Geo Tech portion P-7889 MCRD PARRIS ISLAND CORRECTED FINAL BASIS OF DESIGN - 26 AUGUST 2024.pdf

GEOTECHNICAL ENGINEERING REPORT

Dental Clinic Replacement MCRD, Parris Island, South Carolina FY25 MCON Project P-7889

Schnabel Reference # 21C19027.00

February 20, 2024

February 20, 2024

Mr. Bob Snider, PE SS&A Design Collective 3047 Carter Hill Road Montgomery, AL 36111

Subject: Geotechnical Engineering Report Dental Clinic Replacement MCRD, Parris Island, South Carolina FY23 MCON Project P-7889 Schnabel Reference 21C19027.00

Dear Mr. Snider:

SCHNABEL ENGINEERING, LLC is pleased to submit our geotechnical engineering report for this project. This report includes tables, figures, and appendices with relevant data collected for this study.

This study was performed in accordance with our proposal dated March 29, 2021.

We appreciate the opportunity to be of service for this project. Please call us if you have any questions regarding this report.

Sincerely, SCHNABEL ENGINEERING, LLC

Kevin R. Morgan, PE Project Engineer

Richard H. Wargo, PE Principal

SS&A Design Collective Dental Clinic Replacement, MCRD, Parris Island, SC

February 20, 2024 Page i Schnabel Engineering, LLC Project 21C19027.00 ©2021 All Rights Reserved

GEOTECHNICAL ENGINEERING REPORT

DENTAL CLINIC REPLACEMENT

MCRD, PARRIS ISLAND, SOUTH CAROLINA

FY23 MCON PROJECT P-7889

TABLE OF CONTENTS

1.0 EXECUTIVE SUMMARY

2.0 SCOPE OF SERVICES

3.0 DESCRIPTION OF SITE AND PROPOSED CONSTRUCTION

3.1 Site Description

3.2 Proposed Construction

3.3 Regional Geology

3.4 Previous Investigation

4.0 SUBSURFACE EXPLORATION PROGRAM

4.1 Subsurface Exploration and Field Testing

4.2 Cone Penetrometer Testing

4.3 Geophysical Survey

5.0 LABORATORY TESTING

5.1 Soils Testing

6.0 SITE GEOLOGY AND SUBSURFACE CONDITIONS

6.1 Generalized Subsurface Stratigraphy

6.2 Groundwater

6.3 Seismic Site Classification

7.0 SITE GRADING AND EARTHWORK

7.1 Compacted Fill Subgrades

7.2 Compacted Fill and Backfill

7.3 Fill Induced Settlement

7.4 Slopes

8.0 FOUNDATION RECOMMENDATIONS

8.1 Deep Foundation Alternatives

8.2 Ground Improvement and Shallow Foundation Alternative

8.3 Building Floor Slabs

8.4 Utility Excavations and Bedding

9.0 BELOW GRADE WALL RECOMMENDATIONS

9.1 Earth Pressure Parameters

9.2 Subdrainage for Below-Grade Walls

10.0 PAVEMENT RECOMMENDATIONS

10.1 Flexible Pavements

February 20, 2024 Page ii Schnabel Engineering, LLC Project 21C19027.00 ©2021 All Rights Reserved

10.2 Rigid Pavements

10.3 General Pavement Considerations

11.0 CONSTRUCTION CONSIDERATIONS

11.1 Site Grading and Earthwork

11.2 Foundations

11.3 Temporary Excavations, Shoring, and Slopes

11.4 Engineering Services During Construction

12.0 GENERAL SPECIFICATION RECOMMENDATIONS

13.0 LIMITATIONS

LIST OF FIGURES

Figure 1: Test Boring Location Plan – Existing Site Conditions Figure 2: Test Boring Location Plan – Proposed Site Development Plan Figure 3: Test Pit & Test Boring Photo Log

APPENDICES

Appendix A: Subsurface Exploration Data Appendix B: Soil Laboratory Test Data Appendix C: Environmental Testing Results Appendix D: Engineering Calculations

February 20, 2024 Page 1 Schnabel Engineering, LLC Project 21C19027.00 ©2024 All Rights Reserved

1.0 EXECUTIVE SUMMARY

This report presents the results of data collected for the geotechnical study conducted by Schnabel Engineering, LLC. (Schnabel) at the proposed Dental Clinic Replacement site in Parris Island, South Carolina. The purpose of the exploration was to acquire subsurface information and provide geotechnical recommendations for the proposed development.

We understand the proposed development will consist of a new reinforced masonry, two-story 56,236 gross sf Dental Clinic building with a 1,500-sf covered staging area. The lowest floor level will be supported on-grade. There will also be new parking areas to the south and west of the new Dental Clinic.

The site is currently occupied by one existing building (Building 602), pavements, trees, and grassed areas. The planned western parking area contains existing Building 674.

Based on the boring and laboratory test data, the on-site soils predominantly consist of interbedded layers of Poorly Graded Sand (SP), Poorly Graded Sand with Silt (SP-SM), Poorly Graded Sand with Clay (SP-SC), Silty Sand (SM), Clayey Sand (SC), and layers of Silt (ML) with varying amounts of sand, Fat Clay (CH) with varying amounts of sand, and Sandy Lean Clay (CL).

We evaluated the site for possible liquefaction susceptibility. Based on our review of the field investigation and soil laboratory test data, soils between ~6 to 20 ft depth encountered primarily consist of loose sands which are non-plastic and are below the water table. Based on our evaluation, these sandy soils are considered liquifiable under a seismic event. The existing soils below 20 ft depth are not considered susceptible to liquefaction as they are dense with N-values above 30.

Since liquefaction is inevitable under existing conditions, and as such the Seismic Site Class is F per ASCE 7-16 Section 20.3.1. The Seismic Site Class will not improve if any deep foundation system is used, but can improve to a Site Class D if a suitable liquefaction mitigation technique, such as rammed aggregate piers, is used (and proof tested).

The very soft and loose soils were encountered across the site are not considered suitable for direct support of conventional shallow spread footings in their current conditions, as the anticipated structural foundation loads would result in excessive settlements under both static and seismic conditions. Various foundation alternatives were initially considered. Based on our preliminary evaluation, Concrete Piles were given further consideration for building support. Detailed recommendations for these alternatives are provided herein.

We evaluated the site considering ground improvement consisting of rammed aggregate piers (stone columns) on the order of about 20 to 25 ft depth across the building footprint and several feet beyond the footprint in each direction. With an effective ground improvement program (to be design and implemented by a specialty geotechnical design-build contractor), we anticipate a Seismic Site Class D can be justified.

Shallow footings founded on stone column improved soils can be preliminarily designed for an allowable composite bearing pressure of about 3,500 to 4,000 psf. The final allowable soil bearing pressure should be determined by the specialty geotechnical design-build Contractor.

Consideration should also be given to installing earthquake drains around the perimeter of the building area and beneath the mechanical yard, as a cost saving alternative to reduce the number of stone

February 20, 2024 Page 2 Schnabel Engineering, LLC columns, and to also reduce settlements due to a seismic event to an acceptable level. Earthquake drains should be designed by the specialty geotechnical design-build contractor.

Concrete slabs may be supported on-grade on suitable new compacted structural fill upon ground improved areas. Slabs may be designed based on a maximum modulus of subgrade reaction, k, of 200 pci. A minimum four-inch-thick crushed stone or washed gravel capillary moisture barrier should underlie concrete slabs on grade. A minimum 6-mil polyethylene layer should also overlie the capillary moisture barrier.

Water level measurements taken in the test borings indicate groundwater to depths of between 4.0 to 6.0 feet below the existing ground surface, and as shallow as 2.4 feet below the ground surface in the temporary well installed in Boring B-4 about two weeks after drilling.

Field infiltration testing resulted in saturated hydraulic conductivity (Ksat) rates ranging from 6.39x10-4 to 1.13x10-3 cm/s (0.38 to 1.60 in/hr) for the soils above the existing groundwater table.

The final design should anticipate fluctuations in the water table depending upon variations in precipitation, surface runoff, pumping from any nearby wells, evaporation and similar factors. Based on our groundwater observations, we do not expect groundwater levels to have a major impact on the proposed construction, except possibly for the deeper utilities.

Flexible Pavement section recommendations for parking and driveways are provided herein.

We are providing this executive summary solely for purposes of overview. Any party that relies on this report must read the full report. This executive summary omits several details, any one of which could be very important to the proper application of the report.

February 20, 2024 Page 3 Schnabel Engineering, LLC

2.0 SCOPE OF SERVICES

The objective of this study was to evaluate the subsurface conditions at the site and provide geotechnical engineering recommendations regarding the design of foundations, earthwork, and pavements for this project. This study was conducted under the supervision of a Professional Engineer registered in the state of South Carolina.

Our scope of services was outlined in our proposal dated March 29, 2021. The scope of services included:

Historical Data Review & Evaluation Subsurface Investigation Field Engineering Services Soil Laboratory Testing Environmental Analytical Laboratory Testing Preparation of this Geotechnical Engineering Report

Services not described in our agreement are not included in this study. We would be happy to provide additional support services to the design team as the project demands.

February 20, 2024 Page 4 Schnabel Engineering, LLC

3.0 DESCRIPTION OF SITE AND PROPOSED CONSTRUCTION

3.1 Site Description

Based on our review of available data and after our site visit, the project area is currently occupied by one existing buildings, pavements, trees, and grassed areas. The proposed Dental Clinic replacement building (Building 602) lies at the northeast corner of Alaska St. and Boulevard De France. On the west side of Alaska St. is the current Dental Clinic Building (Building 674) which will be replaced by parking lots. Existing asphalt-paved parking lots exist to the south of Building 602 which will be removed and replaced with new parking lots. The property is also generally flat.

We obtained the site information from the topographic site plan, historical data, and through our site visits.

3.2 Proposed Construction

We understand the proposed development will consist of a new two-story 56,236 gross sf Dental Clinic building with a 1,500-sf covered staging area. The lowest floor level will be supported on-grade. We understand trenching in the first floor slab will be used for utilities in the dental treatment area. There will also be new parking areas to the south and west of the new Dental Clinic after demolition of the existing dental clinic.

We estimate within the proposed building footprint the northwest corner of the building will require approximately 1-foot of fill or less and will gradually increase towards the southeast corner of the building where approximately 4-feet of fill will be required to reach the proposed finished floor of EL 11.5 feet.

We understand the expected dead load of the proposed dental clinic is 280 kips and the live load is 225 kips. This gives a maximum column loading of 505 kips.

3.3 Regional Geology

Parris Island is located in the Jasper-Beaufort County area, widely referred to as the Low Country in South Carolina. In the MCRD Parris Island area, the shallow, unconfined deposits generally consist of tidal marsh deposits of sand, silts, and clays of Quaternary age.

3.4 Previous Investigation

We conducted a Site Characterization report, dated July 15, 2021, for the proposed Dental Clinic Replacement at Parris Island. Our report characterizes the geologic conditions within the area and the subsurface stratigraphy based on historical data, previous site visits, and geotechnical reports furnished by others. This report was previously submitted as a separate document.

February 20, 2024 Page 5 Schnabel Engineering, LLC

4.0 SUBSURFACE EXPLORATION PROGRAM

We performed a subsurface exploration to identify the subsurface stratigraphy underlying the site and to evaluate the geotechnical properties of the materials encountered. This program consisted of Standard Penetration Testing (SPT) test borings. Exploration methods used are discussed below. The appendices to this report contain the results of our exploration.

4.1 Subsurface Exploration and Field Testing

4.1.1 Test Borings

Our subcontractor, Elite Techniques, Inc. of Camden, SC, drilled six (6) test borings (B-1 through B-6) under our observation between September 7 and 9, 2021. The Standard Penetration Test (SPT) was performed at selected depths in the borings. The boring depths ranged from selected depths of 6.0 to

80.0 feet below the existing ground surface grades. Borings were abandoned with a bentonite grout mixture after obtaining the final water level reading.

As a precaution to soil contamination, during drilling appropriate environmental protocols were followed for decontamination of the drilling equipment and augers. Drilling spoils and drilling mud were contained on-site during drilling and placed within appropriate environmental 55-gallon drums. At the completion drilling the borings, composite samples of the drilling spoils were collected using appropriate environmental protocols and sent to a lab to test for contamination.

The Standard Penetration Test (SPT) was performed at selected depths in the borings. The SPT samples were obtained using a manual hammer within borings B-1 and B-2. The SPT samples were obtained using a hydraulically driven automatic trip hammer (ATH) in borings B-3 through B-6. Most correlations with the SPT data are based on N-values collected with a safety hammer. The energy applied to the split-spoon sampler using the ATH is about 33 percent greater than that applied using the safety hammer, resulting in lower N-values. The hammer blows shown on the boring logs and cross sections are uncorrected for the higher energy.

Appendix A includes specific observations, remarks, and logs for the borings; classification criteria; drilling methods; and sampling protocols. Figure 1, included at the end of this report, indicates the approximate test boring locations. We will retain soil samples up to 45 days beyond the issuance of our final report, unless you request other disposition.

4.1.2 Test Pits

Our subcontractor, Elite Techniques, Inc. of Camden, SC, excavated two (2) test pits (TP-1 and TP-2) under our observation on September 27, 2021. Appendix A includes specific observations, remarks, and logs for the test pits; classification criteria; excavation methods; and sampling protocols. Figure 1, included at the end of this report, indicates the approximate test pit locations. We will retain soil samples up to 45 days beyond the issuance of our final report, unless you request other disposition.

There were two locations during the geophysical survey in which test pits were excavated as we believe there were anomalies in the area that warranted further investigation. Soil Cement fill material was encountered within the upper 1.4 feet of TP-1 underlain by natural Silty, Clayey Sand (SC-SM). Within TP-2 what we believe to be an abandoned utility pad was encountered. The utility pad is a 4 ft. long x 3 ft.

wide x 5 in. thick concrete pad with rebar sitting upon brick. Test pits were backfilled with the excavated

February 20, 2024 Page 6 Schnabel Engineering, LLC soils and surficial organic soil after completion. Hay bales and seed were spread upon the completed test pit locations as well. See photos 10 and 14 of the Photo Log included at the end of this report.

4.1.3 Field Infiltration Testing

Schnabel representatives performed three (3) field infiltration tests on September 28, 2021. The locations of INF-1 through INF-3 are shown on Figure 1. Details of the infiltration test and the results are included in Appendix A.

The on-site soils encountered in the upper three feet at the testing locations was classified as Silty, Clayey Sand (SC-SM) at INF-1 and INF-2 while INF-3 classified as Poorly Graded Sand with Silty Clay (SP-SC). Based on USDA classifications, the soil types are consistent with that of a Sandy Loam, Loamy Sand, and/or Sand. Field infiltration testing resulted in saturated hydraulic conductivity values (Ksat) infiltration rates of 2.70x10-4, 6.39x10-4, and 1.13x10-3 cm/s (0.38, 0.91, and 1.60 in/hr), respectively.

Schnabel conducted the infiltration testing using an Aardvark Permeameter 2840. A 10 cm diameter hole is hand augered to the prescribed testing depth of 90 cm. The pressure regulator unit is lowered into the hole to the bottom of the borehole and secured in position. The unit is connected to the computer and automated readings are taken while the test is being conducted. The Aardvark is a constant-head permeameter. This means the depth of water within the borehole does not change during the measurement period. The rate of water being supplied is constantly recorded and corresponds to the soil infiltration rate from the bottom and side surfaces of the borehole.

4.2 Cone Penetrometer Testing

In addition to the SPT borings, we performed in situ tests consisting of cone penetrometer testing (CPT) to establish further the geotechnical properties of the materials encountered at the site. Our subcontractor, ConeTec, performed CPT at a total of two (2) locations on the site (CPT-1 and CPT-2).

The CPTs were performed to depths of 100.7 and 100.9 ft below the ground surface.

In-situ pore pressure dissipation testing was also performed at four (4) discrete locations of CPT-1.

Seismic CPT tests were also performed for the entire depth of CPT-1.

CPT holes were abandoned with a bentonite grout mixture after completion. Details of the CPTs and test results are included in Appendix A.

4.3 Geophysical Survey

Our subcontractor, GEL Solutions, conducted a geophysical survey of the proposed Dental Clinic site on August 24 to 27, 2021. The geophysical surveys consisted of ground penetrating radar (GPR) and various electromagnetic (EM) instrumentation on the site to evaluate geologic stratigraphy between test boring locations. While conducting the geophysical two locations indicating anomalies. These locations were further investigated by excavating test pits (TP-1 and TP-2). The GEL Solutions report dated September 7, 2021, with details of the geophysical procedures and data collected was previously submitted as a separate document.

February 20, 2024 Page 7 Schnabel Engineering, LLC

5.0 LABORATORY TESTING

Our laboratory performed tests on selected samples obtained during the subsurface exploration. The testing aided in the classification of materials encountered in the subsurface exploration and provided data for use in the development of recommendations for design of foundations, earthwork, and pavements. Moisture contents and index test results are shown on the boring logs in Appendix A. The remainder of the test results is included in Appendix B.

5.1 Soils Testing

5.1.1 Index Testing

We performed natural moisture content, Atterberg Limit, and gradation tests on several samples of soil to provide soil classifications and to provide parameters for use with published correlations with soil properties. The results are presented in the Summary of Laboratory Tests in Appendix B.

5.1.2 Compaction and CBR Testing

We performed Standard Proctor compaction and CBR testing of soil samples representative of soils near the surface to evaluate compaction characteristics and to provide soil parameters for pavement design.

The test results are included in Appendix B.

One bulk sample predominantly classified as Poorly Graded Sand with Silt from Boring B-5. Based on the soil classification and our soil laboratory testing, these soils will exhibit soaked CBR value of 20.8 when properly compacted.

5.1.3 Corrosivity Testing

We performed tests for pH, sulfides, redox potential, and resistivity testing on a soil sample representative of the upper on-site soils.

The test results are presented in the table below:

Table 5.1: Soil Corrosivity

Parameter Boring No. Resistivity pH Redox Sulfide Sulfate Chloride

Unit - ohm-cm - mV ppm ppm ppm

Value Depth (ft.)

B-3 / B-5 Composite

2.0 – 4.0

3,600 7.88 167.0 89.3 18.0 14.0

*BRL: Below Reporting Limit

These results are also presented in Appendix B, along with the various guidelines and criteria from DIPRA, AWWA, and ACI for evaluating soil corrosivity. Laboratory corrosivity testing indicates the corrosivity potential based on total cumulative soil corrosion values, per the various criteria for cast iron, steel, and concrete. Based on these test results, we anticipate the soil to have a mild corrosive potential for underground iron pipes, buried steel structures, reinforcing steel in buried concrete, and sulfate

February 20, 2024 Page 8 Schnabel Engineering, LLC exposure in concrete. Various techniques can be utilized to mitigate corrosion in iron and steel, including the use of cathodic protection, coating of reinforcing steel (i.e. epoxy), thickening steel members. Sulfate exposure to concrete can be mitigated by using different Type cements, reducing water-cement ratio and/or increasing compressive strength of concrete mixes to reduce permeability.

5.1.4 Environmental Testing

We engaged an environmental analytical laboratory, Pace Analytical, to perform the following tests on the samples obtained for environmental testing:

% Solids SGT – HEM (non-polar material) TCL Volatiles (DOD QSM 5.3) TCL Semivolatiles (DOD QSM 5.3)

TPH - GRO & DRO (DOD QSM 5.3)

TCLP Metals (DOD QSM 5.3)

Testing was conducted on samples representative of the on-site soils encountered. Investigation Derived Waste (IDW) samples were obtained as a composite from the drilling spoils across the project site. A sample of the liquid IDW and the solids IDW was obtained for testing. A composite sample from borings B-1 and B-2 from 0 to 4 ft below the ground surface was also obtained for testing. The results from Pace Analytical’s testing is provided within Appendix C.

Water samples were also collected (TW-1 and TW-2) from the two temporary piezometers located within borings B-3 and B-4 and tested by Pace Analytical for environmental testing:

TCLP Volatiles (DOD QSM 5.3) TCLP Semivolatiles (DOD QSM 5.3) TCLP Metals (DOD QSM 5.3)

The results from Pace Analytical’s testing is provided within Appendix C.

Samples of investigation derived wastes (IDW) were collected for the purpose of characterizing wastes generated during the investigation in order to appropriately dispose of the waste materials. One sample was collected from solid waste (IDW-1S) and one sample was collected from liquid waste (IDW-L) during this investigation. The presence of total petroleum hydrocarbon gasoline range organics (TPH-GRO) and diesel range organics (TPH-DRO) in IDW samples may provide some insight into the nature of contaminants within the subsurface at the site; however, the wastes are likely to include materials introduced by the drilling process and equipment (including pre-rinse decontamination water, PPE, etc.)

and should not be considered representative of site conditions. The detections from IDW samples are not suggestive of a significant site source for any of the parameters analyzed.

One soil sample (B1+B2) was collected from native soils on the site. Two groundwater samples (TW-1 and TW-2) were collected on the site. The TPH-DRO detection in the soil sample (4.7 mg/kg) is well below the United States Environmental Protection Agency (USEPA) Regional Screening Level (RSL) for Total Petroleum Hydrocarbons-Aromatic Low of 82 mg/kg for residential soil. (Note: TPH-DRO analysis is based on a range that is not an exact match for the RSLs; the RSL applied in this instance is the most conservative option). Metals analysis of the soil sample was performed using a TCLP method that measures the leachability potential of the analytes under conditions expected within a landfill. This does

February 20, 2024 Page 9 Schnabel Engineering, LLC not allow for a direct comparison with RSLs; however, the barium detection (0.11 mg/L) does not suggest an issue of concern as the residential soil RSL for barium is 15,000 mg/kg. The detections of barium in groundwater samples were analyzed using a TCLP method that would be conservative if compared to drinking water standards. The barium results for TW-1 and TW-2 are well below the drinking water standard of 2.0 mg/L. The chromium detection (0.07 mg/L) in TW-2 via TCLP is also conservative and below the drinking water standard of 0.10 mg/L for total chromium.

The detection of arsenic in TW-1 (0.044 mg/L) via TCLP is conservative and exceeds the drinking water standard of 0.01 mg/L. The detection of lead in TW-2 (0.09 mg/L) via TCLP is conservative and exceeds the drinking water standard of 0.015 mg/L. Both detections are likely to be the result of naturally occurring levels present in site soils. The groundwater samples were collected from temporary wells that are likely to have resulted in turbid samples containing solids which would likely contribute to detection levels. Based on results from the soil sample and the levels of metals detected in groundwater no additional safety considerations beyond standard worker hygiene practices appear to be warranted.

February 20, 2024 Page 10 Schnabel Engineering, LLC

6.0 SITE GEOLOGY AND SUBSURFACE CONDITIONS

This section presents the stratigraphy and groundwater conditions encountered during our field exploration:

6.1 Generalized Subsurface Stratigraphy

We characterized the following generalized subsurface stratigraphy based on the exploration results and laboratory test data that are included in the appendices. The boring logs, included within Appendix A, also display the stratum classifications.

At the test boring and test pit locations Surficial Organic Laden Soils (SOLS) was encountered to depths of up to 9.5-inches below the ground surface. While excavating Test Pit TP-1 Fill material sampled as a soil cement was encountered from a depth of 0.8 to 1.4 feet below the ground surface. Within Test Pit TP- 2, an abandoned utility pad was encountered 0.8 feet below the ground surface and is sitting upon brick.

The abandoned utility pad is approximately 4 ft x 3 ft and 5 inches thick.

Table 6.1: Soil Stratigraphy

Type Test Depth (ft)

Description

STRATUM F

(Probable Fill

Material)

Ground surface to depths of up to 1.4 feet within TP-1 Sampled as: Soil Cement

STRATUM A

(Alluvial)

Ground surface to depths of 23.0 feet, interlayered, and below Stratum F within TP-1

Poorly Graded Sand with Silt (SP-SM), Poorly Graded Sand with Clay (SP-SC), Silty Sand (SM), Clayey Sand (SC), and Silty Clayey Sand (SC-SM) (SPT N Value = 1 to 16 bpf) Very loose to Medium Dense

STRATUM A1

(Alluvial)

Ground surface to depths of 18.0 feet, interlayered, and below Stratum A

Silt with Sand (ML), and Sandy Silt (ML) (SPT N Value = 2 to 9 bpf) Very Loose to Loose

STRATUM B

(Alluvial)

Below Stratum A and A1 to depths of 23.0 feet

Fat Clay (CH), Fat Clay with Sand (CH), and Sandy Lean Clay (CL) (SPT N value = 1 to 2 bpf) Very Soft

STRATUM C

(Alluvial)

Below Stratum A and/or B to termination depths of 80.0 feet

Poorly Graded Sand (SP), Poorly Graded Sand with Silt (SP-SM), Poorly Graded Sand with Clay (SP-SC), Clayey Sand (SC), and Silty Sand (SM) (SPT N value = 4 to 42 bpf) Loose to Dense

The above “N” values indicate the Standard Penetration Test resistances encountered in a particular layer as determined from the number of blows required to drive a 2-inch O.D., 1-3/8 inch I.D. sampling spoon one foot using a 140-pound hammer falling 30 inches. This test is conducted after seating the sampler six inches in the bottom of the hole according to ASTM D1586.

February 20, 2024 Page 11 Schnabel Engineering, LLC

Soil samples have been classified in accordance with ASTM D2488. The ASTM D2488 group symbols (e.g. SM), indicated above and on the boring logs, are based on visual observations and laboratory testing of recovered soil samples. Criteria for soil classification are given in Appendix A.

6.2 Groundwater

The test boring logs in Appendix A include groundwater observations obtained during our subsurface exploration. These data include depths to groundwater encountered during drilling and upon drilling completion.

At the completion of drilling borings B-3 and B-4 on September 9, 2021 temporary wells were installed to monitor ground water levels at these locations. These wells indicated a rise in the water table from the encountered depth of 6.0 and 4.0 feet respectively, below the ground surface to 2.4 feet below the ground surface on September 27, 2021. The temporary wells were removed on September 27, 2021 and abandoned with a bentonite grout mix.

Water level measurements taken in the test borings indicate groundwater to depths of between 4.0 to 6.0 feet below the ground surface, and as shallow as 2.4 feet below the ground surface in the temporary well installed in Boring B-4, about two weeks after drilling.

Based on the above data, seasonal high water table is generally anticipated to be at about EL 5.5.

The final design should anticipate fluctuations in the water table depending upon variations in precipitation, surface runoff, pumping from any nearby wells, evaporation and similar factors.

Groundwater may be encountered in trenched spaces during periods of heavy precipitation; as such permanent dewatering provisions should be provided in trenched spaces. Groundwater may also impact construction during excavation of deeper utilities across the site. It is possible that a temporary wellpoint system may be required to lower the groundwater level during construction.

6.3 Seismic Site Classification

We evaluated the site for possible liquefaction susceptibility. Liquefaction is a phenomenon where loose, granular soils below the water table experience a sudden reduction in shear strength in response to strong earthquake shaking over successive cycles of ground motion. Liquefaction of granular soil layers may result in excessive settlements of shallow foundations, and/or downdrag on deep foundations.

Based on our evaluation of the test boring and CPT data, we find that the upper 13 to 18 ft of soil below existing ground surface sandy/silty soils of upper 13 to 18 ft that are below water table, are susceptible to liquefaction. Sandy soils below fat clay layer are high blow count, which indicates Pleistocene or older deposit which have much lower susceptibility to liquefaction. Lower blows below ~50 ft have clay fines in the mix that have PI> 7, so aren’t considered susceptible. Liquefaction Potential Index (LPI) was above 8, which also supports surface manifestation due to liquefaction is likely. The results of our liquefaction evaluation is included in Appendix D.

Based on the above evaluations, estimated settlement due to liquefaction is between about 3 to 5 inches.

February 20, 2024 Page 12 Schnabel Engineering, LLC

Since liquefaction is inevitable under existing conditions, and as such the Seismic Site Class is F per ASCE 7-16 Section 20.3.1. The Seismic Site Class will not improve if any deep foundation system is used, but can improve to a Site Class D if a suitable liquefaction mitigation technique, such as rammed aggregate piers, is used (and proof tested).

Assuming that the fundamental period of the proposed structure is less than 0.5 seconds (since the building will be a two-story reinforced masonry structure) and based on ASCE 7-16 Section 20.3.1 Exception, Site Response Analysis (SRA) is not required to obtain seismic design parameters: SDS, SD1 and PGAM. Rather, Site Class can be determined using ASCE 7-16 Section 20.3. Per ASCE 7-16 Section 11.4.8, a Ground Motion Hazard Analysis (GMHA) is required or the condition described in ASCE 7-16 Section 11.4.8 Exception #2 will apply as detailed below:

Based on the measured shear wave velocity we calculated the average shear wave velocity in the upper 100 ft as about 780 ft/sec. Based on ASCE 7-16 Chapter 20, the site is classified as Site Class D. However, due to Liquefaction potential at this site, Site Class was reduced to F.

We understand, the structure is a low-rise structure that has natural period of less than 0.5 seconds. The seismic design parameters were calculated based on ASCE 7-16 Section 11.4. Considering the ‘Exception’ criteria for Site Class F in ASCE 7-16 Section 20.3.1, the design parameters are same as the parameters obtained for Site Class D.

The design parameters for both the above mentioned foundation alternatives, and for the conditions assumed, are provided in the below Table based on ASCE 7-16 Section 11.4.

February 20, 2024 Page 13 Schnabel Engineering, LLC

Table 6.2: Seismic Design Acceleration Parameters (IBC 2018 / ASCE 7-16)

Site Class

SS

(g)

S1

(g)

PGA

(g) Fa Fv FPGA

SDS

(g)

SD1

(g)

PGAM

(g)

Seismic Design Category (SDC)

RC I-IV

D 0.558 0.18 0.318 1.354 2.24 1.282 0.503 0.269 0.408 III

February 20, 2024 Page 14 Schnabel Engineering, LLC

7.0 SITE GRADING AND EARTHWORK

Recommendations for compacted fill subgrade preparation, fill soil requirements, placement and compaction criteria, are presented in subsequent sections. The geotechnical engineering analysis was based on the information developed from our subsurface exploration and soil laboratory testing, along with the project site plans and structural loading conditions furnished to our office.

7.1 Compacted Fill Subgrades

Subgrades to receive compacted structural fill for building and pavement support should be stripped of vegetation, organic matter, and any soft or otherwise unsuitable materials. Based on the test boring data, organic laden soils were present to depths up to about 10 inches. The existing building foundations and floor slabs should be completely removed as part of their demolition. Any existing utilities to be abandoned should be removed and properly backfilled with compacted structural fill.

The Geotechnical Engineer should evaluate the suitability of the fill subgrades. The stripped subgrades should be proofrolled with a loaded dump truck to evaluate the subgrade suitability for support of the compacted structural fill prior to any undercutting or initiation of fill placement. Areas that exhibit excessive pumping, weaving, or rutting should be scarified, dried and re-compacted, or undercut and replaced with compacted structural fill as recommended by the Geotechnical Engineer. In locations that may be inaccessible to a loaded dump truck, subgrade evaluation techniques complementary to proofrolling could include a combination of probing with a penetrometer, drilling hand augers, probing with a steel probe rod, and/or dynamic cone penetrometer (DCP) testing.

No fill material should be placed until the subgrades have been observed and are considered suitable by the Geotechnical Engineer. The stripped subgrades should be re-compacted to at least 95 percent of the maximum dry density per ASTM D698 (Standard Proctor) prior to placing any new fill. The contractor should also proofroll the final pavement and slab subgrades under the observation of the Geotechnical Engineer within 24 hours prior to placement, to ensure no excessive disturbance has occurred.

The non-organic portions of the undercut materials may be reused as common fill across the site if they can be moisture conditioned and be adequately compacted. The use of these materials as compacted structural fill is not allowed per NAVFAC policy.

When excavation of unsuitable materials is required, it should be performed in a manner to limit disturbance of the underlying suitable material. To evaluate required excavation depths, the excavation should be performed under the observation of the Geotechnical Engineer.

Compacted structural fill subgrades should be kept free of ponded water. If springs or other flowing water is present at the compacted structural fill subgrade level, the Contractor should direct water to discharge beyond the fill limits. Recommendations for discharging springs should be provided by the Geotechnical Engineer.

7.2 Compacted Fill and Backfill

If unsuitable subgrade material is discovered at the bearing elevation, it should be removed and replaced with new compacted structural fill. Material used as compacted structural fill and backfill (for use in structure and pavement areas) should be imported and classify as SM, SC, SW, and/or SP-SM according to ASTM D2487. In addition, structural fill should exhibit Liquid Limit (LL) and Plasticity Index (PI) values

February 20, 2024 Page 15 Schnabel Engineering, LLC of less than 35 and 12, respectively. Compacted structural fill should contain no more than 35% fines (material smaller than No. 200 sieve).

If off-site borrow materials are needed, these soils should classify as Fill materials mentioned above and should not contain particles larger than 3-inches. Note that some of these soils may also be soft and wet at the time of construction, and therefore may require aeration and drying to be attain moisture contents for adequate compaction to be achieved.

Samples of borrow fill material proposed for use as compacted structural fill should be submitted to the Geotechnical Engineer for an evaluation of their suitability.

Backfill placed in excavations, trenches, and other areas that large compaction equipment cannot access should be placed in maximum 6-inch-thick lifts. Backfill should meet the material, placement, and compaction requirements outlined above.

Compacted structural fill and general backfill should be placed in maximum 8-inch thick horizontal, loose lifts and compacted to the following minimum compaction requirements:

Table 7.2: Soil Compaction

Area Compaction Requirements*

(per ASTM D698)

Building & Pavement Subgrades (Top 12 inches)

95%

Building & Pavement Subgrades (Below Top 12 inches)

92%

Structures, Retaining Walls, Trenches, & Walkways

92%

Lawn or Unimproved Areas (general backfill)

90%

*With moisture content within +/- 3% of the optimum moisture content.

Compacted structural fill should extend laterally at least five feet beyond the building and pavement limits, and then slope as needed to meet existing grades.

7.3 Fill Induced Settlement

It is anticipated that approximately one to four feet of fill will be placed across the site. Based on our evaluation, it is anticipated that about 0.5 inch of settlement will occur in the deepest fill areas. This settlement will occur immediately as the fill is placed, since the underlying natural materials are predominantly non-plastic granular soils.

7.4 Slopes

Permanent cut and fill slopes should not be designed or built steeper than 3H:1V, unless verified by further geotechnical evaluation.

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8.0 FOUNDATION RECOMMENDATIONS

We based our geotechnical engineering recommendations on field and soil laboratory test data from the subsurface exploration along with project plans, site plans, and structural loading furnished to our office.

Very soft and loose soils were encountered across the site and these soils are not considered suitable for direct support of conventional shallow spread footings in their current conditions, as the anticipated structural foundation loads would result in excessive settlements under both static and seismic conditions.

Various foundation alternatives were initially considered. Based on our preliminary evaluation, Driven Prestressed-Precast Concrete Piles, and shallow foundations supported on ground improved soils using rammed aggregate piers were given further consideration for building support.

It should be noted that during a seismic event, there is high potential for liquefaction if ground improvement is not completed, and the floor slabs on site could potentially settle.

The following sections of the report provide our detailed recommendations.

8.1 Deep Foundation Alternatives

8.1.1 Concrete Piles

We consider driven pile foundations a suitable alternative for support of the proposed structure. We anticipate pre-stressed precast concrete piles is a possible deep foundation option for this project.

Piles will develop the majority of their capacity is through shaft friction starting at depths about 20 feet below existing ground surface grades. However, due to the high liquefaction potential of the soft/loose soils within the upper 18 feet, resulting in liquefaction-induced settlements throughout the site, a downdrag loading from this settlement must be considered in the pile capacities. This downdrag load is caused by the reversal of shaft friction (from positive to negative) in the liquefied soil zone (mobilized as the liquefied soil settles along the shaft and “drags” the pile downward). Pile allowable axial capacity alternatives based on a factor of safety of 2.5 applied to ultimate loads are as follows:

Table 8.1: Allowable Pile Capacity

Pile Type/Size

1Downdrag Load (tons)

Pile Length (ft BGS)

Allowable Axial

Capacity (tons)

2Required Driving Resistance (RDR)

(tons)

3Lateral Capacity for

0.5-inch Deflection

3Lateral Capacity for

1.0-inch Deflection

12-inch

PCC

45 60 76

23.0 kips 30.0 kips 70 65 81

85 85 101

14-inch

PCC

45 75 94

30.5 kips 40.5 kips 70 85 104

85 110 129

BGS = Below Ground Surface

1. Downdrag Load = Reversal of shaft friction in liquefied soil zone (top 30 feet BGS).

2. RDR = Allowable Axial Capacity + Downdrag Resistance to be overcome during driving.

3. Ultimate lateral capacity based on the load that results in the stated deflection.

February 20, 2024 Page 17 Schnabel Engineering, LLC

Pile settlement is expected to be less than one (1.0) inch under the allowable compressive load.

Differential settlement between similarly loaded foundations is not expected to exceed about half this value. Provided a pile center-to-center spacing of at least three pile diameters is maintained, the capacity of a pile group will be equal to the individual pile capacity multiplied by the number of piles in the group.

Per UFC 3-220-01 (November 2012) piles evaluated by means of static load testing should have a factor of safety of 2.0, while piles evaluated by means of dynamic pile testing should have a factor of safety of 2.5.

A test pile program consisting of the installation of a minimum of three control piles should be performed to provide data for developing production pile tip grades. The Contractor should install control piles at locations across the building site. Control piles should be at least 10 ft longer than required to reach the estimated tip grades. Control piles should be restruck to design tip grade after waiting at least 72 hours after initial driving.

Dynamic testing of control piles should be performed according to ASTM D4945, High-Strain Dynamic Testing of Deep Foundations during both initial driving and restrike. Signal matching analyses should be performed on selected hammer blows recorded near the end of initial driving and near the beginning of restrike. The Geotechnical Engineer should establish production pile tip grades and driving criteria based on the test pile program results. The Contractor should not order production piles until completion of the test pile program.

We can also evaluate lateral load resistances of the driven pipe pile option if the Structural Consultant can provide the anticipated lateral loadings.

8.2 Ground Improvement and Shallow Foundation Alternative

8.2.1 Ground Improvement

Vibro-replacement is a ground improvement technique that densifies and reinforces soils by constructing dense aggregate piers (stone columns) using a downhole vibratory probe or hollow mandrel. The probe/mandrel is vibrated/driven to a specified depth, densifying the surrounding soils as it passes.

Aggregate is introduced to the bottom of the probe/mandrel through a central tube. The probe/mandrel is lifted a few feet to allow the aggregate to fill the resulting void below the tip. The probe/mandrel is lowered into the aggregate, forcing it against the surrounding soil, expanding the stone column and further densifying the surrounding soils. The process is repeated, ultimately resulting in a dense aggregate pier extending to the surface.

Vibro-replacement may be used to improve the very loose/soft soils of Strata A and A1. Ground improvement to an elevation of no higher than EL -20.0 should be performed. The stone columns should also be designed for sufficient permeability to provide an adequate drainage path so that excess pore pressures do not build during a seismic event. A drainage layer of open-graded aggregate should typically be placed over the entire improved footprint to allow for drainage of pore water pressure during a seismic event. This drainage layer will also serve as a load transfer platform between the footings and stone columns. Although designed by the specialty contractor, this drainage layer should typically be a minimum of 1-foot-thick and be underlain by a drainage type geotextile such as Tencate Mirafi 140N.

Stone columns should typically be installed on a grid spacing across the building footprint, as well as some distance beyond the footprint for adequate lateral confinement of the stone columns and to provide

February 20, 2024 Page 18 Schnabel Engineering, LLC stability against any liquefaction borne settlement that may occur outside of the perimeter of the improved footprint.

Ground improvement should extend to about 1 ft below the bottom of footing elevation. Then the 1 ft drainage layer will be placed 1 ft above that. Compacted structural fill should be placed above the drainage layer up to the building finished floor elevation. The drainage layer should also be wrapped in a drainage type geotextile to prevent sands from entering the drainage layer and causing clogging within the voids. Maximum spacing for ground improvement elements supporting footings should be no greater than 6 feet on center. Maximum spacing for ground improvement elements supporting slabs should be no greater than 8 feet on center.

Since this ground improvement technique is a specialty system, the ground improvement design should be performed by the specialty geotechnical design-build contractor. The specialty contractor should verify that their design will allow for shallow foundations to be designed for an allowable soil bearing pressure on the order of 3,500 to 4,000 psf, that total and differential settlement of foundations supported on improved soils will not exceed 1.0 inch and 0.5-inch, respectively.

Consideration should also be given to installing earthquake drains around the perimeter of the building area, as a cost saving alternative to reduce the number of stone columns, and to also reduce settlements due to a seismic event to less than 0.5 inch. Earthquake drains may also be utilized beneath the mechanical yard to mitigate liquefaction potential. The same specialty contractor who is designing and installing the ground improvement should also design and install the earthquake drains. The design of the earthquake drains should be developed such that the pore pressure ratio (RU) is maintained under 0.6.

Prior to installation of production stone columns, the effectiveness of the stone column improvement should be evaluated by performing an area load test. The design-build contractor should provide a detailed load testing plan for review by the Geotechnical Engineer prior to proceeding with the load test.

Additionally, in order to confirm an improved Seismic Site Class, the Geotechnical Engineer should be contacted to provide a post-ground improvement proof testing CPT program and/or a multichannel analysis of surface waves (MASW) geophysical survey following the specialty contractor’s completion of the ground improvement. The testing is intended to verify that the average shear-wave velocities within the ground improvement zone will be at least 600 ft/s. If this criteria is not met after ground improvement, possible redesign and additional ground improvement by the specialty contractor may be required.

Because vibro-replacement may result in a lowering (or heaving) of the ground surface, it is important that vibro-replacement be performed prior to installation of site utilities or construction of any other site structures.

Installation of test stone columns, the area load test, and production stone columns should be observed and documented by the Geotechnical Engineer.

8.2.2 Fill Settlement Monitoring

As there will be some settlement due to fill placement for the building floor slabs, we recommend settlement plates be installed within the building footprint at its four corners within fill areas to monitor settlement. Settlement plates should be installed prior to the placement of compacted structural fill (excluding the 1 ft thick stone drainage layer) to confirm settlement has ceased. Settlement plates should

February 20, 2024 Page 19 Schnabel Engineering, LLC consist of a 24 x 24 x ½-inch steel plate with a 2-inch steel riser pipe welded to its center. The elevation of the riser pipe should be recorded by a licensed Surveyor every third or fourth day for at least 60 days, and be provided to the Geotechnical Engineer as readings are obtained. If the Geotechnical Engineer determines settlement is continuing beyond 60 days, additional readings should be obtained. Settlement plate readings should be taken to the nearest 0.005 ft and referenced to a benchmark well beyond the influence of the fill placed.

The construction of the aggregate piers must not start until settlement has essentially ceased from the placement of this new compacted structural fill as verified by the Geotechnical Engineer.

8.2.3 Shallow Footings

The existing very loose/soft soils of Stratum A may be improved to support shallow spread and strip footings by using ground improvement techniques that will limit settlements from static loading conditions to within tolerable levels. Shallow footings founded on stone column improved soils can be preliminarily designed for an allowable composite bearing pressure of about 3,500 to 4,000 psf. The final allowable soil bearing pressure should be determined by the specialty geotechnical design-build Contractor.

The specialty geotechnical design-build contractor should design the ground improvement system such that total and differential settlements of shallow foundations supported on improved soils will not exceed 0.5-inch during a seismic event.

The allowable bearing pressures stated…