interfaces that can be used to obtain the seismic information. The user needs to enter the design
code reference document, site soil classification, risk category, site latitude, and site longitude.
Foundation Bearing Pressure (Shallow Foundation/Footings)
As long as our shallow foundation support recommendations are followed (ie. mass exc.), the allowable
bearing pressure for all perimeter, interior, and exterior footings and any other foundation component
is 3,000 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: For this project, we are recommending mass over-excavation under the entire building footprint
area (down to native, “target” sandy gravel) and placement of a thick, building pad section of granular
structural fill (back up to footing and slab grades). As a result, all footings will either bear on the native
gravel or on compacted, granular structural fill that in turn bears on the native gravel.
Final Geotechnical Report
Blk. 14, Ph. IV, Gran Cielo Sub. – Bozeman, MT
Project: 18-130.08
January 26, 2023
Allied Engineering Services, Inc. Page 9
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” sandy gravel (or granular structural fill that is
placed to build back up to footing grade from the “target” gravel subgrade). 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 (under Slabs)
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 gravel or crushed rock.
Note: For this project, we are recommending a minimum 18-inch thick, gravel support section under
the interior slab area that consists of an upper 6-inch section of clean crushed rock and a lower 12-inch
section of granular structural fill. In all actuality (since we are also recommending mass over-excavation
of the entire building area down to “target” gravel), the entire slab area will be underlain by a thick
section of compacted, granular structural fill that in turn bears on native gravel.
Final Geotechnical Report
Blk. 14, Ph. IV, Gran Cielo Sub. – Bozeman, MT
Project: 18-130.08
January 26, 2023
Allied Engineering Services, Inc. Page 10
Interior Slab Thickness
Given the multi-family, residential use of the buildings, we expect that the interior slab will be 4 inches
thick (minimum). With that said, the structural design will dictate the slab thickness.
Soil Corrosivity to Concrete
According to Montana Department of Transportation (MDT) highway design standards, Type I-II cement
is used when soil sulfate contents are less than 0.20%. However, if sulfate levels are between 0.20 and
2.00%, then Type V cement is used.
Note: Over the years, we have tested several samples of Bozeman-area silt/clay for soil corrosivity. All
sample results have come back as being non-corrosive to standard concrete. There is no reason to use
Type V cement for the foundation concrete. Normal cement can be used.
FOUNDATION RECOMMENDATIONS
General
A detailed illustration showing our earthwork, foundation bearing, slab support, and building moisture
protection recommendations for an at-grade slab (slab-on-grade) configuration is included as Figure 5.
Please refer to this figure during the review of the report.
Note: Figure 5 shows mass over-excavation of the entire building footprint (down to native gravel) and
a building pad of compacted, granular structural fill (back up to footing and slab grades).
Foundation Design and Support
• All buildings will be underlain by an at-grade slab (slab-on-grade) and they will contain no crawl
space areas.
• The building foundations will be designed as a shallow, conventional foundations consisting of
perimeter footings/foundation walls along with interior and exterior footings.
• Parking lot covered canopies will bear on standard, spread footings and columns/sono tubes.
• The “target” foundation bearing material for all footings (including the canopy footings) is the
“clean”, sandy gravel at depths of 2.0 to 4.0 feet. All footings must bear directly on the native
gravel or on granular structural fill that in turn is supported on the native gravel.
• The minimum depth of cover for frost protection of perimeter and exterior footings is four feet.
This dimension is measured from bottom of footing up to the final grade of the ground surface.
Final Geotechnical Report
Blk. 14, Ph. IV, Gran Cielo Sub. – Bozeman, MT
Project: 18-130.08
January 26, 2023
Allied Engineering Services, Inc. Page 11
Foundation Excavation and Earthwork
• We recommend mass over-excavation (“bathtub” excavation) of the entire building area down
to the “target” sandy gravel. The excavation area shall extend a minimum of 5.0 feet beyond
the outside edge of perimeter footings and must encapsulate all exterior footings (for roof over-
hangs) on the outside of the foundation walls. This method of excavation will prevent having to
excavate/over-excavate under all footings on an individual basis (in trench and pad excavations).
• We recommend that a building pad section of imported, granular structural fill (3”-minus, sandy
gravel) be placed throughout the building mass over-excavation area. The gravel fill material
must extend from the “target” gravel surface up to the bottom of footing and slab grades.
• All covered canopy footings must be excavated down to “target” gravel and either bear on the
native gravel or on granular structural fill that in turn bears on the native gravel.
• There is a chance that shallow groundwater conditions could be above the top of the “target”
gravel, depending on the time of year (namely during the spring). This will require groundwater
dewatering to lower the water level during excavation and before structural fill placement.
• If the “target” gravel subgrade is wet or contains some areas of shallow standing water, then
granular structural fill cannot be placed. Instead, the initial lift of gravel fill material will need to
consist of 1”-minus, clean crushed rock. The crushed rock layer shall be vibratory compacted
and covered with a layer of 8 oz. non-woven geotextile separator fabric (Mirafi 180N or equal)
before placing the first lift of granular structural fill.
• If the “target” gravel surface is dry, it must be vibratory compacted with a large roller to a dense
and unyielding condition prior to pouring footings or placing granular structural fill.
• If the “target” gravel surface is wet or contains shallow standing water, it must be track-packed
with the excavator and static rolled with a roller prior to placing the initial crushed rock layer.
Shallow Footings (Standard Foundation)
• The “target” bearing material for all footings (incl. perimeter, interior, and exterior footings as
well as canopy footings) is native sandy gravel that underlies the site at depths of 2.0 to 4.0 feet.
None of the overlying soil materials (incl. topsoil, silt/clay or “dirty” gravel) shall be left in-place
under any footings. The “target” gravel is identifiable based on its brown color, “clean” sandy
composition, and abundant rounded gravels and cobbles.
• All footings must bear directly on the “target” gravel (ie. “clean” sandy gravel) or on compacted
granular structural that in turn is supported on the native gravel.
Final Geotechnical Report
Blk. 14, Ph. IV, Gran Cielo Sub. – Bozeman, MT
Project: 18-130.08
January 26, 2023
Allied Engineering Services, Inc. Page 12
• Depending on perimeter footing grades (and canopy footing grades) relative to the top of the
native gravel, some footing areas may bear directly on “target” gravel, while others will need to
be over-excavated down to gravel and built back up to footing grade with granular structural fill.
• All of the interior footings located directly under the slab will need to bear on a thicker granular
structural fill section that in turn is supported on the “target” gravel. Based on the mass over-
excavation method, the entire area inside of the perimeter foundation walls will be in-filled with
granular structural fill (back up to interior footing and slab grades) following the pouring of the
perimeter foundation walls.
• To minimize disturbance to the native gravel subgrade surface, the excavation should be dug
with a smooth-edge foundation bucket.
• Prior to pouring footings or placing granular structural fill, the native gravel subgrade shall be
cleaned of loose spoil materials and re-compacted to a dense and unyielding condition with a
smooth drum roller. Track packing of the gravel subgrade with the excavator (to smooth it out)
prior to compaction with the roller works well.
• In areas where the foundation will need to be over-excavated down to native gravel, the limits
of the excavation will need to extend wide enough beyond the outside edge of footings such
that enough compacted structural fill is placed to keep the footing load transfer in the structural
fill materials down to the “target” gravel.
• The required minimum width that the granular structural fill section must extend beyond the
outside edge of footing is dependent on the structural fill thickness. The formula is as follows:
Structural Fill Thickness / 2.0 = Min. Width of Structural Fill Beyond Edge of Footing. Here are
some examples: For 2.0 feet of fill, the fill must extend 1.0-foot beyond the edge of footing; For
4.0 feet of fill, the fill must extend 2.0 feet beyond the edge of footing. To ensure the structural
fill extends far enough beyond the outside edge of footing and can be properly compacted along
the sides of the excavation, we recommend that the structural fill extend a minimum of 5.0 feet
beyond footings in all areas. This distance will need to be increased for structural thicknesses
greater than 10.0 feet (which will not occur on this project site).
• All granular structural fill that is placed under footings must consist of either 3”-minus, sandy
(pitrun) gravel or 1.5”-minus, crushed (roadmix) gravel. Specifications for these materials are
provided in a later section of the report. We recommend 3”-minus gravel for the building pad.
• 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. A large, smooth drum roller should be used wherever possible. Small,
walk-behind sheepsfoot rollers and hand-held, jumping jack compactors should be used in
narrow/confined excavations and along edges and in corners of the excavation.
Final Geotechnical Report
Blk. 14, Ph. IV, Gran Cielo Sub. – Bozeman, MT
Project: 18-130.08
January 26, 2023
Allied Engineering Services, Inc. Page 13
FOUNDATION WALL BACKFILL RECOMMENDATIONS
Provided below are our general recommendations for interior and exterior foundation wall backfill.
• For interior foundation wall backfill (under interior slab areas), all backfill material must consist
exclusively of high quality, 3”-minus granular structural fill. This material is easy to compact and
will minimize any settlement potential under the slab. All backfill must be placed in thin lifts and
be vibratory compacted to a dense and unyielding condition. We do not recommend using any
native silt/clay soils for any interior backfill.
• Select native silt/clay soils can be used for exterior foundation wall backfill. These materials
must be well compacted to prevent unwanted settlements, especially under exterior slab areas.
Use only the driest material available. All backfill must be placed in lifts and be well compacted.
• To prevent any exterior slab settlement or exterior slab frost heaving issues for those slabs that
are adjacent to doorways and foundation walls, we are recommending a minimum 12-inch thick,
clean crushed rock section under these slab areas. During construction, some consideration
should be given (by the Contractor) to fully backfilling these relatively small areas (from the
perimeter footing grade up to slab grade) under all “building-adjacent slabs” with granular
structural fill or clean crushed rock. By doing so, all frost heaving risk would be removed.
INTERIOR SLAB RECOMMENDATIONS
Provided below are our recommendations for interior slab support:
• All interior slabs shall be supported on a minimum, 18-inch thick, compacted gravel section
consisting of 6 inches of clean crushed rock underlain by 12 inches of granular structural fill.
• Since we are recommending mass over-excavation of the entire building area down to “target”
gravel and the placement of a building pad section of granular structural fill, the sub-slab gravel
section will be much thicker (ie. 4.0 to 6.0 feet) than the 18-inch (min.) thickness in all areas.
MOISTURE AND SUBSURFACE DRAINAGE RECOMMENDATIONS
Provided below are our moisture protection and subsurface drainage recommendations for at-grade
slab (slab-on-grade) foundation configurations.
Moisture Protection (At Grade Slabs)
• A heavy-duty vapor barrier shall underlie the entire floor area of the interior slab (directly under
the slab and above the clean crushed rock layer). The purpose of the barrier is to minimize the
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upward migration of water vapor into the building. The vapor barrier that we exclusively
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). All seams, joints, and pipe penetrations in the vapor
barrier shall be sealed with Stego wrap polyethylene tape. Also, the barrier should be secured
and sealed along the perimeter foundation walls.
• Perimeter frost walls around at-grade slab areas shall be damp-proofed (per the current code).
• If the current code does not require damp-proofing, then damp-proofing of the foundation walls
can be omitted.
Subsurface Drainage (At-Grade Slabs)
• For at-grade slab areas (set above exterior grades), no perimeter footing drains are required.
Elevator Pits (Beneath At-Grade Slabs)
• All elevator pits shall be underlain by a 15-mil vapor barrier.
• We recommend that foundation walls of elevator pits be water-proofed (per the code).
• A sump chamber shall be part of the bottom of the pit.
EXTERIOR SLAB RECOMMENDATIONS
Provided in Table 1 is our recommendations for the design section under the light-duty, exterior slabs
(including standard pedestrian sidewalks away from the building foundation and next to streets).
Table 1. Exterior Concrete Slab (Light-Duty) – Sidewalks Away From Building – Stable Subgrade
COMPONENT COMPACTED THICKNESS (IN)
Concrete Slab: 4 (min.)
1”-Minus Clean Crushed Rock: 6
Granular Structural Fill – 3”-Minus Gravel or 1.5”-Minus Roadmix: No
315 lb. Woven Geotextile Separation Fabric (Mirafi 600X or Equal): No
Stable Subgrade Soils (Less Topsoil) or Embankment Fill: Compacted to 95%
TOTAL SECTION THICKNESS: 6 + Slab Thickness
Notes: 1) We recommend this section for std. pedestrian sidewalks away from the building foundation and next to streets.
2) We expect pedestrian slabs will be 4 inches thick (min.).
3) City of Bozeman specs call for 3 inches (min.) of crushed rock; we recommend increasing this to 6 inches.
4) The purpose of the 6-inch thick, crushed rock section is to provide better support under the slab.
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5) Stable subgrade is required for this section.
6) If unstable subgrade exists, the soils must first be scarified and attempted to be dried out.
Provided in Table 2 is our recommendations for the design section under the medium-duty, exterior
slabs (including pedestrian sidewalks next to the building foundation wall, slabs at all doorway entries,
and “patio/porch/deck area” slabs).
Note: In the table below, we recommend a minimum of 12 inches of crushed rock under these slabs. A
better recommendation to further lower the potential for frost heaving is to increase the gravel section
under the “doorway and patio/porch/deck area slabs” to 24 inches (instead of 12 inches). This 24-inch
sub-slab section can consist of 12 to 18 inches of granular structural fill topped by 6 to 12 inches of clean
crushed rock.
Note: To remove all frost heaving risk under slabs adjacent to doorways, strong consideration should be
given to fully backfilling these relatively small slab areas with granular structural fill and/or clean crushed
rock from footing grade up to bottom of slab.
Table 2. Exterior Concrete Slab (Medium-Duty) – Sidewalks Next To Building – Stable Subgrade
COMPONENT COMPACTED THICKNESS (IN)
Concrete Slab: 4 (min.)
1”-Minus Clean Crushed Rock: 12 (See Below for Recommendations)
Granular Structural Fill – 3”-Minus Gravel or 1.5”-Minus Roadmix: No
315 lb. Woven Geotextile Separation Fabric (Mirafi 600X or Equal): No
Stable Subgrade Soils (Less Topsoil) or Embankment Fill: Compacted to 95%
TOTAL SECTION THICKNESS: 12 + Slab Thickness
Notes: 1) We recommend this section for pedestrian sidewalks next to the building, at doorways, and patios/porches/decks.
2) We expect pedestrian slabs will be 4 inches thick (min.).
3) City of Bozeman specs call for 3 inches (min.) of crushed rock; we recommend increasing this to 12 inches.
4) The purpose of the 12-inch thick, crushed rock section is to lower the frost heaving risk of the underlying silt/clay.
5) For doorway and patio/porch/deck slabs, we recommend the sub-slab gravel section be increased to 24 inches.
6) The purpose of the “expanded” 24-inch gravel section under slabs is to further reduce frost heaving potential.
7) Option 1: The 24-inch gravel section can consist of 6 inches of crushed rock and 18 inches of structural fill.
8) Option 2: The 24-inch gravel section can consist of 12 inches of crushed rock and 12 inches of structural fill.
9) Option 3: The 24-inch gravel section can consist entirely of 24 inches of crushed rock.
10) Stable subgrade is required for this section.
11) If unstable subgrade exists, the soils must first be scarified and attempted to be dried out.
12) An option for removing all frost heaving risk next to doors is to fully backfill under slabs w/ granular structural fill.
13) The granular backfill material shall extend from footing grade up to the bottom of the layer of clean crushed rock.
14) In lieu of granular structural fill, the doorway slabs can be fully backfilled with clean crushed rock.
Provided in Table 3 (on the following page) is our recommendations for the design section under the
heavy-duty, exterior slabs (including driveway aprons and sidewalks; as well as any other vehicle slabs).
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Table 3. Exterior Concrete Slab (Heavy-Duty) – Driveway Aprons and Sidewalks – Stable Subgrade
COMPONENT COMPACTED THICKNESS (IN)
Concrete Slab: 6 (min.)
1”-Minus Clean Crushed Rock or 1.5”-Minus Base Course Gravel: 6
Sub-Base Course – 6”-Minus Uncrushed Sandy (Pitrun) Gravel: 12
315 lb. Woven Geotextile Separation Fabric (Mirafi 600X or Equal): Yes
Stable Subgrade Soils (Less Topsoil) or Embankment Fill: Compacted to 95%
TOTAL SECTION THICKNESS: 18 + Slab Thickness
Notes: 1) We recommend this section for driveway aprons and sidewalks; and any other vehicle slabs.
2) We expect driveway apron/sidewalk slabs and vehicle slabs will be 6 inches thick (min.).
3) City of Bozeman specs call for 3 inches (min.) of crushed rock; we recommend increasing this to 6 inches.
4) The purpose of the 18-inch thick, total gravel section is to provide better support under the vehicle slabs.
5) We recommend a 24-inch total section thickness for slabs that will be subjected to vehicle/truck traffic loading.
6) If the slab thickness will be 8 inches instead of 6 inches, then reduce the crushed rock thickness from 6 to 4 inches.
7) Stable subgrade is required for this section.
8) If unstable subgrade exists, the soils must first be scarified and attempted to be dried out.
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 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.
FOUNDATION-RELATED FILL MATERIAL RECOMMENDATIONS
Provided below (on the following page) 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.
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Excavated Foundation Soils
For more information on this, please refer to an earlier section of the report that is entitled “Excavation
and Re-Use of On-Site Soils”.
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 three-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 3”-minus, uncrushed, sub-base course gravel.
Note: We recommend the use of 3”-minus sandy gravel for all building pad structural fill material (from
“target” gravel up to footing and slab grades) and for all interior foundation wall backfill.
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. Crushed rock shall be a clean assortment of angular
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 containing 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 all 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
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content of any material to be compacted should be within approximately two percent (+/-) of its
optimum value for maximum compaction.
Provided in Table 4 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 4. Compaction Recommendations (Application vs. Percent Compaction)
APPLICATION % COMPACTION
Granular Structural Fill Under Footings and Slabs: 97
Interior Wall Backfill under Slabs (Granular Structural Fill): 97
Exterior Wall Backfill (Native Soil or Granular Structural Fill): 95
Clean Crushed Rock Under Footings/Slabs and Behind Walls: N/A (Vibration Required)
Site Fill Around Building and Under Concrete and Pavement Areas: 95
UNDERGROUND UTILITIES
General
The underground “wet” utilities on this project (in addition storm drainage piping) will include building
services (for water, fire, and sewer), a looped water main extension in the parking lot area, and the
underslab piping/plumbing.
Soil Corrosivity Potential for DIP Pipes
For sure, the water main piping and building fire service lines will be ductile iron pipe (DIP). Depending
on the size of the water services, they may be either be copper or DIP.
Back in 2019, AESI performed a soil corrosivity analysis for the Gran Cielo Subdivision. This was required
by the City at the time of subdivision development to determine if any of the on-site soils are corrosive
to DIP pipes and if so, what level of corrosion protection would be recommended by DIPRA guidelines.
Our work included four test pits throughout the area, soil sampling, and the lab testing of four samples
of sandy gravel soils at depths of 6.0 feet (which is standard water main installation depth). Due to the
shallow depth and thin soil layer configuration of the overlying silt/clay, these soils were not tested.
What we learned through this analysis was that none of the area wide, sandy gravel soils (in Gran Cielo)
are corrosive to DIP. The recommendations based on lab testing and DIPRA design guidance follows:
• None of the soil conditions require the use of special, zinc-coated DIP pipe.
• None of the soil conditions require the use of polyethylene encasement.
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Provided in Table 5 is the DIPRA scores and recommendations for each of the four soil samples that
were collected and analyzed as part of the 2019 Gran Cielo soil corrosivity analysis. This table is an
excerpt from the 2019 report, which was submitted to the City at that time.
Table 5. Summary of DIPRA Scores and Recommendations from TP-1 – TP-4
TP # SAMPLE
COMPOSITION
TABLE 2
LIKELIHOOD SCORE
TABLE 3
CONSEQUENCE SCORE
TABLE 1
DIPRA RECOMMENDATION
1 Sandy Gravel 11 8 Standard Shop Coat
2 Sandy Gravel 11 8 Standard Shop Coat
3 Sandy Gravel 11 8 Standard Shop Coat
4 Sandy Gravel 13.5 8 Standard Shop Coat
Notes: 1) TP-1 through TP-4 were dug in the SW, NW, NE, and SE corners of the property, respectively. 2) For likelihood scores of 1 to 20, the DIPRA recommendation is “as manufactured with shop coat”.
3) For likelihood scores of 21 to 40, the DIPRA recommendation is “V-Bio Enhanced Polyethylene Encasement”.
4) For likelihood scores of 41 to 50, the DIPRA recommendation is “V-Bio Poly Encsmnt w/ Zinc Coated Pipe”. 5) Based on the test results, use standard DIP pipe and no polyethylene encasement is required.
DIP Corrosion Protection Recommendations for Gran Cielo Project Site (Block 14, Phase IV)
Based on the test results and the shallow gravel conditions (2.0 to 4.0 feet) across the site, standard DIP
pipe can be installed (ie. zinc-coated pipe is not needed) and no poly-wrapping is required for any of the
water main, water service, and fire service improvements.
Sub-Slab Plumbing Excavation and Trench Backfill
Based on the mass over-excavation and building pad granular structural fill recommendation, all of the
sub-slab materials that will be excavated during plumbing installation will be previously placed, 3”-minus
granular structural fill or native sandy gravel. All of these gravelly materials can be readily re-used for
trench backfill above the pipe bedding gravel. These materials must be placed in lifts and be compacted.
As an option (for ease of backfill/compaction, faster backfilling, and convenience), the Contactor can
choose to use 1”-minus, clean crushed rock for all of the plumbing trench backfill under the slab area.
We still recommend that the crushed rock be placed in reasonable lifts and be vibratory compacted to a
dense and unyielding condition. The use of crushed rock is not a requirement or a recommendation; it
is simply an available option that the Contractor can choose to use. In our opinion, there should not be
any change orders for the Contractor’s decision to use crushed rock.
Final Geotechnical Report
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Project: 18-130.08
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ASPHALT PAVEMENT SECTION RECOMMENDATIONS
Pavement Section Design and Options
All parking lot subgrade will consist of native silt/clay. In most areas, we expect the subgrade soils will
be slightly moist to moist and consequently stiff to very stiff. As a result, we are recommending a design
pavement section (Option 1) with a 24-inch total thickness for all pavement areas. This section requires
dry, hard, compacted, and “stable” subgrade soils and is presented in Table 6. Some areas of the
subgrade may be overly moist and softer. This may require that the subgrade be dried and scarified to
improve the performance of subgrade and get it to a stable condition.
Table 6. Pavement Section Design – Option 1 – All Parking Lot Areas – Stable Subgrade
COMPONENT COMPACTED THICKNESS (IN)
Asphalt Concrete: 3
Base Course – 1.5”-Minus Crushed (Roadmix) Gravel: 6
Sub-Base Course – 6”-Minus Uncrushed Sandy (Pitrun) Gravel: 15
315 lb. Woven Geotextile Fabric (Mirafi 600X or Approved Equal): Yes
Stable Subgrade Soils (Less Topsoil): Hard and Compacted
TOTAL SECTION THICKNESS: 24
Notes: 1) This is the standard pavement section design for all areas of the project site (parking lots and access drives).
2) The use of this design section requires that the subgrade soils are dry, hard, compacted, and stable.
3) To confirm the subgrade stability, all areas should be prepared and proof-rolled with a loaded gravel/water truck.
4) For stable silt/clay subgrade, place a 315 lb. woven fabric for subgrade separation.
5) At all seams, over-lap the fabric by 12 inches (min.).
If areas of the parking lot subgrade are very moist to wet and unstable, then we have provided a second
pavement section option (Option 2) for “unstable” subgrade. This section is presented in Table 7 and
has a 33-inch total thickness. We do not expect that this option will be needed.
Table 7. Pavement Section Design – Option 2 – All Parking Lot Areas – Unstable Subgrade
COMPONENT COMPACTED THICKNESS (IN)
Asphalt Concrete: 3
Base Course – 1.5”-Minus Crushed (Roadmix) Gravel: 6
Sub-Base Course – 6”-Minus Uncrushed Sandy (Pitrun) Gravel: 24
Tensar TriAx TX-190L Geogrid: Yes
8 oz. Non-Woven Geotextile Fabric (Mirafi 180N or Approved Equal): Yes
Unstable Subgrade Soils (Less Topsoil): Smooth and Rut-Free
TOTAL SECTION THICKNESS: 33
Final Geotechnical Report
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Project: 18-130.08
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Notes: 1) This heavy-duty pavement section is designed for unstable and soft soil conditions.
2) The non-woven fabric and geogrid layers shall be installed with 12-inch (min.) over-laps at the seams.
3) The geogrid layer shall be zip-tied together at the seams.
4) Depending on severity, the 24-inch sub-base gravel section may or may not be able to be placed in two lifts.
5) For firmer subgrade, the lower lift of sub-base should be 15 to 18 inches (+/-) if the conditions will allow.
6) For very soft subgrade, the entire 24-inch thick section should be placed/compacted in one single lift.
7) If the 24-inch sub-base will not bridge the soft soils, then the sub-base will need to be thickened (> 24 inches).
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,
respectively. Both gravel courses shall meet the material and gradation specifications as presented in
the MPWSS, Sections 02234 and 02235. All gravels shall be placed in loose lifts not exceeding 12 inches
in thickness and be compacted to at least 95 percent of the material’s maximum dry density as defined
in ASTM D-698. Asphalt pavement shall meet specifications in MPWSS Section 02510 and be compacted
to a minimum of 93 percent of the Rice mix density.
PRODUCTS
Provided in Table 8 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
attached at the end of the report.
Note: Several notes are presented under the table that describe the recommended products, where
they can be obtained, and where they can be used.
Table 8. Product Reference Guide
PRODUCT USE SOURCE PHONE
Stego 15-mil Vapor Barrier Moisture Protection Under Slab MaCon Supply – Bozeman 551-4281
Mirafi 180N Non-Woven Fabric Wet Exc. & Soft Subgrade w/ Grid Multiple Sources – Bzn/Blgd N/A
Mirafi 600X Woven Fabric Road Subgrade Separation Multiple Sources – Bzn/Blgd N/A
Tensar TriAx TX-190L Geogrid Road Subgrade Stabilization Core & Main – Belgrade 388-5980
Notes: 1) Use Stego 15-mil vapor barrier only. There are no approved equals for this product.
2) Stego 15-mil vapor barrier has a water transmission rate that meets national standards for vapor barriers.
3) Stego 15-mil vapor barrier is a heavy-duty vapor barrier for placement under interior slabs and in crawl spaces.
4) Use Mirafi 180N non-woven fabric or an approved equal that meets or exceeds Mirafi 180N fabric specifications. 5) Approved equals for Mirafi 180N non-woven fabric are available from multiple sources in the Bzn/Blgd area.
6) Mirafi 180N is a medium-weight, 8 oz. non-woven fabric.
7) There are two potential uses for Mirafi 180N non-woven fabric on this project site.
8) Use 1: If the bottom of the foundation excavation is wet, an initial layer of clean crushed rock will be required.
9) Following vibratory compaction, the crushed rock layer must be covered with a layer of 8 oz. non-woven fabric.
Final Geotechnical Report
Blk. 14, Ph. IV, Gran Cielo Sub. – Bozeman, MT
Project: 18-130.08
January 26, 2023
Allied Engineering Services, Inc. Page 23
enc: Figure 1 – Site Location w/ Area Test Pits
Figure 2 – Concept Site Plan
Figure 3 – Test Pit Locations w/ Depth to Native Gravel (Excerpt from 2007 HKM Geotech Rpt)
Figure 4 – Table w/ Depth to Native Gravel (Excerpt from 2007 HKM Geotech Rpt)
Figure 5 – Foundation Detail – At-Grade Slab
Products (Vapor Barrier, Non-Woven Fabric, Woven Fabric, Geogrid)
Limitations of your Geotechnical Report
REFERENCES
International Code Council, 2021, “International Building Code”.
Montana Contractors’ Association, April 2021, “Montana Public Works Std. Specifications”, 7th Edition.
P:\2018\18-130 Gran Cielo Sub.\Design\Geotech\Report – Block 14, Phase IV\Text\Block 14, Phase IV, Gran Cielo - Geotech Report.01.26.23
Figure 5
18-130 Jan. 2023
Gran Cielo Sub. (Block 14, Phase IV)
Foundation Detail - At-Grade Slab
Bozeman, Montana
Damp-Proofing As Required (typ.)
Foundation Wall (typ.)Approved Non-Woven Filter Fabric To Encase Bedding Gravel (typ.) Interior Floor Slab (typ.)Interior Steel Column (typ.)Interior Spread Footing (typ.)
6” Of 3/4" Minus Crushed Washed Gravel
Hydraulically Connected To Sub-Drain or
Existing Surface Drainage (typ.)
Native Topsoil andRandom Surface Fill Imported 4-Inch Minus Sandy Pitrun Gravel Native Silt/ClayImported Flowable Fill
Six Inch Diameter Sub-Drain Pipe
(Graded To Drain To Sump Area)
Concrete SidewalkLow Permeability Soils(Landscaped Area)LegendConcrete Wall and/or Footing Low Permeable Topsoil No Scale (Parts Of This Exhibit Have Been Exaggerated For Clarity)
ALLIEDENGINEERING
SERVICES, INC.
Civil Engineering
Geotechnical Engineering
Land Surveying
32 Discovery Drive
Bozeman, MT 59718
Phone: (406) 582-0221
Fax: (406) 582-5770
Slope Away @ 2%
In All Concrete Or
Pavement Areas (typ.)
Footings 6’ max.
depth below
existing ground
Native Topsoil 6” Minus Sandy (Pitrun) Gravel 4” Minus Sandy PitrunGravel (ie. Structural Fill)4’ max fill above existing ground
4' min.
4’ Max Fill Above
Existing Ground
3” (min.)
Thickness Will Vary Due To
Depth Of Bedbrock Strata
6” (min.)
3” (min.)
8” (min.)
4.0’ (min.)
6” (min.) Of Rock Bedding To Be
Placed Around Drain Piping (typ.)
Under-Slab Rock Layer To Be Hydraulically
Connected To Sub-Drain System By 3” Of Rock
Or 2” Sch. 80 Piping Spaced On 10’ Centers (typ.)
B
H (Variable; Depends
On Depth To Gravel)
18” (min.)
18” (min.)
6” (min.)
6” (min.)
1’ (min.)
H = 3.5’ (Based On4.0’ Footing Depth And The Depth To Gravel In TP-4) H = 5.5’ (Based On4.0’ Footing Depth And The Depth To Gravel In TP-2)
D D
Woven Geotextile Filter Fabric (Amoco 2004)Vapor Barrier Under Slab (typ.)
9.5’ Deep
(TP-2)
7.5’ Deep
(TP-4)
Non-Woven Filter
Fabric To Encase
1-Inch Minus Rock
6” (min.) Rock Layer (typ.)
Landscape Areas To Slope Away
@ 5% (min.) Within 10’ Of Wall.
Upper 4” - 6” Of Backfill Should
Consist Of Low Permeable Topsoil.
Note: Asphalt/Concrete Surfacing Placed Adjacent To
Foundation Walls Shall Slope Away @ 2% (min.).
6” (min.)
6” (min.)4” PE Sub-Drain (typ.)
Crawl Space Opening
Must Be Properly Vented.
Note: Elevation Difference Between The Top Back Of Curb
And The Finished Floor Should Be Maximized. I Believe The
Subdivision Covenants Call For A Minimum Separation Of 2.0’
And A Maximum Of 5.0’. Due To High Groundwater Concerns,
An Elevation Difference Of More Than 2.0’ Is Recommended.
This Should Be Thoroughly Considered On A Case By Case
Basis. Please Refer To The Covenants For More Detail.
Important Notes: The Three-Foot Wide (Min.) Over-Excavation From The Center Of The Footing Is Calculated Based On A 16-Inch
Footing Width (B) And An Average Depth To Native Gravel (GD) Below The Footing Elevation Equal To Five Feet. If The Footing
Is Substantially Wider Or The Depth To Gravel Substantially Deeper; The Width Of The Excavation Will Need To Be Increased. The
Equation For Determining Excavation Width (EW) From The Center Of Footing Is: EW = (B + GD) / 2.0. If Caving (ie. Sloughing)
Of The Excavation Side Walls Is A Problem; EW Will Need To Be Increased Accordingly. Since The Footings Are Supported On
Structural Fill That Bears On Native Gravel; There Is No BenefitTo Increasing Footing Size Beyond What Is Shown On The Plans.
If Groundwater Is Encountered In The Over-Excavation Above The Native Sandy Gravel Surface,
We Recommend A Layer Of Crushed Rock First Be Used To Get Above The Groundwater Elevation.
The Crushed Rock Should Be Placed In A Single Lift That Does Not Extend More Than Four Inches
Above The Groundwater. After Placement, The Crushed Rock MUST Be Compacted By Vibratory
Methods. Compactors That Are Suitable For Crushed Rock Include Walk-Behind Plate Compactors;
Remote-Controlled Sheepsfoot Trench Rollers; And Self-Propelled Smooth Drum Rollers.
Note: If Groundwater Is Not Encountered, The Use Of Crushed Rock Is Not Necessary.
Compacted Structural Fill. Use Sandy Pitrun Gravel,
Not Crushed Rock. Gravelly Materials Are Not Only
Less Expensive But They Will Also Reduce The In-Flow
Of Groundwater Into The Crawl Space In The Event That
High Groundwater Exceeds The Crawl Space Elevation.
Place The Pitun In Lifts (Six-Inch Thick Max. For Small
Remote-Controlled Sheepsfoot Trench Rollers And
Twelve-Inch Thick Max. For Self- Propelled Smooth
Drum Rollers) And Compact To An Unyielding Condition.
Note: A Material That Works Very Well For Foundation
Structural FilI Is The 3” Minus Pitrun Gravel Product
That Is Available From TMC In Belgrade.
Pay Special Attention To Compaction
Of Crushed Rock And Structural Fill
Along Edges. Native Soils Could Be
Soft. Rock / Fill Will Need To Be
Compacted Into Side Of Excavation.
Place Woven Geotextile
Fabric Over The Crushed
Rock. This Will Prevent
Fines Migration Into The
Rock After Placement Of
The Structural Fill.
4” (max.)
3’ (min.)
3’ (min.)
Interior Footing
As A Precaution For Groundwater,
Install 4” PE Slotted Drain Piping
Along The Inside Of The Perimeter
Footings And Grade To A Shallow
Sump Chamber In The Crawl Space.
If Water Becomes An Issue, Install
Sump Pump And Discharge Out Of
The Crawl Space. A Four-Inch Layer
Of Crushed Rock Will Facilitate
Rapid Drainage And Eliminate The
Sight Of Standing Water. If A Vapor
Barrier Is Placed Above The Crushed
Rock; Ensure It Is A Material That
Can Breathe (Not Polyethylene).
All Interior Footings Shall Bear On Structural Fill.
Finished Floor Elev. (At-Grade Slab)
GD
Existing Ground Surface
Existing
Ground
4” Slotted PE Pipe. Install Drain Piping Around Inside Perimeter Of Foundation. Piping
Should Be Placed At Footing Grade Or Preferably Below The Top Of The Crushed Rock
Fill (When Used). Connect Piping To Shallow Sump Chamber. If High Groundwater Is An
Issue, A Pump Can Be Installed At A Later Time.
32”
48”
Reviewed By: __________________
4” To 6” (Min.)
Thickness
As Required
2.5’
4’ (min.)
Damp
Proofing
4” Footing
Drain (typ.)
Min. Depth Of Cover
For Frost Protection
Min. Required Width Of
Mass Over-Excavation
Beyond Edge Of Footing
1.0’ - 17.0’ Depth To
“Target” Bearing Material.
Silt/Clay Below 2.5’ (+/-) Is
Generally V. Moist To Wet.
See TP Logs For Soil And
Groundwater Conditions.
5.0’ - 13.5’ Depth To
“Target” Bearing Material.
Groundwater Depth Ranged From 6.0’ to 13.5’. Depending
On Time Of Year, Groundwater May Be At Or Above The
Sandy Gravel (“Target” Bearing Material). Therefore,
Groundwater Dewatering May Be Needed. Dewatering Wells
Are Recommended To Lower Water Below Gravel Surface.
Strip, Remove, And Replace All Random Fill
From Under The Entire Building Area, Including
Under Interior House And Garage Slabs (typ.)
Note: De-Watering Will Likely Not Be
Required For Foundation Excavation.
Based On Our Test Pits,
All Evidence Suggests
The Groundwater Table
Stays Within The Sandy
Gravel Most Of The Time.
LSE, 1/25/23
Prior To The Placement Of Granular Structural Fill,
The Site’s Shallow Groundwater Conditions May
Require That An Initial Layer Of Clean Crushed Rock
Be Placed And Compacted Up To A Height Of At Least
6 Inches Above The Level Of The Standing Water.
Structural Fill: Use 4” Minus Sandy (pitrun) Gravel
Due To Shallow, Seasonal High Groundwater Conditions,
Footing And Crawl Space Depth Must Be Minimized Below
The Existing Ground Surface. Bottom Of Footing Elevation
Should Be Kept Within At Least 2.5’ To 3.0’ Of Existing Grades.
As An Added Precaution Against High Groundwater In The Crawl Space (And Especially
If Footing Depth Nears Or Exceeds 2.5’ To 3.0’ Below Existing Site Grades), We Strongly
Encourage The Placement Of A 6” To 8” Layer Of Crushed Rock In The Crawl Space To
Raise The Floor Elevation Up To The Top Of Footings. In The Event That Groundwater
Ever Rises Above The Crushed Rock Layer, A Sump Chamber And Pump Can Easily Be
Installed Later To Address The Problem.
We Do Not Recommend Placing The Initial Layer Of Clean Crushed Rock In Standing Water Exceeding 10 Inches In Depth.
Therefore, Depending On The Time Of Year, Some Groundwater De-Watering May Be Required During Foundation Earthwork.
All Perimeter, Interior, And Exterior Footings Must Bear
On A Minimum 2.0’ Thickness Of Granular Structural Fill
That In Turn Is Supported On The Native Sandy Gravel
(Which Is The ”Target” Foundation Bearing Material).
Given The 4.5’ To 6.5’ Depth To Gravel, Along With The
Anticipated Slab Grade, Perimeter Footings Will Likely
Lie 2.0’ to 6.0’ Above The Top Of The “Target” Gravel.
Mass Over-Excavate The Entire Foundation Footprint Area, Including All Exterior Footing Locations, Down To The “Target”
Bearing Material (Native Sandy Gravel); Thereby, Completely Removing All Native Silt, Clay, Sand From Under The Building.
Over-Dig The Excavation To The Minimum Width Dimensions As Shown On This Figure And As Stated In The Report.
Important Note: Mass Over-Excavation Of The Foundation (As Illustrated By Option #2)
Will Be Required If The Individual Footing Over-ExcavationsThat Are Depicted As Option #1
Will Not Stay “Open” Due To Trench Wall Collapse.
Foundation Earthwork Notes: 1) Slab On Grade - Option “B” Consists Of Over-Excavating Under All Perimeter, Interior, And Exterior Footings.2) This Is Most Applicable Where The Building Is Underlain By Relatively Deep Gravels And The Foundation Contains Less Interior Footings.3) Where Present, All Random Surface Fill Material Must Be Fully Removed From Under The Entire Building Area Down To Native Soils. Foundation Excavation Recommendations: Due To The Large Number and Close Spacing Of Interior Footings (Many Of Which Are 13 To 14 Feet On-Center), We Recommend The Entire Foundation Footprint Area Of The Apartment Buildings Be Mass Over-Excavated Down to Native Sandy Gravel And Built Back Up To Footing And Slab Grades With Compacted Structural Fill. The Limits Of The Mass Excavation Must Encapsulate All Perimeter And Exterior Footings. Important Note: It Is Now COB Policy That The Foundation Earthwork Be Inspected And Certified By The Geotechnical Engineer.
Suggestions: In Order To Reduce The Amount Of Required Structural Fill Under
Footings And The Slab Area, The Finished Floor Elevation Should Be Minimized
Above Existing Site Grades. Another Option To Reduce Fill Under Perimeter
Footings Is To Use A 6’ Tall Foundation Wall.
Foundation Backfill and Embankment Fill Granular Structural Fill(1.5”Minus Roadmix Gravel)Granular Structural Fill(1.5”Minus Roadmix Gravel)Sandy Gravel(”Target” Bearing Material) Low Permeable Topsoil Native Silt/Clay(Unsuitable Bearing Material) Native Silt
Native Silt/Clay
(Unsuitable Bearing Material)
Native Topsoil Granular Structural Fill(4” Minus Sandy Gravel)Granular Structural Fill(1.5” Minus Roadmix Gravel)1” Minus CleanCrushed Rock Groundwater (on 4/19/16) Concrete Slab
Exterior Foundation Wall Backfill
Should Only Consist Of Excavated
Soils That Are Not Overly Moist. It
Must Be Placed In Multiple Lifts
And Properly Compacted.
Slab Grade Should Be Set Above
Existing Grades. For The Mass Over-
Excavation Option, There Is No Limit
On Slab Height Above Existing Grades.
H
W = Footing Width + H; (5’ min.)
All Foundation Fill Materials Should Be Placed In Uniform,
Horizontal Lifts And Be Well Compacted. Granular Structural Fill
Shall Be Compacted To A Dense, Unyielding Condition, While Clean
Crushed Rock Or Lean Mix Concrete Must Be Compacted By
Vibratory Means. In General, The “Loose” Thickness Of Each Lift
Prior To Compaction Should Not Exceed 12 Inches For Large, Self-
Propelled Rollers; 6 Inches For Remote-Controlled Trench Rollers
And Walk-Behind Jumping Jack Compactors; And 4 Inches For Walk-
Behind, Plate Compactors. Pay Special Attention To Compaction Of
Structural Fill Along Edges And In Corners Of The Excavation.
Place Crushed Rock As Fill Under
Slab (6” min.) And Interior Wall Backfill
Strip Topsoil
Under Slab and
Re-Compact The
Subgrade Surface.
Vapor Barrier Under Slab. Seal Barrier At Seams/Penetrations.
Minimize
New Fill
Height For
Settlement
Reasons
The Uppermost 6” Of Lean Mix
Concrete Fill Can Be Replaced w/
Clean Crushed Rock For Easier
Leveling Of Footing Grade.
Bearing Pressure
4000 psf (max.)
6” (min.) Crushed Rock Layer Under Slab Areas (typ.) Important Note: To Stabilize The Trench Excavations And Minimize The Potential For Caving/Sloughing, Groundwater Dewatering May Be Required.
Shallow Frost-
Proof Foundation.
Insulate As Per
Applicable Codes.
Interior Footing (typ.)
Radon Mitigation System Should
Be Considered Under Interior Slab.
Important Note: If Foundation Construction Will Occur During The Cold/Winter Weather Season, The
Contractor Shall Take All Necessary
Precautions To Prevent The Earth-
Work From Freezing And/Or From
Being Contaminated With Snow.
Note: At A Minimum, Use A Large, Smooth Drum Roller To Compact
The Upper-Most Lift Of Structural Fill Under Footings And Slabs.
Additional Thickness
Of Gravel Building Pad
As Req’d To Bear On
“Target” Gravel.
For Mass Excavation, Over-Excavation
Width Beyond Perimeter Ftgs Is 5.0’ (typ.)
See Fig. 6 For Over-Excavation Width
Under Individual Ftg Excavations.
Embankment Fill Can Be Used Below 18” Of Slab Grade.
Note: No Topsoil Observed In On-Site Borings. Product Recommendation: A Stego 15-mil Vapor Barrier Is Recommended.Available From MaCon Supply In Bozeman.
W = Footing Width + H; (5’ min.)
Min. Width = 1/2(H);
But Must Be 5’ Min.
H
H = 2’ Min.
Important Note: If TP-3, A Clay
Layer Was Observed Under The
Native Sandy Gravel At A Depth
Of 6.0’. It Is Recommended That
All Footings Bear On A Minimum
24” Thickness Of Native Gravel
Or Granular Structural Fill. This
Should Be Confirmed With Test
Pits Around The Perimeter Of The
Building During Construction.
Important Note: If The Trench
Excavations Are Prone To Minor
Caving, Their Width Will Have To
Be Increased Accordingly To
Prevent Slough From Underlying
Or Being Mixed Into The Minimum
Required Width Of Structural Fill.
Given The 4.5’ To 6.0’ Depth To
Native Sandy Gravel, We Do Not
Expect That Most (If Any) Of The
Perimeter Footings Will Bear
Directly On Native Gravel. Most
Likely, Footings Will Need To Be
Supported On Structural Fill That
In Turn Bears On Native Gravel
(Similar To All Interior Footings).
Excavation Alternative: In Lieu Of Only
Excavating Footings, The Entire Foundation
Footprint Area Of The Building Can Be Mass
Over-Excavated Down To Native Sandy Gravel
And Filled With Granular Structural Fill. Given
The Gravel Depth, This Is Far Less Economical
As Compared To The Above Recommendations.
Prior To Granular Structural Fill Placement, The Excavated Gravel Surface (Under Entire Foundation Footprint Area)
Must Be Vibratory Re-Compacted With A Large, Smooth Drum Roller In Order To Densify The Native Sandy Gravel.
Due To Groundwater Depths Of 7.8’ To 9.8’, Wet Subgrade Conditions Should Not Be An Issue.
Depending On Location, Groundwater Could
Be At Or Above The Top Of Native Sandy Gravel
During The Seasonal High Water Time Of Year.
A Large, Smooth Drum
Roller Must Be Used To
Compact All Granular
Structural Fill Whenever
and Wherever Possible.
Lean Mix Concrete(Flowable Fill)Embankment Fill(On-Site or Import Material)
Embankment Fill
(On-Site Or Import Material)
3000 psf (max.)
B
3000 psf (max.)
B
Mass Excavate Under Entire Foundation Footprint Area Down To Native, Clean Sandy Gravel; Thereby
Removing All Of The Silt/Clay Under The Interior Slab. All Footings Must Bear On Native Sandy Gravel
Or On Compacted Granular Structural Fill That In Turn Is Supported On This “Target” Bearing Material.
Shallow Frost-Proof Foundation
Per IBC Is Also Acceptable.
H
H
If Exc. Walls Slough,
Widen Exc. To Ensure
Min. Struct. Fill Width
Beyond Edge Of Ftg.
Bottom Of Exc. Measurement
Centered Under The Footing.
If Exc. Walls Slough,
Widen Exc. To Ensure
Min. Struct. Fill Width
Beyond Edge Of Ftg.
Bottom Of Exc. Measurement
Centered Under The Footing.
Min. Width = (B + H); But 5’ (min.)
Crushed Rock
Is Only Needed
If Gravel Subgrade
Is Wet Or Contains
Standing Water.
All Fill Material Placed Under Footings And
Slabs To Consist Of Compacted Granular
Structural Fill. No On-Site Soils Are To Be
Used As Embankment Fill Under Slabs.
Do Not Place Granular Structural Fill Materials Over
Wet Subgrade Or In Shallow Standing Water. De-Water
The Excavation If Required. If Bottom Of Excavation
Is Wet, Place An Initial, Thin Layer Of Clean Crushed
Rock Under The Structural Fill. The Crushed Rock
Should Extend A Minimum Of About 4” Above The Wet
Conditions. Vibratory Compact The Crushed Rock And
Then Cover With A Medium-Weight, Non-Woven Fabric
Prior To Structural Fill Placement. Overlap Seams Of
Fabric By 12” Minimum.
Over-Excavate Under All Perimeter,
Interior, And Exterior Footings Down
To Native, Clean Sandy Gravel; Thereby
Removing All Silt/Clay Under Footings.
All Footings Must Bear On Native Sandy
Gravel Or On Compacted Granular
Structural Fill That In Turn Is Supported
On This “Target” Bearing Material.
Embankment Fill Under Structural Fill Layer
Must Be Compacted To Project Specifications.
See Figure 7 For
Recommendations
For Foundation Fill
Material Placement
And Compaction.
See Figure 7 For
Recommendations
For Ext. Foundation
Wall Backfill Material
And Compaction.
For Basements, Additional SubsurfaceDrainage And Moisture Protection Recommendations Will Need To BeIncorporated That Are Not Shown On This Exhibit. See Report For More Details.
No Scale (Parts Of This Exhibit Have Been Exaggerated For Clarity)
Geotechnical Notes:
1) Figure 5 Illustrates A Slab-On-Grade Foundation With Perimeter Frost Walls And Footings. Interior Footings Are Shown Directly Under The Slab. All Footings Shall Bear On Native Sandy Gravel
Or On Granular Structural Fill That In Turn Is Supported On The “Target” Gravel. We Recommend A “Bathtub” Excavation (Down To Gravel) And Gran. Struct. Fill Bldg Pad (Up To Ftg/Slab Grades).
Granular Structural Under Footings And Slabs Can Consist Of4”-Minus Sandy Pitrun Gravel Or 1.5”-Minus Roadmix Gravel. Based On Test Pits, Depth To “Target” Bearing Material Is 4’ To 5’ On Downhill Side And 3’ On Uphill Side Of The Lot.
Legend
Random Fill (Unsuitable Bearing Material) Random Fill (Unsuitable Bearing Material)
Low Permeable Topsoil
Granular Structural Fill(4”-Minus Sandy Gravel)
Granular Structural Fill (*)
1” Minus CleanCrushed Rock
1” Minus Clean
Crushed Rock
1” Minus CleanCrushed RockExisting Grade (Ground Surface)
Native Topsoil
Topsoil or Asphalt/GravelSurfacing Materials Native Topsoil Floor Joist
Exterior Foundation Backfill
Native Sandy Gravel
(“Target” Bearing Material)
Native “Dirty” Sandy Gravel(Unsuitable Bearing Material)
Native Topsoil
Interior Wall Backfill
(3”-Minus Sandy Gravel
Granular Structural Fill)
“Target” Bearing Material Is The Glacial Till. It Is Identifiable Based On Its Clean
Sandy Composition, Abundance Of 6”-Minus, Sub-Rounded Gravels, And Dense
Configuration. It Looks Like “Clean Pitrun Gravel” w/ Large Cobbles And Boulders.
All Footings Shall Bear On A Minimum Of 1’ Of
Granular Structural Fill That In Turn Bears On
“Target” Glacial Till (typ). Additional Structural Fill
Thickness Will Be Required Under Some Footings
In Order To Reach “Target” Bearing Material.
Recompact Subgrade Prior To Fill Placement (typ).
All Foundation Fill Materials Should Be Placed In Uniform, Horizontal Lifts
And Be Well Compacted. Granular Structural Fill, Embankment Fill, And Wall
Backfill Shall Be Compacted To A Dense, Unyielding Condition, While Clean
Crushed Rock Must Be Compacted By Vibratory Means. In General, The “Loose”
Thickness Of Each Lift Prior To Compaction Should Not Exceed 12 Inches For
Large, Self-Propelled Rollers; 6 Inches For Remote-Controlled Trench Rollers
And Walk-Behind Jumping Jack Compactors; And 4 Inches For Walk-Behind,
Plate Compactors. Pay Special Attention To Compaction Of Fill Materials Along
Edges And In Corners Of The Excavation; And Along Foundation Walls.
Daylight Footing And
Sub-Slab Drains (typ.)
See Figures 8 And 9
For Note On Exterior
Foundation Wall Backfill.
Granular Structural Fill
Should Be Used For
Interior Wall Backfill
Under Slabs.
See Figures 8 And 9 For Note
On Foundation Fill Material
Placement And Compaction.
All Excavated Soils Can Be Re-Used For Exterior Wall Backfill
Or Embankment Fill Provided They Are Not Organic Or Overly Moist.
All Fill Must Be Placed In Thin, Level Lifts And Properly Compacted.
H = 1’ or 2’ (Depending On Ftg Width)
H = 1.0’ (min.)
H
H = 1.0’ (min.)
15-mil Vapor Barrier Under Slab (Above Rock Layer).
Seal Barrier At Seams, Penetrations, And Footings.
Vapor Barrier Not Typ. Under Garage Slabs. Note: Due To Unheated/Non-Insulated Buildings, Consider Insulating Under Interior Slabs To Minimize Frost Heaving Potential Of Silt/Clay.
(*) Granular Structural Fill Can Consist
Of 3”-Minus Sandy (Pitrun) Gravel Or
1.5”-Minus Crushed (Roadmix) Gravel
Note: Groundwater Depths Are Expected To Be Below The Top Of “Target” Sandy Gravel
Most Of The Year. During Spring, Seasonal High Water May Rise Near Or Above The Gravel.
Note: Depending On Time Of Year, Groundwater Levels Could Be Near Or Above The Top Of Native Sandy Gravel.
4’ (min.)
For Frost
Protection
No Ftg
Drains
Req’d
Strip Topsoil And
Bench Subgrade Level
Prior To Placing Fill (typ.)
About 6” Of
Dirty Gravel
Overlies The
Clean Gravel.It Is Important To Vibratory Re-Compact The
Excavated “Target” Gravel Subgrade Surface
Prior To Pouring Ftgs Or Placing Struct. Fill.
Where Possible, Enlarge The Excavation To
Allow For Use Of Large, Smooth Drum Roller.
Product Recommendation:
A Stego 15-mil Vapor Barrier
Is Recommended.
Perimeter Footing Drain
To Wrap Around The
Exterior Of Home (typ.)
Over-Excavate Under All Perimeter, Interior, And
Exterior Footings Such That They Bear On A
Minimum Of 1’ Of Compacted Granular Structural
Fill That In Turn Bears On “Target” Glacial Till.
Min. Width Is B+H, But It Shall Not Be Less Than 5’.
Use Light-Weight Fabric Around Footing Drains (typ.).
Over-Excavation Width
Must Be Centered On
The Footings (typ.)
More Than 1.0’
Of Structural Fill
Is Expected (typ.)
Min. Width = (B + H);
But Shall Be 5.0’ (min.)
This Is A Bottom
Of Exc. Dimension.
Assumes No Sloughing
Of Exc. Side Walls.
Min. Width = (B + H);
But Shall Be 5.0’ (min.)
This Is A Bottom
Of Exc. Dimension.
Assumes No Sloughing
Of Exc. Side Walls.
A Large, Smooth Drum
Roller Should Be Used
To Vibratory Compact
Subgrade Soils And
Granular Structural Fill
Wherever Possible.
Concrete Slab
The Excavated Gravel Surface (Under All Footings) Must Consist Of Dense, Clean, Native Sandy Gravel. Use A Smooth Foundation
Bucket To Prevent Unnecessary Disturbance To The Native Gravel Subgrade. Do Not Stop Excavation In Lowermost Silt/Clay, Which
Does Contain Some Scattered Gravels. The Silt/Clay w/ Gravels (Which Looks Like A “Dirty Gravel”) Does Not Constitute The Clean,
Native Sandy Gravel (“Target” Bearing Material). Vibratory Re-Compact Subgrade Surface Whenever Possible.
Re-Compact Subgrade
Prior To Fill Placement.
Additional Structural Fill
Thickness As Required.
For Strip Footings With Width
Of 2.0’ Or Less, Min. Structural
Fill Thickness (H) Is 1.0’.
For Larger Pad Footings With Width
Of 3.0’ To 6.0’, Min. Structural Fill
Thickness (H) Is 2.0’.
Exterior Wall Backfill Can Consist Of Any Non-Organic Soil.
Suggest Removing Cobbles Over 6” Directly Next To Walls.
Strip Topsoil/Surfacing Material And Cut To A Min.
Depth Of 18 Inches Below Bottom Of Slab Grade.
For Easier Compaction, Consider
Using Only High Quality Granular
Material Or Clean Crushed Rock
For Interior Backfill. Place In
Lifts / Vibratory Compact.
“Target” Clean Gravel Surface.
Re-Compact Prior To Placing Fill.
Pad Footing
Over-Excavation
On Individual Basis
“Target” Clean
Gravel Surface.
Re-Compact Prior
To Pouring Ftgs Or
Placing Struct. Fill.
“Target” Clean
Gravel Surface.
Re-Compact Prior
To Pouring Ftgs Or
Placing Struct. Fill.
All Footings Must Bear On “Target”
Sandy Gravel Or On Granular Structural
Fill That In Turn Bears On “Target” Gravel.
All Excavations And Structural Fill
Under Footings Must Be Centered
Under The Footing.
Note: If Native Gravel Is Wet, Place An Initial Thin Layer
Of Clean Crushed Rock Covered By Non-Woven Fabric
Prior To Structural Fill. Vibratory Compact The Rock.
Excavations Should Be Wide Enough
To Permit The Use Of A Large, Smooth
Drum Roller For Compaction Of Gravel
Subgrade And Granular Structural Fill.
Footing Subgrade Will Consist Of
Native Silt/Clay. Dig With Smooth-
Edged Bucket To Prevent Disturbance.
Vibratory Compact To Re-Tighten Soils
And Induce Consolidation/Settlement.
Due To Dry Soils, Construction Water
May Need To Be Added To Facilitate
Better Compaction. (Typ. All Locations)
Over-Excavation And Structural Fill
To Be Centered Under Footing And
Extend A Minimum Of 2.0’ Beyond
Outside Edge Of Ftg In All Directions.
Over-Excavation And
Structural Fill To Be
Centered Under Footing
And Extend A Minimum Of
2.0’ Beyond Outside Edge
Of Ftg In All Directions.
Strip Topsoil Before
Placing Fill Material.
Strip Gravel.
Depending On The Number/Spacing Of Interior Footings.
Consideration Should Be Given To Mass Excavating Down
To “Target” Gravel Throughout Foundation Footprint And
Increasing Thickness Of The 12-Inch Structural Fill Layer.
By Doing This, Over-Excavation (On An Individual Basis)
Under Interior Footings Could Be Avoided.
H
Min. Width = H / 2 Min. Width = H / 2
Existing
Ground
If Required,
Damp Proofing
Per Bldg Code
Perimeter
Footing And
Foundation
Wall (typ.)
Depth To “Target” Sandy
Gravel Is 2.0’ To 4.0’ (typ.).
(See Fig. 1 & 3 For Gravel
Depth In Project Area.)
Note: Some Perimeter Footing Locations
May Bear In The “Target” Clean Gravel.
Strip All Topsoil
Prior To Filling.
Most Likely, Perimeter Footings Will
Readily Bear In Or Near “Target” Gravel
(Meaning Either No Req’d Structural Fill
Or Only A Relatively Thin Amount).
The Benefit Of Mass Over-Excavation
And Replacement Is That Interior
Footings Now Do Not Have To Be Over-
Excavated On An Individual Basis.
“Target” Clean Gravel Must
Be Exposed Throughout
The Bottom Of Excavation.
Re-Compact Subgrade Prior To Structural Fill Placement.
See Figure 5 For An Illustration That ShowsA Crawl Space Foundation Configuration.
We Recommend Mass Over-Excavation Under Slab-On-Grade Foundations Down To “Target”
Bearing (In Lieu Of Trench Excavating Under All Perimeter, Interior, And Exterior Footings On
An Individual Basis). This Excavation Approach Is Faster; But It Requires In-Filling/Backfilling
Inside The Foundation Walls With Granular Structural Fill Back Up To Interior Footing Grade.
For Figure 6, We Have Shown A Deep Native Gravel Surface To Purposely Illustrate The Need
For The Placement Of A Structural Fill Building Pad Back Up To Perimeter Footing Grade. Due
To Shallow Gravels, Most Perimeter Footings Should Readily Bear In/Near The “Target” Gravels.
Due To The Complexity Of Most Foundation Plans (Many/Closely Spaced Interior Footings),Individual Footing Over-Excavation Is Time Consuming, Difficult, And Not Recommended.
Due To The Shallow Gravels, Assumed Complexity Of The Foundation
Plan (Number And Spacing Of Interior Footings), And Need To Fully Remove
All Fill Material (That Was Found In The NE Corner), The Best Approach Will
Likely Be Mass Over-Excavation Of The Entire Foundation Footprint Area.
Some Perimeter
Ftgs May Require
Some Struct. Fill.
No Underslab Drains Req’d.
Due To Shallow Gravels And Likely Complexity
Of The Foundation Plan (Many/Closely Spaced
Interior Footings), We Assume Most Building
Foundations Will Be Mass Over-Excavated
Down To “Target” Gravel And Re-Filled With
Structural Fill Up To Interior Footing Grade.
Interior Footings
Will Most Likely
Require Struct. Fill.
Min. Exc. Width = H / 2; 5.0’ (min.)
Given The Shallow Gravel Depth In Most Areas,
Footing Grade Should Be Close To “Target” Gravel.
H As Required To Build Up To Footing
Grade From “Target” Gravel Surface.
Granular Structural Fill
In-Fill To 18” Below Slab.
Use Large Smooth Drum
Roller For Compaction Of
Native Gravel Subgrade
And Granular Structural Fill.
“Target” Clean Gravel Surface At Bottom
Of Mass Excavation. If The Surface Is Dry,
Vibratory Re-Compact Prior To Pouring
Footings Or Placing Granular Structural Fill.
Dig Foundation Exc. With
Smooth-Edged Bucket
To Prevent Disturbance
To Native Gravel Subgrade.
“Target” Clean Gravel Surface At Bottom
Of Mass Excavation. If The Surface Is Wet,
Track-Pack With Excavator And Static Roll
With Roller Prior To Placing Crushed Rock.
Note: This Figure
Illustrates A Deep
Gravel Surface And
Need For Struct. Fill
Under Perimeter Ftgs.
And Possible Need For
Fabric-Covered, Clean
Crushed Rock To Get
Above Wet Conditions.
If Groundwater Is Above The Native Gravel, Lower Groundwater By De-Watering.
If The Gravel Subgrade Is Wet Or Contains Areas Of Shallow Standing Water,
Place And Vibratory Compact An Initial Layer Of 1”-Minus Clean Crushed Rock
To Get Above The Wet Conditions. Cover The Crushed Rock Layer With A Layer
Of 8 oz. Non-Woven Geotextile Fabric Prior To Placing The Granular Structural Fill.
12” (min.) Structural Fill Layer
Under Slab Areas (typ.)
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.
23 – Geology, Soils, and Slopes
NCRS Soils Report
United States
Department of
Agriculture
A product of the National
Cooperative Soil Survey,
a joint effort of the United
States Department of
Agriculture and other
Federal agencies, State
agencies including the
Agricultural Experiment
Stations, and local
participants
Custom Soil Resource
Report for
Gallatin County
Area, Montana
Gran Cielo Subdivision, Phase 3
Natural
Resources
Conservation
Service
November 18, 2025
Preface
Soil surveys contain information that affects land use planning in survey areas.
They highlight soil limitations that affect various land uses and provide information
about the properties of the soils in the survey areas. Soil surveys are designed for
many different users, including farmers, ranchers, foresters, agronomists, urban
planners, community officials, engineers, developers, builders, and home buyers.
Also, conservationists, teachers, students, and specialists in recreation, waste
disposal, and pollution control can use the surveys to help them understand,
protect, or enhance the environment.
Various land use regulations of Federal, State, and local governments may impose
special restrictions on land use or land treatment. Soil surveys identify soil
properties that are used in making various land use or land treatment decisions.
The information is intended to help the land users identify and reduce the effects of
soil limitations on various land uses. The landowner or user is responsible for
identifying and complying with existing laws and regulations.
Although soil survey information can be used for general farm, local, and wider area
planning, onsite investigation is needed to supplement this information in some
cases. Examples include soil quality assessments (http://www.nrcs.usda.gov/wps/
portal/nrcs/main/soils/health/) and certain conservation and engineering
applications. For more detailed information, contact your local USDA Service Center
(https://offices.sc.egov.usda.gov/locator/app?agency=nrcs) or your NRCS State Soil
Scientist (http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/contactus/?
cid=nrcs142p2_053951).
Great differences in soil properties can occur within short distances. Some soils are
seasonally wet or subject to flooding. Some are too unstable to be used as a
foundation for buildings or roads. Clayey or wet soils are poorly suited to use as
septic tank absorption fields. A high water table makes a soil poorly suited to
basements or underground installations.
The National Cooperative Soil Survey is a joint effort of the United States
Department of Agriculture and other Federal agencies, State agencies including the
Agricultural Experiment Stations, and local agencies. The Natural Resources
Conservation Service (NRCS) has leadership for the Federal part of the National
Cooperative Soil Survey.
Information about soils is updated periodically. Updated information is available
through the NRCS Web Soil Survey, the site for official soil survey information.
The U.S. Department of Agriculture (USDA) prohibits discrimination in all its
programs and activities on the basis of race, color, national origin, age, disability,
and where applicable, sex, marital status, familial status, parental status, religion,
sexual orientation, genetic information, political beliefs, reprisal, or because all or a
part of an individual's income is derived from any public assistance program. (Not
all prohibited bases apply to all programs.) Persons with disabilities who require
2
alternative means for communication of program information (Braille, large print,
audiotape, etc.) should contact USDA's TARGET Center at (202) 720-2600 (voice
and TDD). To file a complaint of discrimination, write to USDA, Director, Office of
Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-9410 or
call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunity
provider and employer.
3
Contents
Preface....................................................................................................................2
How Soil Surveys Are Made..................................................................................5
Soil Map..................................................................................................................8
Soil Map................................................................................................................9
Legend................................................................................................................10
Map Unit Legend................................................................................................11
Map Unit Descriptions.........................................................................................11
Gallatin County Area, Montana.......................................................................13
457A—Turner loam, moderately wet, 0 to 2 percent slopes.......................13
510B—Meadowcreek loam, 0 to 4 percent slopes......................................14
References............................................................................................................16
4
How Soil Surveys Are Made
Soil surveys are made to provide information about the soils and miscellaneous
areas in a specific area. They include a description of the soils and miscellaneous
areas and their location on the landscape and tables that show soil properties and
limitations affecting various uses. Soil scientists observed the steepness, length,
and shape of the slopes; the general pattern of drainage; the kinds of crops and
native plants; and the kinds of bedrock. They observed and described many soil
profiles. A soil profile is the sequence of natural layers, or horizons, in a soil. The
profile extends from the surface down into the unconsolidated material in which the
soil formed or from the surface down to bedrock. The unconsolidated material is
devoid of roots and other living organisms and has not been changed by other
biological activity.
Currently, soils are mapped according to the boundaries of major land resource
areas (MLRAs). MLRAs are geographically associated land resource units that
share common characteristics related to physiography, geology, climate, water
resources, soils, biological resources, and land uses (USDA, 2006). Soil survey
areas typically consist of parts of one or more MLRA.
The soils and miscellaneous areas in a survey area occur in an orderly pattern that
is related to the geology, landforms, relief, climate, and natural vegetation of the
area. Each kind of soil and miscellaneous area is associated with a particular kind
of landform or with a segment of the landform. By observing the soils and
miscellaneous areas in the survey area and relating their position to specific
segments of the landform, a soil scientist develops a concept, or model, of how they
were formed. Thus, during mapping, this model enables the soil scientist to predict
with a considerable degree of accuracy the kind of soil or miscellaneous area at a
specific location on the landscape.
Commonly, individual soils on the landscape merge into one another as their
characteristics gradually change. To construct an accurate soil map, however, soil
scientists must determine the boundaries between the soils. They can observe only
a limited number of soil profiles. Nevertheless, these observations, supplemented
by an understanding of the soil-vegetation-landscape relationship, are sufficient to
verify predictions of the kinds of soil in an area and to determine the boundaries.
Soil scientists recorded the characteristics of the soil profiles that they studied. They
noted soil color, texture, size and shape of soil aggregates, kind and amount of rock
fragments, distribution of plant roots, reaction, and other features that enable them
to identify soils. After describing the soils in the survey area and determining their
properties, the soil scientists assigned the soils to taxonomic classes (units).
Taxonomic classes are concepts. Each taxonomic class has a set of soil
characteristics with precisely defined limits. The classes are used as a basis for
comparison to classify soils systematically. Soil taxonomy, the system of taxonomic
classification used in the United States, is based mainly on the kind and character
of soil properties and the arrangement of horizons within the profile. After the soil
5
scientists classified and named the soils in the survey area, they compared the
individual soils with similar soils in the same taxonomic class in other areas so that
they could confirm data and assemble additional data based on experience and
research.
The objective of soil mapping is not to delineate pure map unit components; the
objective is to separate the landscape into landforms or landform segments that
have similar use and management requirements. Each map unit is defined by a
unique combination of soil components and/or miscellaneous areas in predictable
proportions. Some components may be highly contrasting to the other components
of the map unit. The presence of minor components in a map unit in no way
diminishes the usefulness or accuracy of the data. The delineation of such
landforms and landform segments on the map provides sufficient information for the
development of resource plans. If intensive use of small areas is planned, onsite
investigation is needed to define and locate the soils and miscellaneous areas.
Soil scientists make many field observations in the process of producing a soil map.
The frequency of observation is dependent upon several factors, including scale of
mapping, intensity of mapping, design of map units, complexity of the landscape,
and experience of the soil scientist. Observations are made to test and refine the
soil-landscape model and predictions and to verify the classification of the soils at
specific locations. Once the soil-landscape model is refined, a significantly smaller
number of measurements of individual soil properties are made and recorded.
These measurements may include field measurements, such as those for color,
depth to bedrock, and texture, and laboratory measurements, such as those for
content of sand, silt, clay, salt, and other components. Properties of each soil
typically vary from one point to another across the landscape.
Observations for map unit components are aggregated to develop ranges of
characteristics for the components. The aggregated values are presented. Direct
measurements do not exist for every property presented for every map unit
component. Values for some properties are estimated from combinations of other
properties.
While a soil survey is in progress, samples of some of the soils in the area generally
are collected for laboratory analyses and for engineering tests. Soil scientists
interpret the data from these analyses and tests as well as the field-observed
characteristics and the soil properties to determine the expected behavior of the
soils under different uses. Interpretations for all of the soils are field tested through
observation of the soils in different uses and under different levels of management.
Some interpretations are modified to fit local conditions, and some new
interpretations are developed to meet local needs. Data are assembled from other
sources, such as research information, production records, and field experience of
specialists. For example, data on crop yields under defined levels of management
are assembled from farm records and from field or plot experiments on the same
kinds of soil.
Predictions about soil behavior are based not only on soil properties but also on
such variables as climate and biological activity. Soil conditions are predictable over
long periods of time, but they are not predictable from year to year. For example,
soil scientists can predict with a fairly high degree of accuracy that a given soil will
have a high water table within certain depths in most years, but they cannot predict
that a high water table will always be at a specific level in the soil on a specific date.
After soil scientists located and identified the significant natural bodies of soil in the
survey area, they drew the boundaries of these bodies on aerial photographs and
Custom Soil Resource Report
6
identified each as a specific map unit. Aerial photographs show trees, buildings,
fields, roads, and rivers, all of which help in locating boundaries accurately.
Custom Soil Resource Report
7
Soil Map
The soil map section includes the soil map for the defined area of interest, a list of
soil map units on the map and extent of each map unit, and cartographic symbols
displayed on the map. Also presented are various metadata about data used to
produce the map, and a description of each soil map unit.
8
9
Custom Soil Resource Report
Soil Map
50555005055530505556050555905055620505565050556805055500505553050555605055590505562050556505055680494050 494080 494110 494140 494170 494200 494230 494260 494290 494320 494350 494380
494050 494080 494110 494140 494170 494200 494230 494260 494290 494320 494350 494380
45° 39' 17'' N 111° 4' 34'' W45° 39' 17'' N111° 4' 19'' W45° 39' 10'' N
111° 4' 34'' W45° 39' 10'' N
111° 4' 19'' WN
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 12N WGS84
0 50 100 200 300
Feet
0 20 40 80 120
Meters
Map Scale: 1:1,520 if printed on A landscape (11" x 8.5") sheet.
Soil Map may not be valid at this scale.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Map Unit Polygons
Soil Map Unit Lines
Soil Map Unit Points
Special Point Features
Blowout
Borrow Pit
Clay Spot
Closed Depression
Gravel Pit
Gravelly Spot
Landfill
Lava Flow
Marsh or swamp
Mine or Quarry
Miscellaneous Water
Perennial Water
Rock Outcrop
Saline Spot
Sandy Spot
Severely Eroded Spot
Sinkhole
Slide or Slip
Sodic Spot
Spoil Area
Stony Spot
Very Stony Spot
Wet Spot
Other
Special Line Features
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: Gallatin County Area, Montana
Survey Area Data: Version 29, Aug 30, 2025
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Aug 18, 2022—Aug
29, 2022
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Custom Soil Resource Report
10
Map Unit Legend
Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI
457A Turner loam, moderately wet, 0
to 2 percent slopes
6.6 98.5%
510B Meadowcreek loam, 0 to 4
percent slopes
0.1 1.5%
Totals for Area of Interest 6.7 100.0%
Map Unit Descriptions
The map units delineated on the detailed soil maps in a soil survey represent the
soils or miscellaneous areas in the survey area. The map unit descriptions, along
with the maps, can be used to determine the composition and properties of a unit.
A map unit delineation on a soil map represents an area dominated by one or more
major kinds of soil or miscellaneous areas. A map unit is identified and named
according to the taxonomic classification of the dominant soils. Within a taxonomic
class there are precisely defined limits for the properties of the soils. On the
landscape, however, the soils are natural phenomena, and they have the
characteristic variability of all natural phenomena. Thus, the range of some
observed properties may extend beyond the limits defined for a taxonomic class.
Areas of soils of a single taxonomic class rarely, if ever, can be mapped without
including areas of other taxonomic classes. Consequently, every map unit is made
up of the soils or miscellaneous areas for which it is named and some minor
components that belong to taxonomic classes other than those of the major soils.
Most minor soils have properties similar to those of the dominant soil or soils in the
map unit, and thus they do not affect use and management. These are called
noncontrasting, or similar, components. They may or may not be mentioned in a
particular map unit description. Other minor components, however, have properties
and behavioral characteristics divergent enough to affect use or to require different
management. These are called contrasting, or dissimilar, components. They
generally are in small areas and could not be mapped separately because of the
scale used. Some small areas of strongly contrasting soils or miscellaneous areas
are identified by a special symbol on the maps. If included in the database for a
given area, the contrasting minor components are identified in the map unit
descriptions along with some characteristics of each. A few areas of minor
components may not have been observed, and consequently they are not
mentioned in the descriptions, especially where the pattern was so complex that it
was impractical to make enough observations to identify all the soils and
miscellaneous areas on the landscape.
The presence of minor components in a map unit in no way diminishes the
usefulness or accuracy of the data. The objective of mapping is not to delineate
pure taxonomic classes but rather to separate the landscape into landforms or
landform segments that have similar use and management requirements. The
delineation of such segments on the map provides sufficient information for the
development of resource plans. If intensive use of small areas is planned, however,
Custom Soil Resource Report
11
onsite investigation is needed to define and locate the soils and miscellaneous
areas.
An identifying symbol precedes the map unit name in the map unit descriptions.
Each description includes general facts about the unit and gives important soil
properties and qualities.
Soils that have profiles that are almost alike make up a soil series. Except for
differences in texture of the surface layer, all the soils of a series have major
horizons that are similar in composition, thickness, and arrangement.
Soils of one series can differ in texture of the surface layer, slope, stoniness,
salinity, degree of erosion, and other characteristics that affect their use. On the
basis of such differences, a soil series is divided into soil phases. Most of the areas
shown on the detailed soil maps are phases of soil series. The name of a soil phase
commonly indicates a feature that affects use or management. For example, Alpha
silt loam, 0 to 2 percent slopes, is a phase of the Alpha series.
Some map units are made up of two or more major soils or miscellaneous areas.
These map units are complexes, associations, or undifferentiated groups.
A complex consists of two or more soils or miscellaneous areas in such an intricate
pattern or in such small areas that they cannot be shown separately on the maps.
The pattern and proportion of the soils or miscellaneous areas are somewhat similar
in all areas. Alpha-Beta complex, 0 to 6 percent slopes, is an example.
An association is made up of two or more geographically associated soils or
miscellaneous areas that are shown as one unit on the maps. Because of present
or anticipated uses of the map units in the survey area, it was not considered
practical or necessary to map the soils or miscellaneous areas separately. The
pattern and relative proportion of the soils or miscellaneous areas are somewhat
similar. Alpha-Beta association, 0 to 2 percent slopes, is an example.
An undifferentiated group is made up of two or more soils or miscellaneous areas
that could be mapped individually but are mapped as one unit because similar
interpretations can be made for use and management. The pattern and proportion
of the soils or miscellaneous areas in a mapped area are not uniform. An area can
be made up of only one of the major soils or miscellaneous areas, or it can be made
up of all of them. Alpha and Beta soils, 0 to 2 percent slopes, is an example.
Some surveys include miscellaneous areas. Such areas have little or no soil
material and support little or no vegetation. Rock outcrop is an example.
Custom Soil Resource Report
12
Gallatin County Area, Montana
457A—Turner loam, moderately wet, 0 to 2 percent slopes
Map Unit Setting
National map unit symbol: 56tb
Elevation: 4,300 to 5,200 feet
Mean annual precipitation: 15 to 19 inches
Mean annual air temperature: 39 to 45 degrees F
Frost-free period: 90 to 110 days
Farmland classification: Prime farmland if irrigated
Map Unit Composition
Turner and similar soils:85 percent
Minor components:15 percent
Estimates are based on observations, descriptions, and transects of the mapunit.
Description of Turner
Setting
Landform:Stream terraces
Down-slope shape:Linear
Across-slope shape:Linear
Parent material:Alluvium
Typical profile
A - 0 to 6 inches: loam
Bt - 6 to 12 inches: clay loam
Bk - 12 to 26 inches: clay loam
2C - 26 to 60 inches: very gravelly loamy sand
Properties and qualities
Slope:0 to 2 percent
Depth to restrictive feature:More than 80 inches
Drainage class:Well drained
Capacity of the most limiting layer to transmit water (Ksat):Moderately high to high
(0.57 to 1.98 in/hr)
Depth to water table:About 48 to 96 inches
Frequency of flooding:None
Frequency of ponding:None
Calcium carbonate, maximum content:15 percent
Maximum salinity:Nonsaline to very slightly saline (0.0 to 2.0 mmhos/cm)
Available water supply, 0 to 60 inches: Low (about 5.4 inches)
Interpretive groups
Land capability classification (irrigated): 3e
Land capability classification (nonirrigated): 3e
Hydrologic Soil Group: B
Ecological site: R044BC032MT - Loamy (Lo) 15-19" PZ Frigid North
Hydric soil rating: No
Minor Components
Turner
Percent of map unit:5 percent
Landform:Stream terraces
Custom Soil Resource Report
13
Down-slope shape:Linear
Across-slope shape:Linear
Ecological site:R044BC032MT - Loamy (Lo) 15-19" PZ Frigid North
Hydric soil rating: No
Meadowcreek
Percent of map unit:5 percent
Landform:Stream terraces
Down-slope shape:Linear
Across-slope shape:Linear
Ecological site:R044BP815MT - Subirrigated Grassland
Hydric soil rating: No
Beaverton
Percent of map unit:5 percent
Landform:Alluvial fans, stream terraces
Down-slope shape:Linear
Across-slope shape:Linear
Ecological site:R044BP818MT - Upland Grassland
Hydric soil rating: No
510B—Meadowcreek loam, 0 to 4 percent slopes
Map Unit Setting
National map unit symbol: 56vt
Elevation: 4,200 to 5,950 feet
Mean annual precipitation: 12 to 18 inches
Mean annual air temperature: 39 to 45 degrees F
Frost-free period: 90 to 110 days
Farmland classification: Prime farmland if irrigated
Map Unit Composition
Meadowcreek and similar soils:85 percent
Minor components:15 percent
Estimates are based on observations, descriptions, and transects of the mapunit.
Description of Meadowcreek
Setting
Landform:Stream terraces
Down-slope shape:Linear
Across-slope shape:Linear
Parent material:Alluvium
Typical profile
A - 0 to 11 inches: loam
Bg - 11 to 25 inches: silt loam
2C - 25 to 60 inches: very gravelly sand
Properties and qualities
Slope:0 to 4 percent
Custom Soil Resource Report
14
Depth to restrictive feature:More than 80 inches
Drainage class:Somewhat poorly drained
Capacity of the most limiting layer to transmit water (Ksat):Moderately high to high
(0.57 to 1.98 in/hr)
Depth to water table:About 24 to 42 inches
Frequency of flooding:None
Frequency of ponding:None
Maximum salinity:Nonsaline to slightly saline (0.0 to 4.0 mmhos/cm)
Available water supply, 0 to 60 inches: Low (about 5.1 inches)
Interpretive groups
Land capability classification (irrigated): 2e
Land capability classification (nonirrigated): 3e
Hydrologic Soil Group: C
Ecological site: R044BP815MT - Subirrigated Grassland
Hydric soil rating: No
Minor Components
Blossberg
Percent of map unit:10 percent
Landform:Terraces
Down-slope shape:Linear
Across-slope shape:Linear
Ecological site:R044BP815MT - Subirrigated Grassland
Hydric soil rating: Yes
Beaverton
Percent of map unit:5 percent
Landform:Alluvial fans, stream terraces
Down-slope shape:Linear
Across-slope shape:Linear
Ecological site:R044BP818MT - Upland Grassland
Hydric soil rating: No
Custom Soil Resource Report
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References
American Association of State Highway and Transportation Officials (AASHTO).
2004. Standard specifications for transportation materials and methods of sampling
and testing. 24th edition.
American Society for Testing and Materials (ASTM). 2005. Standard classification of
soils for engineering purposes. ASTM Standard D2487-00.
Cowardin, L.M., V. Carter, F.C. Golet, and E.T. LaRoe. 1979. Classification of
wetlands and deep-water habitats of the United States. U.S. Fish and Wildlife
Service FWS/OBS-79/31.
Federal Register. July 13, 1994. Changes in hydric soils of the United States.
Federal Register. September 18, 2002. Hydric soils of the United States.
Hurt, G.W., and L.M. Vasilas, editors. Version 6.0, 2006. Field indicators of hydric
soils in the United States.
National Research Council. 1995. Wetlands: Characteristics and boundaries.
Soil Survey Division Staff. 1993. Soil survey manual. Soil Conservation Service.
U.S. Department of Agriculture Handbook 18. http://www.nrcs.usda.gov/wps/portal/
nrcs/detail/national/soils/?cid=nrcs142p2_054262
Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for
making and interpreting soil surveys. 2nd edition. Natural Resources Conservation
Service, U.S. Department of Agriculture Handbook 436. http://
www.nrcs.usda.gov/wps/portal/nrcs/detail/national/soils/?cid=nrcs142p2_053577
Soil Survey Staff. 2010. Keys to soil taxonomy. 11th edition. U.S. Department of
Agriculture, Natural Resources Conservation Service. http://
www.nrcs.usda.gov/wps/portal/nrcs/detail/national/soils/?cid=nrcs142p2_053580
Tiner, R.W., Jr. 1985. Wetlands of Delaware. U.S. Fish and Wildlife Service and
Delaware Department of Natural Resources and Environmental Control, Wetlands
Section.
United States Army Corps of Engineers, Environmental Laboratory. 1987. Corps of
Engineers wetlands delineation manual. Waterways Experiment Station Technical
Report Y-87-1.
United States Department of Agriculture, Natural Resources Conservation Service.
National forestry manual. http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/
home/?cid=nrcs142p2_053374
United States Department of Agriculture, Natural Resources Conservation Service.
National range and pasture handbook. http://www.nrcs.usda.gov/wps/portal/nrcs/
detail/national/landuse/rangepasture/?cid=stelprdb1043084
16
United States Department of Agriculture, Natural Resources Conservation Service.
National soil survey handbook, title 430-VI. http://www.nrcs.usda.gov/wps/portal/
nrcs/detail/soils/scientists/?cid=nrcs142p2_054242
United States Department of Agriculture, Natural Resources Conservation Service.
2006. Land resource regions and major land resource areas of the United States,
the Caribbean, and the Pacific Basin. U.S. Department of Agriculture Handbook
296. http://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/soils/?
cid=nrcs142p2_053624
United States Department of Agriculture, Soil Conservation Service. 1961. Land
capability classification. U.S. Department of Agriculture Handbook 210. http://
www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_052290.pdf
Custom Soil Resource Report
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