ADDENDUM_1_20231129_Miles_Jamison_Soild_Waste_Convenience_Center_Geotechnical_Report.pdf

GEOTECHNICAL REPORT

PROPOSED MILES JAMISON SOLID WASTE

CONVENIENCE CENTER

130 SUBURBAN ROAD

SUMMERVILLE, SC

PREPARED FOR

HDR, INC.

SCI PROJECT 230108

NOVEMBER 29, 2023

SCDOT DBE and SBE Charleston County SBE City of Charleston WBE

November 29, 2023

HDR, Inc.

440 S. Church Street, Suite 1200 Charlotte, NC 28202

Attention: Mr. Phillip Westmoreland, P.E.

SCI Project 230108

Dear Mr. Westmoreland:

Soil Consultants, Inc. (SCI) submits this report to provide results of the geotechnical services provided for the proposed Miles Jamison Solid Waste Convenience Center located at 130 Suburban Road in Summerville, SC. Our services were performed in accordance with SCI Proposal No. 14-23-010, dated January 25, 2023. This report provides a discussion of the proposed development, exploration procedures used, subsurface conditions encountered, seismic analysis, and recommendations for site preparation and foundation and pavement design.

We appreciate the opportunity to be of service to you during the design phase of this project. If we may be of further assistance during design or as construction proceeds, please call.

Analyses by: Reviewed by:

11/29/2023

11/29/2023

Ronald R. Austin, P.E. A. Talbot Henderson, III, P.E.

TABLE OF CONTENTS

Page

Page i SCI Project No. 230108

INTRODUCTION

SCOPE OF PROJECT

SITE DESCRIPTION

FIELD EXPLORATION

LABORATORY TESTING

BORING LOGS

SUBSURFACE CONDITIONS

Stratigraphy

Groundwater

SEISMIC CONSIDERATIONS

Liquefaction Potential

Seismic Design Parameters

FOUNDATION DESIGN AND CONSTRUCTION CONSIDERATIONS

Remedial Action

Shallow Foundations

Soil-Supported Concrete Floor Slabs

Lateral Earth Pressure Coefficients

Site Preparation in Construction Areas

PAVEMENT DESIGN AND CONSTRUCTION RECOMMENDATIONS

Design Methodology

Section Thicknesses

Section Materials and Placement Criteria

Site Preparation in Pavement Areas

LIMITATIONS OF REPORT

FIGURES

Boring Location Plan

ATTACHMENTS

Soil Boring Logs

Key to Boring Log Symbols and Terms

Laboratory Test Results

Page 1 SCI Project No. 230108

INTRODUCTION

Soil Consultants, Inc. (SCI) presents this report to document geotechnical findings and recommendations for the proposed Miles Jamison Solid Waste Convenience Center located at

130 Suburban Road in Summerville, SC. Geotechnical services were performed in accordance with SCI Proposal No. 14-23-010, dated January 25, 2023. Our services were authorized via the

HDR, Inc. Task Order No. 10360335-01, which was executed on August 22, 2023.

SCOPE OF PROJECT

It is our understanding that the proposed project includes infrastructure improvements and structural upgrades to the existing convenience center facility located at the site. We have been provided a preliminary set of drawings for the project, including survey, site plan, grading plan, and section view drawings. The survey drawing shows the existing conditions at the site, and the site plan drawing shows the layout of the proposed development at the site. Based on project information provided, we understand that the proposed improvements consist largely of pavement areas, concrete slab areas, divider/retaining walls, and a small attendant building. For the purposes of this report, we assume that the proposed building will be a 1-story structure and the floor of the proposed building will be a concrete slab supported at grade on compacted fill

We have not been provided structural loading information for the proposed structure. However, based on previous experience with similar projects, we anticipate that maximum column loads will not exceed 50 kips, and maximum wall loads will not exceed 3 kips per linear foot.

Based on the grading plan provided, required fill heights across most of the site will not exceed

2 feet. However, the required fill height in one Citizen Disposal Area at the site will be on the order of 5 to 6 feet. Fill heights refer to the net fill heights above the existing ground surface elevation at the time of our subsurface exploration neglecting any fill that is placed where existing soils

(such as topsoil) will be removed.

SITE DESCRIPTION

The 7-acre property is bound by a vacant disposal service property and undeveloped wooded property to the north, by undeveloped wooded properties to the east and west, and by commercial properties to the south. At the time of our investigation, the site was developed and the existing convenience center structures and facilities were present. Most of the site was cleared, but the northeast portion of the site was wooded. A small mound of buried debris was located in the eastern portion of the site. The ground surfaces traveled by the drilling equipment were generally noted to be relatively firm.

Based on topographic contour lines on the provided survey drawing, the ground surface elevations across the property generally range from approximately 48 feet to 60 feet. No datum for the elevations was indicated on the drawing. Based on observations at the site, the ground surface appeared to be relatively flat, sloping gently to the southeast. In addition, the ground surface elevations appeared similar to the adjacent properties.

Based on review of current FEMA Flood Insurance Rate Maps, it appears the property is located within Flood Zone X and is not located within an area where flooding or wave action is expected during the design flood event.

Page 2 SCI Project No. 230108

FIELD EXPLORATION

On October 13 and 16, 2023, we performed seven soil borings, designated B-1 through B-7, using mud-rotary drilling procedures at the site at selected locations. Boring locations were staked at the site by a representative of our firm using the site plan drawing provided with reference to existing site features. Approximate boring locations are shown on Figure 1, Boring Location Plan, included as an attachment.

Boring B-5 was advanced to a depth of approximately 40 feet below the existing ground surface, and Borings B-1 through B-4, B-6, and B-7 were advanced to depths of approximately 20 feet.

The borings were performed using track-mounted drilling equipment. During drilling, split-spoon sampling and Standard Penetration Testing (SPT) was performed at selected intervals. Our experienced drilling personnel visually classified the recovered samples and placed portions into sealed sample containers for transport to our laboratory.

Soil samples from this exploration will be retained for a period of 3 months from the date of this report. Unless other arrangements are made, they will be disposed of following this period.

LABORATORY TESTING

We performed soil mechanics laboratory tests on selected samples to aid in soil classification and to determine engineering properties for use in liquefaction analyses. The test name, test method, and number of tests that we performed are presented in Table 1. Results are included as an attachment.

Table 1 Laboratory Testing Program

Test Name Test Method Number of Tests

Natural Moisture Content ASTM D2216 10

Percent Finer than 75-m sieve ASTM D1140 10

Atterberg Limits ASTM D4318 6

BORING LOGS

SCI’s geotechnical engineer developed the final log for each boring using SPT data and visual descriptions recorded during the field exploration, visual classification of the recovered materials after return to the SCI laboratory, and results of laboratory testing. The boring logs attached to this report represent SCI’s interpretation of stratigraphy and groundwater conditions at the explored locations based on visual classification of recovered samples. Transition boundaries between soil types noted on the boring logs are approximate.

SUBSURFACE CONDITIONS

Generalized stratigraphy and groundwater are discussed in the following paragraphs. The subsurface and groundwater conditions are based on conditions encountered at the boring locations and to the depths explored. All references to depth are approximate and are made with respect to the existing ground surface at the time the borings were performed.

Page 3 SCI Project No. 230108

Stratigraphy

Subsurface conditions encountered in the borings were generally similar.

Below the ground surface, the borings generally encountered coarse-grained and fine-grained soils typical of Coastal Plain sediments to depths of 21½ feet (termination of Borings B-1 through

B-4, B-6, and B-7), and 28 feet. The coarse-grained soils consisted of very loose to medium dense, fine to medium-grained sands with varying amounts of silt and clay. SPT resistance (N) values obtained in the sands ranged from 3 to 15 blows per foot (bpf). The fine-grained soils consisted of very soft to stiff silts and clays with N values ranging from 1 to 13 bpf. Below a depth of 28 feet, Boring B-5 encountered medium dense and very stiff to hard sediments of the Cooper

“Marl” Formation with a N values ranging from 18 to 32 bpf to termination of the boring at a depth of 41½ feet.

The Cooper Marl sediments are typically calcareous silty soils that contain varying sand, shell, and phosphate nodule content. They typically vary in the Unified Soil Classification System from silty or clayey sands (SM or SC) to silts or clays of low to high plasticity (ML/MH or CL/CH). The

Cooper Marl sediments encountered at this site were generally classified as clayey sands (SC) and elastic silts (MH) using the ASTM D2488 Visual-Manual classification procedures.

The soil borings did not encounter any topsoil or root content in the near surface soils. Although this data is an indication of the depths of root content at the site, it should be noted that the depth of roots and organic material can be expected to vary across the site and will likely be more significant within more heavily vegetated/wooded portions or low-lying areas of the site. The actual depth to which roots of significant size and quantity will be encountered will best be determined by visual inspection during site stripping operations.

Groundwater

The depths to groundwater were measured in the borings at least 24 hours after completion of drilling and sampling to allow drilling fluids to dissipate and groundwater levels to somewhat stabilize. The measured depths to groundwater ranged from 9 feet to 13¾ feet.

Fluctuations in the level of groundwater may occur due to variations in ground elevation, rainfall, drainage, types of soil encountered, temperature, and other factors not evident at the time the measurement was made. Since the probability of such variations is anticipated, design drawings and specifications should accommodate such possibilities, and construction planning should be based on such assumptions of variation. If excavation is required below groundwater during construction, dewatering should be anticipated.

SEISMIC CONSIDERATIONS

Seismic analysis is required in accordance with the International Building Code, 2021 Edition

(IBC). The IBC references the American Society of Civil Engineers (ASCE) 7-16, Minimum Design

Loads for Buildings and Other Structures. Therefore, the procedures described in ASCE 7-16 were used.

Page 4 SCI Project No. 230108

Seismic considerations include liquefaction of relatively clean, submerged loose sands due to shaking as well as subsequent ground movements associated with shearing or consolidation of the liquefied soils. In addition, when potentially liquefiable soils exist near the ground surface, surface disruptions such as sand boils are possible. Such disruptions beneath structures supported at grade or on shallow foundations could result in a bearing capacity failure.

Liquefaction Potential

To evaluate the potential for liquefaction, initial determination of site class is needed. The IBC requires soil information to a depth of 100 feet be used in site classification. However, ASCE 7-

16, Section 20.1 states “Where site-specific data are not available to a depth of 100 feet, appropriate soil properties are permitted to be estimated by the registered design professional preparing the soil investigation report based on known geologic conditions.” SCI used weighted average N values, with extrapolated soil conditions between the 41½-foot boring termination depth and 100 feet as permitted by ASCE 7-16, to determine the site class. Based on the weighted average N values, the site may be initially considered as Site Class E.

Liquefaction analyses were performed using Seed's simplified procedure, as updated and documented by Youd et al (2001), considering the material types and depths to groundwater encountered in the borings and a design earthquake with a magnitude of 7.3 having a 2% probability of exceedance in a 50-year period as required by IBC 2021. The Maximum Considered

Earthquake Geometric Mean (MCEG) peak ground acceleration adjusted for site class effects

(PGAM) used in liquefaction analyses was 1.419g. We used the USGS Earthquake Hazards program to determine PGAM based on Site Class E.

Results of the liquefaction analysis indicate that the soils at the site show a low potential for liquefaction due to the clayey nature of the soils encountered below the groundwater table in all of the borings, except Boring B-4. Calculations indicate that approximately 3 inches of liquefaction-induced total settlement could occur at the location of Boring B-4 as a result of the design seismic event. Based on our experience with past projects, we expect the calculated liquefaction settlement is within the range that is generally considered acceptable for similar construction. However, the magnitude of liquefaction-induced settlement should be evaluated by the project structural engineer considering the settlement tolerance of the proposed structure(s).

Seismic Design Parameters

Because of the potential for liquefaction, the site is characterized as Site Class F. However, ASCE

7-16 allows the design spectral response accelerations for a site to be determined without regard to liquefaction provided structures have a fundamental period of less than or equal to 0.5 second and the risks of liquefaction are considered in structure design. If the proposed structure meets the requirements of the exception, as determined by the structural engineer, and liquefaction risks are considered in the design, Site Class E could be used for this project. If the proposed structure does not meet the requirements of the exception, please contact us because a site-specific ground motion hazard analysis may be required.

Section 11.4.8 of ASCE 7-16 states that a (site specific) ground motion hazard analysis shall be performed for structures on Site Class E sites with SS greater than 1.0g or S1 greater than 0.2g.

SS for the project site is 1.917, and S1 is 0.574g. However, for the purposes of this report, we assume that Exceptions 1 and 3 in Section 11.4.8 of ASCE 7-16 would apply for this project, so

Page 5 SCI Project No. 230108 a site-specific ground motion hazard analysis would not be required. The applicability of

Exceptions 1 and 3 should be verified by the project structural engineer. If Exceptions 1 and 3 are not applicable, please contact us because a site-specific ground motion hazard analysis may be required. Seismic design parameters based on Site Class E are presented in Table 2.

Table 2 Seismic Design Parameters

Seismic Design Parameter Design Value

Short-period site coefficient (at 0.2 s period) Fa 1.20

Long-period site coefficient (at 1.0 s period) Fv 2.052

Mapped MCER, 5 percent damped, spectral response acceleration parameter at short periods

SS 1.917

Mapped MCER, 5 percent damped, spectral response acceleration parameter at a period of 1 s

S1 0.574

Design, 5% damped, spectral response acceleration parameter at short periods

SDS 1.534

Design, 5 % damped, spectral response acceleration parameter at a period of 1 s

SD1 0.785

Based on Site Class E.

Assumes exception for fundamental period applies; otherwise, Site Class F will apply requiring a site response analysis.

Assumes Exceptions 1 and 3 in Section 11.4.8 of ASCE 7-16 applies.

FOUNDATION DESIGN AND CONSTRUCTION CONSIDERATIONS

Subsurface conditions encountered in the soil borings indicates that soft clayey soils were encountered at shallow depths in some of the borings. These soft clayey soils are expected to be highly compressible under load, and may not provide sufficient bearing capacity for support of shallow foundations for the proposed building structure. Calculations, which were based on the assumed structural loading and fill height discussed in the Scope of Project section of this report, indicate total settlement of the proposed attendant building structure is expected to be on the order of 1½ to 2 inches. Therefore, a preloading and settlement monitoring program would need to be performed to allow the use of shallow foundations to support the proposed building. In addition, some remedial action discussed below will likely need to be performed during foundation construction. Alternatively, the proposed building could be supported on deep foundations. Please contact us if recommendations for deep foundations are desired.

It is also recommended that a preloading and settlement monitoring program be performed in the proposed pavement and concrete slab areas of the site prior to construction of these facilities.

Recommendations for the preloading and settlement monitoring program and shallow foundations are presented in the following sections. In addition, site preparation recommendations are provided later in this report.

Preloading and Settlement Monitoring Program

If the project schedule can accommodate it and use of deep foundations are not desired for support of the proposed structure, a preloading program could be performed to reduce the

Page 6 SCI Project No. 230108 anticipated settlement due to fill placement prior to construction of the proposed improvements.

The preload program should generally consist of placing the permanent fill required for grading for this project, and allowing it to remain in place for a time period prior to foundation construction.

The preload fill should meet the requirements for controlled fill stated later in this report, and should be placed and compacted as described later in this report. The preload fill should be a continuous operation extending across the entire area of the proposed improvements. In addition, the preload fill should extend at least 5 feet outside of the proposed construction limits on all sides.

Before fill placement, the recommended site preparation measures (i.e. stripping and compaction) described later in this report should be performed. After these site preparation measures are performed, settlement plates should be installed. Settlement plates should be placed at locations across the construction area selected by the geotechnical engineer. Once the settlement plates are installed and initial readings taken, the permanent fill may be placed. Care must be exercised during placement and compaction of the fill to avoid disturbing the settlement plate riser pipes.

Settlement plate readings are typically taken twice in the first week by a land surveyor after installation and once per week thereafter until the settlement has ceased. SCI can provide assistance during installation of the settlement plates, which would be provided by others, and can evaluate the settlement plate data to determine when the settlement has ceased and the settlement plates can be removed.

Remedial Action

Remedial action would consist of excavation and removal of the softer clayey soils beneath the building foundations. Since no borings were performed in the area of the proposed attendant building, the need for or the exact lateral and vertical extent that remedial action will be required cannot be determined without performing additional borings at the site. Based on the soil conditions encountered in the borings, we expect remedial action may be required to depths of approximately 5 feet below the existing ground surface.

The actual extents and depths to which remedial action will be required will best be determined by the recommended inspection and testing during foundation construction as described in the

Shallow Foundations section. After removal of the clayey soils, thoroughly compacted backfill or granite aggregate as described later in this report should be placed to the desired foundation subgrade elevation.

Shallow Foundations

If the site preparation procedures and remedial action described in this report are followed and the preload program described herein is performed, we recommend designing the foundations using a maximum allowable soil contact pressure of 1,500 pounds per square foot (psf). To prevent punching failure of the foundations, minimum widths of 24 and 36 inches should be used for sizing of wall and column foundations, respectively. All foundations should bear at a minimum depth of 18 inches below the proposed ground surface.

Based on the assumed structural loading and fill height, total settlement of the proposed structure is expected to be 1 inch, approximately half of which is expected to be differential in nature. Please note that fill placement greater than the assumed fill height may increase the estimated settlement, and SCI should be contacted to evaluate the recommendations provided herein if any additional fill will be required.

Page 7 SCI Project No. 230108

The final foundation bearing elevations should be evaluated by SCI personnel to verify that the bearing soils are capable of supporting the recommended maximum soil contact pressure and are suitable for foundation construction. These evaluations should include visual observations, hand rod probing, and dynamic cone penetrometer (DCP) testing among other methods deemed appropriate by the geotechnical engineer at the time of construction. These evaluations should be performed within each foundation excavation, and hand rod probing and DCP testing should be performed in continuous foundation excavations at intervals not greater than 5 feet and 50 feet, respectively.

Exposure to the environment may weaken the soils at the foundation bearing level if the foundation excavations remain open for too long. Therefore, foundation concrete should be placed the same day that excavations are dug and compacted, if possible. If the bearing soils are softened by surface water intrusion or exposure, the softened soils must be either removed from the foundation excavation bottom or re-compacted before placement of concrete. Groundwater levels should be maintained at least 1 foot below the foundation subgrade to prevent softening and destabilization during construction. If necessary, dewatering may be accomplished by pumping from sumps located within the foundation excavations.

Soil-Supported Concrete Floor Slabs

Concrete slabs constructed on properly prepared and compacted fill material may be designed using a modulus of subgrade reaction (Ks) of 150 pounds per cubic inch (pci). Concrete slabs constructed on properly prepared existing site soils may be designed using a modulus of subgrade reaction (Ks) of 100 pci. The recommended modulus is based on a 30-inch diameter plate load test and is only applicable for light point loads. The recommended modulus would be lower for loads applied over a larger area. The slabs should be designed utilizing the requirements for construction joints, expansion joints, and saw cuts as recommended by the American Concrete

Institute (ACI) and should include a vapor barrier.

To avoid deterioration of the final subgrade soils during construction, the slab area should be graded to at least 1 foot above surrounding grade areas to promote positive drainage from the grade slab area. The slab-on-grade area should be placed with a slight crown in the middle to minimize standing or ponding water in the grade slab area. This crown should be maintained until grade slab construction is ready to proceed.

Lateral Earth Pressure Coefficients

The soil borings generally encountered sands and clays in the top 5 feet below the ground surface.

We have provided recommended lateral earth pressure coefficients in Table 3 for these soils. In addition, we have provided lateral earth pressure coefficients for loose to medium dense sands which are often used as backfill adjacent to below-grade structures/foundations. These coefficients can be used for the design of below grade foundations, walls, and other underground structures.

The recommended earth pressure coefficients provided assume a frictionless wall/face with level backfill and no hydrostatic pressure. We note that the equivalent fluid pressures shown are only valid above the groundwater depth. Below the groundwater depth, the hydrostatic water pressure must first be subtracted from the total earth pressure before applying the lateral earth pressure coefficient to calculate the equivalent fluid pressure. If groundwater will not be drained, the

Page 8 SCI Project No. 230108 hydrostatic water pressure must then be added back with the equivalent fluid pressure.

The earth pressure coefficients provided in Table 3 do not account for surcharge loading or sloped soil conditions. Additional loading from structures or placement of fill material at the ground surface should be considered by the structure designer. Soil backfill placed adjacent to foundations should be compacted in accordance with the recommendations provided in this report. Because soil compaction behind retaining structures can greatly increase the lateral pressures on these structures, temporary bracing may be necessary during backfilling operations.

Table 3 Recommended Earth Pressure Coefficients

Soil Type

Lateral Earth

Pressure Condition Coefficient

Unit Weight of Soil (pcf)

Equivalent Fluid Pressure (psf/foot)

Clays and Clayey Sands (CH and SC)

At Rest (Ko)

Active (Ka)

Passive (Kp)

1.00

0.50

1.00

100.0

50.0

100.0

Loose to Medium Dense Sands and Fill

(SP-SM and SM)

At Rest (Ko)

Active (Ka)

Passive (Kp)

0.47

0.31

3.25

47.0

31.0

325.0

Site Preparation in Construction Areas

Performance of grade-supported features will be directly affected by the quality of site preparation.

Recommendations for site preparation within the proposed construction areas are presented herein.

Clearing and Stripping. The proposed construction areas should be fully cleared and stripped of any topsoil, trees, stumps, or other organic debris. Topsoil and organic material encountered within the project limits should be removed from the site or stored on site away from controlled fill if reuse for non-structural fill is desired. Stripping and undercutting should extend at least 5 feet beyond the proposed structure footprint. In addition, buried debris is present in some areas of the site, and the buried debris should be excavated and removed form the site.

Compaction of Stripped Subgrade. After organic material and soft soils have been stripped, buried debris has been removed, and before placement of fill material, the remaining surface soils within the proposed construction areas should be thoroughly and uniformly compacted in place before proofrolling.

Proofrolling. Following compaction, the proposed construction areas should be proofrolled with a loaded dump truck or other similar rubber-tired, heavy construction equipment. SCI’s geotechnical engineer or an SCI representative should monitor the proofrolling operations. Areas that pump, rut, or perform poorly during the proofrolling operations should be undercut and replaced with controlled backfill. After proofrolling and subsequent repairs, controlled fill should be placed to achieve the desired grades.

Page 9 SCI Project No. 230108

Suitability of Onsite Soils for Use as Structural Fill. As previously discussed in the Subsurface

Conditions section of this report, many of the borings encountered clayey soils at shallow depths.

The clayey soils are generally not recommended for use as structural fill due to the difficulty in achieving proper compaction and due to the poor drainage characteristics of clayey soils.

Backfill and Controlled Fill Material Criteria. Backfill and controlled fill should be non-plastic and granular in nature with a maximum of 15% passing the No. 200 sieve. Backfill and controlled fill soils should be as approved by the project geotechnical engineer and should generally consist of sands classified as SP, SP-SC, SC, SP-SM, or SM soils according to the Unified Soil

Classification System. In addition, backfill and controlled fill should be free of roots, organics, and debris.

Backfill and Controlled Fill Placement Criteria. Backfill and controlled fill should be placed in thin successive layers 8 to 10 inches thick loose measurement, and each layer should be compacted to at least 95% of its maximum laboratory dry density, within ± 2% of its optimum moisture content determined in accordance with ASTM D1557 (Modified Proctor). However, large vibrating compaction equipment should not be used immediately adjacent to existing or recently constructed facilities or structures. Hand operated compaction equipment may be used to compact soils in these areas. If hand-operated compaction equipment is used, the layer thickness should be reduced to approximately 6 inches thick loose measure.

Verification of In-Place Moisture and Density. In-place field density tests should be performed as backfill or controlled fill is being placed and compacted to ensure that required density and moisture conditions are being achieved. The International Building Code requires continuous inspection of structural fill within building footprint during its placement. Since these testing services are within the scope of services we routinely provide for our clients, we urge that SCI be retained to provide testing services during the earthwork phase.

Wet Conditions during Construction. If standing water is noted in the bottom of excavations or stability of wet soils becomes a problem during compaction, a layer of thoroughly compacted granite aggregate meeting the requirements of ASTM C33, Size No. 57 or 67, could be used to establish a stable working mat. The aggregate layer would be covered with a layer of geotextile filter fabric, such as Mirafi® 140NL or equivalent, and then the soil backfill would be placed. If the amount of backfill is small, thoroughly compacted granite aggregate could be used entirely in lieu of soil backfill.

Grading and Drainage. The presence of near-surface fine-grained soils at the site may lead to

"perched" water conditions. A perched condition occurs when water cannot drain quickly through the lower-permeability fine-grained soils. Subsequently, the trapped water moves laterally across the site to pond in low areas before it slowly descends to the true groundwater level or evaporates.

Before site work begins, the installation of additional or temporary drainage ditches will help control perched water conditions. If site work takes place during extended periods of dry weather, the need for extensive drainage improvements may be less critical. However, if site work takes place during wet weather conditions, more extensive drainage improvements may be required.

Even during dry weather conditions, ditches and drainage improvements should be in place to handle any heavy rainfall that might occur during construction.

Page 10 SCI Project No. 230108

Groundwater was encountered at depths ranging from approximately 9 feet to 13¾ feet below the existing ground surfaces in the borings. Although unlikely, dewatering should be anticipated if excavation below the groundwater is required. Safety precautions must be taken to maintain the side slopes and bottoms of deeper excavations.

Temporary and permanent site drainage should be established to facilitate drainage away from the proposed improvements. This will prevent soils beneath floor slabs and foundation elements from becoming saturated and reduce fluctuations in moisture contents. Positive site drainage is one of the most important factors influencing the long-term performance of structural foundation elements and pavements.

PAVEMENT DESIGN AND CONSTRUCTION RECOMMENDATIONS

As requested, we have provided recommendations for both asphalt cement concrete (flexible) and Portland cement concrete (rigid) pavements. We have also provided recommendations for both light-duty and heavy-duty pavement alternatives. We define light-duty paved areas as areas having a heavy concentration of automobiles and no loaded trucks, such as automobile parking lots. We define heavy-duty paved areas as areas traveled by heavy vehicles, including fire trucks and loaded trucks, such as truck driveway and loading/unloading areas. In addition, rigid pavement is recommended for loading docks, dumpster pads, and other areas where heavy wheel loads will be concentrated.

The section view drawings provided show pavement details, consisting of 4 inches of asphaltic concrete underlain by 10 inches of stone, in all the section views. The pavement section indicated on the provided drawings would serve as a heavy-duty pavement section.

Design Methodology

Traffic data has not been provided; therefore, our pavement design is based on our experience with similar projects. We assumed an average daily traffic (ADT) volume of 1,500 vehicles and that truck traffic will not exceed 10% of the ADT. Therefore, we have assumed typical design traffic loading 18-kip equivalent single axle loads (ESALs) over a 20-year pavement design life to be 100,000 and 1,100,000 for light-duty and heavy-duty pavements, respectively. The pavement design considers an initial serviceability of 4.2, a terminal serviceability of 2.0, and a reliability of

90%.

The flexible pavement section is designed using the American Association of State Highway and

Transportation Officials (AASHTO) “structural number” (SN) system. The SN used for design is based on a minimum subgrade California Bearing Ratio (CBR) of 4 for properly compacted existing site soils or fill material. The rigid pavement section is designed in accordance with ACI

330R-08 “Guide for the Design and Construction of Concrete Parking Lots”.

Section Thicknesses

Table 4 presents the recommended minimum thicknesses for the flexible pavements. Table 5 presents the recommended minimum thicknesses for the rigid pavements.

Page 11 SCI Project No. 230108

Table 4 Recommended Section Thicknesses for Flexible Pavement

Traffic

Rating Compacted Subgrade

Aggregate Base

(SCDOT GABC)

HMA

Intermediate

(SCDOT

Type B)

HMA Surface

(SCDOT

Type B)

Light Duty 12 inches 6 inches -- 2½ inches

Heavy Duty 18 inches 10 inches 2 inches 2 inches

Table 5 Recommended Section Thicknesses for Rigid Pavement

Traffic

Rating

Compacted Subgrade

Aggregate Base

(SCDOT GABC)

Portland Cement Concrete

(Fc’ = 4,500 psi)

Light Duty 12 inches 6 inches 6 inches

Heavy Duty 18 inches 6 inches 8 inches

Section Materials and Placement Criteria

Graded aggregate base course (GABC) should be compacted to at least 100% of its maximum laboratory dry density within ± 2% of its optimum moisture content determined in accordance with

ASTM D1557 (Modified Proctor). The hot-mix asphalt (HMA) concrete should be compacted to at least 94% of its maximum theoretical density. All subgrade, base and pavement construction operations and materials should meet the minimum requirements of the South Carolina

Department of Transportation (SCDOT) Standard Specifications for Highway Construction (2007

Edition).

Rigid concrete pavement should conform to the SCDOT Standard Specifications, Sections 701 and 702, for Portland Cement and Portland Cement Concrete. In addition, all aspects of concrete placement, joints, sealants, etc. should conform to ACI 330, Guide for Design and Construction of Concrete Parking Lots.

Site Preparation in Pavement Areas

In general, sands are considered good to excellent for use as pavement subgrade. Near-surface soils within the proposed pavement areas predominantly consisted of sands with varying amounts of silt and clay. Therefore, the near-surface soils should be suitable for pavement subgrade.

However, clayey soils were encountered at shallow depths in many of the borings. In general, clayey soils are considered marginal to poor for use as pavement subgrade material and would require a design with emphasis on proper drainage for long-term pavement life. In addition, undercutting and replacement with controlled fill may be required in areas where clayey soils are encountered at or near the pavement subgrade elevations and if the subgrade soils are allowed to get wet during periods of rainfall.

Page 12 SCI Project No. 230108

Drainage. The single most destructive element that the pavement will be subjected to is the presence of excess water. Pavements should be adequately sloped and sufficient drainage provided such that excess water is allowed to runoff before it can migrate into the pavement system. In addition, in areas where runoff is expected to accumulate, under drains should be installed to prevent continual saturation of the base course and subgrade soils.

Clearing and Stripping. The proposed pavement areas should be fully cleared and stripped of any topsoil, trees, stumps, or other organic debris. Topsoil and organic material encountered within the project limits should be removed from the site or stored on site away from controlled fill if reuse for non-structural fill is desired. Stripping and undercutting should extend at least 3 feet beyond the proposed pavement limits.

Compaction of Stripped Subgrade. After organic material and soft soils have been stripped and before placement of fill material, the remaining surface soils within the proposed pavement areas should be thoroughly and uniformly compacted in place before proofrolling.

Proofrolling. Following compaction, the proposed pavement areas should be proofrolled with a loaded dump truck. SCI’s geotechnical engineer or an SCI representative should monitor the proofrolling operations. Areas that pump, rut, or perform poorly during the proofrolling operations should be undercut and replaced with controlled backfill. After proofrolling and subsequent repairs, controlled fill should be placed to achieve the desired grades.

Undercutting. If required, undercut depths and lateral extents would be determined based on the results of the proofrolling. The extent of undercutting will be dependent on weather conditions and the effectiveness of site drainage in place at the time earthwork is in progress. While stable near optimum moisture content, the stability of clayey soils will deteriorate rapidly when exposed to excessive moisture. Therefore, any undercut clayey soils could be used as non-structural fill in landscaped and grassed areas but are not recommended for controlled structural fill.

Controlled Fill Material Criteria. Controlled fill, if needed to raise the grade in the pavement areas, should be non-plastic and granular in nature with a maximum of 10% passing the No. 200 sieve. Backfill and controlled fill soils should be as approved by the project geotechnical engineer and should generally consist of sands classified as SP, SP-SC, or SP-SM soils according to the

Unified Soil Classification System. In addition, backfill and controlled fill should be free of roots, organics, and debris.

Controlled Fill Placement Criteria. Controlled fill should be placed in thin successive layers 8 to 10 inches thick loose measurement, and each layer should be compacted to at least 95% of its maximum laboratory dry density within ± 2% of its optimum moisture content determined in accordance with ASTM D1557 (Modified Proctor). However, large vibrating compaction equipment should not be used immediately adjacent to existing or recently constructed facilities or structures. Hand operated compaction equipment may be used to compact soils in these areas.

If hand-operated compaction equipment is used, the layer thickness should be reduced to approximately 6 inches thick loose measure.

Verification of In-Place Moisture and Density. In-place field density tests should be performed as controlled fill is being placed and compacted to ensure that required density and moisture conditions are being achieved. We recommend that in-place testing be performed at 1 test per lift

Page 13 SCI Project No. 230108 per 5,000 sf of pavement area, with a minimum of 3 tests being performed per lift. Since these testing services are within the scope of services we provide, we urge that SCI be retained to provide testing services.

LIMITATIONS OF REPORT

This report was prepared as an instrument of service exclusively for HDR, Inc. and the project design team in preparation of the foundation design, construction drawings, and construction specifications for the proposed Miles Jamison Solid Waste Convenience Center located at 130

Suburban Road in Summerville, SC. Recommendations and comments given in this report are based on the results of the soil borings, combined with interpolation of the subsurface conditions between borings, and the provided and assumed design data. If any changes occur in the design concept or if conditions are encountered during construction that appear to be different from those represented, the conclusions and recommendations contained in this report shall not be considered valid until the changes are reviewed by SCI and our findings and conclusions are verified in writing.

SCI should be given the opportunity to review the design and construction documents. The purpose of this review is to verify that our recommendations are properly incorporated into the project plans and specifications. Review of design and construction documents is not within the scope of authorized services outlined in our proposal; therefore, additional fees would apply.

SCI’s report has been prepared in accordance with generally accepted geotechnical engineering practice with a degree of care and skill ordinarily exercised by reputable geotechnical engineers practicing in this area and the area of the site. Verification of subsurface conditions for the purpose of determining the difficulty of excavation, dewatering, and other construction issues is the responsibility of others specializing in those areas.

SCI Project No. 230108

FIGURES

Reference: Base map provided by Client. Legend:

Note: Boring locations are approximate. Test Boring Location

Scale Not to scale 230108

Date 1

BORING LOCATION PLAN

Proposed Miles Jamison Solid Waste Convenience Center

130 Suburban Road

Summerville, SC

Project No.

11/28/2023 Figure

B-2

B-1

B-3

B-4 B-5

B-6

B-7

SCI Project No. 230108

ATTACHMENTS

2.0

21.5

CLAYEY SAND (SC): loose, brown, fine to medium, moist

FAT CLAY WITH SAND (CH): very soft to firm, gray and reddish yellow, moist

- reddish yellow

Boring terminated at 21.5 feet below referenced grade.

3-3-3

2-2-3

2-2-4

1-1-2

1-1-3

1-1-1

1-1-1

1-1-1

1-1-2

Project:

Ground Surface Total Depth:

Drilling Method:

10/13/2023

Water Level:

21.5 ft

SCI Project:

Drill Rig:

230108

CME 45C (Track)

Proposed Miles Jamison Solid Waste Convenience Center 130 Suburban Road, Summerville, SC

The Soil Consultants, Inc. Key to Boring Log Symbols and Terms contains explanations about symbols and terms used on the boring log.

See Boring Plan Benbow

Remarks:

Not known to SCI 11.4 ft (24-hour) Mud Rotary (4-in. diameter)

Location:

Datum:

Elevation:

LOG OF BORING B-1

Date Drilled:

Driller:

-0

P R

IM

A

R Y

L O

G S

.G P

J/

-0

T

E M

P

LA

T E

.G D

T

/2

9/

Corrected N Value

20 40 60 80

(Clays to N60 and Sands to (N1)60)

Material Graphic

D ep th (f t)

Material Description

Sample

T yp e

D ep th

N um be r

Actual Blows (6-in.

interval)

7.0

12.0

19.5

21.5

CLAYEY SAND (SC): loose, gray and reddish yellow, fine to medium, moist

FAT CLAY WITH SAND (CH): soft to firm, gray and reddish yellow, moist

LEAN SANDY CLAY (CL): very soft, gray and reddish yellow, moist

FAT CLAY WITH SAND (CH): very soft to soft, gray and reddish yellow, moist

- reddish yellow

CLAYEY SAND (SC): loose, reddish yellow, fine to medium, moist

Boring terminated at 21.5 feet below referenced grade.

1-1-3

2-2-3

1-2-2

1-1-1

1-1-1

1/18"

1-1-1

1-1-1

1-2-3

Project:

Ground Surface Total Depth:

Drilling Method:

10/13/2023

Water Level:

21.5 ft

SCI Project:

Drill Rig:

230108

CME 45C (Track)

Proposed Miles Jamison Solid Waste Convenience Center 130 Suburban Road, Summerville, SC

The Soil Consultants, Inc. Key to Boring Log Symbols and Terms contains explanations about symbols and terms used on the boring log.

See Boring Plan Benbow

Remarks:

Not known to SCI 12.4 ft (24-hour) Mud Rotary (4-in. diameter)

Location:

Datum:

Elevation:

LOG OF BORING B-2

Date Drilled:

Driller:

-0

P R

IM

A

R Y

L O

G S

.G P

J/

-0

T

E M

P

LA

T E

.G D

T

/2

9/

Corrected N Value

20 40 60 80

(Clays to N60 and Sands to (N1)60)

Material Graphic

D ep th (f t)

Material Description

Sample

T yp e

D ep th

N um be r

Actual Blows (6-in.

interval)

4.5

7.0

21.5

POORLY GRADED SAND WITH SILT (SP-SM): medium dense, brown, fine to medium, moist

CLAYEY SAND (SC): very loose, brown, fine to medium, moist

DEBRIS FILL: wood and brick debris

FAT CLAY WITH SAND (CH): very soft to soft, gray and reddish yellow, moist

- reddish yellow

Boring terminated at 21.5 feet below referenced grade.

2-3-3

1-1-1

1-1-2

1-1-1

1-1-1

1-1-1

1-1-1

1-1-1

2-2-1

Project:

Ground Surface Total Depth:

Drilling Method:

10/16/2023

Water Level:

21.5 ft

SCI Project:

Drill Rig:

230108

CME 45C (Track)

Proposed Miles Jamison Solid Waste Convenience Center 130 Suburban Road, Summerville, SC

The Soil Consultants, Inc. Key to Boring Log Symbols and Terms contains explanations about symbols and terms used on the boring log.

See Boring Plan Benbow

Remarks:

Not known to SCI 10.0 ft (24-hour) Mud Rotary (4-in. diameter)

Location:

Datum:

Elevation:

LOG OF BORING B-3

Date Drilled:

Driller:

-0

P R

IM

A

R Y

L O

G S

.G P

J/

-0

T

E M

P

LA

T E

.G D

T

/2

9/

Corrected N Value

20 40 60 80

(Clays to N60 and Sands to (N1)60)

Material Graphic

D ep th (f t)

Material Description

Sample

T yp e

D ep th

N um be r

Actual Blows (6-in.

interval)

7.0

17.0

21.5

POORLY GRADED SAND WITH SILT (SP-SM): medium dense, brown, fine to medium, moist

SILTY SAND (SM): very loose, brown, fine to medium, moist

POORLY GRADED SAND WITH SILT (SP-SM): very loose, pale yellow, fine to medium, moist

FAT CLAY WITH SAND (CH): very soft, gray and reddish yellow, moist

- reddish yellow

SILTY SAND (SM): very loose, reddish yellow, fine, wet

Boring terminated at 21.5 feet below referenced grade.

1-3-5

1-1-1

1-1-1

1-1-1

1-1-1

1-1-1

1-1-1

1-1-1

1-1-2

Project:

Ground Surface Total Depth:

Drilling Method:

10/13/2023

Water Level:

21.5 ft

SCI Project:

Drill Rig:

230108

CME 45C (Track)

Proposed Miles Jamison Solid Waste Convenience Center 130 Suburban Road, Summerville, SC

The Soil Consultants, Inc. Key to Boring Log Symbols and Terms contains explanations about symbols and terms used on the boring log.

See Boring Plan Middleton

Remarks:

Not known to SCI 9.0 ft (24-hour) Mud Rotary (4-in. diameter)

Location:

Datum:

Elevation:

LOG OF BORING B-4

Date Drilled:

Driller:

-0

P R

IM

A

R Y

L O

G S

.G P

J/

-0

T

E M

P

LA

T E

.G D

T

/2

9/

Corrected N Value

20 40 60 80

(Clays to N60 and Sands to (N1)60)

Material Graphic

D ep th (f t)

Material Description

Sample

T yp e

D ep th

N um be r

Actual Blows (6-in.

interval)

28.0

CLAYEY SAND (SC): medium dense, brownish yellow, fine to medium, moist

- brown

FAT CLAY WITH SAND (CH): very soft to firm, gray and reddish yellow, moist

- reddish yellow

CALCAREOUS ELASTIC SILT WITH SAND (MH) (LOCALLY CALLED

MARL): very stiff, olive, moist

3-5-5

2-3-8

2-2-5

1-1-3

1-1-2

1-1-1

1-1-1

1-1-1

1-1-1

1-2-2

Project:

Ground Surface Total Depth:

Drilling Method:

10/13/2023

Water Level:

41.5 ft

SCI Project:

Drill Rig:

230108

CME 45C (Track)

Proposed Miles Jamison Solid Waste Convenience Center 130 Suburban Road, Summerville, SC

The Soil Consultants, Inc. Key to Boring Log Symbols and Terms contains explanations about symbols and terms used on the boring log.

See Boring Plan Middleton

Remarks:

Not known to SCI 13.8 ft (24-hour) Mud Rotary (4-in. diameter)

Location:

Datum:

Elevation:

LOG OF BORING B-5

Date Drilled:

Driller:

-0

P R

IM

A

R Y

L O

G S

.G P

J/

-0

T

E M

P

LA

T E

.G D

T

/2

9/

Corrected N Value

20 40 60 80

(Clays to N60 and Sands to (N1)60)

Material Graphic

D ep th (f t)

Material Description

Sample

T yp e

D ep th

N um be r

Actual Blows (6-in.

interval)

33.0

38.0

41.5

CALCAREOUS ELASTIC SILT WITH SAND (MH) (LOCALLY CALLED

MARL): very stiff, olive, moist (continued)

CALCAREOUS CLAYEY SAND (SC) (LOCALLY CALLED MARL): medium dense, olive, moist

CALCAREOUS ELASTIC SILT WITH SAND (MH) (LOCALLY CALLED

MARL): hard, olive, moist

Boring terminated at 41.5 feet below referenced grade.

2-7-12

4-6-7

10-13-10

Project:

Ground Surface Total Depth:

Drilling Method:

10/13/2023

Water Level:

41.5 ft

SCI Project:

Drill Rig:

230108

CME 45C (Track)

Proposed Miles Jamison Solid Waste Convenience Center 130 Suburban Road, Summerville, SC

The Soil Consultants, Inc. Key to Boring Log Symbols and Terms contains explanations about symbols and terms used on the boring log.

See Boring Plan Middleton

Remarks:

Not known to SCI 13.8 ft (24-hour) Mud Rotary (4-in. diameter)

Location:

Datum:

Elevation:

LOG OF BORING B-5

Date Drilled:

Driller:

-0

P R

IM

A

R Y

L O

G S

.G P

J/

-0

T

E M

P

LA

T E

.G D

T

/2

9/

Corrected N Value

20 40 60 80

(Clays to N60 and Sands to (N1)60)

Material Graphic

D ep th (f t)

Material Description

Sample

T yp e

D ep th

N um be r

Actual Blows (6-in.

interval)

7.0

12.0

21.5

POORLY GRADED SAND WITH SILT (SP-SM): loose, brown, fine to medium, moist

- brown and gray

SANDY SILT (ML): firm, brown and gray, moist

FAT CLAY WITH SAND (CH): stiff, gray and reddish yellow, moist

CLAYEY SAND (SC): very loose to loose, reddish yellow, fine to medium, moist

Boring terminated at 21.5 feet below referenced grade.

1-3-2

2-2-3

4-3-3

2-3-6

2-3-6

2-2-3

2-1-2

1-1-1

1-1-1

Project:

Ground Surface Total Depth:

Drilling Method:

10/13/2023

Water Level:

21.5 ft

SCI Project:

Drill Rig:

230108

CME 45C (Track)

Proposed Miles Jamison Solid Waste Convenience Center 130 Suburban Road, Summerville, SC

The Soil Consultants, Inc. Key to Boring Log Symbols and Terms contains explanations about symbols and terms used on the boring log.

See Boring Plan Middleton

Remarks:

Not known to SCI 10.0 ft (24-hour) Mud Rotary (4-in. diameter)

Location:

Datum:

Elevation:

LOG OF BORING B-6

Date Drilled:

Driller:

-0

P R

IM

A

R Y

L O

G S

.G P

J/

-0

T

E M

P

LA

T E

.G D

T

/2

9/

Corrected N Value

20 40 60 80

(Clays to N60 and Sands to (N1)60)

Material Graphic

D ep th (f t)

Material Description

Sample

T yp e

D ep th

N um be r

Actual Blows (6-in.

interval)

14.5

21.5

POORLY GRADED SAND WITH SILT (SP-SM): loose, brown, fine to medium, moist

SILTY SAND (SM): medium dense, brown, fine to medium, moist

FAT CLAY WITH SAND (CH): soft to stiff, gray and reddish yellow, moist

CLAYEY SAND (SC): very loose, reddish yellow and gray,…