250088_Geotechnical_Report.pdf

PROPOSED CONCRETE PAVEMENT

REPLACEMENT

N. CHARLESTON FIRE STATION NO. 8

8045 DORCHESTER ROAD

N. CHARLESTON, SC

PREPARED FOR

DORCHESTER COUNTY

SCI PROJECT 250088

NOVEMBER 5, 2025

SCDOT DBE and SBE Charleston County SBE City of Charleston WBE

November 5, 2025

Dorchester County

201 Johnston Street

St. George, SC 29477

Attention: Ms. Rebecca Dantzler, Purchasing Service Manager

SCI Project 250088

Dear Ms. Dantzler:

Soil Consultants, Inc. (SCI) submits this report to provide results of the geotechnical services provided for the proposed concrete pavement replacement at the existing N. Charleston Fire Station No. 8 facility located at 8045 Dorchester Road in N. Charleston, SC. Our services were performed in accordance with SCI Proposal No. 14-25-142, dated October 3, 2025. This report provides a discussion of the exploration procedures used, pavement and subsurface conditions encountered, and recommendations for pavement replacement. 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:

11/5/2025

11/5/2025

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

TABLE OF CONTENTS

Page

Page i SCI Project No. 250088

INTRODUCTION

SCOPE OF PROJECT

SITE DESCRIPTION

FIELD EXPLORATION

LABORATORY TESTING

BORING LOGS

EXISTING PAVEMENT AND SUBSURFACE CONDITIONS

Pavement Materials

Subgrade and Subsurface Conditions

PAVEMENT RECOMMENDATIONS AND CONSTRUCTION CONSIDERATIONS

Proposed Concrete Pavement Evaluation

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

Concrete Core Logs

Page 1 SCI Project No. 250088

INTRODUCTION

Soil Consultants, Inc. (SCI) presents this report to document geotechnical findings for the proposed concrete pavement replacement at the existing N. Charleston Fire Station No. 8 facility located at 8045 Dorchester Road in N. Charleston, SC. Geotechnical services were performed in accordance with SCI Proposal No. 14-25-142, dated October 3, 2025. Our services were authorized by the Dorchester County Purchase Order No. 261741, dated October 14, 2025.

SCOPE OF PROJECT

It is our understanding that the proposed project includes replacement of an area of existing concrete paved driveway at the fire station site. Based on project information provided, we understand that the area of replacement is located on the south side of the existing fire station building. In addition, we understand that the replacement concrete pavement section is planned to be 8 inches thick with #5 rebar each way at 24-inches on center.

SITE DESCRIPTION

The fire station property is bound by Dorchester Road to the north and by Robert Bosch, LLC property on all other sides. At the time of our investigation, the existing fire station building and associated paved areas were present at the site. Asphalt-paved driveway and parking areas were present on the east side of the existing fire station building, and concrete-paved driveways were present on the north and south sides of the existing fire station building. The unpaved areas surrounding the building were mostly cleared with trees in some areas.

Topographic information was not provided. However, based on observations at the site, the site appears to be relatively flat. In addition, the ground surface elevations appeared similar to the adjacent properties and slightly higher than the adjacent Dorchester Road pavement surfaces.

FIELD EXPLORATION

On October 17, 2025, SCI representatives performed coring of the pavement and hand-auger borings at three locations, designated C-1 through C-3. The boring locations were selected and marked at the site by our representative. The approximate boring locations are shown on Figure

1, Boring Location Plan, attached.

At each boring location, the existing concrete pavement was cored, and the thicknesses of the concrete materials and underlying aggregate base course, if present, were measured. Following completion of the coring, borings were manually advanced using hand-auger equipment to identify the underlying soil conditions. In the hand-auger borings, we performed dynamic cone penetrometer (DCP) testing at the soil subgrade and at 2-foot intervals to depths of approximately

4 feet below the existing pavement subgrade surface. The DCP testing was performed using the

Dual-Mass Cone Penetrometer, which was developed by the U.S. Army Corps of Engineers

(ASTM D-6951) to determine California Bearing Ratio (CBR) values of pavement subgrade soils.

Following completion of the hand-auger borings, the boreholes were backfilled with soil cuttings, and the holes through the pavement were patched using non-shrink grout material. After completion of the field investigation, the soil samples collected were transported to our laboratory.

The soil samples were examined by a geotechnical engineer and visually classified in accordance with the Unified Soil Classification System (USCS).

Page 2 SCI Project No. 250088

LABORATORY TESTING

We performed soil mechanics laboratory tests on selected samples to aid in soil classification and to determine engineering properties for use in engineering 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 6

Percent Finer than 75-m sieve ASTM D1140 6

Atterberg Limits ASTM D4318 4

BORING LOGS

SCI’s geotechnical engineer developed the final log for each boring using DCP data, laboratory test results, and visual descriptions of the soils recorded during the field exploration after return to the SCI laboratory. 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. The boring logs include CBR values which were correlated from the measured DCP resistances. Transition boundaries between soil types noted on the boring logs are approximate.

EXISTING PAVEMENT AND SUBSURFACE CONDITIONS

The existing pavement and underlying soil and subsurface conditions encountered in our investigation are described in the following sections.

Pavement Materials

Based on observations at the site, numerous cracks were present in the concrete pavement in the planned replacement area. Steel welded wire mesh was observed in the concrete cores near the center of Core C-1 and at the bottoms of Cores C-2 and C-3. No aggregate base course materials were present beneath the concrete pavement at any of the core locations. The measured thicknesses of the concrete materials at the core locations are presented in Table 2.

Concrete core logs, including photos of the concrete cores, are attached.

Table 2 Concrete and Base Course Thicknesses

Boring Number Concrete Thickness (inches)

Base Course Thickness (inches)

B-1 5½ Not Present

B-2 5 Not Present

B-3 5 Not Present

Compressive strength testing of the concrete cores was performed in the laboratory, and the test report is attached. The compressive strengths of Cores C-1, C-2, and C-3 were 6,040 pounds per square inch (psi), 6,060 psi, and 5,060 psi.

Page 3 SCI Project No. 250088

Subgrade and Subsurface Conditions

The borings generally encountered sands with varying amounts of silt and clay to termination of the borings at depths of 4 feet below the existing pavement subgrade surface. Using the procedures outlined in the American Standard for Testing and Materials (ASTM) D 2487, “Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification

System),” these soils are classified as SP-SM, SC-SM, and SC. Correlated CBR values of the soils encountered in the borings ranged from 3 to 13. The lower CBR values were encountered at depths below 2 feet in the borings.

Groundwater was not encountered in the borings. It must be noted that 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.

PAVEMENT RECOMMENDATIONS AND CONSTRUCTION CONSIDERATIONS

As stated in the Project Information section of this report, we understand that the replacement concrete pavement section is planned to be 8 inches thick with #5 rebar each way at 24-inches on center.

Near-surface soils within the proposed pavement areas predominantly consisted of sands with varying amounts of silt and clay. In general, sands are considered good to excellent for use as pavement subgrade. However, clayey soils are generally 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 are allowed to get wet during construction.

Proposed Concrete Pavement Evaluation

The proposed concrete pavement section was evaluated in accordance with ACI 330 PRC-21

“Commercial Concrete Parking Lots and Site Paving Design and Construction-Guide” (ACI 330).

For the purposes of our evaluation, we assumed a modulus of subgrade reaction (Ks) of 100 pounds per cubic inch (pci) for the subgrade soils and a 28-day flexural strength or modulus of rupture of 650 psi for the proposed concrete pavement.

Based on our evaluation, the proposed concrete pavement section exceeds the recommendations outlined in ACI 330. Therefore, we recommend using the proposed concrete pavement section for this project. However, to ensure better performance of the concrete pavement, we recommend that a 6-inch-thick layer of graded aggregate base course material be placed beneath the concrete pavement.

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). 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).

Page 4 SCI Project No. 250088

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.

Site Preparation in Pavement Areas

Performance of the new pavement system will be directly affected by the quality of site preparation.

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, if necessary, to prevent continual saturation of the base course and subgrade soils.

Removal of Existing Pavements. The existing concrete pavement and any soft or wet subgrade soils underlying the pavement should be removed from the site.

Compaction of Stripped Subgrade. After pavement materials and soft, wet, or organic soils have been removed, and before placement of fill material, the remaining surface soils within the pavement areas should be thoroughly and uniformly compacted in place using a 5-ton (minimum) steel drum vibratory roller, except in areas immediately adjacent to the existing building. Hand operated compaction equipment may be used to compact soils in these areas.

Proofrolling. Following compaction, the 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 can then be placed in uniform lifts to bring the pavement areas to finished grade, if required.

Backfill and Controlled Fill Material Criteria. Backfill and controlled fill 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, and SP-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 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. Since these testing services are within the scope of

Page 5 SCI Project No. 250088 services we routinely provide, we urge that SCI be retained to provide testing services during the earthwork phase.

Wet Conditions during Construction. Although not anticipated, 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.

LIMITATIONS OF REPORT

This report was prepared as an instrument of service exclusively for Dorchester County and the project design team in preparation of the pavement design, construction drawings, and construction specifications for the proposed concrete pavement replacement at the existing N.

Charleston Fire Station No. 8 facility located at 8045 Dorchester Road in N. Charleston, SC.

Recommendations and comments given in this report are based on the results of the soil borings, combined with 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. 250088

FIGURES

Reference: Base map from Google Maps Legend:

Note: Boring locations are approximate.

Scale Not to scale 250088

Date 1

BORING LOCATION PLAN

Proposed Concrete Pavement Replacement

Fire Station #8, 8045 Dorchester Road

N. Charleston, SC

Project No.

11/4/2025 Figure

Test Boring Location

C-1

C-2 C-3

SCI Project No. 250088

ATTACHMENTS

0.5

2.5

4.5

CONCRETE (5.5 inches thick)

CLAYEY SAND (SC) brown and gray, fine, moist

SILTY CLAYEY SAND (SC-SM) brown and gray, fine, moist, with gravel

Boring terminated at 4.5 feet below referenced grade.

Project:

Ground Surface Total Depth:

Drilling Method:

10/17/2025

Water Level:

4.5 ft

SCI Project:

Drill Rig:

250088

Hand Auger

Proposed Concrete Pavement Replacement, Fire Station No. 8 8045 Dorchester Road, N. Charleston, SC

Groundwater not encountered in boring.

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 Hanckel

Remarks:

Not known to SCI Auger (3.5-in. diameter)

Location:

Datum:

Elevation:

LOG OF BORING C-1

Date Drilled:

Driller:

-0

P R

IM

A

R Y

B O

R

IN

G L

O G

S .G

P J/

-0

T E

M P

LA

T

E .G

D T

/5 /2

Material Graphic

D ep th (f t)

Material Description

California Bearing Ratio

CBR

Sample

T yp e

D ep th

N um be r

0.4

4.5

CONCRETE (5 inches thick)

POORLY GRADED SAND WITH SILT (SP-SM) brown and yellow, fine, moist

- brown and gray

Boring terminated at 4.5 feet below referenced grade.

Project:

Ground Surface Total Depth:

Drilling Method:

10/17/2025

Water Level:

4.5 ft

SCI Project:

Drill Rig:

250088

Hand Auger

Proposed Concrete Pavement Replacement, Fire Station No. 8 8045 Dorchester Road, N. Charleston, SC

Groundwater not encountered in boring.

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 Hanckel

Remarks:

Not known to SCI Auger (3.5-in. diameter)

Location:

Datum:

Elevation:

LOG OF BORING C-2

Date Drilled:

Driller:

-0

P R

IM

A

R Y

B O

R

IN

G L

O G

S .G

P J/

-0

T E

M P

LA

T

E .G

D T

/5 /2

Material Graphic

D ep th (f t)

Material Description

California Bearing Ratio

CBR

Sample

T yp e

D ep th

N um

0.4

2.4

4.5

CONCRETE (5 inches thick)

POORLY GRADED SAND WITH SILT (SP-SM) light brown, fine, moist

SILTY CLAYEY SAND (SC-SM) black and gray, fine, moist, with organics

Boring terminated at 4.5 feet below referenced grade.

Project:

Ground Surface Total Depth:

Drilling Method:

10/17/2025

Water Level:

4.5 ft

SCI Project:

Drill Rig:

250088

Hand Auger

Proposed Concrete Pavement Replacement, Fire Station No. 8 8045 Dorchester Road, N. Charleston, SC

Groundwater not encountered in boring.

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 Hanckel

Remarks:

Not known to SCI Auger (3.5-in. diameter)

Location:

Datum:

Elevation:

LOG OF BORING C-3

Date Drilled:

Driller:

-0

P R

IM

A

R Y

B O

R

IN

G L

O G

S .G

P J/

-0

T E

M P

LA

T

E .G

D T

/5 /2

Material Graphic

D ep th (f t)

Material Description

California Bearing Ratio

CBR

Sample

T yp e

D ep th

N um

Concrete Asphalt

Silty Sand (SM)

Standard Penetration Resistance Value (N value) corrected to N60 for clays and to (N1)60 for sands.

Sandy Lean Clay (CL)

Well-Graded Gravel

(GW)

Clayey Sand (SC) Fat Clay (CH) Sandy Fat Clay (CH) Lean Clay (CL)

Silty Clay (CL-ML)

Organic Clay (OH) Organic Silt (OH)

Elastic Silt (MH) Sandy Elastic Silt

(MH)

Organic Clay (OL)

CONSISTENCY OF FINE-GRAINED SOILS

(50% or more passing the No. 200 Sieve)

Silts and Clays Consistency determined by laboratory strength testing, standard penetration resistance, or field visual-manual procedures.

SPT N Value

The sampler penetrated the full 18-in. test depth under the weight of the drill rod.WOR

WOH

1/18"

Ncorrected

Within a desired sampling interval, the SPT test includes seating the split-barrel sampler to 6-in. depth with blows from a 140-lb hammer. The sampler is advanced through two additional 6-in. deep intervals with blow counts recorded for each interval. The "N" value is the sum of the blows for the final 12 in. of the 18-inch penetration.

STANDARD PENETRATION TEST (SPT)

Thin-walled tube

Split barrel Core No Recovery

SAMPLER SYMBOLS

Organic Silt (OL)

DENSITY OF COARSE-GRAINED SOILS

Peat (PT)

Sandy Silt (ML)

Poorly-Graded Gravel with Sand (GP-GM)

Well-Graded Gravel with Sand (GW-GM)

Consistency Unconfined

Compressive Strength, tsf

50/3"

Auger Sample

LOCAL MATERIAL TYPES AND SYMBOLS

Well-Graded Sand with Silt (SW-SM)

Silt (ML)

(More than 50% retained on the No. 200 Sieve)

< 0.25 Very Soft 0 - 2

3 - 4Soft0.25 to 0.50

1.00 to 2.00

2.00 - 4.00

0.50 to 1.00 Medium (Firm)

Stiff

5 - 8

9 - 15

16 - 30Very Stiff

> 30Hard> 4.00

KEY TO BORING LOG SYMBOLS AND TERMS

USCS MATERIAL TYPES AND SYMBOLS

Clayey Gravel (GC)

Well-Graded Gravel with Clay (GW-GC)

Poorly-Graded Sand with Clay (SP-SC)

Well-Graded Sand

(SW)

Poorly-Graded Gravel

(GP)

RELATIVE DENSITY AND CONSISTENCY

> 50

0 - 4

SPT N ValueRelative Density

Base Wood

Very Loose

Loose

Medium Dense

Dense

Very Dense

Density determined by Standard Penetration Resistance.

Gravels and Sands

Poorly-Graded Gravel with Clay (GP-GC)

11 - 30

Well-Graded Sand with Clay (SW-SC)

Silty Gravel (GM)

Poorly-Graded Sand

(SP)

Poorly-Graded Sand with Silt (SP-SM)

Soil Consultants, Inc.'s geotechnical engineer reviewed recovered samples, field data, and laboratory data to develop each boring log. Each log represents our interpretation of general soil and water conditions at the boring location. Soil classifications presented on the boring log are based on the Unified Soil Classification System (USCS) as outlined in ASTM D2487. The system is used to classify coarse-grained materials (boulders, cobbles, gravel, and sand) and fine-grained materials (silt and clay). Descriptors are added to describe additional constituents based on percentages of these constituents. In the absence of laboratory data required to classify soils in complete accordance with ASTM D2487, visual descriptions of the materials are provided with their interpreted USCS group name.

Subsurface conditions at the explored location(s) may not be indicative of subsurface conditions at other locations or at other times. Strata lines on the log may be transitional and are approximate in nature.

50 blow limit was recorded with 3 in. penetration of the sampler.

Hard Layer

The sampler was driven the full 18-in. test depth by 1 blow of the 140-lb hammer.

The sampler penetrated the full 18-in. test depth under the weight of the hammer.

31 - 50

5 - 10

PROJECT: Concrete Pavement Replacement, N. Charleston Fire Station #8 LOCATION: 8045 Dorchester Road, N. Charleston, SC Approximate Location

West Side of Driveway Slab

Sample Number C-1

Directional Lane NA

Date Cored 10/17/2025

Total Core Length 5½ inches Core Diameter 4.0”

Comments: No aggregate base present beneath concrete

Approximate Location

South Side of Driveway Slab

Sample Number C-2

Directional Lane NA

Date Cored 10/17/2025

Total Core Length 5 inches Core Diameter 4.0”

Approximate Location

East Side of Driveway Slab

Sample Number C-3

Directional Lane NA

Date Cored 10/17/2025

Total Core Length 5 inches Core Diameter 4.0”

SCI project 250088