Attachment_7_MORUGeotechnical_Report.pdf

Geotechnical ● Materials Forensic ● Environmental

Building Technology Petrography/Chemistry

American Engineering Testing 1745 Samco Road Rapid City, South Dakota 57702 TeamAET.com • 605.388.0029

Report of Geotechnical Exploration Wastewater Treatment Plant Expansion Mt. Rushmore National Memorial Keystone, South Dakota

AET Project No. P-0014492

Date:

August 17, 2022

Prepared for:

HDR Engineering, Inc.

703 Main Street, Suite 200 Rapid City, South Dakota 57701

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1745 Samco Road | Rapid City, SD 57702 Phone (605) 388-0029 | teamAET.com | AA/EEO

This document shall not be reproduced, except in full, without written approval from American Engineering Testing, Inc.

HDR Engineering, Inc.

703 Main Street, Suite 200 Rapid City, South Dakota 57701

Attn: Mr. Chris Robinson, PE

RE: Report of Geotechnical Exploration Wastewater Treatment Plant Rehabilitation and Expansion Project Mt. Rushmore National Memorial Keystone, South Dakota AET Project No. P-0014492

Dear Chris, American Engineering Testing, Inc. (AET) is pleased to present the results of our subsurface exploration program and geotechnical engineering review for the above referenced project to be constructed at the Mt. Rushmore National Memorial near Keystone, South Dakota. These services were performed in general accordance with our proposal dated March 25. 2022, and written authorization to proceed provided on June 29, 2022. We are submitting one (1) electronic copy of the report to you.

Please contact me if you have any questions about the report. I can also be contacted to arrange observation and testing services during construction of the project.

Sincerely, American Engineering Testing, Inc.

Walt Feeger, PE Senior Geotechnical Engineer wfeeger@teamaet.com Phone: (605) 388-0029 mailto:wfeeger@teamaet.com

Mt. Rushmore WWTP Rehabilitation & Expansion Project – Keystone, South Dakota

Copyright 2022 American Engineering Testing, Inc.

All Rights Reserved

Unauthorized use or copying of this document is strictly prohibited by anyone other than the client for the specific project.

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SIGNATURE PAGE

Prepared for: Prepared by:

HDR Engineering, Inc. American Engineering Testing, Inc.

703 Main Street, Suite 200 1745 Samco Road Rapid City, Dakota 57701 Rapid City, South Dakota 57702

(605) 388-0029 Attn: Mr. Chris Robinson, PE www.teamAET.com

Authored by: Reviewed by:

Walt Feeger, PE Robert Temme, PE Senior Geotechnical Engineer Vice President – Western Region http://www.teamaet.com/

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TABLE OF CONTENTS

Transmittal Letter ............................................................................................................. i Signature Page ................................................................................................................ ii

1.0 INTRODUCTION

2.0 SCOPE OF SERVICES

3.0 PROJECT INFORMATION

4.0 SUBSURFACE EXPLORATION AND TESTING

4.1 Field Exploration Program

4.2 Laboratory Testing

5.0 SITE CONDITIONS

5.1 Surface Observations

5.2 Subsurface Soils/Geology

5.3 Groundwater

6.0 RECOMMENDATIONS

6.1 Discussion

6.2 Site Preparation

6.3 Foundation Design Recommendations

6.4 Interior Concrete Floor Slabs

6.5 Construction of Building Addition

6.6 Exterior Backfill Considerations

6.7 Trench Excavation

6.8 Retaining Wall Recommendations

6.9 Pavements

7.0 CONSTRUCTION CONSIDERATIONS

7.1 Potential Difficulties

7.2 Excavation Backsloping

7.3 Observation and Testing

8.0 LIMITATIONS

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TABLE OF CONTENTS

STANDARD SHEETS

Floor Slab Moisture/Vapor Protection Freezing Weather Effects on Building Construction Excavation and Refilling for Structural Support

APPENDIX A

Geotechnical Field Exploration and Testing Boring Log Notes Unified Soil Classification System Figure 1: Site Location Map Figure 2: Boring Location Map Subsurface Boring Logs Gradation Curves Unconfined Compression Tests Moisture-Density Relationship (Proctor) Test Reports California Bearing Ratio (CBR) Test Report

APPENDIX B

Geotechnical Report Limitations and Guidelines for Use

1.0 INTRODUCTION

We understand improvements to the existing wastewater treatment plant (WWTP) at the Mt. Rushmore National Memorial, near Keystone, South Dakota, have been proposed.

Please refer to Figure 1: Site Location Map within Appendix A for the location of the site.

To assist with the planning and design, American Engineering Testing, Inc. (AET) has been authorized to conduct a subsurface exploration program at the site, conduct soil laboratory testing, and perform a geotechnical engineering review for the project. This report presents the results of the above services and provides our engineering recommendations based on this data.

2.0 SCOPE OF SERVICES

AET's services were performed in general accordance with our proposal dated March 25, 2020. The authorized scope consists of the following:

• Perform twenty-two (22) Standard Penetration Test (SPT) borings at the following locations and depths, or practical auger refusal, whichever is less:

South Building Addition – Two (2) borings to depths of 15’ below grade North Building Addition – Two (2) borings to depths of 15’ below grade New Treatment Basin – Two (2) borings to depths of 15’ below grade New Clarifier – Two (2) borings to depths of 15’ below grade New Retaining Wall – Eight (8) borings to depths of 10’ below grade New Paved Access Drives and Parking – Six (6) borings to depths of 5’ below grade

• Soil laboratory testing.

• Geotechnical engineering analysis based on the gained data and preparation of this report.

These services are intended for geotechnical purposes only. The scope is not intended to explore for the presence or extent of environmental contamination in the soil or groundwater.

3.0 PROJECT INFORMATION

Based on the information provided, we understand that the existing WWTP was constructed in 2001 as an activated sludge mechanical treatment system to treat wastewater from the Mt. Rushmore National Memorial facilities. Increasing visitation numbers have led to increased loading on the WWTP. Wastewater loading exceeds the capacity of the existing facility during peak visitation events.

The rehabilitation and expansion project will, in part, consist of the following:

• South Building Addition – Approximate 1,250 ft2 per floor (upper and lower level) concrete slab-on-grade structure with exterior concrete masonry unit (CMU) walls.

The new addition will be located on the north side of the existing building.

• North Building Addition – Approximate 800 ft2 per floor (upper and lower level) concrete slab-on-grade structure with exterior wood framed walls. The new addition will be located on the northeast side of the existing building.

• New Aeration Basin – The new aeration basin will consist of a rectangular cast-in-place concrete mat slab foundation with cast-in-place concrete walls. Elevated walkway slabs will be cast on top of the wall to provide support and access to piping, gates, and other process equipment.

• New Clarifier – The proposed new circular clarifier will consist of a cast-in-place concrete mat slab foundation with cast-in-place concrete walls. A central column will support the process mechanism and access walkways.

• New Site Retaining Walls – Site retaining walls will be added to the west side of the new Equalization Basin and along a portion of the existing east access drive.

These site retaining walls will facilitate an elevation difference of approximately ten feet and will be constructed of either cast-in-place concrete foundations with block assembly above grade, or driven sheet piling.

• New Asphalt Paved Access Drives & Parking Areas.

The purpose of the geotechnical study was to determine the subsurface conditions within the proposed expansion areas and to evaluate the suitability of the site soils for their use in constructing the proposed structures, retaining wall, and associated paving.

The previously stated information represents our understanding of the proposed construction. This information is an integral part of our engineering review. It is important that you contact us if there are changes from that described so that we can evaluate whether modifications to our recommendations are appropriate.

4.0 SUBSURFACE EXPLORATION AND TESTING

4.1 Field Exploration Program

The proposed subsurface exploration program conducted for the project consisted of twenty-two (22) standard penetration test (SPT) borings.

Please note that due to site access issues and/or the presence of underground utilities, three (3) of the borings (Borings B-4, B-5, and B-16) were not drilled. The remaining nineteen (19) borings were drilled from July 18 to 20, 2022 at locations selected by AET and HDR personnel. The logs of the borings and details of the methods used appear in Appendix A. The logs contain information concerning soil layering, soil classification, geologic origins, and moisture condition. A density description or consistency is also noted for the natural soils, which is based on the standard penetration resistance (N-value).

The boring locations are shown on Figure 2: Boring Location Map included in Appendix A. Surface elevations at the boring locations were referenced to two (2) Temporary Bench Marks (TBMs). The TBMs selected for this project were the finished floor of the North and South Buildings. For purposes of this report, an assumed elevation of 100.00 were assigned to the TBMs.

4.2 Laboratory Testing

The laboratory test program included natural moisture content, dry density, Atterberg Limits, percent passing the #200 sieve, gradation (sieve) analysis, unconfined compression, pH, resistivity, moisture-density relationship (Proctor), and California Bearing Ratio (CBR). The test results appear in Appendix A on the individual boring logs adjacent to the samples upon which they were performed or on the data sheets following the boring logs.

The CBR test was remolded to approximately 95% of maximum dry density at the optimum moisture content for the specific boring/material. Results are summarized as follows:

Boring Depth, ft Soil Classification Optimum Moisture

Content, % 1 Maximum Dry Density, pcf 1

CBR

Value2

B-11 1-5 Micaceous Silty Lean Clay (CL) 12.2 117.1 5.5 B-21 1-5 Micaceous Silty Lean Clay (CL) 10.0 121.8 --

1 Based on ASTM D698 (standard Proctor) 2 Based on ASTM D1883

It should be noted that the bulk soil samples represent a mixture of the soils encountered within the upper 5-foot interval of each of the boreholes. As such, the soil classification as presented on the Moisture-Density Relationship and CBR data sheets may differ from the classifications of the individual soil layers identified on the respective Subsurface Boring Logs.

Two (2) laboratory pH and resistivity tests were performed on selected bulk samples obtained from the soil borings. The results are summarized below.

Boring Depth, ft Soil Type pH Resistivity, ohm-cm Corrosion Potential

B-11 1-5 Micaceous Silty Lean Clay (CL) 8.03 2,530 Moderate to Severe

B-21 1-5 Micaceous Silty Lean Clay (CL) 8.14 3,750 Moderate to Severe

The corrosion potentials provided are based on information published in the Department of the Army’s Technical Manual TM 5-811-7 “Electrical Design, Cathodic Protection. Based on this information, the site clay soils have a moderate to severe corrosion potential towards iron and other buried metals. If corrosion of buried metal is critical, it should be protected using a non-corrosive backfill, wrapping, coating, sacrificial anodes, or a combination of these methods, as designed by a qualified corrosion engineer.

5.0 SITE CONDITIONS

5.1 Surface Observations

At the time of our field work, the site consisted of the existing wastewater treatment facility utilized for the Mt. Rushmore National Memorial. The areas of the proposed improvements are vegetated with native grasses and weeds, and also include areas of asphalt pavement. In general, the overall site slopes downward to the east, with an elevation difference of about 15 feet noted between the borings.

5.2 Subsurface Soils/Geology

Underlying a layer of topsoil or asphalt pavement, the subsurface soils encountered within the borings consisted of colluvium overlying weathered schist bedrock. The colluvium is generally comprised of loose to very dense micaceous silty sands, and soft to hard micaceous silty lean clays. Where encountered, the colluvium extended to the total depths explored in Borings B-1, B-7 through B-11, B-14 through B-18, and B-21. Within the remaining borings, the weathered schist bedrock extended to the total depths explored.

The Subsurface Boring Logs included in Appendix A give a more detailed description of the soils encountered within the borings.

5.3 Groundwater

At the time of our field work, groundwater was not encountered in the borings drilled at the site. The lack of groundwater noted at the boring locations should not be taken as an accurate representation of the actual groundwater levels. Groundwater levels can fluctuate due to varying seasonal and annual rainfall and snow melt amounts, as well as other factors including local irrigation practices. A long period of time may be required for groundwater to stabilize in the soils present at the site; this period of time is generally not available during a typical subsurface exploration program.

6.0 RECOMMENDATIONS

6.1 Discussion

We have assumed that minor site grading, on the order of 2 feet or less, will be required to reach the desired site grades. Based on the laboratory testing, the site soils have a slight compression potential when loaded. Therefore, to limit post construction total and differential movements and provide a uniform bearing surface, we recommend foundations and concrete slab-on-grade floor bear on a minimum of two (2) feet of imported granular engineered fill.

Our recommendations in the following sections are intended to minimize, to varying degrees, movement related problems associated with the proposed foundations and floor slabs. Even if our recommendations are followed, we cannot guarantee that some movement will not occur. The present state of the art is such that the risk of movement cannot be accurately assessed. It depends on a number of uncontrolled variables such as climatic conditions during and after construction, long term fluctuations of the groundwater level, utility line leakage, landscaping, and other similar aspects. The risk of detrimental movement must be assumed by the project owner.

To reduce the risk of movement of the bearing strata, good drainage must be maintained during and after construction. For this reason, we recommend that the excavations be left open a minimal amount of time. Additionally, where applicable, slab-on-grade floors should be structurally independent of walls and columns and all footings should be founded below the depth of seasonal moisture change.

6.2 Site Preparation

Based on site topography, minor cut and fill balances will likely be required within the proposed structure footprints in order to reach the desired grade elevations. We recommend all organic matter, topsoil, pavement, and any construction/manmade debris, if encountered, be removed from within the construction limits. Excavations should continue to the design grade and structure elevations, and to allow for the placement of at least two

(2) feet of imported granular engineered fill material below all foundations and concrete slab-on-grade floor systems. Where applicable, the footing excavations should be laterally oversized at a 1H:1V ratio to accommodate the recommended over excavation and granular engineered fill placement.

Conventional large construction equipment, such as tracked excavators, should be able to make the required cuts into the site soils. Please note that deeper excavations for will likely encountered dense weathered schist bedrock, which may require ripping teeth to facilitate removal of the material. The excavated soils, cleaned of all unsuitable materials and aggregate greater than 2-inches in nominal size, may be stockpiled on-site and reused as overlot fill, utility trench/exterior wall backfill, and backfill above any buried structures.

Prior to placement of overlot/engineered fill required to reach the desired site grades, we recommend that, to the extent practical, the exposed subgrade soils be scarified to a depth of at least 8-inches, the moisture content adjusted to near optimum, and the soils compacted to at least 95 percent of the maximum dry density, as determined by ASTM D698 (standard Proctor). All exposed surfaces should be free of mounds and depressions which could prevent uniform compaction.

This process will help to delineate soft or disturbed areas. Unstable areas identified during scarification and compaction should either be stabilized or undercut to expose stable material. If isolated soft or unstable areas are encountered, it may be necessary to place a layer of crushed stone to stabilize the subgrade and help expedite construction.

The imported granular engineered fill placed below foundations and concrete slab-on-grade floors should be a non-expansive material with a maximum aggregate size of 3-inches, 40 to 85% passing the No.4 sieve, and no more than 15% passing the #200 sieve with a Liquid Limit less than 25. The moisture content of the imported granular engineered fill should be adjusted to within ±3% of optimum, the material placed in 8-inch thick maximum loose lifts, and compacted to at least 97% of the maximum dry density as determined by ASTM D698 (standard Proctor).

All overlot fill material placed to reach the desired design subgrade elevations should be moisture conditioned to ±3% of optimum, placed in 8-inch loose lifts, and compacted to at least 95% of the maximum dry density (ASTM D698). Please note that, based on the laboratory test results, processing and moisture conditioning of these soils before their re-use as engineered fill should be anticipated.

Experience has shown that the site micaceous soils are moisture sensitive and extra care must be taken during reworking and compaction of these soils to obtain a uniform moisture content throughout the fill. To obtain the recommended compaction requirements, experience has shown that the in-place moisture content should be within the specified range. Moisture contents outside this range will result in greater difficulty in obtaining specified compaction. The geotechnical engineer should be consulted at the time of construction to discuss what type(s) of compaction equipment should be used.

Groundwater was not encountered during our site work. Therefore, we do not anticipate groundwater will be encountered in the footing or utility excavations; however, be aware that temporary dewatering of these excavations may be necessary if groundwater is encountered, or surface drainage is allowed to accumulate in the excavations. Contractors working on the project should have equipment on-site that will lower and maintain the groundwater level below the base of the excavations.

6.3 Foundation Design Recommendations

Due to the slight compressibility of the site soils, and to limit post construction total and differential movements, we recommend conventional spread footing and mat foundation systems be constructed on a minimum of two (2) feet of imported granular engineered fill material over the reconditioned site soils.

The foundations may be designed for an allowable bearing capacity of 2,000 pounds per square foot (psf). As designed, loadings should provide a theoretical safety factor of three or more with respect to a general shear or base failure of the footings. If properly constructed, total and differential settlement should not exceed 1 inch and 1/2-inch, respectively

Exterior footings, interior footings in unheated portions of the building, or footings placed during freezing conditions should be placed at least 4 feet below final grades for frost protection. Interior footings in heated areas may be placed directly below the floor slab. For additional information please refer to the attached Standard Sheet “Freezing Weather Effects on Building Construction”.

We recommend the base of the footing and floor slab excavations be observed and properly compacted to verify a firm and unyielding subgrade has been obtained on which to place the granular engineered fill and structural elements. Additionally, we recommend the lower elevation of the aeration basin, clarifier, and the two (2) building additions include a perimeter drain to collect and reroute any groundwater accumulation to a sump and pump system or to a daylighted location beyond the limits of the facility.

6.4 Interior Concrete Floor Slabs

Concrete floor slabs should be placed on a minimum of two (2) feet of imported granular engineered fill material as specified above. Prior to placement of the floor system, we recommend the exposed subgrade be scarified to a depth of at least 8-inches, the moisture content of the material adjusted to ±3% of the optimum moisture content and the material compacted to at least 95% of maximum standard Proctor dry density (ASTM D698).

We recommend the floor slabs be constructed with properly spaced construction joints and independent of the foundations, in the event some movement does occur. We also recommend providing a minimum 6-inch thick continuous sand/gravel cushion layer directly below the floor slab to prevent capillary moisture rise to the slab. This granular fill should contain less than 12% by weight passing the #200 sieve, and less than 40% passing the #40 sieve.

Please refer to the “Floor Slab Moisture/Vapor Protection” document in the Standard Sheets section at the back of this report for additional information.

6.5 Construction of Building Addition

Due to the possibility of differential movement between the existing North and South Buildings and the new additions, an expansion joint should be incorporated at the interface between the two structures. The expansion joint should be capable of tolerating up to 1-inch of potential differential movement.

During site excavation work for the new additions, care should be taken not to undermine the existing foundation system during the recommended over-excavations for engineered fill placement. Where applicable, we highly recommend a 1H:1V fill wedge be left in-place from the outside edge of the existing footing to the base of the required excavations.

The excavations should not be left open for a significant amount of time and imported granular engineered fill should be placed and compacted in a timely manner.

6.6 Exterior Backfill Considerations

It is our opinion the site soils may be re-used as utility trench backfill, exterior wall backfill, and as overlot fill required to reach the general site grade elevations. Based on the existing moisture content of the site soils, processing of the material will likely be required prior to re-use. All recommendations are based on the standard Proctor method (ASTM D698).

1. All backfill should be free of deleterious/frozen material, and construction debris, and have a maximum aggregate size of 3-inches.

2. Backfill should be moisture conditioned to within ±3% of optimum moisture content prior to being placed.

3. All backfill should be placed in loose lift thicknesses of 8-inches or less. If hand-operated compaction equipment is used, the loose lift thickness should be reduced to 4-inches or less.

4. Each lift should be compacted to at least 95% of maximum proctor density. We recommend the final lift of backfill be compacted to at least 97% of the maximum dry density.

5. Compaction density tests should be performed on alternating lifts to ensure the minimum density is maintained.

6. Utility lines entering or exiting the structures should be leak tested prior to the placement of the slab.

6.7 Trench Excavation

If excavation faces are not retained, the excavations should maintain maximum allowable slopes in accordance with OSHA Regulations (Standards 29 CFR), Part 1926, Subpart P, “Excavations” (can be found on www.osha.gov). Even with the required OSHA sloping, water seepage or surface runoff can potentially induce side slope erosion or running which could require slope maintenance.

For trench excavations, it is our opinion the site colluvial soils and weathered bedrock should be classified as Type C soils with recommended slope laybacks of 1.5H:1V. This classification should be considered preliminary and should be verified in the field on a daily basis by the contractor and/or geotechnical engineer.

http://www.osha.gov/

Excavations deeper than 20 feet and/or in saturated soils or below the ground water table should be considered on an individual basis. Water levels, due to climatic conditions should be evaluated at the time of construction. If the above trench layback recommendations are not feasible, due to space limitations or other factors, the OSHA rules should be consulted for alternative trench stabilization methods. Trench boxes or shoring in compliance with OSHA rules may be acceptable alternatives.

6.8 Retaining Wall Recommendations

We understand that new retaining walls will be added to the west side of the new Equalization Basin and along a portion of the existing east access drive. These site retaining walls will facilitate an elevation difference of approximately ten feet and will be constructed of either cast-in-place concrete foundations with block assembly above grade, or driven sheet piling (if required).

We recommend all retaining walls constructed at this site be placed on a leveling pad comprised of a minimum of 1 foot of crushed limestone aggregate base course material. If placed on the crushed limestone aggregate, the wall systems may be designed for an allowable bearing capacity of 1,500 pounds per square foot (psf). As designed, loadings should provide a theoretical safety factor of three or more with respect to a general shear or base failure of the footings.

To promote drainage, we recommend a clean granular backfill be used directly behind the walls that extends at least 1 foot out from the back face of the wall. This gravel backfill should have a maximum aggregate size of 1½ inches with less than 5% passing the #200 sieve. We also recommend a perforated drain tile be placed at the bottom inside edge of the layer of clean rock behind the wall system. The drain tile should be placed with a minimum slope sufficient to route collected water to the end(s) of the wall and/or points where it can be discharged through gravity flow.

Cleaned and approved site soils or imported material may be used as the remainder of the backfill behind the walls. We have assumed that the site sand and clay soils will be mixed and reused as backfill material. The material should be processed to the extent practical to provide a moisture content within ±3% of optimum, as determined by ASTM D698 (standard Proctor) and compacted to a minimum of 95% of the maximum dry density for wall heights of 10-feet or less. The minimum compactive effort should be increased to 98% for wall heights greater than 10 feet. Compaction of the backfill should be accomplished with hand-operated tampers or other lightweight compactors. Over-compaction may cause excessive lateral earth pressures which could result in unexpected wall movements.

For soils above any free water surface, recommended equivalent fluid pressures for unrestrained foundation elements are:

Active:

Mixed site soils .............................................................. 55 psf/ft Imported granular material ............................................. 40 psf/ft Imported clean rock ....................................................... 35 psf/ft

Passive:

Mixed site soils ............................................................ 265 psf/ft Imported granular material ........................................... 425 psf/ft Imported clean rock ..................................................... 520 psf/ft

Where the design includes restrained elements, the following equivalent fluid pressures are recommended:

At Rest:

Mixed site soils .............................................................. 75 psf/ft Imported granular material ............................................. 60 psf/ft Imported clean rock ....................................................... 55 psf/ft

The following soil parameters should be considered in the design and construction of site retaining walls:

Coefficient of Friction (limestone aggregate base) .................... 0.45 Friction Angle (mixed site soils) ................................................... 22° Friction Angle (imported granular material) ................................. 32° Friction Angle (imported clean rock) ............................................ 36° Cohesion (mixed site clay/sand soils) .................................. 125 psf Unit Weight (mixed site soils) ............................................... 120 pcf Unit Weight (imported granular material) ............................. 130 pcf Unit Weight (imported clean rock) ........................................ 135 pcf

6.9 Pavements

6.9.1 Considerations

The following pavement section was designed based on the procedures outlined in the 1993 AASHTO Empirical Equation for Flexible Pavements and Rigid Pavements. It is anticipated that pavement subgrade soils will consist of the site soils, which are considered fair to good materials for pavement support. Based on the laboratory test results, a California Bearing Ratio (CBR) value of 5.5 was used in the pavement design analysis. We have used a correlation of 1500 x CBR value to estimate the resilient modulus (MR).

As no anticipated traffic volumes or ESAL values have been provided to us at this time, and based on our understanding of the project, we have assumed mainly utility pickups, delivery vans, and equipment/supply trucks within the parking areas and access drives. Therefore, we have assumed a 20 year traffic count of 125,000 equivalent single axle load (ESAL).

Please notify us if any of the parameters used in the pavement design do not adequately define the anticipated conditions.

The 20-year design period is considered to be the interval over which, with proper maintenance, the pavement will not require major repairs. A continuing regular maintenance program should be implemented to maintain satisfactory serviceability over the design life. The maintenance program should include sealing cracks and repairing minor deficiencies. Please notify us if any of the parameters used in the pavement design do not adequately define the anticipated conditions.

6.9.2 Subgrade Preparation

Prior to placement of base course/new pavement or any fill to obtain final subgrade elevations, the exposed subgrade soils should be scarified to a depth of 8-inches, the moisture content of the scarified soils adjusted to near optimum moisture content and the material compacted to at least 95% of maximum standard Proctor dry density (ASTM D698). All prepared subgrades should be proof rolled to verify a firm and unyielding subgrade has been obtained prior to the placement of new fill.

To obtain a firm and unyielding subgrade, on which to construct the new pavement section, scarification and drying of the subgrade soils should be anticipated. This scarification process may need to be repeated over several days in order to allow the soils to dry back to an acceptable moisture content. The earthwork contractor should be made aware of the soil conditions at the site and account for the anticipated subgrade preparation work.

Any areas that "pump" under the loaded dump truck should be evaluated by the engineer to determine whether additional excavation and replacement with a coarse, clean rock or the use of a geo-textile fabric should be used to stabilize the subgrade. Once the subgrade has been proof rolled and approved by the geotechnical engineer, fil material may be placed.

If additional imported fill is required, the material should be submitted to the geotechnical engineer for approval prior to use.

6.9.3 Aggregate Base Course

Aggregate base course should meet the requirements as outlined in Section 882 “Aggregates for Granular Bases and Surfacing” of the SDDOT Specifications. Aggregate base course should be compacted to a minimum of 95 percent of the maximum dry density at a moisture content of ±3% of optimum, as determined by ASTM D698 (Standard Proctor).

6.9.4 Pavement Section Recommendations

Based on the above stated information and our analysis, we recommend the following pavement sections be considered for this project:

We recommend the asphalt be obtained from an approved mix design conforming to the South Dakota Department of Transportation (SDDOT) Class E Specifications as defined in Sections 320 and 321 of the “Standard Specifications for Road and Bridges”, current edition.

Where rigid pavements are used, the concrete should be obtained from an approved mix design conforming to Section 380 “Portland Cement Concrete Pavement” and Section 460 “Structural Concrete” of the SDDOT Specifications, current edition.

Recommended Pavement Section Thickness (inches)

Traffic Area Flexible (Asphalt), in.

Rigid (Concrete), in

Aggregate Base Course, in. Total, in.

Parking Areas & Access Drives

4 -- 6 10

-- 5 4 9

Longitudinal and transverse joints should be provided as needed in concrete pavements for expansion/contraction and isolation. The location and extent of joints should be based upon the final pavement geometry. Sawed joints should be cut within 24-hours of concrete placement. All joints should be sealed to prevent entry of foreign material and dowelled where necessary for load transfer.

Aggregate used in the concrete and asphalt should meet SDDOT specifications under Sections 800, 820, and 880, respectively, for quality and gradation. Mix designs should be submitted prior to construction to verify their adequacy.

7.0 CONSTRUCTION CONSIDERATIONS

7.1 Potential Difficulties

7.1.1 Soft Subgrade Soils

Depending on the time of year in which construction takes place, unstable subgrade soils could be encountered during the site and building grading operations. If encountered, additional conditioning of the soils may be required to obtain moisture contents which allow for firm and unyielding subgrade and/or compaction.

Localized areas of soft wet subgrades can be remedied with additional excavation to expose firmer soils, placement of coarse rock to provide a solid base on which to place additional fill and/or the use of geotextiles between the soft soils and the overlying fill and/or pavement sections. The appropriate means of subgrade stabilization should be evaluated by the geotechnical engineer at the time of construction.

7.1.2 Runoff Water in Excavation

Water can be expected to collect in the excavation bottom during times of inclement weather or snow melt. To allow observation of the excavation bottom, to reduce the potential for soil disturbance, and to facilitate filling operations, we recommend water be removed from within the excavation during construction. Based on the soils encountered, we anticipate the groundwater can be handled with conventional sump pumping.

7.1.3 Disturbance of Soils

The on-site soils can be disturbed under construction traffic, especially if the soils are wet.

If soils become disturbed, they should be subcut to the underlying undisturbed soils. The subcut soils can then be dried and recompacted back into place, or they should be removed and replaced with drier imported fill.

7.2 Excavation Backsloping

If excavation faces are not retained, the excavations should maintain maximum allowable slopes in accordance with OSHA Regulations (Standards 29 CFR), Part 1926, Subpart P, “Excavations” (can be found on www.osha.gov). Even with the required OSHA sloping, water seepage or surface runoff can potentially induce sideslope erosion or sloughing which could require slope maintenance.

For trench excavations, it is our opinion the site soils should be classified as Type C with recommended slope laybacks of 1½H:1V. This classification should be considered preliminary and should be verified in the field on a daily basis by the contractor and/or geotechnical engineer.

Excavations deeper than 20 feet and/or in saturated soils or below the groundwater table should be considered on an individual basis. Water levels, due to climatic conditions should be evaluated at the time of construction. If the above trench layback recommendations are not feasible, due to space limitations or other factors, the OSHA rules should be consulted for alternative trench stabilization methods. Trench boxes or shoring in compliance with OSHA rules may be acceptable alternatives.

7.3 Observation and Testing

The recommendations in this report are based on the subsurface conditions found at our test boring locations. Since the soil conditions can be expected to vary away from the soil boring locations, we recommend on-site observation by a geotechnical engineer/technician during construction to evaluate these potential changes. Soil density testing should also be performed on new fill placed in order to document that project specifications for compaction have been satisfied.

8.0 LIMITATIONS

Within the limitations of scope, budget, and schedule, we have endeavored to provide our services according to generally accepted geotechnical engineering practices at this time and location. Other than this, no warranty, expressed or implied, is intended. Important information regarding risk management and proper use of this report is given in Appendix B entitled “Geotechnical Report Limitations and Guidelines for Use.”

Standard Sheets

01REP013(2/01) AMERICAN ENGINEERING TESTING, INC.

FLOOR SLAB MOISTURE/VAPOR PROTECTION

Floor slab design relative to moisture/vapor protection should consider the type and location of two elements, a granular layer and a vapor membrane (vapor retarder, water resistant barrier or vapor barrier). In the following sections, the pros and cons of the possible options regarding these elements will be presented, such that you and your specifier can make an engineering decision based on the benefits and costs of the choices.

GRANULAR LAYER

In American Concrete Institute (ACI) 302.1-96, a “base material” is recommended, rather than the conventional cleaner “sand cushion” material. The manual maintains that clean sand (common “cushion” sand) is difficult to compact and maintain until concrete placement is complete. ACI recommends a clean, fine graded material (with at least 10% to 30% of particles passing a #100 sieve) which is not contaminated with clay, silt or organic material. We refer you to ACI 302.1-96 for additional details regarding the requirements for the base material.

In cases where potential static water levels or significant perched water sources appear near or above the floor slab, an underfloor drainage system may be needed wherein a draintile system is placed within a thicker clean sand or gravel layer. Such a system should be properly engineered depending on subgrade soil types and rate/head of water inflow.

VAPOR MEMBRANE

The need for a vapor membrane depends on whether the floor slab will have a vapor sensitive covering, will have vapor sensitive items stored on the slab, or if the space above the slab will be a humidity controlled area. If the project does not have this vapor sensitivity or moisture control need, placement of a vapor membrane may not be necessary. Your decision will then relate to whether to use the ACI base material or a conventional sand cushion layer. However, if any of the above sensitivity issues apply, placement of a vapor membrane is recommended. Some floor covering systems (adhesives and flooring materials) require a vapor membrane to maintain a specified maximum slab moisture content as a condition of their warranty.

VAPOR MEMBRANE/GRANULAR LAYER PLACEMENT

A number of issues should be considered when deciding whether to place the vapor membrane above or below the granular layer.

The benefits of placing the slab on a granular layer, with the vapor membrane placed below the granular layer, include reduction of the following:

• Slab curling during the curing and drying process.

• Time of bleeding, which allows for quicker finishing.

• Vapor membrane puncturing.

• Surface blistering or delamination caused by an extended bleeding period.

• Cracking caused by plastic or drying shrinkage.

The benefits of placing the vapor membrane over the granular layer include the following:

• The moisture emission rate is achieved faster.

• Eliminates a potential water reservoir within the granular layer above the membrane.

• Provides a “slip surface”, thereby reducing slab restraint and the associated random cracking.

If a membrane is to be used in conjunction with a granular layer, the approach recommended depends on slab usage and the construction schedule. The vapor membrane should be placed above the granular layer when:

• Vapor sensitive floor covering systems are used or vapor sensitive items will be directly placed on the slab.

• The area will be humidity controlled, but the slab will be placed before the building is enclosed and sealed from rain.

• Required by a floor covering manufacturer’s system warranty.

The vapor membrane should be placed below the granular layer when:

• Used in humidity controlled areas (without vapor sensitive coverings/stored items), with the roof membrane in place, and the building enclosed to the point where precipitation will not intrude into the slab area. Consideration should be given to slight sloping of the membrane to edges where draintile or other disposal methods can alleviate potential water sources, such as pipe or roof leaks, foundation wall damp proofing failure, fire sprinkler system activation, etc.

There may be cases where membrane placement may have a detrimental effect on the subgrade support system (e.g., expansive soils). In these cases, your decision will need to weigh the cost of subgrade options and the performance risks.

AMERICAN ENGINEERING TESTING, INC.

FREEZING WEATHER EFFECTS ON BUILDING CONSTRUCTION

GENERAL

Because water expands upon freezing and soils contain water, soils which are allowed to freeze will heave and loose density. Upon thawing, these soils will not regain their original strength and density. The extent of heave and density/strength loss depends on the soil type and moisture condition. Heave is greater in soils with higher percentages of fines (silts/clays). High silt content soils are most susceptible, due to their high capillary rise potential which can create ice lenses. Fine grained soils generally heave about 1/4" to 3/8" for each foot of frost penetration. This can translate to 1" to 2" of total frost heave. This total amount can be significantly greater if ice lensing occurs.

DESIGN CONSIDERATIONS

Clayey and silty soils can be used as perimeter backfill, although the effect of their poor drainage and frost properties should be considered. Basement areas will have special drainage and lateral load requirements which are not discussed here. Frost heave may be critical in doorway areas. Stoops or sidewalks adjacent to doorways could be designed as structural slabs supported on frost footings with void spaces below. With this design, movements may then occur between the structural slab and the adjacent on-grade slabs. Non-frost susceptible granular soils (with less than 12% passing a #200 sieve) can be used below such areas.

Depending on the function of surrounding areas, the granular soil layer may need a thickness transition away from the area where movement is critical. With granular soil placement over slower draining soils, subsurface drainage would be needed for the granular layer. High density extruded insulation could be used within the granular soils to reduce frost penetration, thereby reducing the granular soil thickness needed. We caution that insulation placed near the surface can increate the potential for ice glazing of the surface.

The possible effects of adfreezing should be considered if clayey or silty soils are used as backfill.

Adfreezing occurs when backfill adheres to rough surfaced foundation walls and lifts the wall as it freezes and heaves. This occurrence is most common with masonry block walls, unheated or poorly heated building situations and clay backfill. The potential is also increased where backfill soils are poorly compacted and become saturated. The risk of adfreezing can be decreased by placing a low friction separating layer between the wall and backfill.

Adfreezing can occur on exterior piers (such as deck, fence or other similar pier footings), even if a smooth surface is provided. This is more likely in poor drainage situations where soils become saturated. Additional footing embedment and/or widened footings below the frost zones (which include tensile reinforcement) can be used to resist uplift forces. Specific designs would require individual analysis.

CONSTRUCTION CONSIDERATIONS

Foundations, slabs, and other improvements which may be affected by frost movements should be insulated from frost penetration during freezing weather. If filling takes place during freezing weather, all frozen soils, snow, and ice should be stripped from areas to be filled prior to new fill placement. The new fill should not be allowed to freeze during transit, placement, or compaction. This should be considered in the project scheduling, budgeting, and quantity estimating. It is usually beneficial to perform cold weather earthwork operations in small areas where grade can be attained quickly rather than working large areas where a greater amount of frost stripping may be needed. If slab subgrade areas freeze, we recommend the subgrade be thawed prior to floor slab placement. The frost action may also require reworking and recompaction of the thawed subgrade.

01REP011(12/09) AMERICAN ENGINEERING TESTING, INC.

EXCAVATION AND REFILLING FOR STRUCTURAL SUPPORT

EXCAVATION

Excavations for structural support at soil boring locations should be taken to depths recommended in the geotechnical report. Since conditions can vary, recommended excavation depths between and beyond the boring location should be evaluated by geotechnical field personnel. If groundwater is present, the excavation should be dewatered to avoid the risk of unobservable poor soils being left in-place. Excavation base soils may become disturbed due to construction traffic, groundwater or other reasons. Such soils should be subcut to underlying undisturbed soils. Where the excavation base slopes steeper than 4:1, the excavation bottom should be benched across the slope parallel to the excavation contour.

Soil stresses under footings spread out with depth. Therefore, the excavation bottom and subsequent fill system should be laterally oversized beyond footing edges to support the footing stresses. A lateral oversize equal to the depth of fill below the footing (i.e., 1:1 oversize) is usually recommended.

Unless the excavation is retained, the backslopes should be maintained in accordance with OSHA Regulations (Standards-29 CFR), Part 1926, Subpart P, "Excavations" (found on www.osha.gov). Even with the required OSHA sloping, groundwater can induce sideslope raveling or running which could require that flatter slopes or other approaches be used.

FILLING

Filling should proceed only after the excavation bottom has been approved by the geotechnical engineer/technician. Approved fill material should be uniformly compacted in thin lifts to the compaction levels specified in the geotechnical report. The lift thickness should be thin enough to achieve specified compaction through the full lift thickness with the compaction equipment utilized.

Typical thicknesses are 6" to 8". Fine grained soils are moisture sensitive and are often wet (water content exceeds the "optimum moisture content" defined by a Proctor test). In this case, the soils should be scarified and dried to achieve a water content suitable for compaction. This drying process can be time consuming, labor intensive, and requires favorable weather.

Filling operations for structural support should be closely monitored for fill type and compaction by a geotechnical technician. Monitoring should be on a full-time basis in cases where vertical fill placement is rapid; during freezing weather conditions; where groundwater is present; or where sensitive bottom conditions are present.

EXCAVATION/REFILLING DURING FREEZING TEMPERATURES

Soils that freeze will heave and lose density. Upon thawing, these soils will not regain their original strength and density. The extent of heave and density loss depends on the soil type and moisture condition; and is most pronounced in clays and silts. Foundations, slabs, and other improvements should be protected from frost intrusion during freezing weather. For earthwork during freezing weather, the areas to be filled should be stripped of frozen soil, snow and ice prior to new fill placement. In addition, new fill should not be allowed to freeze during or after placement. For this reason, it may be preferable to do earthwork operations in small plan areas so grade can be quickly attained instead of large areas where much frost stripping may be needed.

Appendix A

Geotechnical Field Exploration and Testing Boring Log Notes

Unified Soil Classification System Figure 1: Site Location Map

Figure 2: Boring Location Map Subsurface Boring Logs

Gradation Curves Unconfined Compression Tests

Moisture-Density Relationship (Proctor) Test Reports California Bearing Ratio (CBR) Test Report

Appendix A - Page 1 of 2 AMERICAN ENGINEERING TESTING, INC.

A.1 FIELD EXPLORATION

The subsurface conditions at the site were explored by drilling and sampling standard penetration test (SPT) borings. The locations of the borings appear on Figure 2, preceding the Subsurface Boring Logs in this appendix.

A.2 SAMPLING METHODS

A.2.1 Split-Spoon Samples (SS) - Calibrated to N60 Values Standard penetration (split-spoon) samples were collected in general accordance with ASTM: D1586 with one primary modification. The ASTM test method consists of driving a 2-inch O.D.