A1-2b FMG Geotech Report.pdf

APPENDIX F

GEOTECHNICAL REPORT

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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

January 27, 2025

Mr. David Martin

Bodwe Group dmartin@bodwegroup.com

Re: Geotechnical Evaluation

Rosebud Hospital

Emergency Department Addition

Rosebud, South Dakota

Dear Mr. Martin:

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

John Lucas, P.E. Alex Fisher, P.E.

Enclosures c: Z:\241479.00 Bodwe Grp-Rosebud ED Addtn Survey & Geotech\Geotech\241479 Bodwe Grp-Rosebud ED Addition -- FMG

Geotech.docx

Geotechnical Engineering Materials Testing Laboratory ii Land Surveying

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

Geotechnical Engineering

Materials Testing Laboratory

Land Surveying

Geotechnical Evaluation for

Rosebud Hospital

Emergency Department Addition

Rosebud, South Dakota

January 27, 2025

Prepared for

Mr. David Martin dmartin@bodwegroup.com

FMG Project No. 241479 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 UNCONFINED COMPRESSION TESTING

3.4 MOISTURE-DENSITY RELATIONSHIP

3.5 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 SLAB SYSTEM SELECTION

5.1.1 Shallow Foundation Design Parameters

5.1.2 Garage Floor Slab System

5.2 SITE SEISMICITY

5.3 GENERAL MATERIAL PLACEMENT REQUIREMENTS

5.3.1 Fill Materials

5.3.2 Fill Placement

5.4 RETAINING STRUCTURES AND LATERAL EARTH PRESSURES

5.5 EXTERIOR CONCRETE FLATWORK

5.6 UTILITY INSTALLATION

5.7 EXCAVATIONS, SHORING AND SITE GRADING

5.7.1 Excavations and Shoring

5.7.2 Site Grading

ii

5.8 GENERAL DESIGN AND CONSTRUCTION PROVISIONS

5.9 PAVEMENT RECOMMENDATIONS

6. PROJECT OBSERVATION AND CONSTRUCTION QUALITY ASSURANCE

7. CONCLUDING STATEMENT

TABLES, FIGURES AND APPENDICES

TABLE 1 –SHALLOW FOUNDATION DESIGN PARAMETERS

TABLE 2 - SEISMIC DESIGN CRITERIA

TABLE 3 - SOIL COMPACTION CRITERIA

TABLE 4 - EQUIVALENT FLUID PRESSURES

TABLE 5 - RECOMMENDED PAVEMENT SECTIONS

TABLE 6 - RECOMMENDED FREQUENCY OF TESTING

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

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

FIGURE 3 .......... TYPICAL OVER-EXCAVATION AND ENGINEERED FILL, FROST-RESISTANT STOOP AND FOUNDATION DRAIN DETAIL

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

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

APPENDIX C ........................................................................................................................ REFERENCES

Rosebud ED Addition

Rosebud, SD

1. INTRODUCTION

We understand an addition is planned to the Rosebud Hospital building located at the intersection of Hospital Drive and Soldier Creek Loop in north Rosebud, South Dakota. The addition is planned for the north side of the existing structure. The addition will consist of a

2-story, steel-framed with metal stud infill building with an approximate 12,000 square foot building footprint. Foundation loads are anticipated to be moderate. No below grade level is planned.

The project will also include asphalt pavement and potentially a 2-bay ambulance garage.

FMG Engineering was retained by Bodwe Group to perform a geotechnical evaluation of the proposed project site. This report presents the findings of our geotechnical evaluation which 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 and AASHTO 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 and pavement 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 five (5) boreholes were drilled at the locations shown on Figure 1 to identify the subsurface characteristics and obtain soil samples for laboratory testing. A sixth borehole, Borehole 1, was initially proposed, however, was unable to drill due to utility conflicts and other nearby obstructions. The boreholes were observed by the FMG field geologist. Field sampling and testing procedures were conducted in general accordance with ASTM D420.

The boreholes were drilled with a Diedrich D-70 track-mounted drill rig and hollow-stem auger. The number of boreholes and the locations were selected by FMG and were adjusted in the field as necessary to avoid existing utilities. If, during subsequent planning, the structure 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.

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.

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 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 UNCONFINED COMPRESSION TESTING

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)

3.4 MOISTURE-DENSITY RELATIONSHIP

Moisture-density relationship tests, or Proctor tests, were performed on bulk soil samples 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)

3.5 SAMPLE STORAGE

The soil samples obtained during this evaluation will be stored for a period of one year. If the client wishes to receive the samples arrangements should be made; otherwise, the samples will be discarded after one year.

4. SITE CONDITIONS

The site for the proposed addition is to the north of the existing Rosebud Hospital in Rosebud, South Dakota. The site topography throughout the site slopes to the north on the order of several percent away from the existing building. The site is generally covered by asphalt pavement and mowed grass.

The site is bound by Soldier Creek Loop to the north and east, the existing building to the south, and an asphalt parking lot to the west.

4.1 MATERIALS PRESENT

The site stratigraphy generally consists of approximately 6 to 7 feet of silty lean clay fill material overlying approximately 5 to 6 feet of silty sand alluvial soils overlying weathered sandstone bedrock to the total depths explored.

4.1.1 Material Descriptions

The near surface lean clay fill materials were found to be very dark brown to brown, moist, low plasticity, and stiff to very stiff in consistency.

The underlying silty sand alluvial soils were found to be pale brown to very pale brown, moist, non-plastic, and very loose to loose in consistency.

The underlying weathered sandstone was found to be highly weathered, pale brown in color, fine to medium grained, and moderately soft rock.

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 not encountered in the boreholes at the site. However, groundwater levels and presence should be anticipated to fluctuate in response to seasonal and short-range changes in precipitation, snowmelt, landscape irrigation and land use, and may not be accurately delineated within the normal scope of a geotechnical evaluation.

4.3 GEOLOGIC CONDITIONS

The geologic conditions of the project site can be generally described as fill material overlying alluvial materials overlying formational sandstone bedrock. The underlying bedrock is interpreted to be the Ogallala Formation, a well cemented, fine- to medium-grained sandstone. (Ellis, Ficken, and Adolphson, 1971)

Geologic mapping of the area indicates no mapped faults or geologic structures within close proximity of the project site that would impact siting, design or construction of the proposed project. (Ellis, Ficken, and Adolphson, 1971)

5. CONCLUSIONS AND RECOMMENDATIONS

From our subsurface exploration and engineering analysis, we have arrived at the following conclusions and have the following recommendations regarding 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 SLAB SYSTEM SELECTION

The foundation subgrade consists of approximately 6 to 7 feet of expansive and compressible fill materials overlying very loose to loose silty sand alluvial soils. The primary geotechnical concern for foundation and slab performance is potential post-construction movement related to the expansive and compressible fill materials and the compressible alluvial soils.

Differential settlements on the order of 2 inches or more are possible if a shallow foundation system founded directly upon on-site soils is utilized.

To mitigate the potential for settlements in response to building loads and expansive soil heave, we recommend the use of a shallow foundation system and over-excavation program.

We recommend removing all existing fill material and replace with properly compacted engineered fill. Additionally, we recommend over-excavating the existing soils a minimum of 3 feet below all foundation elements and floor slabs and replacing the excavated material with properly compacted engineered fill. The over-excavation program and construction of the engineered fill section will serve to replace a thickness of compressible and expansive soil with relatively incompressible and non-expansive engineered fill. The recommended design parameters and construction parameters and criteria for a shallow foundation system are provided below in Section 5.1.1 and Section 5.1.1.1.

Some minor movements of shallow foundations and 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. Total movements of foundation elements and slabs may be on the order of 1 inch; differential movements are anticipated to be on the order of ¾ inch.

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. 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.

5.1.1 Shallow Foundation Design Parameters

Table 1 –Shallow Foundation Design Parameters

Parameter Value

Subgrade Preparation 1. Over-excavate all existing fill soils below all foundation elements and floor slab and replace with properly compacted engineered fill.

2. Over-excavation to extend a minimum of 3-ft and replace with properly compacted engineered fill below foundation elements and floor slabs.

3. All fill material within building footprint shall consist of engineered fill.

Net Allowable Bearing Capacity (FS=3.0) 1,500 psf

Static/Dynamic Modulus of Subgrade Reaction 200 pci for engineered fill

Frost Penetration Depth 48 inches

Sliding Friction Coefficient 0.42

Passive Earth Pressure 255 psf

5.1.1.1 Shallow Foundation Design and Construction Criteria

1. We recommend all existing fill soils below shallow foundations and floor slabs be removed and replaced with properly compacted engineered fill. Additionally, we recommend all existing soils be over-excavated to a minimum depth of 3 feet below bearing depth and replaced with properly compacted engineered fill. The over-excavation should extend beyond the inside and outside edges of the foundation 1 foot for every 1 vertical foot of over-excavation. See Figure 3 for an illustration of this geometry. 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 over-excavation process, prior to placement of engineered fill, to verify removal extents are sufficient.

2. All fill materials placed within the building footprint must consist of engineered fill.

3. We recommend that the excavation subgrade be scarified to a depth of 12 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.

4. The connection to the existing structure should be designed to accommodate some differential movements between the structures. We anticipate the potential differential movements to be on the order of 1 inch.

5. If soft conditions are encountered at the base of the foundation excavations, the excavation should be over-excavated to stable conditions as directed by the

Geotechnical Engineer. As directed by the Geotechnical Engineer, the additional over-excavation 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 bearing elevation. Any stabilization rock should be covered with a non-woven filter fabric prior to placement of engineered fill.

6. A one-third (33%) increase in allowable bearing capacity for wind or seismic cases is permitted based on reducing the factor of safety from 3.0 to 2.25.

7. 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.

8. 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.

9. Debris, fills, and other relics associated with past site developments may be encountered during excavations at the site. 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. The Geotechnical Engineer should observe over-excavations prior to engineered fill placement.

10. 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 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.

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 should be provided for slab-bearing mechanical equipment.

14. Care should be taken to minimize the ingression of water into the slab subgrade.

Water stops and other measures should be considered for floor drain construction, and flexible connections should be provided for sub-slab utilities.

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 consistent with ASTM E1745 – Class A, or equivalent as approved by the

Geotechnical Engineer.

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.

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.

5.1.2 Garage Floor Slab System

A 2-bay ambulance vehicle parking garage is proposed. Due to the heavy loads created by ambulance vehicles, we recommend a heavy-duty floor slab.

To develop the proposed heavy-duty concrete floor slab design parameters for the garage area, we used the “PaveXpress” design software. We also referenced the American Concrete

Institute “Guide for Design and Construction of Concrete Parking Lots, ACI 330R-92” for minimal slab design criteria.

Using the design criteria, standard design calculations indicate that a minimum 5-inch concrete slab would be sufficient. However, based on our experience with heavy-duty concrete parking areas and considering the engineering characteristics of the site soils, we recommend than no thinner than 6 inches of concrete be used for the garage floor slab to avoid excessive cracking and premature deterioration of the floor slab.

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 2 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 D

MCE Spectral Response Accelerations

Short Period, Ss 0.141 g

1-second, S1 0.038 g

Site Coefficients, Fa 1.6

Site Coefficient, Fv 2.4

Design Spectral Response Accelerations

Short Period, SDS 0.151 g

1-second, SD1 0.061 g

5.3 GENERAL MATERIAL PLACEMENT REQUIREMENTS

5.3.1 Fill Materials

The on-site lean clay, silt, and sand 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, and pavement subgrade 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 for non-structural, general site fill areas 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

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)

-1 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%

*a moisture content that facilitates desired compaction.

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 will be necessary to remove frozen soils prior to placement of new fill materials.

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.

5.4 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.

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 255 390

Friction Angle, degrees 20 32

Soil Moist Unit Weight, pcf 125 120

Cohesion, psf 0 0

Notes: *Pressures recommended for on-site soils apply to recompacted site silty gravel soils and in-place native silty gravel 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. A wall drain system should be designed at the base of the wall to collected and convey water from the wall system. 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 EXTERIOR CONCRETE FLATWORK

Due to the 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 12 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 over-excavation subgrade should be sloped at minimum of 1% to drain toward an underdrain which connects to the foundation underdrain system. 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. Figure 3 illustrates a typical frost-resistant stoop detail.

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. 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.

5.6 UTILITY INSTALLATION

Based on the results of our field exploration, the majority of utility trench excavations of up to 8 feet below existing grades will be in silty lean clay fill material and very loose to loose silty sand soils. Recommendations regarding utility trench excavation are provided in the

Excavations section of this report. It is anticipated that the majority of the storm sewer excavation can likely be completed with properly sized excavation equipment in good working order.

Pipe bedding materials should meet the requirements specified in SDDOT “Standard

Specifications for Roads and Bridges” 2015 Edition or per manufacturer’s recommendations.

5.7 EXCAVATIONS, SHORING AND SITE GRADING

5.7.1 Excavations and Shoring

Shallow excavations at the site will likely encounter lean clay, silt, and sand materials and possibly cobbles and boulders. Where encountered, the cobbles and boulders may require additional effort to excavate. Due to the depositional nature of the site soils, the specific material types and engineering characteristics will vary both horizontally and vertically throughout the project. Observations being presented were made during limited subsurface investigations and should be used for general planning purposes. Project plans and specifications should be referred to for contract requirements regarding excavation.

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 C 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.

Based on the proposed construction, some of the excavations at the site will be located in close proximity to and/or below existing structures. To reduce the potential of undermining the existing foundation, we suggest using temporary shoring such as sheet piling or underpinning, or performing the excavation operations in a piecemeal manner to maintain the stability of the existing structures. We recommend monitoring the existing foundations and walls of vertical soils under the existing structures to determine if movements occur. In the event that small piecemeal excavations are made at the site and movements are observed in the existing foundations or in the vertical soil cuts, we suggest that the excavations be backfilled immediately or that temporary shoring, as mentioned above, be provided.

Additionally, if the existing buildings foundation system has an engineered fill section, care should be exercised during foundation excavation, near existing structures, as to not disturb the existing engineered fill section. This will likely require modifications to the excavation geometry in some cases. The proposed engineered fill section should be placed in a manner that extends to the existing engineered fill section.

Temporary excavation slopes should be protected from stormwater run-on via swales, berms, or other methods. Ponding of water within 50 feet of the top of the excavation slopes should not be allowed.

5.7.2 Site Grading

Extensive site grading is not anticipated to prepare the project site. Excavations and shoring recommendations for the site grading efforts are provided in Section 5.7.1 and fill placement recommendations are provided in Section 5.3. We have the following general recommendations about site grading.

1. Any fill materials placed within structure footprints shall be considered structural subgrade 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.

5.8 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. Except for natural gas, we recommend burying all utilities at a minimum depth of six (6) feet below finished grade to receive protection from frost penetration.

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.

5.9 PAVEMENT RECOMMENDATIONS

From our subsurface soil exploration and engineering analysis, we have arrived at the following conclusions and have the following recommendations regarding pavement design for the parking and driving areas. 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.

5.9.1 Flexible Pavement

To develop the proposed flexible pavement design parameters for the proposed new parking areas, we used the design method recommended by the Asphalt Institute. We have assumed that the traffic loadings for the parking lot will fall within Parking Lot Traffic Class I. Traffic

Class I includes parking lots with up to 200 stalls, used only by passenger cars and trucks, for a 20-year ESAL count of 40,000.

5.9.2 Rigid Pavement

To develop the proposed rigid pavement design for the proposed parking areas, dumpster areas, or other heavy duty traffic areas, we used the design methods recommended by the

American Concrete Institute. We have assumed that the traffic loadings for the proposed parking areas will fall within Traffic Category A, which includes autos, pickups, and panel trucks.

5.9.3 Subgrade and Design Criteria

An estimated CBR of 2.5% was used for pavement calculations. The pavement design is based on a 20-year life. Flexible pavement design calculations were made using

“PaveXpress” developed by the Asphalt Institute. Rigid pavement design calculations were made using the American Concrete Institute “Guide for Design and Construction of Concrete

Parking Lots, ACI 330R-92”. Calculations indicate that the following sections are acceptable.

Table 5 - Recommended Pavement Sections

Section Flexible

Pavement

Rigid

Pavement

Hot-Mix Asphalt 4 Inches -

Portland Cement Concrete - 6 Inches

Aggregate Base Course 8 Inches 4 Inches

Subgrade Scarification 8 Inches 8 Inches

5.9.4 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. These topsoil and organic materials may be stockpiled for landscaping at the site. Clean fill materials do not require full removal and replacement. 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. The geotechnical engineer may waive scarification of areas in which bedrock is present at subgrade elevations. 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. Before the fill materials are placed, we suggest that a geotechnical engineer observe the subgrade soils to determine if soft areas exist. If soft areas exist, we recommend that the soft materials be removed and replaced with suitable materials that are recommended by the geotechnical engineer and that they be compacted to meet the specifications of Table 3.

After the subgrade soils have been scarified and recompacted and immediately prior to placing the next pavement or fill section, we recommend proof rolling the site with a large fully loaded piece of earth-moving equipment. We suggest that the proof rolling be performed to identify soft areas across the site that requires additional work. We recommend that a geotechnical engineer observe the proof rolling operations. We suggest that the recommendations made by the geotechnical engineer during the proof rolling operations be implemented and be considered a part of this pavement thickness design.

5.9.5 Aggregate Base

The pavement sections presented in Table 5 require that the pavements be underlain by an untreated aggregate base course. We recommend that the untreated aggregate base course be placed immediately after the subgrade preparation has been completed. We recommend utilizing an untreated aggregate base course below the pavements because it will provide a firm base for the pavement as well as a drain for any ground and surface water that enters the pavement section. We recommend that the aggregate base course meet the South Dakota

Department of Transportation S.D.D.O.T. Limestone Ledge-Rock Base Course requirements that are in Section 882 of the (2015) “Standard Specifications for Roads and Bridges.” We suggest that the untreated aggregate base course be compacted to meet the specifications of

Table 3.

5.9.6 Hot-Mix Asphalt (HMA) Pavement

We suggest that the hot-mix asphalt paving be done in accordance with Sections 320, 321, 324, 330, 880, and 890 of the (2015) “South Dakota DOT Standard Specifications for Roads and Bridges.” We suggest that the hot-mix asphalt be compacted to a maximum single-lift thickness of three (3) inches. We recommend that the lifts of the hot-mix asphalt be compacted to a minimum of ninety-two (92) percent of maximum density as determined by

“Rice” specific gravity method when the specimens are prepared as specified in SD 312 when referenced to the like material.

6. PROJECT OBSERVATION AND CONSTRUCTION QUALITY

ASSURANCE

As the provider of the geotechnical recommendations contained herein, FMG should be retained to provide any necessary pre-construction geotechnical reviews, interpretations, and supplemental information.

If any changes in the nature, design or location of the project are planned, the conclusions and recommendations contained in this report shall not be considered valid unless the changes are reviewed, and conclusions of this report modified or verified in writing.

Frequently, soil conditions vary slightly from those encountered in the borings that were drilled. Therefore, FMG should be retained to review the portions of the plans that pertain to earthwork and foundations.

Additionally, proper placement of site fill, engineered fill, and other structural elements per our recommendations and per the project specifications is essential to the performance of the foundation and floors of the structure. Failure to properly place the construction materials and structural elements can result in excessive movements potentially leading to failure and significant impact to the structural integrity of the structure.

We suggest the following minimum standards and frequency of testing be followed for soil and concrete construction materials placed at the project site.

Table 6 - Recommended Frequency of Testing

Material or Placement Location Recommended Standard or Frequency

Structural Concrete ACI 318 Chapter 26.12

General Site Fill 1 test per 12” lift per 10,000 ft2

Foundation and Slab Excavation Subgrade 1 test per 500 ft2

Engineered Fill Below Foundations and Slabs 1 test per 12” lift per 500 ft2

Foundation Backfill 1 test per 75 linear feet per vertical foot

Utility Trench Backfill 1 test per 12” lift per 200 linear feet

Our recommendations are based on the necessary assumption that the material and structural element placement will occur as specified and that a detailed construction quality assurance program will be provided that clearly documents the proper placement of materials and structural elements at this site through adequate methods and frequency of testing. In the absence of such quality assurance and documentation, FMG cannot assume responsibility or liability for the performance of any foundation systems, embankments, or structural elements of this project. Should another agent perform the construction quality assurance, said agent will necessarily assume the role and responsibilities of construction-phase geotechnical engineer of record.

We are available to observe construction operations, particularly the concrete placement operations, the compaction of the fill materials, and other such field observations as may be necessary. Under no circumstances is it our intent to directly control the physical activities of the contractor or the contractor's workmen. Any field testing or observations performed by FMG would be a part of engineering opinions rendered to the contractor and should not be misconstrued as supervision of the contractor's work or workmen.

7. CONCLUDING STATEMENT

If any changes in the nature, design or location of the project features are planned, the conclusions and recommendations contained in this report shall not be considered valid unless the changes are reviewed, and conclusions of this report modified or verified in writing.

The findings and recommendations in this report were prepared following accepted soil mechanics procedures and practices. We make no other warranty, either implied or expressed.