05. SFC Appendix B - Geotechnical Evaluation.pdf

FMG ENGINEERING 3700 Sturgis Road • Rapid City, SD 55702 • fmgengineering.com • 605-342-4105

Civil Engineering Geotechnical Engineering

Materials Testing Laboratory i Land Surveying

Environmental Services Water Resources

October 8, 2020

Mr. Karsh Pandey, PE, SE Burns & McDonnell Engineering Company, Inc.

9785 Maroon Circle, Suite 400 Centennial, Colorado 80112

Re: Geotechnical Evaluation WAPA Vehicle Maintenance Facility Brandon, SD

Dear Mr. Pandey:

As requested, we have performed a geotechnical evaluation for the referenced project. The purpose of this evaluation was to identify the subsurface characteristics, suggest suitable foundation systems for the proposed structure and provide the geotechnical design parameters.

The findings and recommendations of this report were prepared in accordance with generally accepted professional engineering principles and practices. We make no other warranty, either express or implied.

We trust this information to be sufficient. If you have any questions or desire any additional information, please do not hesitate to contact us.

Respectfully submitted, FMG Engineering

Alex Fisher, P.E.

Enclosures c: Z:\200903 BMcD-WAPA SF Maintenance Bldg Geotech\Geotech

APPENDIX B

Geotechnical Engineering Materials Testing Laboratory ii Land Surveying Environmental Services Water Resources

FMG Engineering ♦ 3700 Sturgis Road ♦ Rapid City, SD 57702 ♦ 605.342.4105 ♦ fmgengineering.com

Geotechnical Engineering

Materials Testing Laboratory Land Surveying

Environmental Services Water Resources

Geotechnical Evaluation for

Western Area Power Administration

Vehicle Maintenance Facility Brandon, South Dakota

October 8, 2020

Prepared for Burns & McDonnell Engineering

Company, Inc.

9785 Maroon Circle, Suite 400

Centennial, Colorado 80112

FMG Project No. 200903 i

TABLE OF CONTENTS

SECTION PAGE

TABLE OF CONTENTS & LIST OF FIGURES .........................................................................................................i, ii

1. INTRODUCTION

2. FIELD SAMPLING AND TESTING PROCEDURES

3. LABORATORY ANALYSIS

3.1 ATTERBERG LIMITS

3.2 GRAIN SIZE ANALYSIS DATA

3.3 CONSOLIDATION ANALYSES

3.4 UNCONFINED COMPRESSION TESTING

3.5 MOISTURE-DENSITY RELATIONSHIP

3.6 CALIFORNIA BEARING RATIO ANALYSIS

3.7 SOIL CHEMICAL ANALYSIS

3.8 SAMPLE STORAGE

4. SITE CONDITIONS

4.1 MATERIALS PRESENT

4.1.1 Material Descriptions

4.2 GROUNDWATER TABLE

4.3 GEOLOGIC CONDITIONS

5. CONCLUSIONS AND RECOMMENDATIONS

5.1 FOUNDATION AND FLOOR SYSTEM SELECTION

5.1.1 Floor System

5.1.2 Foundation System

5.1.3 Shallow Foundation and Slab-on-Grade Systems

5.2 SITE SEISMICITY

5.3 GENERAL MATERIAL PLACEMENT REQUIREMENTS

5.3.1 Fill Materials

5.3.2 Fill Placement

5.3.3 Utility Trench Backfill

5.4 RETAINING STRUCTURES AND LATERAL EARTH PRESSURES

ii

5.5 EXCAVATIONS, SHORING AND SITE GRADING

5.5.1 Excavations and Shoring

5.5.2 Site Grading

5.6 GENERAL DESIGN AND CONSTRUCTION PROVISIONS

5.7 EXTERIOR CONCRETE FLATWORK

5.8 SOIL CORROSIVITY

5.9 PERCOLATION TESTING AND SOIL INFILTRATION

5.10 PAVEMENT THICKNESS DESIGN

5.10.1 Flexible Pavement

5.10.2 Rigid Pavement

5.10.3 Subgrade and Design Criteria

5.10.4 Pavement Subgrade Preparation

5.10.5 Aggregate Base

5.10.6 Hot-Mix Asphalt (HMA) Pavement

5.10.7 Portland Cement Concrete (PCC) Pavement

5.10.8 Potential Pavement Heave

6. PROJECT OBSERVATION AND CONSTRUCTION QUALITY ASSURANCE

7. CONCLUDING STATEMENT

TABLES, FIGURES AND APPENDICES

TABLE 1 –SHALLOW FOUNDATION AND SLAB-ON-GRADE DESIGN CRITERIA

TABLE 2 - SEISMIC DESIGN CRITERIA

TABLE 3 - SOIL COMPACTION CRITERIA

TABLE 4 - EQUIVALENT FLUID PRESSURES

TABLE 5 - SOIL CORROSIVITY TESTING SUMMARY

TABLE 6 – SOIL CORROSIVITY RATINGS

TABLE 7 – SOIL INFILTRATION PARAMETERS

TABLE 8 - RECOMMENDED PAVEMENT SECTIONS

TABLE 9 - RECOMMENDED FREQUENCY OF TESTING

iii

FIGURE 1 ............................................................................................................ BOREHOLE LOCATIONS

FIGURE 2 ......................................................... CLASSIFICATION OF SOILS FOR ENGINEERING PURPOSES

APPENDIX A .................................................................................................................. BOREHOLE LOGS

APPENDIX B ....................................................................................................... LABORATORY TESTING

APPENDIX C ........................................................................................ PERCOLATION TESTING RESULTS

APPENDIX D ........................................................................................................................ REFERENCES

WAPA Vehicle Maintenance Facility

Brandon, SD

1. INTRODUCTION

A new vehicle maintenance facility is proposed for construction at the existing Western Area Power (WAPA) compound at 4400 North Timberline Avenue in Brandon, South Dakota.

The facility will consist of a new pre-engineered metal building with four drive-in bays with the potential for a future drive-through bay. The future drive-through bay will include a pavement apron on each side. Column live loads are anticipated to be on the order of 50 kips.

Finished floor elevations are anticipated to be within 1 foot of existing grades.

The project will also include paved site access and maintenance roadways and the installation of an on-site wastewater treatment system.

FMG Engineering (FMG) was retained by Burns & McDonnell Engineering Company (B&M) to perform a geotechnical evaluation of the of the project site to identify the subsurface conditions, suggest suitable foundation systems for the new structure and provide geotechnical design parameters. If proposed construction or locations differ significantly from that described above or elsewhere described in this report, our office should be contacted to re-evaluate the recommendations contained in this report. Figure 1 illustrates the specific locations of our field explorations.

This report presents our geotechnical evaluation of the project site. Our evaluation included the following general scope of activities:

1. A general review of the regional geology, and related site characteristics.

2. Field exploratory borings, sampling, and testing at representative locations to determine the depth, thickness, orientation, engineering characteristics, and composition of the subsurface conditions.

3. Laboratory tests to identify the soil types, classifications, and engineering properties of the subsurface materials encountered at the site.

4. An analysis of the data obtained, and determination of suitable geotechnical design parameters and other such recommendations as considered applicable to satisfactory design and performance.

Field and laboratory tests were generally accomplished in accordance with current ASTM, AASHTO and IEEE procedures, where applicable. The evaluation was accomplished under the direction of a registered professional engineer. This report presents the geotechnical engineering evaluation with recommendations for foundation design. We have also included a discussion of our field sampling and testing procedures, laboratory analyses, and site conditions.

2. FIELD SAMPLING AND TESTING PROCEDURES

A total of six (6) boreholes were drilled at the locations shown on Figure 1 to identify the subsurface characteristics and obtain soil samples for laboratory testing. The boreholes were observed by the FMG field geologist. Field sampling and testing procedures were conducted in general accordance with ASTM D420.

The number of boreholes and the location were selected by B&M and were adjusted in the field as necessary by FMG to avoid existing utilities. If, during subsequent planning, the project locations change significantly from those described in this report and shown on Figure 1, we recommend drilling additional boreholes to verify soil conditions in unexplored areas.

The borehole locations are summarized on Table 1 below.

Borehole field testing consisted of obtaining standard penetration test (SPT) and relatively undisturbed Shelby Tube samples from various depths in the boreholes. The SPT testing was performed to identify the relative field strengths of the subsurface materials and to obtain samples for laboratory analyses; the Shelby Tube samples were obtained for laboratory analyses.

The SPT testing was performed with an auto hammer with an estimated hammer efficiency of 80%. The SPT N-Values presented on the borehole logs are field measured values for the auto hammer and may be adjusted to N60 values by multiplying by a factor of 1.33.

(Thusyanthan & Nawaz, 2017)

Geologic logs of the boreholes were maintained by a field geologist and the materials were classified in accordance with ASTM: D 2487-90 and D 2488-90 (Unified Soil Classification System), Figure 2. The geologic logs include the general drilling method data, depths of major changes in the character of the subsurface materials, visual description of the materials, sample locations, standard penetration data and locations, and groundwater data. In addition, the geologic logs also include the data from certain laboratory classification and physical property analyses. The geologic logs are presented as Appendix A.

The geologic logs and related information depict only the conditions and materials encountered at the specific borehole location and at the particular time designated on the logs.

Soil conditions at other locations may be different from those encountered at the borehole locations. Also, the passage of time may produce a changed soil condition. We have extrapolated the data obtained from the boreholes and our conclusions and recommendations assume that the materials encountered are representative of the soils that exist over the site.

Anomalies may be present around the boreholes.

3. LABORATORY ANALYSIS

The laboratory analysis was directed towards the determination of soil types drilled on the site and their engineering properties. The laboratory testing was performed in general conformance with current ASTM and AASHTO procedures, where applicable. The laboratory testing results are provided in Appendix B, and on the borehole logs where applicable.

3.1 ATTERBERG LIMITS

The Atterberg limits were determined for select samples. These tests allow for more detailed classification of soils and provide information relative to the expected engineering characteristics and properties. (ASTM D4318-05)

3.2 GRAIN SIZE ANALYSIS DATA

Standard grain size analysis determinations were performed to determine the grain size distribution and assist in the determination of the physical characteristics and engineering properties of the subsurface materials. (ASTM D422-63(2007))

3.3 CONSOLIDATION ANALYSES

Consolidation/swell tests were performed on relatively undisturbed samples that were obtained from the soil encountered at the site. The consolidation/swell test allows determination of the soil's swell pressure, percentage of swell, collapse potential, and approximate volume change potential with varying moisture conditions. The data from the consolidation/swell test can be used to develop potential uplift pressures or consolidation characteristics which may affect the performance of the foundation. (ASTM D2435)

3.4 UNCONFINED COMPRESSION TESTING

In order to help quantify the strength characteristics of the on-site materials, unconfined compression testing was performed on select samples. The unconfined compressive test results provide indications of the strength of the soils. Results are provided in pounds per square foot (psf). (ASTM D7012)

3.5 MOISTURE-DENSITY RELATIONSHIP

A moisture-density relationship test, or Proctor test, was performed on a bulk soil sample obtained from the site. The moisture-density relationship test indicates the maximum soil density that can be achieved in each soil type with various moisture contents. (ASTM D1557)

3.6 CALIFORNIA BEARING RATIO ANALYSIS

California Bearing Ratio testing was performed on bulk soil samples obtained from the site.

The California Bearing Ratio test results are used in pavement thickness designs to indicate the strength of the subgrade soils. (ASTM D1883)

3.7 SOIL CHEMICAL ANALYSIS

To assess corrosivity to concrete and steel, select soil samples were tested for pH, Chlorides, Soluble Sulfates, Electrical Resistivity, Redox Potential and Sulfides. The results of the chemical analysis are presented in Appendix B and discussed in Section 5.9. (ASTM G200-

09, EPA SW846 9045C, SM 4500)

3.8 SAMPLE STORAGE

The soil samples obtained during this evaluation will not be stored. If the client wishes to receive the samples arrangements should be made; otherwise the samples will be discarded.

4. SITE CONDITIONS

The project site is located at the existing WAPA Sioux Falls Substation facility at 4400 North Timberline Avenue in Brandon, South Dakota. Specifically, the proposed project site is located approximately 150 feet south of the southwest corner of the existing substation fence in an open, vacant area. The site is relatively flat with a slight slope to the southeast.

Vegetation at the site consists of short grass and several deciduous trees. Multiple overhead transmission lines transect the area.

The site is generally bound by railroad tracks to the south, open space to the east and west, and the existing Sioux Falls Substation to the north. No natural or manmade drainage features were noted at the site.

4.1 MATERIALS PRESENT

The stratigraphy of the project site generally consists of generally unstratified lenses of clay, gravel, sand and silt which extend to the total depths explored. The clay, gravel and sand lenses ranged in thickness from several feet to over 15 feet.

4.1.1 Material Descriptions

The lean clay soils were found to be brown, dry to moist, medium plastic, and medium stiff to stiff in consistency. The clay soils were found to have a low expansive potential, exhibiting up to 1.3% swell upon saturation against a 100 psf surcharge with a swell pressure of approximately 3.6 ksf. The clay soils were also found to exhibit Liquid Limits on the order of 25 to 41 and Plasticity Indices on the order of 17 to 19, also indicating expansive potential.

The sandy soils were found to be brown, dry to moist, low to non-plastic, dense and contained a variable silt and clay fraction. The gravels were found to be brown, dry to moist, non-plastic and dense.

The geologic logs indicate the specific soil characteristics observed throughout the profiles in each of the boreholes advanced at the site.

4.2 GROUNDWATER TABLE

A shallow groundwater table was encountered at the site at depths ranging from 22.5 to 24 feet below existing grades. However, groundwater presence and levels should be anticipated to vary in response to seasonal changes in precipitation, bedrock fracture patterns, high precipitation events, and snow melt, and may not be accurately delineated within the normal scope of a geotechnical evaluation.

4.3 GEOLOGIC CONDITIONS

The specific geologic conditions of the site can be described as a thin layer of alluvial sediments underlain by generally unstratified glacial till. Available geologic mapping indicates a till thickness of approximately 65 feet. Underlying the till is the Split Rock Creek Formation, a siltstone, claystone, chert, shale and clay formation of Late Cretaceous age.

(Tomhave, 1994)

Available geologic mapping of the area does not indicate faulting or significant geologic structures which may impact siting, design or performance of the proposed project.

(Tomhave, 1994)

5. CONCLUSIONS AND RECOMMENDATIONS

From our subsurface exploration and engineering analysis, we have arrived at the following conclusions and have the following recommendations with regard to foundation design for the proposed construction. The conclusions and recommendations presented in this report do not reflect variations in subsurface conditions that are likely to exist in unexplored areas.

Should such variations be revealed during construction, it may be necessary to re-evaluate our recommendations based upon on-site observation of the variations. Also, we should be retained to review the foundation plans, as well as applicable portions of the specifications when they become available.

5.1 FOUNDATION AND FLOOR SYSTEM SELECTION

5.1.1 Floor System

The near surface clayey subgrade soils at anticipated floor slab subgrade elevations were found to be expansive, exhibiting up to up to 1.3% swell upon saturation against a 100 psf surcharge with a swell pressure of approximately 3.6 ksf as determined by laboratory testing (ASTM 2435). The clay soils were also found to exhibit Liquid Limits on the order of 25 to 41 and Plasticity Indices on the order of 17 to 19. Soils are typically considered to have an expansive potential at Liquid Limits over 30 to 50 and a Plasticity Index of over 18. (Holtz, 1950) (Snethen, 1984)

The potential heave of floor slabs founded directly upon the site soils was estimated by considering a depth of potential moisture variation of 5 feet for interior floor slabs, a minimum floor slab dead load of approximately 50 psf, and laboratory swell potential and swell pressure testing. Based on this information, potentially damaging heave on the order of 0.75 inches for the floor slab are possible if the subgrade soils are exposed to moisture variations during the post-construction service life of the building.

Because of the elevated risk for floor system-related building distress related to expansive soils, we recommend that structure floor slabs be founded on an engineered fill section which replaces a thickness of expansive soil with non-expansive material. To reduce potential heave of the floor slab to less than 0.5 inches, the engineered fill section should be a minimum of 2 feet in thickness.

The use of an engineered fill section will serve to mitigate post construction movements of slabs-on-grade at the site but will not eliminate risk of movements. Some minor movements of slabs-on-grade are possible due to inherent, natural variations in native soils and geologic materials. Minor movements can still result in cosmetic distress to architectural building components, floors, drywall, etc.

5.1.2 Foundation System

Based on an assumed finished floor elevation of approximately 1365, dense sands and gravels will be present at anticipated shallow foundation bearing elevations and will be suitable to support moderately to highly loaded shallow foundations.

Foundation settlement due to consolidation of the subgrade soils in response to building loads is anticipated to be less than 1-inch total and ½ inch differential across the building footprint.

The design parameters and construction criteria presented in Section 5.1.3 should be observed for shallow foundation and slab-on-grade floor systems.

It should be noted that the settlement and heave values obtained from these analyses are subject to the inherent variability of the soil profile and idealized methods used in the analysis. It is not uncommon for actual movements to vary from estimates based on accepted geotechnical methodologies by ± 50 percent. Although the potential movement values presented in this report have been rounded to the nearest ¼ inch for presentation purposes, the client is cautioned that the accuracy of these estimates could likely vary. The actual magnitude of movement that will occur beneath the foundation or floor system will depend on the inherent variability of soil mineralogy and profile, the actual in-service loading conditions, the extent to which the subgrade soils are exposed to moisture variations, and the quality of the earthwork and foundation preparation procedures.

Brandon, SD

5.1.3 Shallow Foundation and Slab-on-Grade Systems

Table 1 –Shallow Foundation and Slab-on-Grade Design Criteria

Parameter Value

Subgrade Preparation Scarification and recompaction of subgrade below foundations and overexcavation and installation of 2-foot engineered fill section below slabs-on-grade.

Net Allowable Bearing Capacity (FS=3.0) 2,500 psf

Static/Dynamic Modulus of Subgrade Reaction 150 pci for foundation subgrade

200 pci for slab subgrade

Frost Depth (City of Sioux Falls) 42 inches

Sliding Friction Coefficient 0.40

Passive Earth Pressure 245 psf

5.1.3.1 Design and Construction Criteria

1. We recommend all existing soils below shallow foundations be scarified to a minimum depth of 8 inches and recompacted in accordance with the soil compaction criteria provide in Table 3. Should clay soils be present at foundation subgrade elevations, the clay soils should be overexcavated down to native granular soils and replaced with properly compacted engineered fill.

2. We recommend all existing soils below slabs-on-grade be overexcavated, or new site fill materials placed, to allow a minimum depth of 2 feet of engineered fill below slab bearing depth. The engineered fill should meet the requirements outlined in Section

5.3 of this report and be compacted in accordance with the soil compaction criteria provided in Table 3. The Geotechnical Engineer shall observe the overexcavation process to verify removal extents are sufficient.

3. All fill materials necessary within the building footprint should consist of properly compacted engineered fill.

4. If soft conditions are encountered at the base of the foundation or slab excavations, the excavation should be overexcavated to stable conditions as directed by the

Geotechnical Engineer. As directed by the Geotechnical Engineer, the additional overexcavation should be replaced with properly compacted engineered fill or stabilization rock meeting the requirements outlined in Section 5.3.1 of this report.

The engineered fill should be compacted in accordance with Table 3. If utilized, stabilization rock should be used to the extents necessary to provide a stable subgrade, above which properly compacted engineered fill should be installed up to foundation or slab bearing elevation. Any stabilization rock should be covered with a non-woven filter fabric prior to placement of engineered fill.

5. Compacted fill placed against the sides of the footings to resist lateral loads may be moisture-conditioned, on-site soil. The fill should be placed in accordance with the fill and soil compaction criteria provided in Table 3.

6. Precipitation events or fluctuations in groundwater levels could cause the base of the foundation excavations to be within the range of possible groundwater fluctuations.

Dewatering efforts may be necessary. It may be necessary to install sump pits and dewater the excavations to allow proper excavations, fill placement, subgrade preparation and foundation construction. We recommend that the contractor obtain the necessary permits for the dewatering operations and that the dewatering be performed in accordance with local, county, state, and federal regulations.

7. Care should be exercised during slab excavation as to not disturb the excavation subgrade. We recommend that an excavator with a smooth cutting edge be utilized as excavations near designed depths. Should the excavation subgrade be disturbed, we recommend that the excavation subgrade be scarified to a depth of 8 inches, moisture conditioned and recompacted in accordance with the criteria provided in Table 3 of this report prior to placement of concrete, reinforcing steel or engineered fill to provide a uniform subgrade.

8. Debris, fills, utilities and other relics associated with past site developments may be encountered during excavations within the building footprint. If encountered, such items should be removed in their entirety and the resulting voids should be backfilled with properly compacted engineered fill meeting the material and compaction requirements of Section 5.3 of this report.

9. The natural soils may pump or deform excessively under the wheel loads of heavy construction vehicles as the excavations approach footing levels. Construction equipment should be as light as possible to avoid this difficulty. The movement of vehicles over proposed foundation or floor areas should be restricted. Any areas disturbed by construction traffic should be stabilized or over-excavated and replaced with stabilization rock or compacted engineered fill.

10. Due to the presence of expansive soils at the site, foundation and floor slab subgrade materials should not be allowed to desiccate or become saturated during construction.

Time of exposure to the elements should be limited to the greatest extents practical for the native subgrade materials. Should the native subgrade become desiccated prior to placement of engineered fill, the subgrade should be moisture conditioned and recompacted before placement of engineered fill. While exposed during construction, foundation and floor slab excavations should be protected from stormwater run-in via berms or other methods.

11. Where possible, floor slabs should be separated from all bearing walls and columns with expansion joints, which allow unrestrained vertical movement.

12. Floor slabs should be provided with control joints to reduce damage due to shrinkage cracking and should be adequately reinforced.

13. A positive bond break should be provided where utility lines enter through the floor.

Flexible connections, oversized sleeves at wall and floor penetrations or other such mechanical controls should be provided for slab-bearing mechanical equipment.

Such controls should be designed to accommodate up to 1 inch of potential movement.

14. The sub-slab engineered fill section should be extended to any exterior concrete flatwork that may be sensitive to differential or total vertical movements.

15. Materials immediately below the slab should consist of properly compacted engineered fill meeting the requirements of Section 5.3 or a free-draining gravel or sand leveling course. In no case should clay soils be placed directly below the floor slab. If floor coverings are, or have the potential to be, moisture or vapor sensitive, a vapor membrane is recommended below the floor slab. The membrane should be a 10-mil polyethylene material, or equivalent as approved by the Geotechnical Engineer.

A qualified Geotechnical Engineer should observe all footing excavations prior to concrete placement. A representative of the Geotechnical Engineer should perform compaction testing during any moisture-conditioned fill placement.

We suggest that final testing of the floor slab area be performed (in addition to testing during placement) immediately before concrete placement to determine the integrity of the materials. Severe changes in the condition of these materials can occur after initial preparation as the result of rain, drying, freezing, and construction activities. Any subgrade or foundation material that becomes disturbed, desiccated or does not conform to the moisture content and compaction requirements indicated in Table 3 should either be removed and replaced or reworked to meet these recommendations.

Regarding the concrete floor slab, it should be noted that Portland cement concrete is not a perfect construction material. Due to the characteristics of Portland cement concrete itself, cracking of the floor slab may occur. Cracking will be minimized, but not eliminated, by providing appropriate control, isolation, and construction joints. Drying and thermal shrinkage of the slabs with resultant hairline cracking or curling may occur if the slabs are cured under anything less than optimum curing conditions. In short, there is no practical method of ensuring that all floor slab cracking is eliminated due to the nature and performance of the Portland cement and the consolidation properties of the subgrade soils.

5.2 SITE SEISMICITY

Seismic design should be in accordance with the ASCE 7-16 seismic design parameters provided below. The Seismic Site Class indicated below in Table 3 assumes the soil conditions encountered at the bottom of the borings continue to a depth of 100 feet. A more detailed and accurate Site Class evaluation may be achieved by performing geophysical seismic surveys to develop the shear wave velocity profile for the site to a depth of 100 feet.

Table 2 - Seismic Design Criteria

ASCE 7-16 Seismic Design Parameters

Seismic Category A

Site Class C

MCE Spectral Response Accelerations

Short Period, Ss 0.089 g

1-second, S1 0.035 g

Site Coefficients, Fa 1.3

Site Coefficient, Fv 1.5

Design Spectral Response Accelerations

Short Period, SDS 0.077 g

1-second, SD1 0.035 g

5.3 GENERAL MATERIAL PLACEMENT REQUIREMENTS

5.3.1 Fill Materials

The on-site clay materials, segregated from debris, deleterious material and any oversized material greater that 6-inches in maximum dimension, will be suitable for use as exterior foundation backfill, utility trench backfill, and general site fill, but will not be suitable for use as engineered fill.

On-site sources of engineered fill were not identified. These materials will have to be imported to the site. We recommend that all engineered fill materials consist of non-expansive, well-graded natural or crushed gravel with 100% passing the 3-inch sieve and between 8% and 20% passing the #200 sieve. The engineered fill material should also have a liquid limit less than 30 and a plasticity index of less than 15.

On-site sources of stabilization rock were not identified. These materials will have to be imported to the site, if necessary. The stabilization rock should be a clean rock with 100% passing the 3-inch sieve, 0 to 15% passing the 1-inch sieve, and 0 to 8% passing the #4 sieve.

If necessary, imported, non-engineered fill materials shall have a maximum particle size of 3 inches and shall meet one of the following USCS classifications: GM, GC, SM, SC, CL.

The imported fill material shall have a free swell of less than 1.0% as determined by ASTM D4546 or D2435.

5.3.2 Fill Placement

We suggest that sufficient density tests be taken by qualified personnel to indicate the degree of compaction being attained. We recommend controlling scarification, fill and backfill operations using the moisture content and dry density relationship as determined by ASTM D 1557 (Modified Proctor Density). Site fill materials, including engineered fill below foundations and slabs, should be placed in 6-12-inch loose lifts and compacted to the densities and moisture contents outlined in Table 3 below. Any additional moisture required to achieve compaction in a layer should be added and the entire lift mixed to obtain uniform moisture content.

We suggest that final testing of the footing subgrade and other fills in "structural areas" be performed (in addition to testing during placement) immediately before concrete placement to determine the integrity of the materials. Severe changes in the condition of these materials can occur after initial preparation as the result of rain, snow, drying, freezing, excessive heat, and construction activities. Any subgrade or foundation material that becomes disturbed desiccated or does not conform to the moisture content and compaction requirements indicated in Table 3 should either be removed and replaced or reworked to meet these recommendations.

Table 3 - Soil Compaction Criteria

Placement Location Soil Type Moisture Content Compaction

Degree

Scarification of Subgrade

Utility Trench Backfill

Foundation & Floor Subgrade

Foundation/Retaining Wall

Backfill

Pavement Subgrade

Sidewalk Subgrade

Free-Draining Materials

(Stabilization Rock and

Sand and Gravels - Less

Than 8% Fines)

Workable 90%

(ASTM D-4253)

Cohesive Materials

(Clays and Silts)

0 to 3% Above

Optimum

92%

(ASTM D-1557)

Cohesionless Materials

(Engineered fill and

Sands and Gravels –

More Than 8% Fines)

Workable

95%

Site Grading Approx. 15 Feet

Away from Structures

Landscape Areas

Cohesive Materials

(Clays and Silts)

+3% of Optimum 85%

(ASTM D-1557)

Cohesionless Materials

(Sands and Gravels –

More Than 8% Fines)

Workable 90%

The earthen site construction materials should not be placed on frozen ground and compaction operations should not be performed during periods when temperatures are below 25 degrees Fahrenheit. During cold weather construction periods, it may be necessary to remove frozen soils prior to placement of new fill materials. The local foundation frost depth is 42 inches. (City of Sioux Falls)

Placement of earthen site construction materials at temperatures below 35 degrees Fahrenheit may result in frost entering the soils and making placement at the required specifications difficult. Therefore, we suggest when temperatures are below 40 degrees Fahrenheit and earthen materials are being placed below structures, that the earthen site construction materials be continuously observed and tested. If frozen materials are observed being placed below structures, we suggest that they be removed and replaced with unfrozen materials as directed by the geotechnical engineer or testing personnel.

Soils having relatively high silt or fine sand contents are often difficult to compact to the desired specifications although they may be compacted well enough to suit the intended purpose. If great difficulty is encountered during construction regarding meeting the compaction specifications, a qualified geotechnical engineer should be consulted to determine if the placement of the soils at lower densities could still provide suitable characteristics.

5.3.3 Utility Trench Backfill

Utility trench excavations at the site will generally encounter lean clay and sand soils. The on-site soils excavated from trenches are suitable, in general, for use as trench backfill.

Utility trench backfill soils should be free of vegetation, debris and other deleterious materials.

5.4 RETAINING STRUCTURES AND LATERAL EARTH PRESSURES

Any retaining structures on the site can be expected to deflect sufficiently to mobilize the full active earth pressure condition. Retaining walls which can be expected to deflect may be designed using the “active” earth pressures. Foundation walls or grade beams that will be laterally supported and are expected to undergo only a limited amount of deflection, thus requiring the consideration of the “at-rest” earth pressure condition.

The lateral resistance of wall foundations will be the combination of the sliding resistance of the footing on the foundation materials and the passive resistance of the soil against the side of the footing. Sliding friction at the bottom of the footing can be taken at 0.40 if founded on properly compacted engineered fill.

An imported granular wall backfill material may be utilized to reduce the lateral pressures exerted on the walls. If an imported granular material is used as backfill, the granular wall backfill should extend laterally behind the wall a minimum distance equal to one half (1/2) the wall height to prevent the laterally heavier on-site cohesive soils from exerting lateral forces on the wall. The upper 6 to 8 inches of wall backfill should consist of on-site cohesive soils to limit moisture ingression into the granular backfill. If the granular wall backfill extends laterally behind the wall a distance less than one half (1/2) the wall height, the retaining structure or wall should be designed for the lateral earth pressures for the on-site soils. Imported granular wall backfill should have an internal angle of friction of no less than 32 degrees and meet the requirements for Select Granular Backfill as defined in Section 850 of the 2015 SDDOT Standard Specifications for Roads and Bridges.

We recommend that foundation walls, vaults and retention structures at the site be designed for soil parameters and lateral earth pressures calculated based on the equivalent fluid pressures presented in Table 4.

Table 4 - Equivalent Fluid Pressures

Drained Conditions

Parameter On-Site

Soils*

Imported Granular

Backfill**

Active, pcf 60 35

At-Rest, pcf 80 55

Passive, pcf 245 390

Notes: *Pressures recommended for on-site soils apply to recompacted site clay soils and in-place native clay soils.

**The pressures recommended for imported granular backfill are contingent on the material demonstrating an internal angle of friction of at least 32 degrees.

An upward sloping backfill surface or the buildup of water behind a wall will increase the earth pressures on foundation and retaining walls. To prevent the buildup of water behind the walls designed for drained conditions, we recommend that the backfill immediately behind the wall consist of a free draining granular material or that a synthetic drainage material be installed between the wall and backfill materials. The free draining granular material should consist of a South Dakota Department of Transportation (SDDOT) Select Granular Backfill as defined in Section 850 of the 2015 SDDOT Standard Specifications for Roads and Bridges. Wall backfill should be compacted in accordance with the criteria provided in Table 3. The upper 6 to 8 inches of wall backfill should consist of on-site cohesive soils to limit moisture ingression into the granular backfill.

Care should be taken not to over compact the backfill behind the walls as this could cause excessive lateral pressures on the walls. Some settlement of deep wall backfills will occur even if the material is placed correctly. All foundation and retaining structures should be designed for surcharge pressures such as adjacent traffic and construction materials and equipment. The lateral earth pressures provided herein are unfactored. An appropriate factor of safety should be applied to retaining wall system design.

5.5 EXCAVATIONS, SHORING AND SITE GRADING

5.5.1 Excavations and Shoring

Shallow excavations at the site will likely encounter lean clay and sand soils. It is possible that cobbles or boulder sized material, or debris associated with past site developments may be encountered and require additional effort. Any debris encountered should be transported off-site. Any abandoned utilities should be cut and sealed at the perimeter of the site.

Regarding excavations at the sites, we recommend that they be sloped or shored in accordance with OSHA regulations, and to generally maintain adequate safety provisions on the jobsite. The near surface clay soils can be considered OSHA Type B soils. It is the contractor's responsibility to maintain job-site safety, and the occasional or longer-term presence of an FMG, Inc. representative at the site does not constitute a review or a responsibility regarding safety aspects.

5.5.2 Site Grading

Site grading required to achieve desired site grades is anticipated to be minor. We have the following recommendations about site grading.

1. Any fill materials placed within structure footprints shall be considered structural subgrade, shall consist of engineered fill, and shall be compacted accordingly.

2. We recommend that all topsoil, root zones, organics, etc. be stripped in areas to receive fill or from foundation footprints.

3. Soft conditions may be encountered during site grading. If soft conditions are encountered during site grading, stabilization may be necessary to allow proper construction. Stabilization efforts should be as directed by the Geotechnical Engineer based upon site observations.

4. Site grading should provide for positive drainage away from the structure. Preventing moisture ingression to the structure subgrade soils will be critical to foundation and slab performance.

5.6 GENERAL DESIGN AND CONSTRUCTION PROVISIONS

In many cases, foundation failures and movements are associated with changes in moisture conditions. To reduce the potential of foundation and floor system failures and movements at the site, we suggest implementing construction procedures that limit the potential of subgrade soils experiencing substantial changes in moisture. We suggest the following minimum criteria.

1. For a minimum of 8 feet away from the structure, we suggest maintaining a minimum of a 5% slope for soil surfaces and a 2% slope for asphalt and concrete paving. Maintain positive drainage beyond 8 feet from the structure.

2. To prevent the retention of water near the building, we do not recommend the use of a gravel or rock mulch mow strip around the building perimeter. If a mow strip is desired, it should be a solid concrete slab which is sealed at the foundation wall. If a gravel mow strip is desired to convey storm drainage, it should be positioned at least 10 feet from the building.

3. With the exception of natural gas, we recommend burying all utilities at a minimum depth of six (6) feet below finished grade to receive protection from frost penetration. (City of Sioux Falls, 2018) (UFC 3-301-01)

4. We suggest pressure testing of all utility lines prior to backfilling to determine that there are no leaks in the system.

5. We suggest that the maintenance manager be made aware of the importance of limiting moisture ingression into the foundation soils.

5.7 EXTERIOR CONCRETE FLATWORK

Due to the expansive nature of the site soils, concrete flatwork at the site may experience some degree of movement as the subgrade soils are exposed to moisture variations. The extent and magnitude of the movements are difficult to predict and are largely a function of natural variations in soil mineralogy, proper drainage around and within the flatwork, proper maintenance of the flatwork and ultimately the degree to which the subgrade soils are exposed to moisture variations. We have the following suggestions to mitigate and manage potential movements of the flatwork; however, implementation of these suggestions will not necessarily eliminate movements of the flatwork.

1. We recommend that an engineered fill section a minimum of 24 inches thick be constructed below the concrete flatwork adjacent to building entryways, at stoops and at areas sensitive to tripping hazards. The engineered fill section at entryways should extent below the limits of the stoop or extend 3 feet laterally and 5 feet perpendicularly from the entryway in areas of extended concrete flatwork. The engineered fill, meeting the requirements outlined in Section 5.3.1 of this report, should be compacted in accordance with the soil compaction criteria provided in Table 3. The engineered fill section will serve to mitigate movements of the flatwork but may not eliminate all risk of movement.

2. In addition to the engineered fill section, concrete flatwork should be doweled into the building foundation at building entryways to minimize differential movements.

3. Positive drainage should be maintained around and within the flatwork. In no case should water be allowed to pond or collect near or within the flatwork. Downspouts should be designed to discharge a minimum of 10 feet past the limits of the building.

4. Construction and expansion joints should be sealed to prevent water infiltration to the subgrade.

5. A regular maintenance program should be implemented to identify and repair any differential movements of the flatwork. Sealed construction and expansion joints should be maintained.

6. Irrigation of vegetation within the flatwork should be limited to the minimum amount required to sustain the vegetation. Excessive irrigation will result in movements of the flatwork.

7. For areas of sidewalk or flatwork sensitive to tripping hazards, reinforcement of joints should be considered to mitigate differential movements. We recommend a minimum sidewalk thickness of 4 inches and a minimum aggregate base thickness of 2 inches.

Final compaction testing of the flatwork subgrade should be performed immediately before concrete placement to determine the integrity of the materials. Any subgrade material that becomes disturbed, desiccated or does not conform to the moisture content and compaction requirements indicated in Table 3 should either be removed and replaced, or reworked to meet these recommendations.

5.8 SOIL CORROSIVITY

To assess the corrosivity of the site soils to buried concrete and steel, laboratory chemical analyses and resistivity testing was performed. The results of the laboratory testing are summarized below and presented in Appendix B.

Table 5 - Soil Corrosivity Testing Summary

Parameter Sample Location Value Soil Type pH BH-1, P1A, 5Ft 7.98 Silty Sand (SM)

Soluble Sulfates BH-1, P1A, 5Ft 15.5 ppm Silty Sand (SM)

Chloride BH-1, P1A, 5Ft 13.1 ppm Silty Sand (SM)

Electrical Resistivity BH-2, P2A, 5Ft 5670 ohm-cm Silty Sand (SM)

Redox Potential BH-1, P1A, 5Ft 237 mV Silty Sand (SM)

Sulfides BH-1, P1A, 5Ft 0.074 ppm Silty Sand (SM)

Based on the results of laboratory reactivity testing of representative samples, concrete in contact with the on-site soils will have a negligible exposure (up to 15.5 ppm) to sulfate-containing soils (ACI 318, Table 4.3.1). As such, no special recommendation for sulphate resistant cement is made.

Average soil resistivity values indicate moderate corrosivity potential. Table 6 indicates the generally accepted corrosivity ratings based on soil electrical resistivity. All cathodic protection measures should be reviewed and designed by a professional with adequate experience to design such features.

Table 6 – Soil Corrosivity Ratings

Soil Resistivity (ohm-cm) Corrosivity Rating*

>20,000 Essentially Non-Corrosive

10,000 to 20,000 Mildly Corrosive

5,000 to 10,000 Moderately Corrosive

3,000 to 5,000 Corrosive

1,000 to 3,000 Highly Corrosive

<1,000 Extremely Corrosive

*from Roberge, 2013

5.9 PERCOLATION TESTING AND SOIL INFILTRATION

An on-site wastewater treatment system is proposed for installation approximately 200 feet east of the proposed building footprint. In support of design of the system, a percolation test was performed in the proposed leach field drainage area. The testing was performed in accordance with the procedures provided in the Administrative Rules of South Dakota, 74:6:01:30. The results of the percolation testing is presented as Appendix C.

The soil data presented below in Table 7 should be utilized for design of the wastewater system.

Table 7 – Soil Infiltration Parameters

Parameter Value

Infiltration Rate 10.08 min/inch

Hydraulic Conductivity 2.94E-04 cm/sec

NRCS Hydrologic Soil Group B

NRCS Soil Textural Class Sandy Clay Loam

*Soil Parameters for the sandy gravel present from 3 to 7 feet below existing grades.

5.10 PAVEMENT THICKNESS DESIGN

From our subsurface soil exploration and engineering analysis, we have arrived at the following conclusions and have the following recommendations regarding pavement section design at the site. The conclusions and recommendations presented in this report do not reflect variations in subsurface conditions that are likely to exist in unexplored areas. Should such variations be revealed during construction, it may be necessary to re-evaluate our recommendations based upon on-site observation of the variations.

5.10.1 Flexible Pavement

To develop the proposed flexible pavement design parameters for the proposed new pavement areas, we used the PerRoadExpress 1.0 design software developed by the Asphalt Paving Alliance.

5.10.2 Rigid Pavement

A rigid, concrete pavement section may also be considered for the new pavement areas. To develop the proposed rigid pavement design, we used the design methods recommended by the American Concrete Institute and the American Concrete Pavement Association.

5.10.3 Subgrade and Design Criteria

The on-site pavement subgrade soils will likely consist of sandy lean clay soils. Some variations are expected. A CBR value of 3.2% was utilized in the calculation of the appropriate pavement section thicknesses. A resilient modulus (MR) of 4,200 psi and a subgrade modulus (k) of 100 pci should also be used for the unmodified site subgrade soils.

Traffic loadings for the access and maintenance roads as provided by B&M are 40% autos/light trucks (Traffic Index (TI)=5.0), 40% light delivery trucks and forklifts (TI=6.0) and 20% tractor trailer trucks (TI=7.0). Two-way Annual Average Daily Traffic (AADT) is estimated to be 500 or less. The flexible pavement design parameter inputs are summarized below.

For the rigid pavement section, we have assumed that the traffic loadings for the proposed pavement areas will fall within Traffic Category A-1, truck access lanes with an average daily truck traffic of 10. The design manual indicates that a thinner concrete section than is indicated in Table 8, however, based on our experience with concrete paving in this area and considering the engineering characteristics of the site soils, we recommend than no thinner than 6 inches of concrete be used to avoid excessive cracking and premature deterioration of the pavement. We recommend a rigid pavement for loading docks and forklift operation areas, truck parking areas and areas of high turning stresses. Flexible pavement is susceptible to “bird-bathing” and shoving or tearing in such areas.

The pavement designs are based on a 20-year life. The recommended pavement section is provided in Table 8 below.

Table 8 - Recommended Pavement Sections

Section Flexible

Paving

Rigid

Paving*

Hot-Mix Asphalt (SDDOT Class E) 6 Inches

Portland Cement Concrete

(SDDOT 380.3 A)

6 Inches

Aggregate

Base Course 6 Inches 4 Inches

Subgrade

Scarification 8 Inches 8 Inches

*includes building bay aprons

5.10.4 Pavement Subgrade Preparation

We suggest that the existing subgrade soils be prepared in accordance with the standard engineering practices and procedures outlined as follows. We recommend grading the existing soils across the site to a uniform surface before the fill materials are placed. We suggest removing any topsoil, organics, and debris from these subgrade soils. Topsoil materials may be stockpiled for landscaping at the site. After removal of any topsoil, organics, and debris, we suggest that the subgrade soils be scarified and thoroughly mixed to a minimum depth of eight (8) inches, the moisture content adjusted, and then recompacted to meet the specifications set forth in Table 3. We suggest that the grading be performed so that positive drainage occurs off the pavement areas and that no puddling of water occurs. We suggest a minimum slope of one (1) percent.

We recommend that fill materials required to build up the site be placed in accordance with the criteria provided in Table 3 and meet the requirements outlined in Section 5.3.1 of this report. Before the fill materials are placed, we suggest that a geotechnical engineer observe the subgrade soils to determine if soft areas exist.