Amend_3_Atch_1_DC_Booth_Shop_Geotechnical_Report-Final_0003.pdf

PEOPLE WHO MAKE IT HAPPEN

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

R e p o r t

G e o t e c h n i c p o r t

G e o t e c h n i c p o r t

G e o t e c h n i c p o r t

PEOPLE WHO MAKE IT HAPPEN dowl.com

DC BOOTH HISTORIC FISH

HATCHERY SHOP

SPEARFISH, SD

May 2020

Prepared By:

222 N. 32nd Street, #700 Billings, MT 59101 4021.21857.01

Prepared For:

U.S. Fish & Wildlife Service P.O. Box 25486 Denver, CO 80225

DC BOOTH HISTORIC FISH HATCHERY SHOP

Geotechnical Engineering Report

#140F0719D0008

Prepared for:

U.S. Fish & Wildlife Service

P.O. Box 25486 Denver, CO 80225

Prepared by:

DOWL

222 N. 32nd Street, #700 Billings, MT 59101

May 2020

4021.21857.01

\\bil-fs\bil-projects\21\21857-01\31geotech\final dc booth shop geotechnical report.docx

DC Booth Historic Fish Hatchery Shop Geotechnical Engineering Report May 2020

Page I

TABLE OF CONTENTS

1.0 SUMMARY

2.0 REPORT PREPARATION

3.0 PROPOSED CONSTRUCTION

4.0 INVESTIGATION PROCEDURE

4.1 Field Investigation

4.2 Laboratory Testing

5.0 SITE CONDITIONS

5.1 Site Description

Site Overview

Site History

Area Geology

Site Topography

5.2 Soils

5.3 Possible Hydrocarbon Contamination

5.4 Bedrock

5.5 Groundwater

5.6 Earthquakes and Seismicity

Area Earthquakes and Seismicity

Design Response Spectrum

6.0 ENGINEERING ANALYSES AND RECOMMENDATIONS

6.1 Foundations

Shallow Foundation System

6.1.1.1 Structural Fill

6.1.1.2 Bearing Capacity and Settlement

Slab-On-Grade

Lateral Loads on Foundation Walls

6.1.3.1 Soil Friction Factor

Earthwork

6.1.4.1 Site Clearing and Subgrade Preparation

6.1.4.2 Excavation

6.1.4.3 Fill Material

6.1.4.4 Fill Placement and Compaction

Site Grading and Surface Water Control

Foundation Drains

6.2 Utility Excavations

6.3 Pavement Design

Paved Area Clearing and Subgrade Preparation

Pavement Fill Materials

Pavement Fill Placement and Compaction

6.4 Cold Weather Construction

6.5 Wet Weather Construction

6.6 Corrosion Potential

Minimum Resistivity

Water Soluble Sulfates

6.7 Other Considerations

6.8 Radon

Page II

6.9 Construction Testing

7.0 GEOTECHNICAL DESIGN CONTINUITY

8.0 LIMITATIONS

9.0 REFERENCES

PHOTOGRAPHS

Photograph 1: Project Site

FIGURES

Figure 1: Vicinity and Project Location

Figure 2: Borehole Location Map

Figure 3: Spearfish, SD Geologic Map (Lisenbee et al, 2013)

TABLES

Table 1: Exploration Summary

Table 2: Laboratory Testing Summary

Table 3: Soil Type Descriptions

Table 4: Residuum Summary

Table 5: Site Ground Motion and Design Response Spectrum

Table 6: Elevation Summary

Table 7: Foundation Recommendation Summary

Table 8: Woven Geotextile Specifications

Table 9: Lateral Loads

Table 10: Structural Fill Recommendations

Table 11: Low Frost Susceptibility Recommendations

Table 12: Compaction Recommendations

Table 13: Pavement Design Parameters

Table 14: Pavement Design Options

Table 15: Marshall Design Criteria

Table 16: Geogrid Specifications

Table 17: Crushed Aggregate Base Specification - SDDOT

Table 18: Soil Resistivity Measurements

Table 19: Water Soluble Sulfates

APPENDICES

Appendix A: Soil Boring Logs

Appendix B: Laboratory Test Results

Appendix C: Photographs

1.0 SUMMARY

DOWL conducted a geotechnical investigation for the proposed DC Booth Historic Fish Hatchery Shop in Spearfish, South Dakota (Figure 1).

The scope of services included drilling exploratory boreholes, field observations, laboratory testing, engineering analyses, and furnishing this geotechnical report. The purposes were to investigate soil and groundwater conditions, evaluate soil-engineering properties, and to provide recommendations to support design and construction of foundation, utility, and pavement elements. This report is consistent with the International Building Code (IBC) guidelines for soil and foundation investigations.

Soil conditions at the site generally consist of previously placed fine to coarse-grained fill overlying fine-grained alluvial terrace deposits underlain by residual bedrock. The site is underlain by 10 to 17 feet of undocumented fill. Foundations bearing directly on previously placed fill are not recommended because of potential risk of differential movement that could result in cracked concrete floors and structural distress. The nature of this fill can be problematic, even with subgrade improvement. The preferred route is to completely remove all undocumented fill from beneath the structure footprint. If this is not feasible, shallow foundations bearing on improved subgrade consisting of imported structural fill should provide adequate support for the proposed structure; however, we do not recommend this alternative and the US Fish and Wildlife Services should be aware that undocumented fill may result in unwanted movement over the life of the structure.

If properly constructed, the recommended subgrade improvements and foundation modifications should provide adequate support for the anticipated foundation loads and reduce the risk of potential differential movement of the structure.

2.0 REPORT PREPARATION

This report presents site and borehole location maps; geologic logs; geotechnical engineering analyses; and recommendations.

3.0 PROPOSED CONSTRUCTION

Proposed new construction for DC Booth Historic Fish Hatchery Shop includes an approximate 3,400 square foot (SF) shop. The shop will include a wood shop area, storage, and a fish truck parking area. Site improvements will include utilities necessary for the building, concrete sidewalks, and asphalt pavement.

Preliminary foundation loads provided by DOWL structural engineers include wall loads of 275 to 325 pounds per lineal foot and column loads on the order of 18 to 28 kips. DOWL structural engineers have designated tolerable settlements of ½ of an inch for differential settlement and 1-inch for total settlement. A preliminary finish floor elevation has been set at 3,713 feet above sea level. This is one to three feet higher than current site elevations. If actual foundation loads or finish floor elevations vary from these assumptions, contact DOWL geotechnical personnel to revise our recommendations as necessary.

At the time of the investigation, construction had not begun.

DC BOOTH HISTORIC FISH HATCHERY

GEOTECHNICAL INVESTIGATION

307-686-4181

1901 Energy Court, #170

Gillette, Wyoming 82718

WWW.DOWL.COM

VICINITY MAP

FIGURE 1

4.0 INVESTIGATION PROCEDURE

4.1 Field Investigation

Fieldwork conducted on April 13, 2020 consisted of site observations and drilling three (3) exploratory boreholes using a CME 55 truck-mounted drill rig. Boreholes were drilled near the proposed structure to depths of approximately 20 feet in order to observe subgrade conditions and obtain representative samples. Drilling was performed using 4 ¼ -inch inside diameter hollow-stem augers.

Table 1: Exploration Summary1.

Boring Number

Drill Depth (feet)

Surface Elevation

(feet)

Northing (feet)

Easting (feet) Location

BH-1 21.5 3712 259468.9 960735.9 South end of building BH-2 21.5 3710 259545.1 960736.3 NW side of building BH-3 21.5 3710 259546.5 960774.2 NE side of building

1.As surveyed by DOWL March 18, 2020

Drilling and field sampling were performed in general accordance with the following standard specifications:

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

Sampling with a two-inch O.D. split-barrel (split-spoon) per ASTM D1586, “Penetration Test and Split-Barrel Sampling of Soils.”

“Standard Practice for Thin-Walled Tube Geotechnical Sampling of Soils”, ASTM D1587.

Soil type, thickness, consistency, and relative moisture content were observed and documented by a DOWL Geotechnical Engineer. Split-spoon samples, one bulk sample, and one Shelby tube sample were collected. As the drilling progressed, soil samples were taken for field classification (ASTM D2488) and borings were checked for groundwater after drilling and sampling were complete. All soil borings were backfilled with drill cuttings. Soil samples were transported to the DOWL laboratory where index and engineering property tests were conducted. Approximate boring locations are shown on Figure 2. Subsurface logs are attached in Appendix A. Photographs taken during field investigations are included in Appendix C.

Site conditions may be variable and actual soil conditions encountered in excavations may differ somewhat from those represented in the borehole logs. Final boring logs contain factual and interpretive information. On the final logs, horizontal lines, designating the interface between differing materials encountered, represent approximate boundaries. The transition between soil layers may be more gradual or abrupt. The soil and groundwater conditions depicted are only for the specific dates and locations reported, and therefore, are not necessarily representative of other locations or times.

Standard Penetration Tests (SPT) were performed using a 2-inch outside diameter split-spoon sampler driven with an automatic 140-pound hammer in general accordance with ASTM D1586.

During the tests, samples were obtained by driving the sampler 18 inches into the soil with a hammer free falling 30-inches. The number of blows required for each 6-inches of penetration was recorded. The field N-value of the soil is recorded as the number of blows required for the final 12-inches of penetration. The field N-value provides a measure of relative density of granular soils and estimation of relative consistency of cohesive soils. It should be noted that the presence of cobbles or boulders may result in relatively high blow counts that may not properly characterize the in-situ relative density.

4.2 Laboratory Testing

“Disturbed” split-spoon and “undisturbed” Shelby tube samples were collected during the field investigation along with one bulk sample. Laboratory testing was completed on select soil samples to assist in soil classification and to characterize soil engineering properties.

Laboratory testing included the following:

Table 2: Laboratory Testing Summary

Test Purpose Unified Soil Classification System

ASTM D2487

Classifies soils based on general index testing.

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 clay soils.

Particle-Size Distribution

ASTM C117/136/D421

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

Consolidation/ Swell

ASTM D2435

Provides a measure of the magnitude at which a soil will compress when loaded and rebound when unloaded.

Resistivity, pH, and SO4

WREP-125, EPA 9045D, EPA 300.0

Provides a measure of deleterious effects of the soils on buried metals and concrete.

Laboratory tests were performed in general accordance with the most recent ASTM standards or other procedures standard to the industry as summarized above. Results are discussed in the Section 5.2 – Soils and shown on the subsurface boring logs in Appendix A. Laboratory test sheets are attached in Appendix B.

DC BOOTH HISTORIC FISH HATCHERY

GEOTECHNICAL INVESTIGATION

307-686-4181

1901 Energy Court, #170

Gillette, Wyoming 82718

WWW.DOWL.COM

BOREHOLE LOCATION MAP

FIGURE 2

5.0 SITE CONDITIONS

5.1 Site Description

Site Overview

The proposed shop is located at the southern extent of the DC Booth Historical Fish Hatchery facility The facility is located near the southern portion of Spearfish in the southwest ¼ of Section 15, T. 6 N., R. 2 E., Lawrence County, South Dakota (Figure 1). The area is a leveled storage area at the bottom of Fish Hatchery Gulch.

Photograph 1: Project Site.

Site History

Based on our conversations with USFWS, we understand the site was constructed, over an unknown period of time, by placing fill, as it was available, to create the current level area. Site personnel (Mr. Mitch Adams) have indicated that no information is available regarding the nature of the fill other than it is likely variable.

Area Geology

The D.C. Booth Hatchery shop site is located in Fish Hatchery Gulch on the northern edge of the Black Hills dome which is an isolated range in the western Great Plains. The core of this dome structure is composed of Precambrian granite with layers of overlying Paleozoic and Mesozoic sedimentary rocks exposed along the margins of this uplift in a series of hogbacks and valleys. As seen in Figure 3, the Geologic Map of the Spearfish Quadrangle, South Dakota (Lisenbee et al, 2013), the shop site is located on alluvial terrace deposits (Qt1) overlying the Opeche Shale (Po). The alluvial terrace deposits are unconsolidated gravel to boulder-sized clasts with interstitial clay, silt and sand. This geologically young deposit is 3-15 feet above present-day stream drainages and has a maximum thickness of 70 feet. The Opeche Shale is Lower Permian-aged, dark red, orange, to reddish-brown shale and siltstone with calcareous sandstone lenses and some gypsum layers. Thickness is 80-110 feet thick in the northern Black Hills. The formation that overlies the Opeche Shale is the Minnekahta Limestone (Pm) which has been stripped off of this site, but it is present on the sloping benches north of Fish Hatchery Gulch and south of the site towards Spearfish Creek Canyon. Minnekahta limestone outcrops are also visible along the slopes of Fish Hatchery Gulch in the vicinity of the project area. The Minnekahta Limestone is Middle to Upper Permian-aged, pink, purple-gray to beige, micritic, very finely crystalline, limestone that forms resistant uplands, cliffs and cap rock and is typically 40 feet thick. The formation that underlies the Opeche Shale is the Minnelusa Formation (PPm), a red, brown, yellow and beige quartz sandstone, shale, and limestone with layers of anhydrite.

This formation is up to 500 feet thick and contains local solution breccia, vugs (voids), and caves in the upper third of the formation (Lisenbee et al, 2013).

Although the Opeche Formation is predominately shale, siltstone, and fine-grained sandstone, it contains layers of gypsum. Additionally, the Minnelusa Formation that underlies the Opeche Shale contains anhydrite, also an evaporite salt. Gypsum and anhydrite are soluble and when exposed to groundwater or surface water, they dissolve over time leaving behind voids and karst features. Due to the impermeable layers of shale within the Opeche Shale, it serves as a confining unit between the underlying Minnelusa Formation and the overlying Minnekahta Limestone, both of which contain soluble anhydrite or gypsum. The solution of anhydrite and gypsum has resulted in the formation of voids which has caused fragmentation and collapse of overlying rocks including the disruption of bedding, collapse breccia, sinkholes, breccia pipes and pinnacles (Epstein, 2001). This subsidence has caused damage to houses and infrastructure in the region. Interestingly, multiple sinkholes west of Spearfish, which support spring-fed ponds for agricultural use and hatcheries (such as at this site), are located in collapse structures that originate hundreds of feet below the site within the anhydrite layers of the Minnelusa Formation. The presence of gypsum and anhydrite karst in the regional bedrock should be considered in the development of this site. For example, the stratigraphy should be examined for the presence of voids, disrupted bedded, and layers of gypsum or other salts as well as site reconnaissance that evaluates whether any surface features are present that indicate brecciation, sinkholes, depressions, undulating ground surface, or other karst features.

Figure 3: Spearfish, SD Geologic Map (Lisenbee et al, 2013)

Site Topography

The proposed shop location is gently sloping down to the north. There is approximately 2 feet of topographic relief across the proposed building footprint. Site elevations typically range from approximately 3,710 to 3,712 feet above sea level. West of the site, the hillside slopes up from the level area approximately 114 feet. Fish Hatchery Gulch is located east and south of the level area followed by another hillside sloping up approximately 160 feet.

5.2 Soils

Soil conditions at the proposed shop generally consist of fine to coarse-grained undocumented fill overlying fine-grained alluvial terrace deposits underlain by residual Opeche Formation bedrock. In BH-1 and BH-3, the fill is underlain directly by the residual bedrock. The fine-grained material consists of combinations of silt and clay while the coarse-grained material consists of combinations of sand, gravel, and cobbles. The fine-grained soil also contain a sand and gravel fraction that ranges from 23 to nearly 50%. The fill is variable in soil type and consistency and contains trace amounts of organics and occasional limestone cobbles. SPT blow counts in the fill ranged from 4 to 50, and the moisture content ranged from 8 to 19 percent.

Shop site

The fill was encountered at the ground surface and extended to depths ranging from approximately 10.0 to 17.0 feet below the existing ground surface. In general the fill becomes thicker as it transitions away from the slope.

Fine-grained alluvial material was encountered immediately beneath the fill at a depth of approximately 10.0 feet (BH-2) and extended to a depth of approximately 20.5 feet below the existing ground surface. The alluvium contained trace organics and shale fragments.

The fill (BH-1 & BH-3) and alluvium (BH-2) are underlain by residual shale and sandstone (residuum). The residuum extended to the termination depths of the soil borings (~20 feet).

While residual bedrock soils are composed of bedrock matrix soils, they typically exhibit relatively low strength as compared to the parent bedrock and are a product of severe weathering. The residuum was slightly to moderately cemented.

Refer to the soil boring logs in Appendix A for graphical interpretations of the soil profiles.

In Table 3, we describe the various soil types encountered during the subsurface exploration and associated laboratory testing results.

Table 3: Soil Type Descriptions1.

Soil Type2.

USCS3.

Classification Density/ consistency Moist. Color

SPT N

Values, blows/ft

In-situ Moisture

Content, %

Atterberg Limits4.

Misc Engineering Properties4.

Fine-grained Fill CL Frozen to Firm to stiff

Frozen to

Moist

Brown to reddish brown to red 5 to 50 11.6 to 18.6 LL = 29

PI = 12 --

Coarse-grained Fill SM/SC/GC Very loose to dense Moist Red to brown 4 to 38 7.9 to 17.4 LL = NV

PI = NP --

Fine-grained Alluvium CL Soft to stiff Moist Brown to red 4 to 12 20.3 LL = 27

PI = 13

Cc = 0.10 Cs = 0.01 in-situ = 104.8 pcf

Residual Sandstone GC-GM

Medium dense to very dense Moist Light reddish brown to red to yellow 18 to 50+ 4.4 to 6.1 LL = 19

PI = 4 --

Residual Shale CL Very stiff Moist Red 17 1.Typical properties and conditions encountered.

2.Based on field observations and laboratory test results.

3.SC = Clayey Sand/Clayey Sand with Gravel, SM = Silty Sand/Silty Sand with Gravel, CL = Lean Clay/Gravelly Lean Clay, GC-GM =Silty, Clayey Gravel with Sand, GC = Clayey Gravel 4.LL = Liquid Limit, PI = Plasticity Index, NV = non-viscous, NP = non-plastic, Cc = compression index, Cs = swell index, in-situ = in-situ dry unit weight

5.3 Possible Hydrocarbon Contamination

Hydrocarbon contamination was observed (by odor) during the subsurface exploration in BH-3 near the ground surface. No contamination was observed in any other samples. As the area is used for storage, including vehicles, we hypothesize the contamination may be from a leaking vehicle and not due to widespread contamination. Due to the nature of the site and presence of undocumented fill, there is potential for hydrocarbon contamination to be encountered during site excavations.

5.4 Bedrock

Based on the published geologic map of Spearfish by Lisenbee et al (2013), the project site is underlain by bedrock of the Opeche Shale Formation, consisting of shale, siltstone, and sandstone.

Competent bedrock was not encountered during the subsurface exploration; however residuum (residual sandstone and shale) was encountered in all three soil borings at depths ranging from approximately 15.0 to 20.5 feet below the existing ground surface and extended to the termination depths of the soil borings. In the following table we summarize residuum depths.

Table 4: Residuum Summary

Soil Boring Depth to

Residuum Residuum Elevation

BH-1 15.0 ft 3,697.0 ft BH-2 20.5 ft 3,689.5 ft BH-3 17.0 ft 3,693.0 ft

5.5 Groundwater

Groundwater was not encountered during the subsurface exploration; however, zones of increased moisture content were observed and the potential for perched groundwater exists.

Due to the clayey nature of the subsoils and short duration of observation, groundwater is possible at the site.

Groundwater and soil moisture conditions will likely fluctuate in response to seasonal precipitation, runoff, snowmelt, and landscape irrigation. Additionally, concrete slab and asphaltic pavement construction restricts air/soil moisture transfer (evapotranspiration) in arid climates and subsequently increases soil moisture.

5.6 Earthquakes and Seismicity

Area Earthquakes and Seismicity

The Spearfish area is in an area of low seismic activity. Historically two magnitude 2.5 or intensity III and greater earthquakes have been recorded in Lawrence County over the past 100 years (USGS, 2020). The two earthquakes were both located southeast of Spearfish. One event occurred September 5, 1993, was located approximately 5 miles southeast of Spearfish, and had a magnitude of 2.7 as measured on the Richter Scale (USGS 2020). The other event occurred November 5, 1991, was located approximately 10 miles southeast of Spearfish, and had a magnitude of 2.5 as measured on the Richter Scale (USGS 2020).

The faults closest to the site that are thought to be Quaternary age (relatively young and potentially active) is the North Granite Mountains Fault System which is approximately 224 miles to the southwest and is located west of Casper, Wyoming (USGS, 2020).

A maximum horizontal seismic acceleration kh adjusted for site soils of 0.1g is predicted for this site with a uniform likelihood of exceedance of 2 percent in 50 years (SEACAL, 2020).

Design Response Spectrum

Site ground motion accelerations and a design response spectrum were derived in accordance with the general procedure defined in the 2018 International Building Code (IBC) and ASCE 7 – Minimum Design Loads for Buildings and Other Structures. The provisions of the building codes are intended to provide uniform levels of performance for structures, depending on their occupancy and use and the risk inherent to their failure.

Table 5: Site Ground Motion and Design Response Spectrum1.

Parameter Value

Latitude 44.479° Longitude -103.862° Site Class D – Still Soil Profile

SS 0.126

S1 0.04

SMS 0.202

SM1 0.097

Fa 1.6 Fv 2.4

SDS 0.135

SD1 0.065

1.ASCE 7-16

According to the 2018 IBC and ASCE 7, the shop is a Risk Category II structure. Based on the accelerations determined for the site and the Risk Category classification, the structure is assigned to Seismic Design Category “A” as specified by ASCE 7-16.

6.0 ENGINEERING ANALYSES AND RECOMMENDATIONS

6.1 Foundations

The site is underlain by previously placed fill and alluvial terrace deposits overlying residual sandstone and shale bedrock. The fill is predominately composed of a clay-sand-gravel matrix with some larger cobbles. The gravel and cobbles appear to originate from broken limestone bedrock. The alluvial deposit is predominately clay with some shale fragments. The fill and alluvium generally extend to depths of between 15 and 20.5 feet and are potentially problematic due to variable composition and potential for volume changes with increases in loading and changes in moisture contents. As we discussed in Section 5.2, the fill is variable in soil type and

Table 6: Elevation Summary

Soil Boring Ground

Elevation consistency, and we do not have record that the fill was compacted. Inherent to undocumented fill is the potential for burred debris that can decompose over time and loose soil that can settle.

Settlement can result in cracked concrete, broken gypsum board walls, and other structural distress. Again we recommend the existing fill be removed and replaced as structural fill.

The following table compares bedrock and groundwater elevations with anticipated at-grade floor elevations.

Residual Bedrock Elevation

Groundwater Elevation

At-grade Floor

Elevation

BH-1 3,712 ft 3,697 ft NA 3,713.0 ft BH-2 3,710 ft 3,689.5 ft NA

BH-3 3,710 ft 3,693 ft NA

Shallow foundations are acceptable at the site, but only on the condition that subgrade improvement is completed. We recommend overexcavating and replacing the existing fill as compacted structural fill beneath all foundations and floor slabs. Subgrade improvement should consist of soil over-excavation, placement of woven geotextile fabric, and replacement with structural fill.

Footings and foundation walls should be reinforced to resist differential movement.

Consultation with a Structural Engineer to specify adequate reinforcement is recommended.

Steel reinforcement is suggested longitudinally along the top of foundation stem walls. This may reduce cracking if minor settlement occurs.

Local building codes require a minimum of 42 inches of bury for frost protection. Based on a site specific frost depth calculation, frost in the vicinity of the proposed shop may extend as deep as 45 inches. Footings should bear a minimum of 45 inches below finished grade for frost protection or proper frost protection should be implemented.

If some of the existing fill is left inplace, USFWS should anticipate some minor movement and cosmetic cracking over the life of the building.

The 2018 IBC recommends a minimum setback of 15 feet from ascending slopes. The structure should have adequate set back from the slope or incorporate other means of protection from drainage, erosion, and shallow slope failures.

In the following table we summarize foundation recommendations. Additional details and recommendations are provided in subsequent sections.

Table 7: Foundation Recommendation Summary

Footing Design Criteria Recommendations Notes

Perimeter Wall Footings Maximum Allowable

Bearing Pressure

24 inches minimum width, 45 inches minimum below grade

Static Loads (Dead & Sustained Live) 1,500 psf

Transient Loads (Wind & Seismic) 2,000 psf

Column Footings Maximum Allowable

Bearing Pressure Minimum width 36 inches square, 45 inches minimum below grade

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

Thickened Edge SOG Maximum Allowable

Bearing Pressure

18 inches minimum bearing width Static Loads (Dead & Normal Live) 1,500 psf

Transient Loads (Wind & Seismic) 2,000 psf

Maximum Footing Settlement Estimate

Total (in) Differential

(in) Based on a maximum of 325 plf for wall footings and 4.3’x4.3’ interior column footing with a maximum load of 28 kips 1 inch ¾ inch

Subgrade Improvement

If feasible, all undocumented fill should be removed. If unfeasible, subgrade improvement is required

Consists of soil over-excavation, placement of a woven geotextile fabric, and replacement with structural fill

Shallow Foundation System

6.1.1.1 Structural Fill

We recommend removing all undocumented fill from beneath the structure footprint. We under stand USFWS is willing to assume the increased risk of settlement, therefore, we provide reco mmendations for a shallow foundation system (spread footings and slab-on-grade) with subgrade improvement.

We recommend subgrade improvement beneath foundations consisting of over-excavation and replacement with structural (engineered) fill to a minimum depth of 4 feet below the bottoms of the footings. Place the structural fill so that it extends horizontally at least one footing width on the inside and outside of the footings. If subgrade improvement depths greater than the footing width dimension are deemed necessary, the excavation bottom width should be increased by 1 foot on each side of the footing for every additional foot of subgrade improvement. Excavation widths must be wide enough so that compaction equipment can access the bottom of the excavation.

For construction of slab on grade, we recommend that the entire area beneath the slab be over-excavated to a depth of 48-inches and replaced with structural fill. Alternatively, over-excavation and replacement with structural fill may be done under the entire building footprint to the same elevation (whichever is deeper based on the above minimums), depending on practicality and economics.

A thickened edge slab-on-grade may be used instead of a traditional slab-on-grade and footing system. For thickened edge slab-on-grade, subgrade improvement shall consist of over-excavating to a depth of 48 inches and replacing the site soils with imported structural fill.

Under this configuration, a minimum of 20 inches of structural fill is recommended beneath the thickened edge portion of the slab.

As an alternate to the above recommendations regarding subgrade improvement, geogrid reinforced structural fill may be used instead of unreinforced structural fill. This option requires a minimum of 3-feet of reinforced material beneath the entire building footprint and two layers of geogrid.

Partial over-excavation and replacement of the undocumented fill with compacted structural fill will reduce the settlement in the over-excavated zone, but may not significantly reduce total and differential settlement of subgrade materials below the over-excavated zone. The Owner is cautioned that leaving undocumented fill in place beneath the structure may result in unwanted movement over the life of the structure.

Structural fill placed beneath building foundations or floor slabs should be placed in maximum 8-inch loose lifts, moisture-conditioned to near optimum moisture content, and compacted to at least 98 percent of ASTM D698. If density tests taken in the fill indicate compaction is not being achieved, fill should be scarified or removed, moisture conditioned to within +2 percent of the optimum moisture content, and re-compacted and re-tested.

All loose disturbed soil in the base of the over-excavation should be removed from the foundation excavation prior to placement of structural fill. Footings should not be placed on either native clayey soils, undocumented fill, topsoil or soils with high organic content, or un-compacted imported fill. DOWL personnel should observe foundation excavations to confirm subsoil conditions.

Imported (properly moisture conditioned and compacted) 2-inch minus pit run or structural fill may be used as backfill (less compactive effort and ease of constructability are inherent properties of structural fill vs. pit run). The granular material should be compacted using appropriate equipment. Wheel rolling with a bobcat or backhoe is not acceptable. Structural fill or pit run should conform to the requirements in Table 10 and Section 6.1.4.3.

A woven geotextile fabric meeting the following requirements is recommended between the soil exposed in the excavations and structural fill or pit run gravel to reduce migration into the surrounding soil.

Table 8: Woven Geotextile Specifications Property Test Method MARV*

Equivalent or Apparent Opening Size, US Standard Sieve

ASTM D 4751 30-50

Permittivity ASTM D 4491 0.05 sec-1

Grab Tensile Strength ASTM D 4632 250 lbs Elongation, % ASTM D 4632 15 Trapezoidal Tear Strength ASTM D 4533 90 lbs

CBR Puncture Strength ASTM D 6241 750 lbs

UV Resistance (at 500 hrs) ASTM D 4355 70% *Minimum Average Roll Values

6.1.1.2 Bearing Capacity and Settlement

Net allowable bearing capacity for shallow foundations on granular structural fill is provided in Table 7: Foundation Recommendation Summary. In addition to the bearing capacity requirements, continuous footings should not be less than 24-inches in width. Isolated footings should not be less than 36-inches square. For thickened edge slab-on-grade, the bearing width of thickened edges should not be less than 18 inches wide.

Based on detailed settlement analysis the anticipated total settlement for the building is on the order of 1 inch and the differential settlement is approximately ¾ of an inch. Although this exceeds project tolerances, we believe post construction settlements will be within project tolerances. Estimated settlements are based on maximum wall loads of 325 plf and maximum c olumn loads of 28 kips. Actual settlement will depend on final loads and footing dimensions.

These estimates do not include settlement that may result from the undocumented fill.

Allowable loads may include full dead load and design live load. Allowable bearing capacity may be increased by one-third when considering total loads that include wind or seismic loads.

DOWL geotechnical personnel should observe all footing excavations to confirm subsoil conditions.

Slab-On-Grade Cracking of slabs-on-grade is difficult to control and should be expected to occur with time.

Cracking may be the result of many factors such as concrete shrinkage and daily and seasonal variability in temperature and humidity and not necessarily the result of soil movement.

Interior slabs-on-grade should be a minimum of 4 inches thick. A vapor retarder (usually plastic) is suggested beneath the slab, underlain by 4 inches of clean drain gravel. Gravel shall be 1-inch minus with less than 2% passing the #200 sieve. 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. In the event of water accumulation below floor slabs, the gravel bed may also act as a drainage layer. Slab-on-grade construction should be consistent with local codes.

Compacted structural fill is required below slabs as outlined in Section 6.1.1. Wall systems (load bearing and non-load bearing) should be separated and not directly tied to slabs-on-grade.

Slabs constructed on properly compacted imported granular fill may be designed for a modulus of subgrade reaction of 175 psi per inch.

Exterior concrete flatwork often moves in response to changes in temperature and soil moisture, or freeze/thaw cycles. At a minimum, soils beneath exterior concrete should be over-excavated and replaced with structural fill to a depth equal to the concrete thickness. As an alternate, over-excavation to a depth of 12 inches followed by replacement with structural fill may further reduce potential slab movement. Granular materials placed below slabs should be graded to drain. Exterior slabs should be separated from foundation elements. Movement of exterior slabs may be transmitted to the foundation walls, resulting in damage. Additionally, exterior columns should not bear on exterior slabs to reduce slab movement being transferred to the structure. If supporting vehicles, slabs-on-grade should be a minimum of 6-inches thick.

Lateral Loads on Foundation Walls

Lateral pressures were calculated using methods suggested by Bowles (1996) and estimated strength parameters for structural fill used as backfill. As discussed above, the Spearfish area is potentially susceptible to low to moderate ground shaking from earthquakes. A maximum horizontal seismic acceleration kh in bedrock of 0.1g is predicted for this site with a uniform likelihood of exceedance of 2 percent in 50 years (SEACAL, 2020). One-half of the maximum acceleration, or 0.05g, was used to estimate lateral loads during an earthquake (Hynes and Franklin, 1984; Whitman, 1990). Equivalent fluid pressures (K) were calculated for active, passive, and at-rest conditions for level ground adjacent to the foundation. It should be noted that the following lateral loads do not include a factor of safety and do not apply to submerged soils or hydrostatic loading.

Table 9: Lateral Loads Condition Coefficient of Earth Pressure K (equivalent fluid pressure)

Static Condition Level Backfill

Ko = 0.44 Ka = 0.28 Kp = 3.54

57 pcf 37 pcf

460 pcf

Earthquake Condition Level Backfill Ka = 0.31

Kp = 3.44 40 pcf

447 pcf

**assumes soil unit weight of 130 pcf, internal friction angle 34°

The Mononobe-Okabe equations are often used to estimate dynamic forces against retaining walls. The Mononobe-Okabe equations were applied using one-half the maximum horizontal acceleration. The dynamic component is estimated as ½ the difference of Kae – Ka. This force would be in addition to static active earth pressure, and is equivalent to 1.5H2 pounds per horizontal foot of wall applied at 50% of the wall height (H/2) above the base.

6.1.3.1 Soil Friction Factor

Based on published data (NAVFAC, 1986), a maximum value of 30 degrees for the friction angle along a concrete base in granular soils is appropriate. Accordingly, a friction value of 0.58 is suggested. A friction factor of 0.30 is suggested to calculate soil friction for design of foundation walls in contact with any fine-grained soils in the subgrade. The friction value may be combined with the passive pressure to resist horizontal loads.

Earthwork

6.1.4.1 Site Clearing and Subgrade Preparation

Site preparation should consist of stripping the existing vegetation and loose surficial materials from the proposed site. This should include removal of all topsoil and other deleterious materials.

All exposed subgrade surfaces should be free of mounds and depressions which could prevent uniform compaction. If unexpected fills or obstructions are encountered during site clearing or excavation, such features should be removed and the excavation thoroughly cleaned prior to backfill placement and/or construction. Removal of previously placed undocumented fill is recommended to facilitate long term performance of the structure.

All exposed soils that will receive fill materials should be scarified to a minimum depth of 6 inches, conditioned to near optimum moisture content, and re-compacted to 95% of ASTM D698.

All excavations should be observed by DOWL prior to fill or concrete placement.

6.1.4.2 Excavation

Based on the materials encountered in the soil borings, conventional earthmoving equipment should be capable of excavating the site soils. Depending on the time of year, groundwater or very moist soil conditions from capillary rise may be encountered at planned excavation depths.

Soft, wet soil conditions may make foundation construction difficult. To improve construction conditions, a woven geotextile meeting the requirements of Table 8 may be placed at the base of foundation excavations and beneath floor slabs. Structural fill should be placed over the fabric.

Temporary dewatering may be required during installation of structural fill. If groundwater is present at the time of construction, we strongly recommend dewatering prior to foundation construction. Dewatering may require installation of sumps, shallow wells, or well points. The groundwater surface elevation should be controlled to a minimum of 2-feet below the bottom of all excavations to ensure proper compaction of natural subgrade and structural fill. All excavations should be approved by a qualified observer prior to backfill placement.

All 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 majority of the soils at the site are classified as Type C using the OSHA classification system, however soil types may vary over large project areas. Type C soils require excavation slope angles not to exceed 1 ½ H: 1 V (horizontal to vertical).

6.1.4.3 Fill Material

In general, onsite materials, including alluvium, topsoil, fill, and random debris, are not acceptable as structural fill. Site soils, excluding organic topsoil and debris, may be used for general site grading only. Granular site soils that do not meet structural fill requirements, but classify as GC, GM, GC-GM, SC, SM, or SC-SM may be utilized as non-structural backfill.

Structural fill should consist of well-graded sand and gravel mixtures conforming to the following requirements or be approved by the project Geotechnical Engineer.

Table 10: Structural Fill Recommendations Gradation Percent finer by weight

2-inch 100 No. 4 Sieve 35–75

No. 200 Sieve 15 maximum Liquid Limit/Plasticity Index 25/10 maximum Uniformity Coefficient, Cu > 4 (Gravel)

> 6 (Sand) Coefficient of Gradation, Cc Between 1 & 3

LA Abrasion Loss 40 max

Non-frost susceptible soils (if required) should meet the following requirements and should only be utilized in areas approved by the geotechnical engineer:

Table 11: Low Frost Susceptibility Recommendations

Frost Group Soil Description Percent Finer than

0.02 mm

USCS

Classification

FG-1 Gravelly Soils 3 to 10 GW, GP, GW-GM, GP-GM

6.1.4.4 Fill Placement and Compaction

Compaction requirements for imported material used as structural fill should conform to Section

6.1.1. Compaction recommendations are summarized in the following table.

Table 12: Compaction Recommendations

Application Moisture Content (% of optimum)

Minimum Compaction

Subgrade +/-2 95% ASTM D698 Below Foundations +/-2 98% ASTM D698

Below Slabs-On-Grade +/-2 98% ASTM D698 Base and Subbase Courses +/-2 95% ASTM D698

Utility Trenches +/-2 95% ASTM D698 Site Grading Fill (non-structural) +/-2 92% ASTM D698

Foundation Backfill +/-2 95% ASTM D698

Non-structural exterior backfill should be compacted to 92% of maximum dry density as per ASTM D698. Site grading fills are not considered structural. It is important to keep all fills free of construction debris, organics, frozen lumps, and other deleterious materials. Fills should be observed and documented during placement by a representative of DOWL. Fills placed beneath adjacent sidewalks or hardscapes are considered structural and should be compacted in accordance with Section 6.1.1

Additionally, exterior backfill should be over-constructed (higher elevations) to maintain required grading if minor settlement/consolidation of the fill occurs. Care should be taken adjacent to uncured foundation concrete. Over compaction adjacent to uncured concrete may lead to foundation damage and cracking. Under no circumstances shall fill be placed using “hydro-compaction” methods. Excessive water may damage foundation elements.

Site Grading and Surface Water Control

Surface water must not be allowed to accumulate and infiltrate soil near foundations. It must be controlled and directed away from the structures.

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

Per the 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 2% away from the structure. The sloped ground should be initially constructed at a greater slope to account for settlement/consolidation of exterior backfill.

Within ten feet of the foundation, the upper 12 to 18 inches of backfill should consist of less permeable, compacted fine-grained soil (silts and clays).

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 percent, downward, away from the building.

Install eve gutters, downspouts, and extensions such that they dispose of water a minimum of 5 feet away from the structure and beyond all backfill zones.

Do not irrigate within 5 feet of the building. Periodically inspect and flush irrigation systems to detect potential leaks and avoid saturation of foundation backfill.

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.

The area around the foundation should be inspected regularly by the owner– particularly after a rainstorm – to determine if proper drainage away from the structure has been maintained. Post construction changes in site grading by landscapers or owners are a persistent and often damaging problem. It is the owner’s responsibility to control water and maintain the site to prevent infiltration near foundations.

Low-water consumption groundcover are recommended to further reduce the risk of water infiltration near the foundation walls.

Foundation Drains

Current building codes, such as the International Building Code (IBC), require perimeter drains in moderate to low permeability soils, for habitable space below grade. Depending on site specific conditions and construction techniques, case studies may be presented that show both positive and negative consequence of foundation drain installation. If installed correctly, drains may significantly reduce seepage and damage to foundation elements, and are likely to be significantly more costly to install following construction.

If installed, foundation drains may consist of a prefabricated composite drain or perforated PVC pipe encased in a gravel envelope encompassed in a non-woven geotextile. Drains should be located at or below the area to be protected and the gravel envelope should extend a minimum of 1-foot beyond the foundation and 6 inches above the footing.

A properly installed foundation drain should be installed to drain the soil beneath the structural fill below the footing, follow the entire perimeter of the structure, and be sloped to either a sump or daylight down gradient from the structure to prevent saturation of subgrade soils in the vicinity of the footings.

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. Discharge of an interior sump or daylighted pipe should be away from foundation elements and backfill zones.

6.2 Utility Excavations

Based on the materials encountered in the soil borings, conventional earthmoving equipment should be capable of excavating the site soils along the utility alignments. Areas of shallow bedrock may require special excavation methods such as rippers or hammers. Site soils, excluding organic topsoil and debris, may be used for backfill in areas where trench settlement can be tolerated. All other areas should be backfilled with material meeting the recommendations shown in Table 10 or otherwise approved by the Geotechnical Engineer.

Compaction requirements for trench backfill should conform to Section 6.1.4.4.

Depending on the time of year, groundwater or very moist soil conditions from capillary rise may be encountered at planned excavation depths along the alignment, particularly in areas within close proximity to drainages. We strongly recommend dewatering in all areas where wet or saturated soil conditions are encountered prior to utility line installation. Dewatering may require installation of sumps, shallow wells, or well points. Groundwater must be lowered below the trench bottom to allow for compaction of bedding material. All excavations should be approved by a qualified observer prior to backfill placement.

Trench floor instability may include soft or yielding conditions due to saturated clay soil, or by loss of support of granular soils due to saturated conditions. Generally, trench floor instability is not a problem if groundwater is not present. Instability can be minimized by properly dewatering prior to excavation. If saturated granular soils are encountered, the trench should be dewatered to a minimum of 2-feet below the trench bottom elevation and the granular soils compacted or replaced with suitable backfill materials. If soft or yielding clay soils are encountered, the clay should be removed from the trench and replaced with suitable backfill materials. Alternately, trench floor instability may be limited by over-excavation of the trench bottom an additional 2-feet followed by replacement with pit run structural fill. A separation/stabilization fabric is recommended at the base of the 2-foot over-excavation to prevent fines migration into the pit-run gravel. A woven fabric meeting the requirements of Table 8 is recommended.

Where excavations are dewatered from within the trench, the trench floors and walls will remain saturated, increasing the risk for trench collapse.

Observation wells may be needed to monitor water levels prior to construction and anticipate water conditions that may be encountered during trench excavation.

All 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 majority of the soils at the site are classified as Type C using OSHA classification system, however soil types may vary over large project areas. Type C soils require excavation slope angles not to exceed 1½ H: 1 V (horizontal to vertical).

Due to space constraints or to minimize excavation extents, trench boxes may be utilized.

Trench boxes must conform and be utilized according to OSHA regulations.

In locations where the proposed utility alignments are near existing structures or roadways temporary shoring may be required. If temporary shoring is required, shoring methods should be designed by a Professional Engineer registered in the State of South Dakota.

6.3 Pavement Design

Multiple pavement section alternatives are provided for the proposed shop. Design criteria are based on soil boring observations and field and laboratory classification of soil types. Design methodologies are consistent with methods suggested in AASHTO Guide for Design of Pavement Structures, 1993. The AASHTO Low Volume Roads method has been utilized.

If soil conditions vary from those observed in soil borings, DOWL should be notified and provided an opportunity to review design assumptions.

Subgrade soils encountered between 2 to 5 feet below the proposed pavement…