FWS_Long_Lake_Final_Geotech_Report_0006.pdf

PEOPLE WHO MAKE IT HAPPEN

PEOPLE WHO MAKE IT HAPPEN

G e o t e c h n i c a l

R e p o r t

PEOPLE WHO MAKE IT HAPPEN dowl.com

LONG LAKE HEADQUARTERS BUILDING

MOFFIT, NORTH DAKOTA

January 2022

Prepared By:

1300 Cedar Street Helena, Montana 59601 5028.27085.01

Prepared For:

U.S. Fish & Wildlife Service P.O. Box 25486 Denver Federal Center Denver, CO 80225-0486

Long Lake Headquarters Building Geotechnical Engineering Report January 2022

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LONG LAKE HEADQUARTERS BUILDING

Geotechnical Engineering Report

IDIQ Contract No. 140F0719D008/Project # 21-025

Prepared for:

U.S. Fish & Wildlife Service P.O. Box 25486

Denver Federal Center Denver, CO 80225-0486

Prepared by:

1300 Cedar Street Helena, MT 59601

January 2022

5028.27085.01

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TABLE OF CONTENTS

EXECUTIVE SUMMARY ................................................................................................. I

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 Undocumented Fill

3.2.2 Fat Clay

3.2.3 Clayey Sand

3.3 Groundwater

3.4 Seismicity

3.4.1 Design Accelerations

3.4.2 Liquefaction

4.0 ENGINEERING ANALYSIS AND RECOMMENDATIONS

4.1 Foundations

4.1.1 Conventional Spread Footings

4.2 Lateral Earth Pressures

4.2.1 Coefficient of Friction

4.3 Slabs-on-Grade

4.3.1 Interior Slabs

4.3.2 Exterior Slabs

4.4 Drainage

4.4.1 Surface Drainage

4.4.2 Subsurface Drainage

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 Gravel Surfacing

4.5.6 Construction Considerations

4.5.7 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

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4.6.8 Wet Weather/Soil Construction

4.6.9 Geosynthetics

4.7 Soil Chemistry and Corrosion

5.0 GEOTECHNICAL DESIGN CONTINUITY

6.0 LIMITATIONS

7.0 REFERENCES

FIGURES

Figure 1: Vicinity and Project Location

Figure 2: Exploration Locations

Figure 3: Surficial Geologic Map

TABLES

Table 1: Exploration Summary

Table 2: Laboratory Tests

Table 3: UST Investigation Monitoring Well Groundwater Depths

Table 4: Seismic Design Parameters

Table 5: Foundation Design Parameters

Table 6: Lateral Earth Pressures

Table 7: Parking Lot Traffic Loading

Table 8: Driveway Traffic Loading

Table 8: Pavement Design Parameters

Table 9: Fill Specifications

Table 10: Compaction Specifications

Table 11: Minimum Geogrid Properties

Table 12: Soil Chemistry Test Results

APPENDICES

Appendix A Exploration Logs

Appendix B Photograph Log Appendix C Laboratory Test Results

Appendix D Calculations

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ACRONYMS

ACI .................................................................................................... American Concrete Institute ASTM ........................................................................ American Society for Testing and Materials CBR ........................................................................................................ California Bearing Ratio GWIC ......................................................................................... Groundwater Information Center H ................................................................................................................................... Horizontal LI............................................................................................................................. liquidity index LT ............................................................................................................................................ left OSHA .................................................................. Occupational Safety and Health Administration pcf ............................................................................................................... pounds per cubic foot PGA ...................................................................................................... peak ground acceleration psf ............................................................................................................ pounds per square foot RT .......................................................................................................................................... right SPT ..................................................................................................... Standard Penetration Test V ....................................................................................................................................... Vertical

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EXECUTIVE SUMMARY

DOWL prepared this geotechnical report for the new Long Lake National Wildlife Refuge Headquarters Building. In this report we specifically address the recommendations for foundations, floors, and pavement. Based on the information obtained from our subsurface exploration, the site can be developed for the proposed project. We identified the following geotechnical considerations:

• The generalized soil profile encountered at the new Headquarters (HQ) Building and parking lot consists of about 3 to 7 inches of topsoil, a layer of fat clay that is between 25 and 33 feet thick and a bottom horizon of clayey sand that is between 26 and 34 feet below ground. According to water levels measured in monitoring wells to the east of the new HQ site, old Underground Storage Tank (UST) cleanup site, groundwater is between 20.5 and 22.5 feet below ground.

• Expansive soils are present on this site. This report provides recommendations to help reduce the effects of soil shrinkage and expansion. However, even if these procedures are followed, some movement and cracking in the structure should be anticipated.

Eliminating the risk of movement and distress may not be feasible, but it may be possible to further reduce the risk of movement if significantly more expensive measures are used during construction.

• The building may be founded on a shallow foundation; however, we recommend overexcavating and placing three feet of structural fill below the foundations.

• We recommend constructing the building with a structural floor over a crawl space.

• On-site native soils, or soil in the borrow area, are not acceptable for use as structural fill. However, they can be used for utility backfill and general site grading fill.

• The subgrade soil consists of fat clay. The soil will require significant moisture conditioning prior to placing the pavement section. The fat clay will be soft and difficult to work with. We recommend using a geosynthetic at the base of the pavement section to improve the life of the pavement section.

• Close monitoring of the construction operations discussed herein will be critical in achieving the design subgrade support.

This section is only a summary. Recognize that we do not provide details in this section, read the report in its entirety for a comprehensive understanding of the items contained herein.

1.0 INTRODUCTION

1.1 Purpose and Scope

DOWL completed a geotechnical investigation for the proposed Long Lake National Wildlife Refuge Headquarters Building near Moffit, North Dakota. 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. We conducted this referencing our proposal to dated September 7, 2021. Our geotechnical engineering scope of work for this project included the initial site visit, drilling 5 borings to depths ranging from approximately 5 to 30 feet below existing site grades, laboratory testing for soil engineering properties and engineering analyses to provide foundation, parking lot, building floor, and pavement design and construction recommendations.

1.2 Project Understanding

1.2.1 Existing Site Conditions

The Long Lake Headquarters (HQ) Visitor Center is located roughly 4.3 miles east of Moffit North Dakota via 128th Avenue and 353rd Street southeast (see Figure 1). The existing Headquarters (HQ) building is situated on a relatively flat area above the shoreline of Long Lake. Long Lake’s shoreline is roughly 350 feet west and 20 feet lower in elevation than the Headquarters building. The land surface between Long Lake and the existing HQ Building is a gentle slope with few steep features. No rock outcrops were observed. There are several other structures at the facility including a residence, shop, equipment storage buildings, and grain bins.

Vegetation around the HQ Building is a well-maintained sprinkler irrigated lawn with planted trees. Natural vegetation surrounding the Headquarters facilities are native grass with no trees or bushes.

Based on drawings, the existing HQ building is founded on shallow spread footings. The exposed foundations and the concrete driveway appear to be in good condition with minimal cracking or offset panels. There is some separation and offset between the concrete slab/sidewalk and building entry thresholds. According to Jared Newton, the station manager, they have experienced some minor building distress such as small cracks in the office drywall, and movement of the exterior slabs.

Photograph 1: Project Site

Photograph 2: Drilling B-1

1.2.2 Proposed Construction

According to the Contract Documents, the project will include the construction of the Long Lake National Wildlife Refuge Headquarters (HQ) Visitor Center building, parking lot, sidewalks, access road, and utilities to service the building. The new HQ-Visitor Center will be immediately south of the existing HQ building and a new parking lot will be constructed where the existing HQ building now sits.

New sidewalks and concrete slabs will surround the HQ-Visitor Center and provide access to the building and parking lot. The parking lot may be paved or graveled but have concrete curb and gutter systems.

Further, the new HQ-Visitor Center will be a single story, wood framed approximately 4,700 square foot building. No below grade structures are anticipated. Initial program requirements call for steel reinforced footings, foundations, and concrete slabs. Based on the preliminary grading plan, the finished floor elevation will be about 1,741.0 feet. According to DOWL structural engineers, the foundation loads will be up to 20 kips for isolated columns and about

1.9 kips per foot for walls.

LONG LAKE HEADQUARTERS BLDG

GEOTECHNICAL INVESTIGATION

WWW.DOWL.COM VICINITY AND LOCATION MAP FIGURE 1

LONG LAKE HEADQUARTERS BUILDING - NORTH DAKOTA

VICINITY MAP

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LOCATION MAP

PROJECT LOCATION

WOLSEY

VICINITY MAP

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2.0 INVESTIGATION

2.1 Field Investigation

DOWL performed fieldwork on November 16 and 17, 2021 which consisted of site observations, drilling five (5) geotechnical borings, collection of a soil sample from the active borrow source area, and monitoring groundwater levels in existing Monitoring Wells. We present the boring locations in

Figure 2: Exploration Locations. American Engineering and Testing advanced the borings to depths ranging from 6.5 feet to 36.5 feet below the existing ground surface. DOWL surveyed the boring locations during the topographic survey, relative to the project datum. The Borrow Pit sampled is approximately 0.35 miles northwest of the HQ building. The monitoring wells are east of the HQ Building and were installed during the October,1992 gasoline and diesel Underground Storage Tank (UST) removal and cleanup work.

Table 1: Exploration Summary

Boring Number

Drill Depth (feet)

Surface Elevation

(feet)

Northing (feet)

Easting (feet)

Location

B-1 36.5 1741.26 365,892.78 203,6346.51 West end of new building

B-2 31.5 1739.25 365,911.87 203,6479.92 East end of new building

B-3 6.5 1737.66 366,006.76 203,6494.756 Northeast corner of parking area

B-4 6.5 1741.68 365,928.25 203,6389.96 Southwest corner of parking area

B-5 31.5 1741.06 365,881.96 203,6408.06 Center of new building

American Engineering Testing (AET) drilled the borings under the direction of a DOWL geologist using a CME 450 truck-mounted drill rig equipped with 4.5-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.

We performed Standard Penetration Test (SPT) sampling using an automatic hammer and recorded them on the boring logs. We have not corrected SPT values on the logs for hammer efficiency, sampler type, overburden stress, etc. 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 provide exploration logs in Appendix A which include soil and groundwater conditions as well as SPT information. Stratification boundaries on the boring logs represent the approximate location of changes in soil types; in situ, the transition between materials may be gradual and may vary. In Appendix B we present photographs of the site conditions and of the 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.

WWW.DOWL.COM

LONG LAKE NWR

NEW HEADQUARTERS BUILDING

EXPLORATION LOCATIONS FIGURE 2

2.2 Laboratory Testing

We transported samples to DOWL’s laboratory for testing. We 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. 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 D2216

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

Atterberg Limits

ASTM D4318

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

Particle-Size Distribution

ASTM D421

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

Moisture-Density Relationship (Standard Proctor)

ASTM D698

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

California Bearing Ratio

(CBR)

ASTM D1883

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

Consolidation

ASTM D2435

Used to estimate the consolidation or settlement of soil.

Corrosion Tests

(pH, Resistivity, and Soluble Sulfates)

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

We present laboratory test results on the summary table and figures in Appendix C.

3.0 SUBSURFACE CONDITIONS

3.1 Site Geology

We present a surficial geology map of the project area in Figure 3. The Long Lake HQ-Visitor Center is located within the Long Lake Subdistrict and the Physiographic Landform is identified as Lake Plain (Kume, Hansen, & Tuthill, 1965). Lake Plain units are identified as gently undulating to nearly flat accumulation of glacial drift and are generally stratified. Glacial drift is composed of Till, Glaciofluvial sediments, and Glaciolacustrine sediments. In summary:

• Till is composed of unsorted, unstratified and heterogenous materials ranging in size from boulder to clay.

• Glaciofluvial sediments are composed of washed, sorted and stratified sand and gravel.

• Glaciolacustrine sediments are composed mostly of washed sorted, and stratified materials consisting chiefly of silts and clays.

Glacial Drift is reported to range in thickness from 50 to 175 feet. Nearby well logs indicated that the Glacial Drift us up to 146 feet thick. According to our geotechnical drilling boreholes, the site predominantly consists of Glaciolacustrine sediments.

B-5

B-4

P-2P-3

P-1

B-1

B-2

B-3

PROJECT LOCATION

Geology and Water Resources of Burleigh County, North Dakota. North Dakota Geologic Survey Kume, Jack, Hansen, D.E., and Tuthill, S.J.

LONG LAKE HEADQUARTERS BLDG

GEOTECHNICAL INVESTIGATION

WWW.DOWL.COM SURFICIAL GEOLOGY MAP FIGURE 3

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3.2 Observed Soil Conditions

The generalized soil profile encountered at the proposed construction site consists of an undulating zone of native topsoil that ranged in thickness from approximately three to seven inches. At two of the borings, located in the shoulder of the gravel alongside the south side of the HQ building there is approximately 1.3 feet of undocumented fill. Underlying the topsoil and undocumented fill is fat clay that extends to between 26 and 34 feet below ground. Underlying the fat clay is clayey sand. All three deep borings (B-1, B-2 and B-5) were terminated in the clayey sand, did not penetrate it, and consequently its full thickness is unknown. B-1 is located close to Monitoring Well (MW-1) and the UST site cleanup work conducted in October 1992. We did not observe indications of petroleum contaminated soils or groundwater. 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 Undocumented Fill

We encountered undocumented fill in B-2 and B-5 which consisted of sandy lean clay. Based on experience and the location of these borings the undocumented fill appears to have been placed during the construction of the gravel road that surrounds the existing HQ building.

Undocumented fill is not suitable for support of foundation elements or concrete floor slabs.

Remove and replace undocumented fill with suitable structural fill. Contact DOWL to evaluate fill encountered under the new HQ Building footprint, parking or access roadway areas. These will have to be evaluated for suitability to support these elements.

3.2.2 Fat Clay

Fat clay is the predominate soil at the site and extends from below the topsoil, or undocumented fill to between 26 and 34 feet below ground surface. It is consistently stiff throughout, mottled to about 15 feet, and moist to approximately 25 feet. At 25 feet the fat clay becomes wet. There are occasional very thin varves of fine silty sand that are iron stained and wet. The liquid limits of range from 56 to 82 and the plasticity indices range from 41 to 53. Moisture contents vary from 11 to 40 percent with the optimum moisture content is about 23 percent. The soil sampled from the Borrow Pit is also fat clay and exhibits the same range of physical properties.

3.2.3 Clayey Sand

Clayey sand is consistently present below the fat clay in all three of the deep borings. It is also present in shallower horizons between 3 and 5 feet and 2.5 to 3.5 feet in B-1 and B-4 respectively. In the shallower horizons the clayey sand is, fine grained, very loose to medium dense and moist. At depth, below the fat clay, the clayey sand is fine grained, medium dense and wet.

3.3 Groundwater

Groundwater, in the presence of wet soils samples, was encountered at depths of about 25 feet below ground surface in the borings at the time of field exploration. At B-5, when checked 2 hours after drilling, groundwater was measured at depths of 27.5 feet below ground surface.

Groundwater likely would have risen up to about 25 feet below ground surface if given time.

In October 1992 three underground storage tanks (UST’s) were removed from the area east of the existing HQ building. Gasoline and diesel contaminated soils were discovered during the tank removal; consequently, contaminated soils were removed, and a groundwater sampling and groundwater level monitoring program was initiated. We understand this investigation was “closed” long ago and that the threat of contaminated soils and groundwater is low. But the monitoring wells installed for that work are still present and provided an opportunity to measure the depth to groundwater during this investigation. The location of these monitoring wells is shown in

Figure 2 and the results of groundwater monitoring are shown in Table 3. According the depth to water measured at MW-1 this indicates that the depth to water in B-1, B-2 and B-5 ranges from 20.5 to 22.5 feet below ground.

Fluctuations of groundwater can occur due to seasonal moisture conditions, irrigation practices, changes in land use, changes in the lake level, 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 and this should be considered when developing design and construction plans for the project. Fluctuations in groundwater levels can be documented by implementing a groundwater monitoring plan. Such a plan would include periodic measurement of groundwater levels over a period of time, specifically the spring and early summer months.

Table 3: UST Investigation Monitoring Well Groundwater Depths

Monitoring Well Depth to Water (below ground)

Groundwater Elevation (feet)

MW-1 22.08 1718.74

MW-2 14.63 1719.38

MW-3 15.34 1718.19

3.4 Seismicity

3.4.1 Design Accelerations

DOWL utilized site soil and geologic data, our knowledge of local geology, the project location, Minimum Design Loads and Associated Criteria for Buildings and Other Structures (ASCE, 2016) and the National Earthquake Hazards Reduction Program (NEHRP) to estimate Seismic Site Classification of "D" at the project site. We queried the United States Geologic Survey website (USGS, 2020) recommend seismic design reference the seismic parameters provided in Table 4, 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 = 0.028

0.2 (short SDS = 0.053

1.0 (long) SD1 = 0.025

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. Liquefaction is a process where high shear deformations result in progressive build-up of pore water pressure. Because the seismic load occurs rapidly, soil does not have time to drain, and the effective stress may be reduced to near zero, resulting in a temporary loss of shear strength. Earthquake-induced liquefaction generally occurs only under particular conditions which include saturation, strong earthquake ground shaking of long duration, and loose granular soil. Liquefaction can also occur in silts and fine-grained soils. Typically, liquefaction occurs where the groundwater table is shallow (5 to 10 feet deep) and generally only at depths less than approximately 50 feet.

Loose, saturated, sand, silt, and fine gravel may liquefy when exposed to seismic shaking. To be liquefiable a clay or silt (CL or ML) soil must have a plasticity index (PI) of less than 7, or if the soil classifies as a silty clay (CL-ML), the plasticity index must be less than 5 (Idriss R. W., 2006). Based on the laboratory test results, the native fat clay foundation soils not liquefiable due to high-plastic characteristics.

4.0 ENGINEERING ANALYSIS AND RECOMMENDATIONS

Highly plastic, fat clay soils are present on this site. Based on a method developed by Miller and Stoker (2008), the soil classifies as having a “high” to “very high” swell potential. Such soils are commonly referred to as “expansive” or “swelling” soils because they expand or swell as their moisture contents increase. However, these soils also “contract” or “shrink” as their moisture contents decrease. Footings, floor slabs, and pavements supported on expansive soils will experience cycles of upward and downward movement that will result in distortion, possibly causing cracking or other damage to the structure. Based on the plasticity indices, the current moisture content, and the Schneider and Poor (1974) Method, the soil has potential to swell about ½-inch below the foundation and just over three inches below floor slabs.

The recommendations presented in this report are based on our knowledge of the site soil conditions, our experience with similar sites and structures, and our understanding that the client is willing to tolerate risk of post construction movements and damage in order to reduce construction costs. These recommendations will not eliminate the risk of movement and cosmetic distress for slab-on-ground construction, but this risk could be further reduced if significantly more expensive measures are used during construction. Please contact us if you wish to discuss methods to further reduce risks associated with the presence of expansive soils on your site.

4.1 Foundations

Based on information from the subsurface exploration, and laboratory testing results, and our analysis, it is our opinion the proposed structure can be supported on a spread footing foundation system bearing structural fill. We provide specific recommendations in the following sections.

4.1.1 Conventional Spread Footings

The building foundations may be founded on conventional spread footings according to the parameters listed below.

• Remove existing undocumented fill.

• Prior to placement of structural fill, proof roll subgrades to identify soft spots.

• Footing excavation subgrades shall be inspected by a DOWL geotechnical engineer to verify foundation conditions are similar to those encountered in the borings. Remove and replace soft or loose zones or zones of unsuitable material, if encountered, with structural fill.

• Place three feet of structural fill below the footings.

• See Section 4.2 for lateral resistance design parameters.

Table 5: Foundation Design Parameters

Footing Design Criteria Recommendations Notes

Perimeter/Wall Footings Maximum Allowable

Bearing Pressure

16 inches minimum width, 48 inches minimum below grade

Static Loads (Dead &Sustained Live):

1,200 psf

Transient Loads (Wind & Seismic):

1,600 psf

Interior Column Footings Maximum Allowable

Bearing Pressure Minimum width 18 inches square, 24 inches minimum below grade unless constrained by slab

The resultant load is assumed to be in the middle 1/3 of the footing

Static Loads (Dead & Normal Live):

1,500 psf

Transient Loads (Wind & Seismic):

2,000 psf

Maximum Settlement Estimate

Total (in) Differential (in) Based on a continuous footing with a sustained pressure of 1,200 psf. 1 inch

0.5 inch over 25 feet

Subgrade Preparation and Structural Fill

Compact structural fill to 95% modified Proctor

Excavate soil at least three feet below the bottom of the footing and replace with compacted structural fill.

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.

4.2 Lateral Earth 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, account for lateral surcharge loads from equipment, slopes, or vehicles adjacent to the walls in the structural wall design. We provide recommended lateral earth pressures for below-grade wall design are provided below.

Table 6: Lateral Earth Pressures

Lateral Earth Pressure Case Equivalent Fluid Pressure (pcf)

Structural Fill

At-rest (no wall movement) 62

Active (wall moves away from soil mass) 37

Passive (wall moves into soil mass) 350

Native (clay) soil

At-rest (no wall movement) 69

Active (wall moves away from soil mass) 46

Passive (wall moves into soil mass) 200

• 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 walls 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 below-grade wall height to estimate the lateral surcharge loads from equipment, adjacent foundations and slopes behind and above walls.

4.2.1 Coefficient of Friction

We recommend using a coefficient of friction of 0.40 between cast-in-place concrete and structural fill. And 0.30 between cast-in-pace concrete and the native clay soil. The friction value may be combined with the passive pressure to resist horizontal loads.

4.3 Slabs-on-Grade

Due to the expansive soil at this site, we recommend constructing the building with a structural floor over crawl space. Flatwork will be subject to post construction movement. Maximum grades practical should be used for paving and flatwork to reduce the potential for water ponding. Allowances in final grades should also consider post-construction movement of flatwork, particularly if such movement would be critical. Where paving or flatwork abuts the structure, effectively seal and maintain joints to prevent surface water infiltration.

4.3.1 Interior Slabs

To reduce the swell potential, we recommend constructing the building with a structural floor over crawl space. If that is not feasible, we recommend overexcavating a minimum of four feet below the floor slab and replacing the soil with non-expansive fill. Even with this option there is the potential for about one inch of slab movement. The swell potential can be reduced to about ½-inch by increasing the overexcavation to six feet. Design the floor slabs using the recommendations in the following text.

For slabs that will carry significant traffic, we also recommend doweled joints be considered for the slab connections. Subgrade areas that become soft, loose, wet, or disturbed or that cannot be re-compacted to structural fill requirements discussed above must be over-excavated as described in Section 4.6.

Some differential movement of a slab-on-grade floor system is possible if the moisture content of the subgrade soils is increased. To reduce the effects of some differential movement, separate floor slabs from bearing walls and columns with expansion joints, which allow vertical movement. Use floor slab control joints to reduce damage due to shrinkage cracking.

Interior slabs-on-grade should be allowed to float freely and not be structurally tied to the building to reduce the risk of unsightly cracks related to differential movements of the slab. In addition, the following measures should be taken to reduce damage which could result from movement should the slab subgrades be subjected to moisture changes.

1. Separate floor slabs from bearing walls and columns with expansion joints which allow unrestrained vertical movement.

2. Provide interior non-bearing partitions resting on floor slabs with slip joints so that if the slabs move, the movement cannot be transmitted to the structure. This is also important for wallboards, stairways and door frames.

3. Do not extend floor slabs beneath exterior doors or over foundation grade beams unless saw cut or jointed to allow unrestrained movement.

4. Pressure test plumbing lines before operations begin. Where plumbing lines enter through the floor, a positive bond break should be provided. Flexible connections should be provided for slab-bearing mechanical equipment.

5. Structurally tie stoops at building exits to the building to reduce the potential that heaving of slabs that could hamper egress.

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 reduce the potential for drain gravel puncturing the vapor barrier.

4.3.2 Exterior Slabs

Exterior slabs on-grade, exterior architectural features, and utilities founded on, or in backfill or the site soils will likely experience some movement due to the volume change of the material.

Damage from potential movement may be reduced by:

• minimizing moisture increases in the backfill,

• controlling moisture-density during placement of the backfill,

• designing for vertical movement between the exterior features and adjoining structural elements, and

• designing control joints.

Exterior slabs are susceptible, not only to expansive soil, but to frost action. Both of which can generate substantial heave at certain times of the year. The potential for movement 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).

Where some movement of the exterior slabs is acceptable, such as for the propane tank or picnic shelters, we recommend placing at least 12 inches of structural fill below the slabs.

Prepare slab subgrades in accordance with the recommendations in Section 4.6.1.

4.4 Drainage

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

4.4.1 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 percent away from the structure. Slope the ground surface beyond 10 feet of structures downward at least two 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 stem walls. An elastomeric sealant should also be considered between aprons and foundation stem walls to further reduce the potential for moisture to infiltrate the area directly adjacent to foundations. Slope apron slabs and pavement a minimum of two percent, downward, away from the building.

• Install eve gutters that discharge into solid pipes that convey water to the storm drain system or a place about 20 feet downslope of the building. Design grading so that water continues to flow away from the building at the discharge points.

• Do not irrigate within 10 feet of the building. Periodically inspect and flush irrigation systems to detect potential leaks and avoid saturation of foundation backfill.

• We recommend zeriscape or dryland shrub landscaping be used within 10 feet of foundations to reduce the amount of infiltration.

• Install and maintain window well covers.

• Maintain and check sump systems for proper operation.

• Replace sidewalk or driveway pavement sections that slope toward the foundation.

• Seal cracks in sidewalks, driveway and patio slabs, floor slabs, and foundation 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 bury sheet-metal 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.

4.4.2 Subsurface Drainage

To reduce the potential for water collection in the soil around the building, we recommend installing an exterior foundation drain. Construct foundation drains of a prefabricated composite drain or perforated PVC pipe encased in a drain gravel envelope encompassed in a non-woven filtration geotextile around the perimeter of the building. The drain gravel must meet the specifications Class 2 Aggregate in Section 816, Aggregates, in North Dakota Standard Specifications for Road and Bridge Construction. The filtration fabric must meet the specifications for D2 drainage in Section 858, Geosynthetics, in North Dakota Standard Specifications for Road and Bridge Construction. In addition, we recommend foundation damp-proofing. Drains should be located below the area to be protected and the gravel envelope should be placed at the bottom limits of the compacted structural fill. Slope the drain to either a sump or daylight point down gradient from the structure. We recommend constructing cleanouts for the drain at building corners or every 150 linear feet, whichever is less.

A critical element of foundation drain construction includes proper drain pipe grading. Uneven pipe grades or “bellies” are typical defects that may cause water redistribution to unwanted locations. Construct pipes low enough to collect water that may accumulate at the contact between the native subgrade and the structural fill.

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 the AASHTO design methodology (AASHTO, 1993), strength properties of the subgrade soil and pavement materials, along with the design traffic conditions.

4.5.1 Traffic

Specific traffic information was not available for this project. DOWL estimated the traffic breakdown shown in Table 7 and Table 8. We calculated equivalent single axle loads (ESALs) as shown in the table below assuming an annual growth rate of one percent. If future projects are planned that will impact general traffic routes, contact DOWL to revise our recommendations as necessary.

Table 7: Parking Lot Traffic Loading

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

Passenger Car 55 2S 2S

Pickup Truck/Van 25 2S 4S

Recreational Vehicle 1 4S 4S

Garbage Truck 20S 35T

Semi-Tractor Trailer 12S 34T 34T

Calculated 18 kip ESALs 23,430 (flexible)

28,900 (rigid)

*S-Single, T-Tandem

Table 8: Driveway Traffic Loading

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

Passenger Car 55 2S 2S

Pickup Truck/Van 25 2S 4S

Recreational Vehicle 1 4S 4S

Garbage Truck 1 20S 35T

Semi-Tractor Trailer 6 12S 34T 34T

Calculated 18 kip ESALs 61,200 (flexible)

90,560 (rigid)

*S-Single, T-Tandem

4.5.2 Design Parameters

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

Table 9: Pavement Design Parameters

Pavement Design Parameter

Design Value Source

Initial serviceability 4.2 AASHTO 1993

Terminal serviceability 2.0 AASHTO 1993

Reliability 85% AASHTO 1993

Drainage coefficient 0.9 AASHTO 1993

Flexible Pavement

Design life 20 years AASHTO 1993

Standard Deviation 0.45 AASHTO 1993

Asphalt layer coefficient 0.40 AASHTO 1993

Base layer coefficient 0.14 AASHTO 1993

Subbase layer coefficient 0.08 AASHTO 1993

Subgrade resilient modulus

3,300 psi CBR value

Rigid Pavement

Design life 30 years AASHTO 1993

Standard Deviation 0.35 AASHTO 1993

PCC Modulus of Rupture 580 psi AASHTO 1993

Elastic Modulus 3,605,000 psi 4,000 psi concrete strength

Modulus of subgrade reaction, k

90 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 pavement sections shown below for the entire parking lot if the parking lot is paved:

Parking Lot

3.5 inches asphalt

9.0 inches aggregate base course Geotextile separation/stabilization fabric (see Section 4.6.9).

Driveway

4.5 inches asphalt

11.0 inches aggregate base course Geotextile separation/stabilization fabric (see Section 4.6.9).

4.5.4 Rigid Pavement

For areas subject to concentrated and repetitive loading conditions such as dumpster pads and ingress/egress aprons, we recommend using a reinforced concrete pad at least 6.5 inches thick underlain by at least six inches of aggregate base. In addition, we recommend signage and/or curbing be used to restrict truck traffic from the parking area. In the parking area we recommend at least five inches of Portland cement concrete overlying six inches of aggregate base. We recommend placing a geotextile separation/stabilization fabric below the aggregate base.

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

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 Gravel Surfacing

DOWL understands that the parking lot may have a permanent gravel surfacing section and therefore not paved with asphalt. The primary purpose of a gravel surfacing section is to distribute concentrated wheel loads to the subgrade in a manner to reduce rutting. Performance of the surfacing section is a function of subgrade strength and traffic loading. For purposes of designing a section, subgrade soil is represented by a soil strength value such as California Bearing Ratio (CBR). Subgrade strength decreases when the moisture content of the subgrade increases. Therefore, proper drainage both surface and subgrade, is essential for long-term pavement performance. DOWL recommends the following section options if the USF&W desires a permanent gravel surfacing section:

Option 1

14.0 inches aggregate base course Geotextile separation/stabilization fabric (see Section 4.6.9).

Option 2

8.0 inches aggregate base course Combination Triaxial TX5 and separation fabric

Option 3

8.0 inches aggregate base course Mirafi RS280i

4.5.6 Construction Considerations

• Remove unsuitable material including soft and/or organic soil encountered. Scarify, moisture condition and recompact the subgrade soil to a depth of 12 inches below the pavement surfacing materials in accordance with Section 4.6.1.

• Base Course shall meet the requirements for Class 5 Aggregate in Section 816, Aggregates, in North Dakota Standard Specifications for Road and Bridge Construction.

• Sub Base Course shall meet the requirements for Class 3 Aggregate in Section 816, Aggregates, in North Dakota Standard Specifications for Road and Bridge Construction.

• Asphalt shall meet the requirements in Section 430, Hot Mix Asphalt in North Dakota Standard Specifications for Road and Bridge Construction.

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

(ASTM D2041).

• Portland cement pavement shall meet the requirements in Section 802, Portland Cement Concrete Pavement, in North Dakota Standard Specifications for Road and Bridge Construction.

• Compact all pavement materials (and subgrade) in accordance with the Table 10 in Section 4.6.5.

• 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 two percent slope.

4.5.7 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 to 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.

• Maintain grades outside of paved areas to prevent the collection of water adjacent to the pavement.

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

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

• Do not 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 three to seven inches below the existing ground surface in the locations explored. Remove soil containing vegetation and organics below planned improvements or structures.

• Remove uncontrolled fill below planned improvements or structures.

• Scarify the exposed soil to aa minimum depth of eight inches, moisture condition, and compact disturbed subgrade soil, as specified in the table in Section 4.6.5.

• Due to the expansive nature of the on-site soil, be careful to avoid over compacting the fat clay soil. We recommend maintaining the moisture content above optimum and maintaining the level of compaction below 98% of ASTM D698 (standard Proctor).

• Grade the exposed subgrade surfaces to remove 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 the requirements in Table 11: Compaction Specifications. 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. Contact DOWL's geotechnical engineer to 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 classify 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 comply with OSHA requirements.