B01 Att 5 IHS BLACKFEET Housing -Geo Rpt.pdf

BLACKFEET HOSPITAL APARTMENTS

Geotechnical Engineering Report

Browning, Montana

Prepared for:

HFG Architects

1300 E 104th Street, Suite 225 Kansas City, MO 64131

Prepared by:

222N 32nd Street, Suite 700 Billings, MT 5901

August 2019

4027.21815.01

Author: Dennis A. Russell, P.E.

Reviewer: David Barrick, P.E.

\\bil-fs\bil-projects\27\21815-01\50design\geo\browning geo rpt.docx

Page ii

TABLE OF CONTENTS

1.0 INTRODUCTION

1.1 Purpose and Scope

1.2 Project Understanding

1.2.1 Existing Site Conditions

1.2.2 Proposed Construction

2.0 INVESTIGATION

2.1 Field Investigation

2.2 Laboratory Testing

3.0 SUBSURFACE CONDITIONS

3.1 Site Geology

3.2 Observed Soil Conditions

3.2.1 Topsoil

3.2.2 Gravelly Lean Clay with Sand

3.3 Groundwater

3.3.1 Groundwater Information Center Research

3.4 Seismicity

3.4.1 Design Accelerations

3.4.2 Liquefaction

3.4.3 Faulting

4.0 ENGINEERING ANALYSIS AND RECOMMENDATIONS

4.1 Foundations

4.1.1 Conventional Spread Footings

4.2 Slabs-on-Grade

4.3 Drainage

4.3.1 Surface Drainage

4.4 Lateral Earth Pressures

4.4.1 Equivalent Fluid Pressures

4.4.2 Seismic Earth Pressure

4.4.3 Coefficient of Friction

4.5 Pavement Design

4.5.1 Traffic

4.5.2 Design Parameters

4.5.3 Flexible Pavement

4.5.4 Rigid Pavement

4.5.5 Construction Considerations

4.5.6 Maintenance

4.6 Earthwork

4.6.1 Subgrade Preparation

4.6.2 Excavation

4.6.3 Temporary Slopes

4.6.4 Structural Fill

4.6.5 Compaction Requirements

4.6.6 Testing and Observations

4.6.7 Cold Weather Construction

4.6.8 Wet Weather/Soil Construction

4.6.9 Geosynthetics

4.7 Soil Chemistry and Corrosion

Page iii

5.0 GEOTECHNICAL DESIGN CONTINUITY

6.0 LIMITATIONS

7.0 REFERENCES

FIGURES

Figure 1 Vicinity and Project Location

Figure 2 Boring Location Map

Figure 3 Surficial Geology Map

Figure 4 Conventional Spread Footings

TABLES

Table 1 Exploration Summary

Table 2 Laboratory Tests

Table 3 Depth to Groundwater Encountered During Geotechnical Investigation

Table 4 Seismic Design Parameters

Table 5: Lateral Earth Pressures

Table 6: Traffic Loading

Table 7: Pavement Design Parameters

Table 8: Fill Specifications

Table 9: Compaction Specifications

Table 10: Soil Chemistry Test Results

APPENDICES

Appendix A: Exploration Logs

Appendix B: Laboratory Testing

Appendix C: Photograph LoG

Page I

EXECUTIVE SUMMARY

Soil conditions on this project generally consist of glacial till classified as sandy lean clay with gravel or gravelly lean clay with sand. The glacial till extended beyond the deepest depths drilled.

Based on the results of our field exploration and laboratory testing, we recommend the structure be constructed on conventional spread footings and have a slab-on-grade floor.

1.0 INTRODUCTION

1.1 Purpose and Scope

DOWL completed a geotechnical investigation for the proposed hospital apartments in Browning, Montana. The scope of geotechnical services consisted of reviewing existing geotechnical and geological information, field observations, subsurface exploration, laboratory testing, engineering analyses, and preparing this Geotechnical Report. The purpose of these services is to provide geotechnical related recommendations for project planning and design. DOWL conducted this referencing our proposal to HFG Architecture dated June 20, 2019.

1.2 Project Understanding

1.2.1 Existing Site Conditions

The proposed Blackfeet Hospital Apartments are proposed on knoll consisting of glacial till. The topography of the proposed structure is relatively flat but grades significantly to the west and north near the construction limits. Based on the survey performed by DOWL, the elevation varies from 4,406 to 4,409 feet across the proposed building site. Existing hospital single-family housing dwellings exists to the east and west of the proposed development.

Existing overhead electrical bisects the proposed structure on an approximately north-south axis.

Underground communication and water are also present. A gravel surface road exists long the eastern limits of the proposed development. During the geotechnical investigation, grass cuttings, waste debris and excess fill was being placed along the northern construction limits.

Photograph 1: Project Site Looking North

1.2.2 Proposed Construction

Based on preliminary concept drawings provided by HFG Architecture, development will consist of a two-two story, wood framed apartment building that has a footprint of about 230 feet long and about 80 feet wide. The building will contain about 17 one-bedroom apartments, two four-bedroom apartments, common area, lobby, mechanical room, and storage rooms. The building will not have a basement or below-grade space. Based on an e-mail from Professional Engineering Consultants, the maximum reactions will be 5 kips per lineal foot for continuous footings and 70 kips for column footings.

The building will have a parking lot on the east side that will have 20 to 25 parking stalls. Based on the site topography, we anticipate cuts and fills of about three feet will be necessary for site grading. We anticipate the building will connect to the existing water line on the north side of the site and to the existing sewer and franchise utilities. We expect buried utilities will extend from three to eight feet below the existing ground surface.

BLACKFEET COMMUNITY HOSPITAL

GEOTECHNICAL INVESTIGATION

VICINITY AND LOCATION MAP FIGURE 1

BLACKFEET COMMUNITY HOSPITAL - NEW APARTMENT BUILDING

VICINITY MAP

NOT TO SCALE

LOCATION MAP

HAVRE

GLASGOW

SIDNEY

GLENDIVE

MILES CITY

HARDIN

BILLINGS

BOZEMAN

DILLON

BUTTE

HELENA

MISSOULA

KALISPELL

LEWISTOWN

GREAT FALLS

SHELBY

BROWNING

APARTMENT

BUILDING

BROWNING

2.0 INVESTIGATION

2.1 Field Investigation

DOWL performed fieldwork on June 27 and 28, 2019 which consisted of site observations and drilling eight (8) geotechnical borings. We present the boring locations on the Boring Location Map (Figure 2). Boland Drilling advanced the borings to depths ranging from 11.5 feet to 41.5 feet below the existing ground surface (see Table 1). DOWL surveyed the boring locations during the topographic survey relative to the project datum.

Table 1 Exploration Summary

Boring Number

Drill Depth (feet)

Surface Elevation

(feet)

Northing (feet)

Easting (feet)

Location

B-1 41.5 4,406.5 24,251.6 365,733.8 Northwest Corner of Apartment

B-2 31.5 4,406.0 24,160.7 365,674.0 West Center Portion of Apartment

B-3 31.5 4,407.6 24,032.3 365,599.1 Southwest Corner of Apartment

B-4 36.5 4,405.4 24,162.9 365,782.9 Northeast Corner of Apartment

B-5 33.5 4,407.1 24,080.0 365,711.4 East Center Portion of Apartment

B-6 31.5 4,409.7 23,992.9 365,670.3 Southeast Corner of Apartment

B-7 11.5 4,405.7 24,241.1 365,879.4 Parking/Roadway Area

B-8 11.5 4,410.1 24,020.8 365,759.9 Parking/Roadway Area

Boland Construction drilled the borings under the direction of a DOWL geotechnical engineer using a Mobile B-59 truck-mounted drill rig equipped with 3.5-inch I.D. hollow stem augers. We conducted our field exploration referencing the following ASTM standards:

• ASTM D6151 Standard Practice for Using Hollow-Stem Augers for Geotechnical Exploration and Soil Sampling,

• ASTM D1586 Standard Penetration Test (SPT) and Split-Barrel Sampling of Soils,

• ASTM D1587 Standard Practice for Thin-Walled Tube Geotechnical Sampling of Soils,

• ASTM D3550 Standard Practice for Thick Wall Ring-Lined, Split barrel, Drive Sampling of Soils, We performed Standard Penetration Test (SPT) sampling using an automatic hammer. The resistance, or N-value, can be used to estimate the relative density of granular soils and the relative consistency of cohesive soils. We provide the field N-value or resistance data on the exploration logs.

We recorded the standard penetration test SPT N-values (in blows per foot on the boring logs for each soil sample. We have not corrected SPT values on the logs for hammer efficiency, sampler type, overburden stress, etc.

We provide exploration logs in Appendix A which include soil and groundwater conditions as well as SPT information. In Appendix C we present photographs of the site conditions and of the following samples obtained during drilling.

We based the soil descriptions shown on the boring logs on field and laboratory testing referencing ASTM Standards D2487 or D2488. The stratigraphic contacts shown on the individual borehole logs represent the approximate boundaries between soil types. The actual transitions may be more gradual or abrupt. The soil and groundwater conditions depicted are only for the specific dates and locations reported, and therefore, may not necessarily represent of other locations and times.

B-1 B-7

B-4B-2

B-3 B-5

B-6 B-8

BLACKFEET COMUNITY HOSPITAL

GEOTECHNICAL INVESTIGATION

BORING LOCATION MAP FIGURE 2

B-1

LEGEND

GEOTECHNICAL BORING LOCATION

2.2 Laboratory Testing

We transported samples to DOWL’s laboratory for testing. DOWL selected representative field samples for laboratory testing after visual examination of the soil and consideration of the design criteria. DOWL performed tests for index and engineering soils properties in Billings, Montana and Lander, Wyoming. Energy Labs, of Billings, Montana, completed corrosion testing of select soil samples. Laboratory testing included:

Table 2 Laboratory Tests

Test Purpose

Natural Moisture Content

ASTM D 2216

Provides a measure of natural (in-situ) water content.

Atterberg Limits

ASTM D 4318

Provides an indicator of the consistency and swell potential of fine-grained soils.

Particle-Size Distribution

ASTM D 421

Provides a measure of grain sizes of the soils for classification and identification of physical characteristics.

Moisture-Density Relationship

(Standard Proctor)

ASTM D 698

Provides a measure of the relationship of water content to the density of soil during compaction.

California Bearing Ratio (CBR)

ASTM D 1883

To determine the strength and stability of subgrade soil and base course.

Corrosion Tests

(pH, Resistivity, and Soluble Sulfates)

To determine the potential for corrosive interaction of soils with concrete and metal.

We performed laboratory tests referencing ASTM or other procedures standard to the industry.

Appendix B includes laboratory test results on the summary table and in figures.

3.0 SUBSURFACE CONDITIONS

3.1 Site Geology

The proposed development is located within glacial till (Qtp) deposited by Piedmont Glaciers of the Pleistocene to Wisconsin glaciations (United States Geologic Survey – Geology and Ground- Water Resources of the Blackfeet Indian Reservation, NorthWestern, Montana by M.R. Cannon, 1996). A combination of alpine and continental glaciation produced terminal, recessional, and lateral moraines. These moraines consist of gravelly and clayey till with thickness being more than 50 feet thick in some areas. Younger glacial till deposited by the Laurentide ice sheet may also be present in the project area.

Because of the high clay content, the glacial till is commonly exhibiting poor hydraulic conductivity values. However, deposits of sand, gravel, cobbles and boulders allow for perched water tables.

The groundwater recharge within these perched water tables may significantly decline with prolonged pumping.

BLACKFEET COMMUNITY HOSPITAL

SURFICIAL GEOLOGY MAP FIGURE 3

BROWNING

APARTMENT

BUILDING

3.2 Observed Soil Conditions

The generalized soil profile encountered at the proposed construction site consists of topsoil overlying glacial till classified as gravelly lean clay with sand. The glacial till extended beyond the depths explored. In Appendix A we present the exploration logs with lithology descriptions as well as other engineering properties. In the following paragraphs we provide a general description of the soil strata.

3.2.1 Topsoil

The topsoil ranged from 3 to 8 inches with an average thickness of approximately 4.5 inches.

3.2.2 Gravelly Lean Clay with Sand

Glacial till classified as gravelly lean clay with sand (CL) was encountered in all the borings underlying the topsoil. Interbedded layers of sand, gravel, cobbles, and possible boulders exist within the clay stratum. Uncorrected standard penetration test (SPT) N-values in the clay substrate ranged from seven (7) to greater than 50 blows per foot indicating a medium stiff to hard consistency. The color ranged from brown to dark brown to dark gray with multicolored clasts.

Approximate in-situ moisture contents ranged from 3.9 to 13.9 percent with an average of approximately 10 percent. DOWL performed two (2) unconfined compressive strength with ranging from 5.36 to 6.61 kips per square foot (ksf). Dry unit weighs of the clay stratum ranged from 116.8 to 136.5 pound per cubic foot.

3.3 Groundwater

We did encounter groundwater in three (3) of the eight (8) the borings during drilling. DOWL did not encounter groundwater during the drilling. However, we left Borings B-2, B-3, B-5, and B-6 open overnight to let the groundwater tables to fully stabilize and groundwater was encountered in B-5 and B-6. The observed groundwater tables may indicate a perched water table or a potentiometric surface.

Table 3 Depth to Groundwater Encountered During Geotechnical Investigation

Boring Number

Boring Surface Elevation (feet)

Depth to Groundwater During

Drilling (feet)

Depth to Groundwater After

Drilling (feet)

Approximate Elevation of Groundwater

(feet)

B-1 4,406.5 Not Encountered Not Encountered

B-2 4,406.0 Not Encountered Not Encountered

B-3 4,407.6 Not Encountered Not Encountered

B-4 4,405.4 Not Encountered 27.1 4,378.3*

B-5 4,407.1 Not Encountered 9.9 4,395.5

B-6 4,409.7 Not Encountered 10.9 4,398.8

B-7 4,405.7 Not Encountered Not Encountered

B-8 4,410.1 Not Encountered Not Encountered

*Boring left open approximately 2 hours until backfilled

Fluctuations of groundwater can occur due to seasonal moisture conditions, irrigation practices, changes in land use, and many other factors. Groundwater conditions may vary from those encountered at the time of the field investigation depending upon the influence of these factors.

3.3.1 Groundwater Information Center Research

We researched the Montana Bureau of Mines and Geology’s Groundwater Information Center (GWIC) website to estimate static water levels from existing near the project area. GWIC data is for informational purposes only and contains historical well logs, some of which may not be accurate. Based on the GWIC research, static groundwater levels range from approximately 4 to 50 feet below the existing ground surface with an average depth of approximately 18 feet.

3.4 Seismicity

3.4.1 Design Accelerations

DOWL utilized site soil and geologic data, our knowledge of local geology, the project location, the 2010 American Society of Civil Engineers 7 (ASCE 7) and the National Earthquake Hazards Reduction Program (NEHRP) to estimate Seismic Site Classification of "D" at the project site.

We recommend seismic design reference the seismic parameters provided in table below based on the soil conditions and project location:

Table 4 Seismic Design Parameters

Period (seconds)

Modified Acceleration Coefficient for Site Class

D (g)

0.0 (peak) PGAM = 0.297

0.2 (short SDS = 0.416

1.0 (long) SMS = 0.196

3.4.2 Liquefaction

Liquefaction is the partial or total loss of strength of soils that can occur during strong earthquake shaking of significant duration. Earthquake-induced liquefaction generally occurs only under particular conditions, including high groundwater table, strong earthquake ground shaking of long duration, and loose uniform sands. Typically, liquefaction occurs where the groundwater table is shallow (5 to 10 feet deep) and generally only at depths less than about 50 feet.

Due to the presence of cohesive soil and the depth of groundwater at this site, it is our opinion the risk of liquefaction is very low.

3.4.3 Faulting

Based on geologic mapping by the Montana Bureau of Mines and Geology (MBMG), the nearest Quaternary fault to the project is the South Fork Flathead Fault, located about 40 miles west of the project. It is our opinion the potential for fault rupture at this site is low.

4.0 ENGINEERING ANALYSIS AND RECOMMENDATIONS

4.1 Foundations

Based on the laboratory tests of the soil samples we obtained, the clay soil has the potential to collapse three to five percent; however, the soil samples were disturbed due to the presence of gravel in the clay. Glacial till is rarely collapsible, and it is our opinion the collapse observed in the laboratory tests is due to sample disturbance and is not representative of the soil at the site.

Based on our exploration, testing and experience, it is our opinion that structures at this site may be supported by a shallow foundation system utilizing conventional spread footings with subgrade.

4.1.1 Conventional Spread Footings

The building foundations may be founded on conventional spread footings according to the parameters shown in Figure 4.

Design uplift of shallow foundations from wind and seismic events using the weight of the foundation and soil above the footing. You can include soil resistance in the shape of a truncated pyramid above the foundation. The pyramid edges are defined by straight lines extending from the top of the footing on either side at a 2V:1H (vertical:horizontal) slope.

2 2

4'

(m in footing elevation footing design by structural engineer

MATERIAL

DESCRIPTION

Subgrade prep - exposed soil

MISCELLANEOUS NOTES

The building may be founded on conventional shallow spread footings if subgrade is prepared per the detail above.

Subgrade preparations below foundations are critical to the proper performance of a shallow foundation on this site. If not properly prepared, settlements in excess of what we estimate may occur.

On-site clay may be used for foundation wall backfill except where structural fill is required below slabs, including non-frost susceptible fill below exterior slabs-on-grade. We estimate the total settlement will be less than 1" and differential settlement will be less than 1

2". Our settlement calculations are based on a 5.5 foot square footing and a load of 70 kips.

see Section 4.3 for slopefinished exterior grade

FOUNDATION DESIGN PARAMETERS

Parameter Value Net Allowable Bearing Pressure 2,400 psf*

Coefficient of sliding friction 0.45

*An increase of 1 3 can be allowed for transient loads such as wind and seismic

DESCRIPTION

General fill - on-site soil Structural fill

1.

5'

W

W + 1.5

6" 1

6" (m in

BLACKFEET COMMUNITY HOSPITAL

CONVENTIONAL SPREAD FOOTINGS FIGURE 4

4.2 Slabs-on-Grade

The on-site clay soil encountered near the ground surface are suitable for the support of the new fill and lightly loaded concrete slab-on-grade construction. We recommend placing at least six inches of aggregate base course below the floor slabs. Based on correlations to our field and laboratory test results, we recommend concrete slab design utilize a modulus of subgrade reaction (K) of 150 pci with at least six inches of structural fill over the native clay soil. Subgrade areas that become soft, loose, wet, or disturbed or that cannot be re-compacted to structural fill requirements discussed in Section 4.6.5, must be over-excavated to firm undisturbed soil and replaced with granular structural fill prior to placing the free-draining gravel.

To reduce the effects of some differential movement, separate floor slabs from bearing walls and columns with expansion joints, which allow unrestrained vertical movement. Use floor slab control joints to reduce damage due to shrinkage cracking. The structural engineer should design slab thickness and reinforcement based the intended use of the slab.

Exterior slabs are susceptible to frost action which can generate substantial frost heave at certain times of the year. The potential for frost heave may not be acceptable at entries, bays or other critical areas adjacent to the building that will be exposed to weather. One approach to provide partial frost protection would be to place and compact a minimum of 32 inches of aggregate base course beneath the slab. Alternatively, if partial frost protection is unacceptable, over-excavate and replace the native soil with aggregate base course to the anticipated frost depth (48 inches).

If the floor coverings are sensitive to moisture, place a vapor retarder below the slab, underlain by 4 inches of clean drain gravel. A choker layer such as fine-concrete aggregate (ASTM C 33 sand) may be used to prevent clean drain gravel from puncturing the vapor barrier.

4.3 Drainage

Drainage is critical to the long-term performance of the structure. In the following sections we provide recommendations for surface and subsurface drainage.

4.3.1 Surface Drainage

To reduce the potential for movement due to an increase in the moisture content of subgrade soil, we strongly encourage the implementation of the following recommendations.

• Per the 2018 IBC, slope the ground surface within 10 feet of the structure downward a minimum of 5% away from the structure as shown in the detail below. Slope the ground surface beyond 10' of structures downward at least 2 percent away from the structure.

• Apron slabs and pavement may be used to further reduce infiltration adjacent to structures. Aprons should consist of asphalt or Portland cement concrete pavement that is placed directly adjacent to the foundation stemwalls. An elastomeric sealant should also be considered between aprons and foundation stemwalls to further reduce the potential for moisture to infiltrate the area directly adjacent to foundations. Slope apron slabs and pavement a minimum of 2%, downward, away from the building.

• Install eve gutters, downspouts, and extensions such that they dispose of water a minimum of 10 feet away from the structure.

• Limit irrigation within 5 feet of the building to drip systems. Periodically inspect and flush irrigation systems to detect potential leaks and avoid saturation of foundation backfill.

• Seal cracks in sidewalks, exterior slabs, and foundation walls. Maintain sealant between adjacent slabs and between slabs and adjacent walls.

• Remove or repair landscaping, curbs or other barriers that impair drainage.

• Do not burry rain gutter discharge pipes because they can leak, which often goes undetected. Seepage problems can also be caused by clogging, crushing, and poor grading of the pipes.

• Do not construct infiltration basins adjacent to or up gradient of the structures. If detention is required by statute, infiltration basins should be located down gradient and at least 30 feet from foundations.

4.4 Lateral Earth Pressures

4.4.1 Equivalent Fluid Pressures

Design below-grade walls for building, landscape, and retaining walls and any structure retaining soil to resist both lateral earth pressures from the retained soil adjacent to the structure, as well as hydrostatic pressures from retaining water (if undrained, not recommended). Also, lateral surcharge loads from equipment, slopes, or vehicles adjacent to the walls must be accounted for in structural wall design. We provide recommended lateral earth pressures for below-grade wall design are provided below.

Table 5: Lateral Earth Pressures

Lateral Earth Pressure Case Equivalent Fluid

Pressure

Structural Fill

At-rest (no wall movement) 37 pcf

Active (wall moves away from soil mass) 62 pcf

Passive (wall moves into soil mass) 400 pcf

Native (clay) soil

At-rest (no wall movement) 45 pcf

Active (wall moves away from soil mass) 73 pcf

Passive (wall moves into soil mass) 300 pcf

• The above equivalent fluid pressures assume fully drained conditions and no hydrostatic forces acting on the wall.

• Construct below grade walls, retaining walls, or other retaining structures with adequate drainage and water proofing systems as specified by the Architect and Structural Engineer to reduce the potential for instability, leakage or seepage.

• The retaining wall must move away from or toward the soil to develop active and passive resistance, respectively. For walls that cannot tolerate movement, structurally design walls utilizing at-rest equivalent earth pressures.

• We based the above equivalent fluid pressures on the assumption that the surface of backfill adjacent to walls slopes down and away from the wall a minimum of 5 percent for 10 feet to provide drainage.

• Lateral surcharge pressures due to equipment, slopes, storage loads, etc. are not included in the above lateral earth pressure recommendations. Use the lateral earth pressures coefficient of 0.5, acting over the entire below-grade wall height to estimate the lateral surcharge loads from equipment, adjacent foundations and slopes behind and above walls.

4.4.2 Seismic Earth Pressure

We recommend using the Mononobe-Okabe approach to determine the additional earth pressures due to earthquakes. For the assumed unit weight of the retained structural fill at this project 138 pcf and the design peak horizontal ground acceleration 0.149g, estimate the equivalent additional fluid (active) earth pressure acting on the wall is: 51 pcf. We calculated this value using ½ the peak ground acceleration in the horizonal direction.

4.4.3 Coefficient of Friction

We recommend using a coefficient of friction of 0.45 between cast-in-place concrete and structural fill. And 0.3 between cast-in-pace concrete and the native clayey soil. The friction value may be combined with the passive pressure to resist horizontal loads.

4.5 Pavement Design

The primary purpose of a pavement section to distribute concentrated wheel loads to the subgrade in a manner such that the subgrade is not over-stressed. Performance of the pavement section is a function of subgrade strength and traffic loading. For purposes of designing a pavement section, subgrade soil is represented by a soil support value for flexible pavements (asphaltic concrete) or by a modulus of subgrade reaction value for rigid pavements (Portland cement concrete). Subgrade strength decreases when the moisture content of the subgrade increases. Therefore, proper drainage, both surface and subsurface, is essential for long-term pavement performance.

Pavement design procedures are based upon strength properties of the subgrade soil and pavement materials, along with the design traffic conditions (especially truck traffic).

4.5.1 Traffic

We based our pavement design on the estimated traffic breakdown and calculated equivalent single axle loads (ESALs) as shown in the table below assuming an annual growth rate of two percent. If future projects are planned that will impact general traffic routes, contact DOWL to revise our recommendations as necessary.

Table 6: Traffic Loading

Vehicle Description ADT (Design Lane) Axle Load (kips)*

Passenger Car 100 2S 2S

Pickup Truck/Van 100 2S 4S

School Bus 0 6S 14S

Delivery Truck 2 6S 12S

Garbage Truck 1 20S 35T

Dump Truck 0 20S 48T

Semi-Tractor Trailer 0 12S 34T 34T

Calculated 18 kip ESALs 38,670 (flexible)

42,100 (rigid)

*S-Single, T-Tandem

4.5.2 Design Parameters

We used the pavement design parameters shown in the table below.

Table 7: Pavement Design Parameters

Pavement Design Parameter Design Value

Source

Design life 20 years MDT Pavement Design Manual

Initial serviceability 4.2 MDT Pavement Design Manual

Terminal serviceability 2.5 MDT Pavement Design Manual

Reliability 85% Typical Value

Drainage coefficient 1.0 MDT Pavement Design Manual

Flexible Pavement

Standard Deviation 0.45 MDT Pavement Design Manual

Asphalt layer coefficient 0.41 MDT Pavement Design Manual

Base layer coefficient 0.14 MDT Pavement Design Manual

SubBase layer coefficient 0.10 MDT Pavement Design Manual

Subgrade resilient modulus 6,500 psi CBR value

Rigid Pavement

Design life 20 years MDT Pavement Design Manual

Standard Deviation 0.35 AASHTO 1993

PCC Modulus of Rupture 600 psi MDT Pavement Design Manual

Elastic Modulus 4,300,000 psi 4,000 psi concrete strength

Modulus of subgrade reaction, k 110 pci CBR value

JPCP Load Transfer, J 4.2 AASHTO 1993

4.5.3 Flexible Pavement

Based on our design calculations, anticipated traffic, and the field conditions, we recommend the asphalt pavement section shown below.

3.5 inches asphalt

7.0 inches aggregate base course

4.5.4 Rigid Pavement

Based on our design calculations, anticipated traffic, and the field conditions, we recommend the concrete pavement section shown below.

6.0 inches Portland cement concrete

4.0 inches aggregate base course

We recommend the concrete section in areas where trucks will turn such as dumpster aprons.

Provide sawed or hand-formed joints should at spacings not greater than 15 feet on centers.

Construct the joints should be at least one-fourth of the slab thickness. Provide expansion joints at the end of each construction sequence and between the concrete slab and adjacent structures.

4.5.5 Construction Considerations

• Remove unsuitable material including soft and/or organic soil encountered. Overexcavate soil to a depth of 12 inches below the pavement surfacing materials

• Base Course shall meet the requirements for Type A Crushed Base Course in Section 701, Aggregates, in Montana Standard Specifications for Road and Bridge Construction.

• Asphalt shall meet the requirements in Section 401, Plant Mix Surfacing, in the Montana Standard Specifications for Road and Bridge Construction.

• Compact asphaltic concrete to at least 92% of its theoretical maximum Rice density

(ASTM D 2041).

• Portland cement pavement shall meet the requirements in Section 501, Portland Cement Concrete Pavement, in Montana Standard Specifications for Road and Bridge Construction.

• Compact all pavement materials (and subgrade) in accordance with the table in Section 4.6.5.

• Once the subgrade is scarified, moisture conditioned, and recompacted, it should be proofrolled using a loaded dump truck or water truck. Proofrolling should be observed by a DOWL representative and soft areas should be repaired at our discretion.

• Subexcavate any unstable areas and replace with moisture conditioned and compacted aggregate base.

• Place and compact structural fill in level lifts, not more than 8-inches in loose thickness, up to planned grade.

• Grade pavement such that surface water drains into the curb or storm drains at a minimum 2 percent slope.

4.5.6 Maintenance

• The pavement's life will be dependent on achieving adequate drainage throughout the section and especially at the subgrade.

• Surface and subgrade, crushed surfacing, and asphalt surfaces shall slope at no less than 2 percent to an appropriate stormwater disposal system or other appropriate location that does not impact adjacent buildings of properties.

• Seal cracks and perform surface maintenance on all pavement surfaces every 3 to 5 years to reduce the potential for surface water infiltration in to the underlying pavement subgrade.

• Water that ponds at the pavement subgrade surface can induce heaving during freeze-thaw process, which can readily damage pavement.

• Never allow inverted crowns at the subgrade or pavement surfaces without center concrete gutters designed to have asphalt overlap.

4.6 Earthwork

4.6.1 Subgrade Preparation

• Soil containing vegetation and organics (topsoil) extended approximately 3 to 8 inches below the existing ground surface in the locations explored. Remove soil containing vegetation and organics below planned improvements or structures.

• Scarify, moisture condition, and compact subgrade soil as specified in the table in Section 4.6.5.

• Grade the exposed subgrade surfaces so that they are free of mounds and depressions which could prevent uniform compaction. If unexpected fills or obstructions are encountered during site clearing or excavation, remove such features, and clean the excavation prior to placing backfill and/or construction.

• The site soil is moisture sensitive and susceptible to disturbance when moist or wet and may be expected to pump or rut under construction traffic. Soil disturbance negatively impacts the soil's performance. Disturbed soil is not allowed below any structure or pavement, and especially at footing or slab subgrades.

• Moisture condition and compact disturbed soil or fill placed to achieve site grades to general structural fill requirements in Section 8 on this sheet. This may require considerable moisture conditioning and soil processing due to the clayey nature of the on-site soil.

• Remove pumping or rutting subgrade areas to depths between 12 and 18 inches or as directed by DOWL.

• Replace overexcavations with granular structural fill. DOWL's geotechnical engineer shall review and approve the exposed subgrade.

• Once prepared and approved by the DOWL, it is the contractor's sole responsibility to protect subgrades from degradation.

4.6.2 Excavation

Based on the materials encountered in the soil borings, conventional earthmoving equipment should be capable of excavating the site soils.

4.6.3 Temporary Slopes

Excavations must conform to OSHA Standards for Excavations, 29 CFR Part 1926.652 Appendix B to Subpart P. Based on field observations and laboratory tests, the soil at the site are classifiy as OSHA Type B. OSHA requires that Type B soil excavation slope angles not to exceed 1H:1V (horizontal to vertical). The nature and extent of subsurface variations and groundwater conditions between the boring locations may not become evident until construction. Evaluate soil conditions at the time of construction by the contractor’s responsible person to ensure compliance to OSHA requirements. Temporary excavation slopes may be required for soil improvement excavations and utility trenches. Conduct excavations and shoring in accordance with OSHA standards. Do not allow surcharges within a horizontal distance equal to half the excavation depth. Construction vibrations can cause excavations to slough or cave. Ultimately, the contractor is solely responsible for site safety and excavation configurations.

Plan excavations to allow for water collection points and utilizing conventional sumps and pumps to remove nuisance or precipitation. If site soil excavations are not immediately backfilled, they may degrade when exposed to runoff and require overexcavation and replacement with structural fill. We recommend construction activities, particularly earthwork, be performed as rapidly as possible and/or during drier conditions to reduce the potential for remedial earthwork.

4.6.4 Structural Fill

Fill placed within the planned building footprint shall be considered structural fill. The on-site lean clay is not suitable for use below foundation, floor slabs, or exterior concrete flatwork; however, the on-site clay is suitable for use as fill below pavements, exterior foundation wall backfill, utility trenches and landscaped areas.

Table 8: Fill Specifications

Soil/Fill Product Allowable Use Material Specifications

Non-Structural Fill (Landscape Fill)

Any area that will not have structures (typically landscape areas)

• Soil classified as GM, GW, SM, SW, SC, CL, CH or ML according to the USCS.

• Soil may not contain particles larger than 8 inches in median diameter.

• Soil must be reasonably free from deleterious substances such as wood, metal, plastic, waste, etc.

• Approved by Landscape Architect.

General Fill

• Site grading outside the building footprint.

• Utility backfill areas

• Non-structural fill

• Foundation wall backfill

• Soil classified as GP, GM, GW, GC, SP, SM, SW, SC, CL, or ML according to the USCS.

• Site soil free of vegetation, organics and debris meets these requirements.

• Soil may not contain particles larger than 4 inches in diameter.

• Soil must contain less than 3% (by weight) of organics, vegetation, wood, metal, plastic, or other deleterious substances.

Structural Fill

• General fill

• Over-excavations

• Soil improvements

• Retaining Wall backfill

• Soil classified as GP, GM, GW, SP, SM, or SP with at least 30 percent retained on a number 4 sieve and less than 15 percent passing a number 200 sieve.

• Soil may not contain particles larger than 2 inches in diameter.

• Soil must contain less than 3% (by weight) of organics, vegetation, wood, metal, plastic, or other deleterious substances.

Unsatisfactory Soil NONE

• Soil classified as MH, OH, CH, OL or PT may not be used at the project site

• Any soil type not maintaining moisture contents within 5% of optimum during compaction is unsatisfactory soil that must be moisture conditioned prior to disposal and replacement

• Any soil containing more than 3% (by weight) of organics, vegetation, wood, metal, plastic or other deleterious substances.

4.6.5 Compaction Requirements

Place fill material in lifts not exceeding 8 inches in uncompacted thickness. Moisture condition and compact fill according to the table below.

Table 9: Compaction Specifications

Application Moisture Content (% of optimum)

Minimum Compaction

Subgrade ±4 95% ASTM D698

Below Foundations ±4 98% ASTM D698

Below Slabs-On-Grade ±4 97% ASTM D698

Base and Subbase Courses ±4 98% ASTM D698

Utility Trenches ±4 95% ASTM D698

Site Grading Fill ±4 95% ASTM D698

Foundation Backfill ±4 95% ASTM D698

4.6.6 Testing and Observations

We recommend the following compaction testing frequencies:

• Structural Fill below Footing and Subgrade - 1 compaction test every 50 linear feet (lf) of footing trench or 2 tests per wall line, whichever results in the greater number of tests, per each 1-foot lift of fill.

• Foundation/Retaining Wall Backfill - 1 compaction test every 100 lf of wall or 2 tests per wall line (interior and exterior sides), whichever results in the greater number of tests, per each 1' lift of backfill.

• Interior and Exterior Slab Subgrade - 1 compaction test every 1,000 square feet (sf) of slab area or 2 tests per slab area, whichever results in the greater number of tests, per 1-foot lift of fill.

• Pavements - 1 compaction test every 2,500 sf of pavement area on each subgrade, subbase, and base course layer as applicable, per each 1-foot lift of backfill.

• Trenches - 1 compaction test every 150 linear feet or 2 per trench, whichever results in the greater number of tests, per each 1-foot lift of backfill

To verify that construction conforms to the intent of the specifications, we recommend that DOWL be retained to observe and record the following:

• site preparation including grubbing, stripping, excavating and proofrolling,

• removal of topsoil and root zone beneath slabs and pavements,

• interior and exterior slab subgrades,

• excavations and subexcavations prior to placing bakcfill/fill materials or prior to construction of footings and slabs, and

• approve additional excavation, replacement or stabilization if unsuitable soil is identified by the geotechnical engineer during excavation or proofrolling operations.

4.6.7 Cold Weather Construction

Do not place concrete, pavement or fill on frozen soil. Do not use frozen soil as fill or backfill.

Remove frozen soil, snow, and/or ice from the subgrade or fill soil prior to continuing with construction. Limit winter excavations to areas small enough to be refilled to finished floor grade or higher on the same day. A DOWL representative must monitor fill placed during freezing conditions to reduce the potential for placing frozen material.

4.6.8 Wet Weather/Soil Construction

• Ideally perform earthwork construction during dry weather conditions.

• The site clay is susceptible to pumping or rutting from heavy loads such as rubber-tired equipment or vehicles any time of the year.

• If possible, do not perform earthwork immediately after rainfall or until soil can dry sufficiently to allow construction traffic without disturbing the subgrade.

• If the subgrade soil becomes wet, it may be necessary to complete earthwork with track-mounted equipment that reduces vehicular pressure applied to the soil if construction commences in wet areas or before soil can dry.

4.6.9 Geosynthetics

Geosynthetic fabrics are applicable when constructing on soft or wet soil, for foundations soil improvement applications, as separation fabrics between drainage aggregate, below the construction access road and at the base of soft-spot over-excavations. Where required, apply geosynthetics directly on approved subgrades, taut, free of wrinkles, and over-lapped at least 12 inches. Consult DOWL to review geosynthetic applications or other subgrade improvement alternatives. Geogrid is required to help support any area that exhibits unusually high groundwater, soft pumping, or rutting conditions. Geotextile fabric placed at the bottom of the footing excavation must meet the requirements for separation/stabilization geotextile in Section 716, Geotextiles, of the Montana Department of Transportation Standard Specifications for Road and Bridge Construction.

4.7 Soil Chemistry and Corrosion

Based on the results shown in the table below, concrete in contact with the on-site soil classifies as exposure class S0 according to ACI 318 table 19.3.1.1. Special concrete protections are not required against sulfate related corrosion. Details can be found in the above ACI reference and in the Portland Cement Association publication "Design and Control of Concrete Mixtures."

According to Corrosion/Degradation of Soil Reinforcement for Mechanically Stabilized Earth Walls (FHWA, 2009) the soil at the site is “very corrosive” to steel. Based on that publication and the tests above, we estimate a corrosion rate of 1.2 ounce per square foot per year.

Table 10: Soil Chemistry Test Results

Sample Location

Soluble Sulfate (%)

Resistivity (ohm-cm) pH

Boring B-1 at

35.0 to 36.5 feet

0.0392 417 7.5

Boring B-4 at

12.5 to 14.0 feet

0.0514 407 7.8

5.0 GEOTECHNICAL DESIGN CONTINUITY

Geotechnical design continuity will be an important aspect of the successful completion of this project. In our opinion, geotechnical continuity can occur in three stages in the planning, design and construction project aspects. Specifically, we recommend DOWL maintain the geotechnical design continuity in the following aspects:

• Plan and Specification Review: We recommend you retain DOWL to review final design and construction plans and specifications to verify our geotechnical recommendations are incorporated into construction documents as well as to provide additional recommendations based on the final design concepts. These efforts can help provide document continuity and reduce the potential for errors as the project concepts evolve.

• Geotechnical Design Confirmation: The potential soil variation may have a significant impact on foundation construction. As such, we recommend you retain DOWL to provide geotechnical engineering oversight during site grading and foundation excavation to observe the potential variability in the soil conditions and provide consultation regarding potential impacts on foundation construction.

• Construction Observation and Testing: We recommend you retain DOWL to provide observation and testing during site preparation, grading, structural fill placement and backfilling to verify compliance with the recommendations presented in this report. Having DOWL provide inspection and oversight during this process will reduce the potential for an unforeseen construction error which may ultimately impact the project. If we are not retained to perform the recommended services, we cannot be responsible for related construction errors or omissions.

6.0 LIMITATIONS

DOWL based the conclusions and recommendations presented in this report, based on the assumption that site conditions are not substantially different than those exposed by the explorations. If during construction, subsurface conditions are different from those encountered in the explorations, advise DOWL at once to review those conditions and reconsider recommendations if necessary. The geotechnical recommendations provided herein are based on the premise that an adequate program of tests and observations will be conducted during construction in order to document compliance with DOWL’s recommendations and to confirm conditions exposed during subgrade preparations.

If there is a substantial lapse of time between submission of this report and the start of work at the site, and especially if conditions have changed due to natural causes or construction operations at or near the site, contact DOWL to review this report and to evaluate the applicability of the conclusions and recommendations presented herin.

DOWL prepared this report for HFG Architecture and their Consultants use on this project. DOWL recommends you make this report available to prospective contractors for information and factual data only, but not as a warranty of subsurface conditions. DOWL prepared this report, including engineering analyses, recommendations, figures, and design details specifically for the Blackfeet Hospital Apartments. These recommendations are not applicable to other construction sites. Do not separate the figures from the text for independent use.

Any conclusions made by a construction contractor or bidder relating to construction means, methods, techniques, sequences, or costs based upon the information provided in this report are not the responsibility of HFG Architecture or DOWL.

7.0 REFERENCES

American Association of State Highway and Transportation Officials. 1993. AASHTO Guide for Design of Pavement Structures. Vol. 1

American Concrete Institute. 2014. ACI 318: Building Code Requirements for Structural Concrete.

Section 19.3. Design Strength of Materials

Federal Highways Administration. 2009. Corrosion/Degradation of Soil Reinforcement for Mechanically Stabilized Earth Walls. Publication No. FHWA-NHI-09-087

Cannon, M.R. 1996. Geology and Ground-Water Resources of the Blackfeet Indian Reservation, Northwestern Montana. Hydrologic Investigations Atlas HA-737

Montana Department of Transportation. 2016. Montana Department of Transportation Pavement Design Manual.

Montana Department of Transportation. 2016. Standard Specifications for Road and Bridge Construction.

Montana Tech of The University of Montana. 2019. Ground Water Information Center.

http://mbmggwic.mtech.edu. Accessed July 30, 2019

APPENDIX A: EXPLORATION LOGS

SOIL CLASSIFICATION/LEGEND

Relat iv e Densi ty or Consistency

Uti l iz ing Standard Penetrat ion T est Values

Cohesionless Soils(a) Cohesive Soils(b)

Density(c) N blows/ft(c)

Relative Density

Consistency N blows/ft(c)

Undrained Shear

Strength(d)

(psf) Very loose 0 to 4 0 - 15 Very soft 0 to 2 <250

Loose 5 to 10 15 - 35 Soft 3 to 4 250 - 500

Med. Dense 11 to 29 35 - 65 Medium Stiff 5 to 8 500 – 1,000

Dense 30 to 49 65 - 85 Stiff 9 to 15 1,000 – 2,000

Very Dense Over 50 >85 Very Stiff 16 to 30 2,000 – 4,000

Hard Over 30 >4,000

(a) Soils consisting of gravel, sand and silt, either separately or in combination, possessing no characteristics of plasticity and exhibiting drained behavior.

(b) Soils possessing the characteristics of plasticity, and exhibiting undrained behavior.

(c) Undrained shear strength = ½ unconfined compressive strength.

(d) Qp - Denotes pocket penetrometer field measurement (tons per square foot) approximation to unconfined compressive strength.

Component Def in i t ions By Gradat ion Component Size Range

Boulders Greater than 12-in.

Cobbles 3-in. to 12-in.

Gravel 3-in. to No. 4 (4.75 mm)

Coarse gravel 3-in. to ¾-in.

Fine gravel ¾-in. to No. 4 (4.75 mm)

Sand No. 4 (4.75 mm) to No. 200 (.075 mm)

Coarse sand No. 4 (4.75 mm) to No. 10 (2.0 mm)

Medium sand No. 10 (2.0 mm) to No. 40 (0.425 mm)

Fine sand No. 40 (0.425 mm) to No. 200 (0.074 mm)

Silt and Clay Smaller than No. 200 (0.075 mm)

Si l t and C lay Descr ipt ions Description Typical Unified Designation

Silt ML (non-plastic) Clayey Silt CL-ML (low plasticity)

Silty Clay, Lean Clay CL Clay, Fat Clay CH

Plastic Silt MH Organic Soils OL, OH, Pt

Descr ipt iv e T erminology Denot ing Components Propor t ions

Descriptive Terms Range of Proportion

Trace or Scattered 0 - 5% Few 5 - 10%

Some or Adjective(a) 15 - 30% And 30 - 50%

(a)Use gravelly, sandy or silty as appropriate.

Unless otherwise noted, drive samples advanced with 140-lb. hammer and 30-in. drop.

Unif ied Soi l C lassi f icat ion Sy stem

Criteria for Assigning Group Symbols and Names Soil Classification

Generalized Group Descriptions

COARSE-GRAINED SOILS GRAVELS CLEAN GRAVELS GW Well-graded gravels More than 50% More than 50% of Less than 5% fines GP Poorly-graded gravels retained on coarse fraction GRAVELS w/ FINES GM Gravel and silt No. 200 sieve retained on No. 4 More than 12% fines mixtures sieve GC Gravel & clay mixtures SANDS CLEAN SANDS SW Well-graded sands 50% or more of Less than 5% fines SP Poorly-graded sands coarse faction SANDS with FINES SM Sand and silt mixtures passes No. 4 sieve More than 12% fines SC Sand and clay mixtures

FINE-GRAINED SOILS SILTS & CLAYS CL Low-plasticity clays 50% or more passes Liquid limit INORGANIC ML Non-plastic and low-the No. 200 sieve less than 50 plasticity silts

Non-plastic and low plasticity organic clays

ORGANIC OL

Non-plastic and low-plasticity organic silts

SILTS & CLAYS CH High-plasticity clays Liquid limit INORGANIC MH High-plasticity silts greater than 50

High-plasticity organic clays

ORGANIC OH

High-plasticity organic soils

HIGHLY ORGANIC SOILS Primarily organic matter, dark in color and has an organic odor PT peat

Soi l M oisture

Dry Absence of moisture, dusty, dry to the touch

Slightly Moist Minor existence of moisture, not dusty, but still dry to the touch

Moist Damp but no visible water

Very Moist Zones of visible moisture and usually above the water table

Wet Visible free water, usually soil is below water table

Groundwater Elevat ion

Water Elevation Noted During Drilling

Water Elevation Recorded After Drilling Complete

Samples

Split Spoon Sampler (2.0” OD)

Ring Sampler (3.0” OD)* *Indicates increased blow counts due to sampler size.

Shelby Tube Sampler (3.0” OD)

Bulk Sample (auger cuttings)

Core Barrel

3.5

10.5

17.5

4399.5

4392.5

4385.5

5-inches +/- Topsoil, Sandy Lean CLAY; very moist, black, organics

0.4 4406.1

Sandy Lean CLAY; stiff, moist, brown, fine to coarse grained sand

1.6 4404.9

Gravelly Lean CLAY with Sand and Cobbles;

stiff, brown to dark brown with multicolored clasts, rounded to subrounded, fine to coarse grained sand, possible boulders

Grades very stiff at 5.0 feet

Grades hard at 7.5 feet

10.0 4396.5

Sandy Lean CLAY with Gravel, CL; very stiff, slightly moist to moist, brown with multicolored clasts, rounded to subrounded, fine to coarse grained sand, possible cobbles and boulders

Grades hard at 12.5 feet

14.5 4392

Gravelly Lean CLAY with Sand and Cobbles;

hard, slightly moist to moist, brown to light grayish brown with multicolored clasts, rounded to subrounded, fine to coarse grained sand, possible boulders

23.0 4383.5

Sandy Lean CLAY with Gravel and Cobbles, CL; very stiff, moist…