HomeMy WebLinkAbout20 Geotechnical Investigation ReportEngineering and Surveying Inc.
1091 Stoneridge Drive • Bozeman, Montana • Phone (406) 587-1115 • Fax (406) 587-9768
www.chengineers.com • E-Mail: info@chengineers.com
July 2, 2021
Locati Architects, PLLC Attn: Laura Damberger, A.I.A.
E-mail: ldomberger@locatiarchitects.com
RE: Geotechnical Investigation -Lot lA-1, Minor Subdivision 503; Gallatin County, Montana (210228)
Dear Laura,
Thank you for the opportunity to serve your geotechnical engineering needs. Per your request, C&H Engineering and Surveying, Inc. has completed a Geotechnical Investigation Report for the residential improvements to be constructed on the above referenced property in Gallatin County, Montana.
Please find the attached Geotechnical Investigation Report to contain the results of the site investigation, geotechnical evaluation, and recommendations. The recommendations were made for the design and construction,of the foundation elements, slabs-on-grade, and pavements for the proposed development.
Please call if you have any questions or if we can assist you during the future phases of your project.
Respectfully Submitted by
Noah J. Schaible, E.I.
G:\c&h\21\210228\Geotech\Report Documents\Cover Letter (210228).doc
Civil/Structural Engineering and Surveying
GEOTECHNICAL INVESTIGATION REPORT
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Table of Contents
1.0 INTRODUCTION............................................................................................................. 1
2.0 PROPOSED STRUCTURES ........................................................................................... 1
3.0 INVESTIGATION ............................................................................................................ 1
3.1 FIELD INVESTIGATION ...................................................................................................... 1
4.0 SITE EVALUATION ....................................................................................................... 2
4.1 SITE DESCRIPTION ........................................................................................................... 2
4.2 SUBSURFACE SOILS AND CONDITIONS ............................................................................. 2
4.3 NATURAL RESOURCES CONSERVATION SERVICE SOIL SURVEY ...................................... 3 4.4 GEOLOGIC SETTING ......................................................................................................... 3 4.5 SEISMICITY ...................................................................................................................... 4 4.5.1 Regional Faults ........................................................................................................... 5
4.5.2 Liquefaction ................................................................................................................ 5
4.5.3 Lateral Spreading ....................................................................................................... 5 4.6 GROUNDWATER ............................................................................................................... 6
5.0 GEOTECHNICAL ANALYSIS ...................................................................................... 6
5.1 ALLOWABLE BEARING CAPACITY .................................................................................... 6
5.2 SETTLEMENT .................................................................................................................... 6
5.2.1 Collapsible Soils ......................................................................................................... 7 5.3 LATERAL PRESSURES ....................................................................................................... 8
6.0 RECOMMENDATIONS .................................................................................................. 8
6.1 FOUNDATION ................................................................................................................... 9
6.2 FOUNDATION EXCAVATION ............................................................................................. 9
6.3 STRUCTURAL FILL ......................................................................................................... 10 6.4 FOUNDATION WALL BACKFILL ...................................................................................... 10 6.5 INTERIOR SLABS-ON-GRADE ......................................................................................... 11 6.6 EXTERIOR SLABS-ON-GRADE ........................................................................................ 12
6.7 ASPHALT PAVING IMPROVEMENTS ................................................................................ 12 6.8 SITE GRADING ............................................................................................................... 13 6.9 UNDERGROUND UTILITIES ............................................................................................. 13 6.10 CONSTRUCTION ADMINISTRATION ................................................................................. 14
7.0 CONCLUSIONS ............................................................................................................. 14
8.0 REPORT LIMITATIONS ............................................................................................. 15
9.0 REFERENCES ................................................................................................................ 15
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List of Appendices
Appendix A – USGS Topographic Map ..................................................................................... A-1 Appendix B – Test Pit Location Map ......................................................................................... A-2
Appendix C – NRCS Web Soil Survey Map .............................................................................. A-3
Appendix D – Geology Maps ..................................................................................................... A-4 Appendix E – Test Pit Logs ........................................................................................................ A-5 Appendix F – Report Limitations .............................................................................................. A-6
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1.0 Introduction
C&H Engineering and Surveying Inc., (C&H Engineering) has conducted a geotechnical investigation for the residential improvements to be constructed on Lot 1A-1 of Minor Subdivision 503 in Gallatin County, Montana. The project area is found in the Southeast Quarter of Section 14, Township 2 South, Range 5 East, in Gallatin County, Montana. The site location
is shown on a United States Geological Survey (USGS) topographic quadrangle map in
Appendix A, “USGS Topographic Map.” The scope of services was to conduct a site investigation, evaluate the site, and provide a geotechnical investigation report. The report documents the sites’ soil and groundwater
conditions, subsurface soil properties, and provides foundation design and general earthwork
recommendations. 2.0 Proposed Structures
Two multi-family residential structures up to three stories in height are proposed for
construction. It is assumed that the structures are planned to be constructed with a slab-on-grade with frost wall foundation. It has been assumed that the foundation footings of the structure will not be subjected to unusual
loading conditions such as eccentric loads. A footing is eccentrically loaded if the load
transferred to the footing is not directed through the center of the footing. This creates a bending moment in the footing and results in a non-uniform load transfer to the underlying soil. If any of the foundation footings will be eccentrically loaded, please contact this office so we can appropriately revise our allowable bearing capacity and settlement estimates.
3.0 Investigation
The investigation is separated into two parts; the field investigation and the laboratory analysis. While the scope of this project focuses more on the field investigation, we feel it is important to
spend time verifying our field observations and conducting tests that will aid in the geotechnical analysis. 3.1 Field Investigation
On March 30, 2021 a site visit was made to the subject property to conduct a subsurface soils investigation and to observe ground features. The subsurface conditions were investigated across
the subject property under the direction of Noah J. Schaible, E.I. with C&H Engineering. The
subsurface soils investigation consisted of examining five exploratory test pit excavations. The exploratory test pits were excavated with a John Deere Backhoe provided by Val Mencas Excavation, LLC. The test pit locations were chosen based on site topography, accessibility, the location of underground utilities, and the proposed location of the structures. The soil profiles
revealed by the excavations were logged and visually classified according to ASTM D 2488,
which utilizes the nomenclature of the Unified Soil Classification System (USCS).
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The relative density of each soil layer was estimated based on the amount of effort required to excavate the material, probing of the excavation sidewalls with a rock hammer, and the overall
stability of the excavation. Any evidence of seepage or other groundwater conditions were also
noted. The locations of the test pits (TP) are shown on the Test Pit Location Map included in Appendix B. The subsurface soil conditions encountered in the test pits are described briefly in Section 4.2 and in more detail in Appendix E, “Test Pit Logs.” 4.0 Site Evaluation
The site evaluation is based on both the field investigation and research of the sites’ surface geology, soil survey information, and seismic history. 4.1 Site Description
The subject property has a total area of 1.5698 acres and is located on and accessed via Kagy Boulevard. No other significant topographical or geological features are present on the site. 4.2 Subsurface Soils and Conditions
The following paragraphs briefly summarize the subsurface soils and conditions observed in the two exploratory test pits excavated for the field investigation. Please refer to Appendix E, “Test
Pit Logs” for more detailed descriptions and to the Test Pit Location map in Appendix B for the
test pit locations. The first soil horizon encountered in each exploratory excavation was a Silty Clay Organic Soil of low plasticity (OL). This material was dark brown to black in color, moist, and soft. This
material was encountered to depths varying from 1.0 feet to 1.75 feet bgs. Organic soils are
highly compressible and are not suitable for foundation support. This material must also be removed from beneath all interior and exterior slabs as well as beneath all asphalt and/or concrete paving improvements. This material may be stockpiled onsite and used for final site grading purposes.
The second soil horizon encountered in each exploratory excavation was a Clayey Sand with Gravel (SC), which was encountered to depths varying from approximately 1.5 feet to 3.5 feet bgs. This material was brownish gray in color, moist, loose in consistency, and was found to be composed of approximately 30 percent subrounded to subangular gravels, cobbles, and boulders,
approximately 20 percent clayey fines, and 50 percent coarse to fine grained sand.
The third soil horizon encountered in each exploratory excavation was a Poorly Graded Gravel with Sand and Cobbles (GP). This material was medium dense to dense, and estimated to contain approximately 10 percent fines with medium plasticity and no dilatancy, approximately 30
percent coarse to fine grained sand, and approximately 60 percent gravels, cobbles and boulders.
This material was present to the end of each excavation, depths varying from 7.0 feet to 8.5 feet bgs.
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The native Poorly Graded Gravel with Sand and Cobbles encountered in each exploratory excavation at depths varying from 1.5 feet to 3.5 feet bgs, was found to be in medium dense to
dense condition. This material is suitable for foundation support and it is recommended that all
foundation footings bear on this material or on properly placed and compacted structural fill overlying this material. 4.3 Natural Resources Conservation Service Soil Survey
The Natural Resources Conservation Service (NRCS) Web Soil Survey (WSS) provides soil data and information produced by the National Cooperative Soil Survey. The NRCS has determined
the physical characteristics and engineering properties, among other data, of near surface soils
across the United States. These data are reviewed against our observations and analysis of the subsurface soils encountered during the field investigation to determine if a correlation is present. If a strong correlation is determined, it is likely that other engineering properties or characteristics described by the NRCS regarding the soils present on the subject property are
accurate as well. It should be noted that the NRCS typically only describes the soils located
within 5 feet of the surface. NRCS Soil Survey information of the area was taken from the NRCS WSS, Version 2.0. For more information, please visit the NRCS Web Soil Survey on the World Wide Web, at
http://websoilsurvey.nrcs.usda.gov/app/. The NRCS Soils Survey identifies the soils near the
subject property as 448A – Hyalite-Beaverton Complex, 542A – Blossberg Loam, and 457A – Turner Loam. The NRCS describes the upper soil horizons of these complexes as Loamy Alluvium (448A) and Alluvium (542A & 457A). The NRCS also indicates that groundwater is located 48 to 96 inches below the surface for soil types 448A and 457A and 12 to 24 inches for
soil type 542A.
The soils encountered in the exploratory excavations correlate well with the NRCS description of the near surface soils. The Poorly Graded Gravel with Sand and Cobbles encountered within each of the exploratory excavations appeared to be alluvial in origin.
4.4 Geologic Setting
The following paragraphs discuss the geologic setting in the direct vicinity of the subject property. The geologic setting is determined from a review of surface geology maps and reports published by the United States Geological Survey and others that contain the subject property. This information is especially helpful in determining any geologic hazards that may be present in
the immediate area (such as landslide deposits) and what types of soil and rock may be present in the area. Additional information regarding the parent material and depositional environment of a given soil type can also sometimes be obtained or inferred from these maps and reports. The local surface geology in the direct vicinity of the subject property was determined from the
United States Geological Survey (USGS) Geologic Map of the Bozeman 30' x 60' Quadrangle, Southwest Montana. Please refer to Appendix D, “Geology Maps” for a complete geologic description and map. The USGS Geological Map identifies the surface geology in the vicinity of the subject property as Alluvial Fan Deposit, Older. For a narrative description of this formation
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see the Geologic Map in Appendix D.
The subsurface soils encountered during the field investigation do not correlate well with the
USGS description of Alluvial Fan Deposit, Older. The Poorly Graded Gravel with Sand and Cobbles contained an abundance of rounded and subrounded gravels and cobbles, not angular and subangular gravels and cobbles as described by the USGS. It is likely that the older alluvial fan deposit has been reworked by more recent alluvial processes in the vicinity of the subject
property.
4.5 Seismicity
The Bozeman area is located in an earthquake zone known as the intermountain seismic belt, which is a zone of earthquake activity that extends from northwest Montana to Southern Arizona. In general, this zone is expected to experience moderately frequent, potentially damaging earthquakes. With that in mind, it is important that the structure be designed to
withstand horizontal seismic accelerations that may be induced by such an earthquake, as is
required by the International Building Code. The USGS provides seismic design parameters for the design of buildings and bridges across the United States. These parameters are based on the National Earthquake Hazards Reduction
Program (NEHRP) Recommended Seismic Provisions. The primary intent of the NEHRP
Recommended Seismic Provisions is to prevent, for typical buildings and structures, serious injury and life loss caused by damage from earthquake ground shaking. The following seismic design parameters were determined for the subject property using the
USGS Seismic Design Application:
Approximate site Location: Latitude = 45.661° N Longitude = 111.065° W
Maximum Considered Earthquake (MCE) Spectral Response Acceleration Parameters: Short Period (SS) = 0.685g 1- Second Period (S1) = 0.215g
Site Coefficients and Adjusted MCE Spectral Response Acceleration Parameters:
SMS = 0.858 SM1 = 0.467g Design Spectral Response Acceleration Parameters:
SDS = 0.572g
SD1 = 0.312g The Seismic Site Class is D.
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4.5.1 Regional Faults
The USGS and Montana Bureau of Mines and Geology (MBMG) have compiled a map of
Quaternary Class A faults and earthquake epicenters in western Montana; a Class A fault is one that is associated with at least one large magnitude earthquake within the last 1.6 million years. The earthquake epicenters shown on the map (yellow circles) are associated with earthquakes of magnitude 2.5 or greater, with stars indicating epicenters of earthquakes with a magnitude
greater than 5.5. A review of this map indicated that there are 4 Class A faults located within 15
miles of the subject property and 17 earthquake epicenters have been recorded within 10 miles of the subject property. The four faults mapped near the subject property are the Central Park Fault, Bridger Fault, Elk Creek Fault, and the Gallatin Range Fault. Each of these faults is described as a normal fault, indicating that one side of the fault will move downward into the earth relative
the other side during an earthquake.
The Central Park Fault is located approximately 10 miles northwest of the subject property and runs east to west through the middle of the Gallatin Valley. The Bridger Fault is located approximately 5.3 miles northeast of the subject property and runs along the western side of the
Bridger Mountains. The Gallatin Range fault is located approximately 7 miles south of the
subject property and runs along the northern border of the Gallatin Range. The Elk Creek Fault is located approximately 13 miles west-southwest of the subject property and extends from Goose Creek (southwest of Gallatin Gateway) to approximately 13 miles northwest of where Norris Road crosses the Madison River. See the Quaternary Fault and Seismicity Map of Western
Montana in Appendix D for more information regarding the location of these faults and nearby
earthquake epicenters. 4.5.2 Liquefaction
In general terms, liquefaction is defined as the condition when saturated, loose, fine sand-type
soils lose their support capabilities due to the development of excessive pore water pressure, which can develop during a seismic event. Loose silty sandy soils, if located below the groundwater table, have the potential to liquefy during a major seismic event.
Our subsurface investigation did not encounter any loose silt or sand horizons within the depth of
excavation. It is our opinion that the potential for differential settlement resulting from liquefaction during a moderate seismic event is low. 4.5.3 Lateral Spreading
Lateral spreading is the slow-to-rapid lateral extensional movement of rock or soil masses. The primary cause of lateral spreading is liquefaction, usually induced by an earthquake, and subsequent flowage of a weak soil layer within a slope. The potential for, and magnitude of, lateral spreading is dependent upon many conditions, including the presence of a relatively thick,
continuous, potentially liquefiable sand or sensitive clay layer, and the slope of the site.
As stated previously, our subsurface investigation did not reveal any loose silt or sand horizons and also did not encounter any potential slip planes within the depth of excavation. It is our
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opinion that any structure built on the subject property is at a low risk of sustaining damage due to lateral spreading.
4.6 Groundwater
Groundwater was encountered in all five exploratory excavations at depths varying from 7.0 feet bgs to 8.5 feet bgs. Based on our experience in the vicinity of the subject property, the seasonally high groundwater elevation may be as high as 3.5 feet below the grounds surface when groundwater levels are at their highest in the valley, typically around the end of May to the
beginning of July. Groundwater levels beneath the subject property may also be impacted by the irrigation ditch located adjacent to the western property boundary. It should be noted that groundwater monitoring wells were installed on the day of the site visit, and have be routinely check, and the monitoring is still currently ongoing. The highest
groundwater elevation recorded within these wells was approximately 6.23 feet bgs on June 24, 2021. 5.0 Geotechnical Analysis
The geotechnical analysis takes into account the field investigation and site evaluation to make engineering recommendations pertaining to bearing capacity, lateral pressures, settlement, and slope stability. 5.1 Allowable Bearing Capacity
The allowable bearing capacity of a soil is defined as the maximum pressure that can be
permitted on a foundation soil, giving consideration to all pertinent factors (such as settlement and seismic considerations), with adequate safety against rupture of the soil mass or movement of the foundation of such magnitude that the structure is impaired. The allowable bearing capacity is determined from the geotechnical analysis, the field investigation, available soil and
geology information, and our experience in the project area.
Based on the site investigation and the assumption that all recommendations made in this report will be property implemented, it is recommended that all foundation footings be dimensioned for
an allowable bearing capacity of 2,500 pounds per square foot (psf).
The allowable bearing capacity may be increased by one third for short term loading conditions such as those from wind or seismic forces.
5.2 Settlement While the soil at the site may be able to physically support the footings, it is also important to analyze the possible settlement of the structures. In many cases, settlement determines the allowable bearing capacity.
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When a soil deposit is loaded by a structure, deformations within the soil deposit will occur. The total vertical deformation of the soil at the surface is called total settlement. Total settlement is
made up of two components: elastic settlement and consolidation settlement. Elastic settlement is
the result of soil particles rearranging themselves into a denser configuration due to a load being imposed on them and usually occurs during the construction process and shortly after. Consolidation settlement occurs more slowly and over time as water within the pore spaces of a soil are forced out and the soil compresses as the stress from the load is transferred from the
water molecules to the soil particles. Consolidation settlement is more of a concern with fine-
grained soils with low permeability and high in-situ moisture contents. The degree of settlement is a function of the type of bearing material, the bearing pressure of the foundation elements, local groundwater conditions, and in some cases determines the allowable bearing capacity for a structures’ footings.
In addition to analyzing total settlement, the potential for differential settlement must also be considered. Differential settlement occurs in soils that are not homogeneous over the length of the foundation or in situations where the foundation rests on cut and fill surfaces. If the foundation rests on structural fill overlaying properly prepared soils with rock, differential
settlement is expected to be well within tolerable limits. Areas that have significantly more fill
under the foundation footings (four feet of more) create greater potential for differential settlement. In these cases, the structural fill must be installed properly and tested frequently. Compaction efforts and structural fill consistence are vital in minimizing differential settlement. For this project it is not anticipated that significant quantities of structural fill will be required.
A settlement analysis based on conservative soil parameter estimates, the allowable bearing capacity recommended in Section 5.1, and the assumption that all recommendations made in this report are properly adhered to, indicates the total and differential settlement are expected to be ½-inch or less. Structures of the type assumed can generally tolerate this amount of movement,
however, these values should be checked by a structural engineer to verify that they are
acceptable. Please note that the settlement estimates are based on loads originating from the proposed structure. If additional loads are introduced, such as the placement of large quantities of fill, our
office should be contacted to re-evaluate the settlement estimates.
5.2.1 Collapsible Soils Collapsible soils are soils that compact and collapse after wetting. The soil particles are
originally loosely packed and barely touch each other before moisture infiltrates into the soil. As
water infiltrates into the soil, it reduces the friction between the soil particles and allows them to slip past each other and become more tightly packed, often resulting in a radical reduction in volume; this radical reduction in volume can occur without any additional loading of the soil. Another term for collapsible soils is "hydrocompactive soils" because they compact after water is
added. The amount of collapse depends on how loosely the particles are packed originally and
the thickness of the soil layer susceptible to collapse. Soils with dry densities of less than 80 pounds per cubic foot (pcf), generally silts deposited by
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the wind, are considered to be susceptible to collapse. Soils with dry unit weights greater than 90 pcf are not considered susceptible to collapse. Using this correlation, it is our opinion that the
proposed structure is not at risk of sustaining damage due to collapsible soils.
5.3 Lateral Pressures
It is recommended that all foundation and retaining walls be backfilled with well-draining granular material. Well-draining granular backfill has a more predictable behavior in terms of the lateral earth pressure exerted on the foundation or retaining wall and will not generate expansive related forces. If backfill containing significant quantities of clayey material is used, the seepage of water into the backfill could potentially generate horizontal swelling pressures well above at-
rest values. Additionally, seepage into a clayey backfill material will also cause significant hydrostatic pressures to build up against the foundation wall due to the low permeability of clay soils and will make the backfill susceptible to frost action. Lateral pressures imposed upon foundation and retaining walls due to wind, seismic forces, and
earth pressures may be resisted by the development of passive earth pressures and/or frictional resistance between the base of the footings and the supporting soils. If a foundation or retaining wall is restrained from moving, the lateral earth pressure exerted on the wall is called the at-rest earth pressure. If a foundation or retaining wall is allowed to tilt away from the retained soil, the lateral earth pressure exerted on the wall is called the active earth pressure. Passive earth
pressure is the resistance pressure the foundation or retaining wall develops due to the wall being pushed laterally into the earth on the opposite side of the retained soil. Each of these pressures is proportional to the distance below the earth surface, the unit weight of the soil, and the shear strength properties of the soil.
Subsurface walls that are restrained from moving at the top, such as basement walls, are recommended to be designed for an equivalent fluid pressure of 60 pounds per cubic foot (at-rest pressure); Any subsurface walls that are allowed to move away from the restrained soil, such as cantilevered retaining walls, are recommended to be designed for an equivalent fluid pressure of 45 pounds per cubic foot (active pressure). For passive pressures, an equivalent fluid pressure of
300 pcf is recommended, and the coefficient of friction between cast-in-place concrete and the native Poorly Graded Gravel with Sand and Cobbles is estimated to be 0.4. These recommended values were calculated assuming a near horizontal backfill and a mix of the onsite soils with the exception of the organics will be used as foundation wall backfill. Also,
please note that these design pressures do not include a factor of safety and are for static conditions, they do not account for additional forces that may be induced by seismic 6.0 Recommendations
The following recommendations are given as guidance to assure for a safe and effective foundation for the proposed structures. These recommendations are determined by the geotechnical analysis, code requirements, our experience, and local construction practices.
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6.1 Foundation Based on the site evaluation and geotechnical analysis it will be acceptable for the foundation elements to consist of typical strip and column footings. Please find the following as general recommendations for all foundation elements:
• In order to keep the footing out of the active frost zone it is recommended that the bottom of all footing elevations be a minimum of 48 inches below finished grade.
• The foundation footings are to bear on the native Poorly Graded Gravel with Sand and
Cobbles or on properly placed and compacted structural fill overlying the native Poorly Graded Gravel with Sand and Cobbles. All foundation footings may be dimensioned for an allowable bearing capacity of 2,500 psf.
• It is recommended that typical strip footings for this structure have a minimum width of 16 inches and column footings should have a minimum width of 24 inches, provided the allowable soil bearing capacity is not exceeded.
• The subgrade must remain in a dry condition throughout construction of the foundation elements.
• If construction takes place during the colder months of the year, the subgrade must be
protected from freezing. This may require the use of insulating blankets and/or ground heaters. 6.2 Foundation Excavation
In general, the excavation for the foundation must be level and uniform and continue down the native Poorly Graded Gravel with Sand and Cobbles or to the desired bottom of footing elevation, whichever is deeper. If any soft spots, saturated soils or boulders are encountered, they
will need to be removed and backfilled with structural fill. The excavation width must extend a minimum of one footing width from the outer edges of the footings or half the height of the required structural fill, whichever is greater. For example, if 6 feet of structural fill is required, the width of the excavation must extend out a distance of 3 feet on either side of the foundation footings. The purpose of extending the structural fill horizontally outside the foundation footings
to a distance equal to half the height of the structural fill is to ensure that load from the foundation footing is entirely contained within the structural fill. Once the excavation is complete the native subgrade must be proof rolled until it no longer yields with each pass. Following compaction of the native subgrade, any required structural fill may
begin to be placed and compacted as recommended in this report. The subgrade must be kept dry throughout construction. At no time should surface water runoff be allowed to flow into and accumulate within the excavation for the foundation elements. If necessary, a swale or berm should be temporarily constructed to reroute all surface water runoff
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away from the excavation. Excavation should not proceed during large precipitation events. If the subgrade does become excessively moist or saturated, construction should not proceed until
C&H Engineering has inspected the subgrade and determined it has sufficiently dried.
If any of the foundation footings are found to be located on a test pit, the area will need to be excavated down to the full depth of the test pit and structural fill be placed and compacted in lifts to bring the area back up to the desired grade.
6.3 Structural Fill
Structural fill is defined as all fill that will ultimately be subjected to structural loadings, such as
those imposed by footings, floor slabs, pavements, etc. none of the soils encountered in the exploratory excavations are suitable to be used as structural fill. Structural fill will need to be imported if required or desired. Imported structural fill is recommended to be a well graded gravel with sand that contains less than 15 percent material that will pass a No. 200 sieve and
that has a maximum particle size of 3 inches. Also, the fraction of material passing the No. 40
sieve shall have a liquid limit not exceeding 25 and a plasticity index not exceeding 6. If another material is to be used it must be approved by C&H Engineering. The well-graded gravel with sand must be placed in lifts no greater than 12 inches (uncompacted
thickness) and be uniformly compacted to a minimum of 97 percent of its theoretical maximum
dry density, as determined by ASTM D698, at + 2 percent of the material’s optimum moisture content. The structural fill must be compacted with a large vibratory smooth drum roller; a sheep’s foot roller will not be adequate for this purpose. Achieving proper compaction is imperative, as it will ensure no additional settlement of the structure occurs. 6.4 Foundation Wall Backfill
Approved backfill material should be placed and compacted between the foundation wall and the
edge of the excavation. The soils encountered in the exploratory excavations, with the exception of the Silty Clay Organics, are suitable for use as foundation wall backfill along the exterior of the foundation provided it is screened to remove cobbles larger than 6 inches in size and any boulders. Structural fill shall be used as foundation wall backfill in all areas that will be
supporting concrete slabs or other paving improvements. Approved backfill material may also be
imported. Imported foundation wall backfill is recommended to be a well-draining granular material. The backfill shall be placed in uniform lifts and be compacted to a minimum of 95 percent of its
maximum dry density, as determined by ASTM D698. The foundation wall backfill will need to
be compacted with either walk behind compaction equipment or hand operated compaction equipment in order to avoid damaging the foundation walls. If walk behind compaction equipment is used, lifts should not exceed 8-inches (uncompacted thickness) and if hand operated compaction equipment is used, lifts should not exceed 4-inches (uncompacted
thickness). Backfill should not be placed and compacted against foundation walls until the
concrete has achieved acceptable compressive strength.
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A 6 to 12-inch cap of low permeability topsoil should be placed, compacted, and appropriately graded above the approved foundation wall backfill on the outside of the foundation wall. This
will effectively cap the backfill and redirect surface water away from the structure. Please note,
if the foundation wall backfill is not compacted properly it will settle and positive drainage away from the foundation will not be maintained. 6.5 Interior Slabs-On-Grade
In preparation for any interior slabs-on-grade, the excavation must continue through any organic soil to a minimum of 6 inches below the proposed bottom of slab elevation. If required, structural
fill can then be placed and compacted to 6 inches below the bottom of slab elevation.
For all interior concrete slabs-on-grade, preventative measures must be taken to stop moisture from migrating upwards through the slab. Moisture that migrates upwards through the concrete slab can damage floor coverings such as carpet, hardwood and vinyl, in addition to causing
musty odors and mildew growth. Moisture barriers will need to be installed to prevent water
vapor migration and capillary rise through the concrete slab. Capillarity is the result of the liquid property known as surface tension, which arises from an imbalance of cohesive and adhesive forces near the interface between different materials. With
regards to soils, surface tension arises at the interface between groundwater and the mineral
grains and air of a soil. The height of capillary rise within a given soil is controlled by the size of the pores between the soil particles and not the size of the soil particles directly. Soils that have small pore spaces experience a higher magnitude of capillary rise than soils with large pore spaces. Typically soils composed of smaller particles (such as silt and clay) have smaller pore
spaces.
In order to prevent capillary rise through the concrete slab-on-grade it is recommended that 6 inches of ¾-inch washed rock (containing less than 10 percent fines) be placed and compacted once the excavation for the slab is complete. The washed rock has large pore spaces between soil
particles and will act as a capillary break, preventing groundwater from migrating upwards
towards the bottom of the slab. Water vapor is currently understood to act in accordance with the observed physical laws of gases, which state that the water vapor will travel from an area of higher concentration to that of
a lower concentration until equilibrium is achieved. Because Earth contains large quantities of
liquid water, water vapor is ubiquitous in Earth’s atmosphere, and, as a result, also in soils located above the water table (referred to as the vadose zone). Typically, the concentration of water vapor in the vadose zone is greater than that inside the residence. This concentration difference may result in an upward migration of water vapor from the vadose zone through the
concrete slab-on-grade and into the building.
In order to prevent this upward migration of water vapor through the slab, it is recommended that a 15-mil extruded polyolefin plastic that complies with ASTM E1745 (such as a Stego Wrap 15-mil Vapor Barrier) be installed. The vapor barrier should be pulled up at the sides and secured to
the foundation wall or footing. Care must be taken during and after the installation of the vapor
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#210228 – LOT 1A-1, MINOR SUBDIVISION 503; GALLATIN COUNTY, MONTANA 12
barrier to avoid puncturing the material, and all joints are to be sealed per the manufacture’s recommendations.
Once the excavation for the interior slab-on-grade is completed as described in the first paragraph of this section, and the washed rock and vapor barrier have been properly installed, it will be acceptable to form and cast the steel reinforced concrete slab. It is recommended that interior concrete slabs-on-grade have a minimum thickness of 4 inches, except garage slabs have
a recommended minimum thickness of 6 inches, unless directed otherwise by a licensed
structural engineer. 6.6 Exterior Slabs-On-Grade For exterior areas to be paved with concrete slabs, it is recommended that, at a minimum, any organics must be removed. The subgrade soils then need to be compacted to an unyielding condition. Then for non-vehicular traffic areas, a minimum of 6 inches of ¾-inch minus rock
needs to be placed, and 4 inches of 4000 pounds per square inch concrete placed over the ¾-inch
minus rock. For areas with vehicular traffic, a minimum of 9 inches of ¾-inch minus rock should be placed, followed by 6 inches of 4000 pounds per square inch concrete. Exterior slabs that will be located adjacent to the foundation walls need to slope away from the
structures at a minimum grade of 2 percent and should not be physically connected to the
foundation walls. If they are connected, any movement of the exterior slab will be transmitted to the foundation wall, which may result in damage to the structure. Additionally, any exterior columns (such as those for patios or decks) should not bear on exterior slabs. Any movement of the exterior slab will be transmitted to the column, which may also result in damage.
If concrete slabs are to be placed on foundation wall backfill, it is very important that the backfill be compacted to a minimum of 95 percent of its maximum dry density, as determined by ASTM D698, in order to prevent settlement of the backfill. 6.7 Asphalt Paving Improvements
For areas to be paved with asphalt, it is recommended that, as a minimum, the undocumented fill
and organic soil must be removed. The native subgrade then needs to be rolled at ± 2 percent of
its optimum moisture content to a minimum of 95 percent of its maximum dry density, as determined by ASTM D698. Following compaction of the native subgrade, a layer of woven geotextile (such as a Mirafi 160N) shall be installed. Next a 12-inch layer of compacted 6-inch minus gravel needs to be placed (sub-base layer), followed by a 6-inch layer of compacted 1-inch
minus road mix (base layer). Both gravel courses must be compacted at ± 2 percent of their
optimum moisture content to a minimum of 95 percent of their maximum dry density. A 3-inch-thick layer of asphalt pavement can then be placed and compacted over this cross-section. It is recommended that following compaction of the native subgrade, a loaded dump truck or
other heavy piece of equipment should be driven over it to determine the stability of the
subgrade. If any isolated soft spots are found, these areas should be sub-excavated and replaced with compacted fill. If widespread unstable conditions are present (i.e. significant rutting or
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pumping is observed) the sub-base component of the road section will need to be increased and a geotextile may also be required, especially if moisture related issues are the cause of the
instability.
If asphalt paving is to be placed on foundation wall backfill, it is imperative that the backfill be compacted to a minimum of 95 percent of its maximum dry density, as determined by ASTM D698. The backfill must be placed in uniform lifts and compacted as described in Section 6.4.
6.8 Site Grading
Surface water should not be allowed to accumulate and infiltrate the soil near the foundation. Proper site grading will ensure surface water runoff is directed away from the foundation elements and will aid in the mitigation of excessive settlement. Please find the following as general site grading recommendations:
• Finished grade must slope away from the building a minimum of 5 percent within the first 10 feet, in order to quickly drain ground surface and roof runoff away from the foundation walls. Please note that in order to maintain this slope; it is imperative that any
backfill placed against the foundation walls be compacted properly. If the backfill is not
compacted properly, it will settle and positive drainage away from the structure will not be maintained.
• Permanent sprinkler heads for lawn care should be located a sufficient distance from the
structure to prevent water from draining toward the foundation or saturating the soils adjacent to the foundation.
• Rain gutter down spouts are to be placed in such a manner that surface water runoff
drains away from the structure.
• All roads, walkways, and architectural land features must properly drain away from all structures. Special attention should be made during the design of these features to not
create any drainage obstructions that may direct water towards or trap water near the
foundation. 6.9 Underground Utilities The onsite soils contain some clayey material. Clayey material can be moderately corrosive to metallic conduits. We recommended specifying non-corrosive materials or providing corrosion protection unless additional tests are performed to verify the onsite soils are not corrosive.
It is recommended that ¾-inch minus gravel be used as a bedding material, where bedding material is defined as all material located within 6 inches of the utility pipe(s). The bedding material should be thoroughly compacted around all utility pipes. Trench backfill shall be compacted to a minimum of 95 percent of its maximum dry density in landscaped areas and a
minimum of 97 percent of its maximum dry density beneath foundation footings. Backfilling around and above utilities should meet the requirements of Montana Public Works Standard
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Specifications. 6.10 Construction Administration
The foundation is a vital element of a structure; it transfers all of the structure’s dead and live loads to the native soil. It is imperative that the recommendations made in this report are properly adhered to. A representative from C&H Engineering should observe the construction of any foundation or drainage elements recommended in this report and should verify proper compaction has been achieved in all structural fill lifts. The recommendations made in this report
are contingent upon our involvement. If the soils encountered during the excavation differ than those described in this report or any unusual conditions are encountered, our office should be contacted immediately to examine the conditions and re-evaluate our recommendations and provide a written response.
If construction and site grading take place during cold weather, it is recommended that approved winter construction practices be observed. All snow and ice shall be removed from cut and fill areas prior to site grading taking place. No fill should be placed on soils that are frozen or contain frozen material. No frozen soils can be used as fill under any circumstances. Please note that not following the preceding recommendations may potentially result in foundation
settlement issues in the spring when the frost thaws and the snow melts. Additionally, concrete should not be placed on frozen soils and should meet the temperature requirements of ASTM C 94. Any concrete placed during cold weather conditions shall be protected from freezing until the necessary compressive strength has been attained. Once the
footings are placed, frost shall not be permitted to extend below the foundation footings, as this could heave and crack the foundation footings and/or foundation walls. It is the responsibility of the contractor to provide a safe working environment with regards to excavations on the site. All excavations should be sloped or shored in the interest of safety and in
accordance with local and federal regulations, including the excavation and trench safety standards provided by the Occupational Safety and Health Administration (OSHA). According to OSHA regulations (29 CFR 1926 Subpart P Appendix A) the subsurface soils encountered in the test pit excavations can be generally classified as Type C. For Type C soils, OSHA regulations state that cut slopes shall be no steeper than 1.5H:1V for excavations less than 20 feet deep. A
trench box may also be used, provided the system extends at least 18 inches above the top of the trench walls. Please understand the preceding OSHA soil classification is provided for planning purposes only and the actual classification of the onsite soils will need to be determined by the contractor onsite
during excavation. 7.0 Conclusions
The soils present at the site will be adequate to support the proposed structure, provided the recommendations made in this report are properly followed. Please find the following recommendations as particularly crucial:
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• The foundation footings may be dimensioned for an allowable bearing capacity of 2,500
psf and shall bear on the native Poorly Graded Gravel with Sand and Cobbles or on
properly placed and compacted structural fill overlying the native Poorly Graded Gravel with Sand and Cobbles.
• All site grading and drainage recommendations must be properly implemented.
• The exposed subgrade must remain in a dry condition throughout construction of the foundation elements.
• If construction takes place during the colder months of the year, the subgrade must be protected from freezing. This may require the use of insulating blankets and/or ground heaters. 8.0 Report Limitations
This report is for the exclusive use of Locati Architects, PLLC. In the absence of our written approval, we make no representation and assume no responsibility to other parties regarding the use of this report. The recommendations made in this report are based upon data obtained from
test pits excavated at the locations indicated on the attached Test Pit Location Map. It is not
uncommon that variations will occur between these locations, the nature and extent of which will not become evident until additional exploration or construction is conducted. These variations may result in additional construction costs, and it is suggested that a contingency be provided for this purpose. If the soils encountered during the excavation differ than those described in this
report or any unusual conditions are encountered, our office should be contacted immediately to
examine the conditions and re-evaluate our recommendations and provide a written response. This report is applicable to the subject property only and is not applicable to other construction sites. Under no circumstances shall a portion of this report be removed or be used independently
of the rest of the document; this report is applicable as a full document only. The preparation of
this report has been performed in a manner that is consistent with the level and care currently practiced by professionals in this area under similar budget and time restraints. No warranty, expressed or implied, is made. Please review Appendix F, “Report Limitations.” This Appendix has been prepared to relay the risks associated with this report.
9.0 References
Das, Braja M., “Principles of Foundation Engineering” 5th ed., Pacific Grove, CA, Brooks/Cole-Thompson Learning, 2004.
Day, Robert W., “Foundation Engineering Handbook,” McGraw-Hill, 2006. International Code Council, Inc., “2018 International Building Code (IBC),” International Code Council, Inc., 2018.
Kehew, Alan, “Geology for Engineers and Environmental Scientists,” 3rd ed., Prentice Hall, 2006.
GEOTECHNICAL INVESTIGATION REPORT
#210228 – LOT 1A-1, MINOR SUBDIVISION 503; GALLATIN COUNTY, MONTANA 16
Das, Braja M., “Principles of Geotechnical Engineering,” 3rd ed., Boston, MA, PWS Publishing Company, 1994.
Vuke, Susan M., Lonn, Jeffrey D., Berg, Richard B., and Schmidt, Christopher J, “Geologic Map of the Bozeman 30' x 60' Quadrangle, Southwestern Montana,” USGS and Montana Bureau of Mines and Geology, Open File Report MBMG 648, 2014.
GEOTECHNICAL INVESTIGATION REPORT
#210228 – LOT 1A-1, MINOR SUBDIVISION 503; GALLATIN COUNTY, MONTANA
Appendix A
USGS Topographic Map
GEOTECHNICAL INVESTIGATION REPORT
#210228 – LOT 1A-1, MINOR SUBDIVISION 503; GALLATIN COUNTY, MONTANA
Appendix B
Test Pit Location Map
GEOTECHNICAL INVESTIGATION REPORT
#210228 – LOT 1A-1, MINOR SUBDIVISION 503; GALLATIN COUNTY, MONTANA
Appendix C
NRCS Web Soil Survey Map
(APPROXIMATE)(APPROXIMATE)LEGENDNatural Resources Conservation Service Web Soil SurveySource: Natural Resources Conservation Service, "Web Soil Survey - Version 16," April 18, 2012, United States Department of Agriculture, <http://websoilsurvey.nrcs.usda.gov/app/>Aerial Photo Date = August 20, 2005Hyalite-Beaverton Complex described as loamy alluvium with a typical soil profile of Loam (0-5 Inches), Clay Loam (5-9 inches), Silty ClayLoam (9-17 Inches), Very Cobbly Sandy Clay Loam (17-26 Inches), and Very Cobbly Loamy Sand (26-60 inches). Depth to groundwater is listedas 48 to 96 inches.Turner Loam described as alluvium with a typical soil profile of Loam (0-6 Inches), Clay Loam (6-26 inches), and Very Gravelly Loamy Sand(26-60 inches). Depth to groundwater is listed as 48 to 96 inches.Blossberg Loam described as alluvium with a typical soil profile of Loam (0-15 Inches), Sandy Clay Loam (15-24 inches), and Extremly GravellyLoamy Coarse Sand (26-60 inches). Depth to groundwater is listed as 12 to 24 inches.
GEOTECHNICAL INVESTIGATION REPORT
#210228 – LOT 1A-1, MINOR SUBDIVISION 503; GALLATIN COUNTY, MONTANA
Appendix D
Geology Maps
(APPROXIMATE)(APPROXIMATE)LEGENDBraid plain alluvium, older than Qab (Pleistocene)Rounded to well-rounded, dominantly cobble gravel with clasts as large as boulders, and sand, silt, and clay; mostly composed of clasts of Archean metamorphic rock, anddark-colored volcanic rock, with subordinate Paleozoic limestone and Proterozoic Belt rocks. Clast lithologies in general order of decreasing abundance include Precambrianmetamorphic rocks, mafic volcanic rocks, dacite(?) porphyry, quartzite, sandstone, limestone, and chert. A well in this unit indicates a thickness of 9 m (30 ft) of alluviumoverlying Tertiary deposits.Alluvial-fan deposit, older than Qaf (Pleistocene)Light brown, gray, and locally reddish gray, angular and subangular, locally derived gravel in a coarse sand and granule matrix. Clast size ranges from pebble to smallboulder. Fan morphology dissected. Maximum thickness probably about 45 m (150 ft).Source: Vuke, Susan M., Lonn, Jeffrey D., Berg, Richard B., & Schmidt, Christopher J., "Geologic Map of the Bozeman 30' x 60' Quadrangle, Southwestern Montana," MBMG, Open File Report 648, 2014.Braid Plain Alluvium, OlderApproximate Site LocationAlluvial Fan Deposit, OlderGEOLOGIC MAP OF THE BOZEMAN 30' X 60' QUADRANGLE
(APPROXIMATE)(APPROXIMATE)LEGENDQuarternary Fault & Seismicity Map of Western MontanaSource: Stickney, Michael C., Holler, Kathleen M., Machette Michael N., "Quaternary Faults and Seismicity in Western Montana ," MBMG, Special Publication No. 114, 2000.Class A Faults are associated with at least 1 large magnitude earthquake within the last 1.6 million years.
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#210228 – LOT 1A-1, MINOR SUBDIVISION 503; GALLATIN COUNTY, MONTANA
Appendix E
Test Pit Logs
OL
GP
1.8
8.0
0 TO 1.75 FEET: SILTY CLAY ORGANIC SOIL; (OL); dark brown; moist; soft.
1.75 TO 8 FEET: POORLY GRADED GRAVEL WITH SAND; (GP); moist to wet; medium
dense to dense; approximately 60 percent subrounded gravels; approximately 30 percent
fine to coarse grain sand; approximately 10 percent clayey fines.
Bottom of test pit at 8.0 feet.
NOTES
GROUND ELEVATION
LOGGED BY Noah J. Schaible, E.I.
EXCAVATION METHOD John Deere Backhoe
EXCAVATION CONTRACTOR Val Mencas Excavation, LLC GROUND WATER LEVELS:
DATE STARTED 3/30/21 COMPLETED 3/30/21
AT TIME OF EXCAVATION 8.00 ft
AFTER EXCAVATION ---
AT END OF EXCAVATION ---DEPTH(ft)0.0
2.5
5.0
7.5 SAMPLE TYPENUMBERPAGE 1 OF 1
TEST PIT NUMBER TP 1
PROJECT NUMBER 210228
CLIENT Locati Architects, PLLC
PROJECT LOCATION Lot 1A-1, Minor Sub. 503
PROJECT NAME Geotechnical Investigation
GENERAL BH / TP / WELL - GINT STD US.GDT - 7/2/21 15:19 - G:\C&H\21\210228\GEOTECH\TEST PIT LOGS (210228).GPJU.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION
OL
SC-SM
GP
1.0
3.5
8.0
0 TO 1 FEET: SILTY CLAY ORGANIC SOIL; (OL); dark brown; moist; soft.
1 TO 3.5 FEET: CLAYEY SAND WITH GRAVEL; (SC-SM); brown; moist; loose to mediumdense; approximately 30 percent subrounded gravels; approximately 50 percent fine to
coarse grain sand; approximately 20 percent clayey fines.
3.5 TO 8 FEET: POORLY GRADED GRAVEL WITH SAND; (GP); moist to wet; mediumdense to dense; approximately 60 percent subrounded gravels; approximately 30 percent
fine to coarse grain sand; approximately 10 percent clayey fines.
Bottom of test pit at 8.0 feet.
NOTES
GROUND ELEVATION
LOGGED BY Noah J. Schaible, E.I.
EXCAVATION METHOD John Deere Backhoe
EXCAVATION CONTRACTOR Val Mencas Excavation, LLC GROUND WATER LEVELS:
DATE STARTED 3/30/21 COMPLETED 3/30/21
AT TIME OF EXCAVATION 8.00 ft
AFTER EXCAVATION ---
AT END OF EXCAVATION ---DEPTH(ft)0.0
2.5
5.0
7.5 SAMPLE TYPENUMBERPAGE 1 OF 1
TEST PIT NUMBER TP 2
PROJECT NUMBER 210228
CLIENT Locati Architects, PLLC
PROJECT LOCATION Lot 1A-1, Minor Sub. 503
PROJECT NAME Geotechnical Investigation
GENERAL BH / TP / WELL - GINT STD US.GDT - 7/2/21 15:19 - G:\C&H\21\210228\GEOTECH\TEST PIT LOGS (210228).GPJU.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION
OL
SC-
SM
GP
1.0
1.5
8.0
0 TO 1 FEET: SILTY CLAY ORGANIC SOIL; (OL); dark brown; moist; soft.
1 TO 1.5 FEET: CLAYEY SAND WITH GRAVEL; (SC-SM); brown; moist; loose to mediumdense; approximately 30 percent subrounded gravels; approximately 50 percent fine to
coarse grain sand; approximately 20 percent clayey fines.
1.5 TO 8 FEET: POORLY GRADED GRAVEL WITH SAND; (GP); moist to wet; medium
dense to dense; approximately 60 percent subrounded gravels; approximately 30 percent
fine to coarse grain sand; approximately 10 percent clayey fines.
Bottom of test pit at 8.0 feet.
NOTES
GROUND ELEVATION
LOGGED BY Noah J. Schaible, E.I.
EXCAVATION METHOD John Deere Backhoe
EXCAVATION CONTRACTOR Val Mencas Excavation, LLC GROUND WATER LEVELS:
DATE STARTED 3/30/21 COMPLETED 3/30/21
AT TIME OF EXCAVATION 8.00 ft
AFTER EXCAVATION ---
AT END OF EXCAVATION ---DEPTH(ft)0.0
2.5
5.0
7.5 SAMPLE TYPENUMBERPAGE 1 OF 1
TEST PIT NUMBER TP 3
PROJECT NUMBER 210228
CLIENT Locati Architects, PLLC
PROJECT LOCATION Lot 1A-1, Minor Sub. 503
PROJECT NAME Geotechnical Investigation
GENERAL BH / TP / WELL - GINT STD US.GDT - 7/2/21 15:19 - G:\C&H\21\210228\GEOTECH\TEST PIT LOGS (210228).GPJU.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION
OL
SC-SM
GP
1.5
3.0
7.0
0 TO 1.5 FEET: SILTY CLAY ORGANIC SOIL; (OL); dark brown; moist; soft.
1.5 TO 3 FEET: CLAYEY SAND WITH GRAVEL; (SC-SM); brown; moist; loose to medium
dense; approximately 30 percent subrounded gravels; approximately 50 percent fine tocoarse grain sand; approximately 20 percent clayey fines.
3 TO 7 FEET: POORLY GRADED GRAVEL WITH SAND; (GP); moist to wet; medium
dense to dense; approximately 60 percent subrounded gravels; approximately 30 percent
fine to coarse grain sand; approximately 10 percent clayey fines.
Bottom of test pit at 7.0 feet.
NOTES
GROUND ELEVATION
LOGGED BY Noah J. Schaible, E.I.
EXCAVATION METHOD John Deere Backhoe
EXCAVATION CONTRACTOR Val Mencas Excavation, LLC GROUND WATER LEVELS:
DATE STARTED 3/30/21 COMPLETED 3/30/21
AT TIME OF EXCAVATION 7.00 ft
AFTER EXCAVATION ---
AT END OF EXCAVATION ---DEPTH(ft)0.0
2.5
5.0 SAMPLE TYPENUMBERPAGE 1 OF 1
TEST PIT NUMBER TP 4
PROJECT NUMBER 210228
CLIENT Locati Architects, PLLC
PROJECT LOCATION Lot 1A-1, Minor Sub. 503
PROJECT NAME Geotechnical Investigation
GENERAL BH / TP / WELL - GINT STD US.GDT - 7/2/21 15:19 - G:\C&H\21\210228\GEOTECH\TEST PIT LOGS (210228).GPJU.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION
OL
SC-SM
GP
1.0
2.0
8.5
0 TO 1 FEET: SILTY CLAY ORGANIC SOIL; (OL); dark brown; moist; soft.
1 TO 2 FEET: CLAYEY SAND WITH GRAVEL; (SC-SM); brown; moist; loose to mediumdense; approximately 30 percent subrounded gravels; approximately 50 percent fine to
coarse grain sand; approximately 20 percent clayey fines.
2 TO 8.5 FEET: POORLY GRADED GRAVEL WITH SAND; (GP); moist to wet; medium
dense to dense; approximately 60 percent subrounded gravels; approximately 30 percent
fine to coarse grain sand; approximately 10 percent clayey fines.
Bottom of test pit at 8.5 feet.
NOTES
GROUND ELEVATION
LOGGED BY Noah J. Schaible, E.I.
EXCAVATION METHOD John Deere Backhoe
EXCAVATION CONTRACTOR Val Mencas Excavation, LLC GROUND WATER LEVELS:
DATE STARTED 3/30/21 COMPLETED 3/30/21
AT TIME OF EXCAVATION 8.50 ft
AFTER EXCAVATION ---
AT END OF EXCAVATION ---DEPTH(ft)0.0
2.5
5.0
7.5 SAMPLE TYPENUMBERPAGE 1 OF 1
TEST PIT NUMBER TP 5
PROJECT NUMBER 210228
CLIENT Locati Architects, PLLC
PROJECT LOCATION Lot 1A-1, Minor Sub. 503
PROJECT NAME Geotechnical Investigation
GENERAL BH / TP / WELL - GINT STD US.GDT - 7/2/21 15:19 - G:\C&H\21\210228\GEOTECH\TEST PIT LOGS (210228).GPJU.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION
GEOTECHNICAL INVESTIGATION REPORT
#210228 – LOT 1A-1, MINOR SUBDIVISION 503; GALLATIN COUNTY, MONTANA
Appendix F
Report Limitations
GEOTECHNICAL INVESTIGATION REPORT
#210228 – LOT 1A-1, MINOR SUBDIVISION 503; GALLATIN COUNTY, MONTANA
Report Limitations and Guidelines for Use
This appendix has been prepared to help the client understand the risks associated with the use of this report and provide guidelines on the proper use of this report. This report was prepared to be used exclusively by Locati Architects, PLLC for residential improvements to be constructed on Lot 1A-1 of Minor Subdivision 503 in Gallatin County, Montana. All of the work was performed in accordance with generally accepted principles and practices used by geotechnical engineers and geologists practicing in this or similar localities. This report should not be used by anyone it was not prepared for, or for uses it was not intended
for. Field investigations and preparation of this report was conducted in accordance with a specific set of requirements set out by the client, which may not satisfy the requirements of others. This report should not be used for nearby sites or for structures on the same site that differ from the structures that were proposed at the time this report was prepared. Any changes in the structures (type, orientation, size, elevation, etc.) proposed for this site must be discussed with our company for this report to be valid. Our services consist of professional opinions based on subsurface exploration at specific points, surface observation of the site, and the review of available published data. These data are then extrapolated by geologists and geotechnical engineers to give an opinion of the overall subsurface conditions. Based on the subsurface conditions that are thought to occur at the site, we evaluate how those conditions would respond to the construction that is proposed, and give recommendations on foundation design and subgrade improvement. Our subsurface exploration is limited to visual observation of the materials uncovered in an open test pit dug by an
excavator. Soil testing was minimal in this investigation so conservative soil parameters have been estimated for bearing capacity and potential settlement from visual observation of the soil. Sampling and testing necessary for a local and global slope stability analysis have also not been completed for this site. Catastrophic events and other structures can contribute to the global stability of a slope, and have not been analyzed. If a more in-depth subsurface investigation is desired, please contact our office to discuss your options. It is important to note that subsurface exploration identifies actual subsurface conditions only at specific points under the conditions present at the time of exploration. Because of this, actual conditions may differ from those inferred to exist. The transitions between materials observed may be much more gradual or abrupt than inferred and subsurface materials may be uncovered during construction that were not thought to occur when the initial subsurface investigation was carried out. Conditions at the site can also change with time due to natural processes and construction practices on the site or on adjacent sites. With these limitations in mind, it is recommended that our services be retained for observation of the materials encountered during construction and that we are informed of any changes that occur on the site and any unexpected conditions that are encountered.
This report is only a preliminary recommendation, which may change if unexpected conditions are encountered during construction. We cannot be held responsible for damages due to constructing on a site with conditions that are different from conditions thought to occur from our investigation. The only way to verify if the conditions encountered during construction are the same as expected in our report is to have us inspect the subgrade materials during construction. We cannot be held responsible for constructing on materials that we have not seen in person. The scope of our investigation did not include an environmental assessment for determining the presence or absence of hazardous or toxic materials on the site. If information regarding the potential presence of hazardous materials on the site is desired, please contact us to discuss your options for obtaining this information. This report is valid as a complete document only. No portion of this report should be transmitted to other parties as an incomplete document. Misinterpretation of portions of this report (i.e. test pit logs) is possible when this information is transmitted to others without the supporting information presented in other portions of the report. If any questions arise with regards to any aspects of this report, please contact us at your convenience to avoid misinterpretation. Costly mistakes due to misinterpretation of geotechnical reports can usually be avoided by a quick phone call.