CD04-20201022 GER P1395 Marine Raider Bn HQS R4 -ALZ Sealed.pdf

GEOTECHNICAL ENGINEERING REPORT, Rev. 4 P-1395 Special Operations Forces

Marine Raider Regimental HQS Camp Lejeune, North Carolina

Prepared for:

Naval Facilities Engineering Command

Prepared by:

HDR Engineering, Inc.

Glen Allen, Virginia

October 22, 2020

Geotechnical Engineering Report, R4 P-1395 Marine Raider Regimental HQ

Camp Lejeune, NC i hdrinc.com

REPORT VERIFICATION

PROJECT NAME: Geotechnical Engineering Report

REVISION No.: 4

This certifies that I, Aaron L. Zdinak, P.E., have reviewed the attached document and have satisfied myself the work performed was conducted in conformance with generally accepted industry practice. The attached seal in applicable only to the original of the referenced document.

Corporate Seal Professional Engineer Seal

Signature:__________________________

Name: Aaron L. Zdinak, PE

P.E. No.: 050964

Date: October 22, 2020

AZDINAK

Model

AZDINAK

Stamp

AZDINAK

Typewritten Text 10-22-2020

CONTENTS

REPORT VERIFICATION ............................................................................................................ i

1.0 AUTHORIZATION

2.0 SITE DESCRIPTION

3.0 PROJECT DESCRIPTION

4.0 OBJECTIVE AND SCOPE

5.0 SUBSURFACE EXPLORATION

SPT Test Borings Exploration Locations and Elevations Field Infiltration Testing Chemical-Analytical Testing Supplemental Water Levels

6.0 LABORATORY TESTING

7.0 SUBSURFACE CONDITIONS

Area Geology Subsurface Conditions Expansive Soils Corrosion Potential Chemical-Analytical Results Subsurface Water

8.0 ANALYSES AND RECOMMENDATIONS

Assignment of Geotechnical Soil Design Parameters Shallow Foundations Sliding Resistance Seismic Site Classification and Design Parameters Design CBR Pavement Design

Asphalt Concrete Pavement for Parking Lots and Roads Aggregate Truck Loop Pavement Portland Cement Concrete Pavement Consideration for All Pavements

Floor Slabs Site Drainage

Under Building Pad and Other Areas of Elevated Water Stormwater Management Facilities General Considerations

9.0 EARTHWORK AND CONSTRUCTION CONSIDERATIONS

General Site preparation Fill Materials and Compaction Influence of Fill Placement on Foundation and Slab Settlement Temporary Excavations

General Excavation Characteristics

Trench Backfill ii

Subsurface Water Control During Construction Stormwater Management Facilities Additional Geotechnical Services

10.0 LIMITATIONS

11.0 REFERENCES

APPENDICES

Appendix A – Figures Appendix B – Subsurface Exploration Logs and Data Appendix C – Laboratory Test Results Appendix D – Calculations

1.0 AUTHORIZATION

HDR Engineering, Inc. (HDR) is pleased to submit this Geotechnical Engineering Report (GER) to Naval Facilities Engineering Command (NAVFAC) for the P-1395 Special Operations Forces (SOF) Marine Raider Regimental Headquarters in Camp Lejeune, North Carolina. This work was completed in accordance with the delivery order (N4008518F7180) and was authorized by Notice-to-Proceed on September 27, 2018, as well as subsequent modifications.

2.0 SITE DESCRIPTION

The project site is located within the Marine Special Operations Command (MARSOC) section of the Marine Corps Base (MCB) Camp Lejeune military installation. The proposed site is located southeast of the intersection of Loop Road and Everett Creek Road, and is a wooded area surrounded by wetlands. The present grade of the project site declines from approximately elevation (El.) 33 feet 1988 North American Vertical Datum (NAVD 88) on the proposed north side of the building, to El. 20 feet NAVD 88 on the proposed south side of the building. The present grade within the proposed building footprint declines from El. 29 on the north side to El. 24 on the south side. A site vicinity map is provided on Figure A-1 in Appendix A.

3.0 PROJECT DESCRIPTION

The project consists of providing geotechnical design services for the construction of the SOF Marine Raider Regimental Headquarters. The proposed new facility is a single-story building, approximately 240 feet long by 120 feet wide and the floor will be a reinforced concrete slab on grade. The framing will be a Pre-Engineered Metal Building System (PEMB). The PEMB will consist of rigid frames in the plan north/south direction with portal frames in the plan east/west direction. The building is proposed to be founded on reinforced concrete shallow footings (strip footings at exterior walls and spread footings at PEMB columns, which are located around the perimeter of the building).

The finished floor elevation (FFE) is +27.5 feet NAVD 88. The building is categorized as Risk Category II per Table 2-2 of UFC 3-301-01. Design wall loading is expected to be a maximum of approximately 2 kips per lineal foot (1.4 ksf). Rigid frame column design loads are expected to be up to approximately 76 kips and apply a maximum bearing pressure of 1.2 ksf. Loads used in our analyses were obtained from HDR structural designers on November 11, 2019 and the Basis of Design for this project. This document should be consulted for additional information on design loading.

An access roadway will be constructed from the existing Everett Creek Road to the proposed headquarters facility. Parking lots will be constructed to the east of the building. Approximately 134 total parking spaces will be provided, and the western side of the building will also be used for antenna and loading areas. Flexible pavement sections (light duty and heavy-duty asphalt) are intended for the access roads and parking lots. The 2” surface course will be deferred for several years prior to placement. Aggregate pavement is proposed for the truck turn-around loop.

Rigid pavement is proposed for dumpster enclosures, loading docks, and other areas subject to heavy traffic loads (including the antenna and loading areas). Concrete sidewalks will direct pedestrians to the front (eastern side) of the building. Additionally, the design also calls for the construction of storm water management facilities at the southern limit of the site.

4.0 OBJECTIVE AND SCOPE

The objective of this geotechnical evaluation is to characterize subsurface conditions at the project site to develop geotechnical recommendations for to support design and construction of the planned facility. To achieve this objective, HDR executed the following general scope of services:

• Reviewed existing subsurface exploration data in the vicinity of the proposed headquarters, which was provided by NAVFAC

• Developed and conducted an exploration program consisting of 13 Standard Penetration Test (SPT) borings to depths of up to 50 feet below ground surface (bgs)

• Excavated five hand auger holes for supplemental water readings and three hand auger holes for piezometer installation for long term water readings

• Performed laboratory testing on selected soil samples from the test borings to aid in classification and establishment of geotechnical engineering parameters

• Characterized the subsurface conditions encountered and developed recommendations for the design of the proposed building and pavement based on completed analyses

• Prepared this Geotechnical Engineering Report (GER) summarizing the results of the exploration program and geotechnical foundation recommendations for the headquarters building, pavement design, and earthwork recommendations.

An environmental site assessment for the presence of hazardous materials, wetlands identification and delineation, construction cost estimates, or the preparation of plans was beyond the scope of services provided by HDR.

5.0 SUBSURFACE EXPLORATION

NAVFAC provided HDR with geotechnical engineering data report titled “P1396 SOF Intel Operations Facility Expansion” dated May 22, 2014. During that investigation, Fishburne Drilling, Inc. of Chesapeake, Virginia, drilled seventeen standard penetration test borings (SPT), advanced two cone penetrometer tests (CPTu), performed four dilatometer tests (DMT), and pushed one seismic cone penetrometer (SCPTu) test for the proposed site. Pertinent information gathered from the borings of the previous investigation are shown on Figure A-2 in Appendix A.

HDR planned and executed a subsurface exploration program to collect additional data at the locations shown on Figure A-2 in Appendix A. GET Solutions Inc. (GETS) of Virginia Beach, Virginia drilled total of 11 SPT borings on January 15 and 16, 2019, using an ATV-mounted CME- 55 drill rig. On April 22, 2019, GETS returned to the site to confirm water level elevations adjacent to three SPT locations (19B-01, 19B-02, and 19P-02) and two additional locations (19B-05 and 19SW-03) by advancing hand auger excavations to termination depths up to approximately eight feet bgs. With the recent proposed shift of the proposed building location, HDR executed a supplemental boring program consisting of two SPT borings (19B-06 and 19B-07) and three hand auger locations (19PZ-01 through 19PZ-03) to install the temporary piezometers to measure stabilized groundwater readings. GETS performed this additional field exploration on October 3 and 4, 2019. Table 5-1 summarizes the subsurface exploration program.

Table 5-1: Summary of HDR Subsurface Explorations

Test Boring Designation

General Location Approximate

Surface El. (ft)

(NAVD 88)

Total Depth (ft)

Temporary Piezometer(s)

Installed

Shelby Tube(s)

Collected

19B-01 and A Building Footprint 32 50 X

19B-02 and A Building Footprint 33 50

19B-03 Building Footprint 26 40 X

19B-04 Building Footprint 27 40

19B-051 Building Footprint 31 3

19B-06 Building Footprint 24 40

19B-07 Building Footprint 22 40

19P-01 Roadway/Parking Lot 35 10

19P-02 and A Roadway/Parking Lot 31 10

19P-03 Parking Lot 23 10

19P-04 Parking Lot 21 10

19P-05 Parking Lot 24 10

19SW-01 Stormwater Facility 24 15 X

19SW-02 Stormwater Facility 21 15 X

19SW-031 Stormwater Facility 19 6

19PZ-012 Building Footprint 29 15 X

19PZ-022 Building Footprint 23 15 X

19PZ-032 Stormwater Facility 22 15 X 1Hand auger only for supplemental water level determination. SPT boring not completed at this location.

2Hand auger for temporary piezometer installation.

The following sections provide additional details about HDR’s subsurface exploration program.

SPT Test Borings Test borings completed by HDR were advanced to depths up to approximately 50 feet bgs using mud rotary drilling techniques. Standard Penetration Tests (SPT) with split-spoon sampling of soils were conducted in accordance with ASTM D1586 using an automatic hammer with an efficiency of approximate 80% and 84% (for 19B-06 and 19B-07). Seven 24-inch long SPT samples were collected in the upper 15 feet of each borehole (continuous sampling to a depth of 12 feet) and at five-foot intervals below a depth of 15 feet to boring termination.

Upon completion, all test borings were backfilled with grout and the hand auger holes were backfilled with soil cuttings and bentonite chips. Temporary piezometers were installed in test borings 19SW-01 and 19SW-02 with water levels recorded 48 hours after completion. Temporary piezometers were also installed in test holes 19PZ-01, 19PZ-02 and 19PZ-03 in supplemental subsurface exploration program. After 48-hour water level readings were recorded, the piezometers were removed and the test holes were backfilled. Soil samples were transported to GETS’ accredited laboratory in Virginia Beach, Virginia, for testing.

Qualified GETS personnel monitored the drilling in the field, which included overall coordination of drilling activities, visual-manual classification of soil samples in accordance with ASTM Standard D 2488, preparation of field exploration logs, monitoring conformance with drilling and sampling criteria, and observation of general site conditions. Test boring logs (both HDR’s and those previously completed) are provided in Appendix B for reference.

Exploration Locations and Elevations GETS personnel laid out proposed exploration locations in the field using a handheld GPS device.

Surface elevations were determined from surveyed topographic information. Surface elevations at the exploration locations are referenced to NAVD88. The as-drilled subsurface explorations locations are shown on Figure A-2 in Appendix A. Latitude and longitude are provided on the exploration logs, which are provided in Appendix B.

Field Infiltration Testing Field infiltration testing was completed using a constant head permeameter test at the location of boring 19SW-02, which is at the location of a potential storm water basin. The coefficient of hydraulic conductivity (ksat)was estimated to be 0.049 feet per day (1.7x10-5 cm/s) based on procedures for flow from a test-hole located above groundwater level as outlined in “Theory and Problems of Water Percolation” (Zanger 1953). Test results are presented in Appendix C.

Chemical-Analytical Testing A composite soil sample was collected from exploration locations 19B-01, 19B-02, 19P-02, and 19SW-01 from the depth interval of one to four feet using hand auger excavation methods. The hand auger was cleaned and decontaminated using non-phosphate industrial grade detergent and distilled water rinse before collecting each sample. Samples were stored in laboratory provided containers and preserved below 40 degrees Fahrenheit until the laboratory secured custody.

Supplemental Water Levels Under HDR’s direction, GETS returned to the site on April 12, 2019 to complete hand auger excavations adjacent to three of the existing SPT borings (19B-01, 19B-02, and 19P-02) and two new locations (19B-05 and 19SW-03) to determine ground water elevations within/adjacent to the building footprint and at a potential storm water basin. Hand auger explorations completed adjacent to the existing SPT borings are designated with an “A” (i.e.19B-01A, etc.). Later, on October 2019, under HDR’s execution of the supplemental subsurface exploration program, GETS personnel installed temporary piezometers in three locations designated with “PZ” (19PZ- 01, 19PZ-02 and 19PZ-03) and took 48-hour groundwater readings on October 08, 2019.

6.0 LABORATORY TESTING

GETS performed laboratory testing on soil samples collected from the test borings. HDR personnel evaluated the field exploration logs and assigned specific samples for testing. Testing was performed to aid in the classification of representative soils encountered in the explorations and to support development of geotechnical engineering parameters for design. Table 6-1 summarizes the laboratory testing completed for the project.

Table 6-1: Summary of Laboratory Testing Program

Laboratory Test Test Specification Number of

Tests

Moisture Content ASTM D 2216 70

# 200 Sieve Wash ASTM D1140 13

Grain Size Analysis ASTM D 6913 27

Grain Size Analysis with Hydrometer ASTM D6913 and D7928 2

Atterberg Limits ASTM D 4318 27

Standard Proctor ASTM D 698 2

California Bearing Ratio ASTM D 1883 2

Laboratory Test Test Specification Number of

Tests

One-Dimensional Consolidation ASTM D2435 1

Shelby Tube Extrusion and Logging --- 3 pH, soluble sulfates, chlorides, electrical resistivity, redox potential, and sulfides

Refer to appended report for test methods 1 composite

TCLP 8 RCRA Metals, BTEX, and TPH-

DRO & GRO

EPA SW-846 methods (refer to appended report for details) 1 composite

The laboratory tests were performed in accordance with referenced standards. The results are presented in Appendix C of this report.

7.0 SUBSURFACE CONDITIONS

The following sections summarize our review of available geologic data and the results of subsurface conditions encountered at the project site. Specific observations, remarks, and comments are noted on the exploration logs provided in Appendix B of this report.

Area Geology The project site is in the Coastal Plain Physiographic province. The North Carolina Coastal Plain is mostly a relict, Plio-Pleistocene landscape. It is characterized by a series of progressively younger scarps, and intervening terraces that step down in elevations and age towards the coast and into river basins. The surficial deposits that underlie the earlier landscape include marine barrier island, estuarine, fluvial and other Coastal Plain deposits. The regional geology is complex, and generally consists of interbedded layers of varying mixtures of sands, silts, and clays.

Locally, the upper geologic units at the site are composed of unconsolidated Holocene and Upper Pleistocene age deposits of undivided members. Older underlying units include consolidated Tertiary deposits of the Belgrade, River Bend and Castle Hayne Formations, undivided, described as fossiliferous clay and shelly sand deposits (NCGS, 1985). Basement bedrock is expected at depths exceeding 1,000 feet below sea level.

Subsurface Conditions

HDR completed a total of thirteen SPT borings and drilled eight hand auger holes/test pits for groundwater measurements. Table 7-1 provides a summary of these borings and the hand auger holes/test pits including surface elevations, exploration depths, surficial soil thickness, and observed groundwater depths and approximate elevations. The B-Series SPT borings and borings 19P-03 and 19P-04 are located within or near the proposed building footprint. Additionally, previously conducted SPT boring, P-4, was also completed near the proposed building footprint.

Table 7-1: Summary of Explorations and Groundwater Measurements

Test Boring

Surface El. Test Boring1

(ft)

Test Boring Depth

(ft)

Surficial Soil

Thickness (ft)

Subsurface Water

At End of Drilling (EOD)

Supplemental Subsurface

Water Readings At EOD

Stabilized Water Table (48 hour)

Readings

Interpreted Seasonal High

Water Table

Depth (ft)

El.1 (ft)

Depth

19B-01 32.36 50.0 0.1 6.0 26.4 --- --- --- --- 6 26

19B-01A 32.29 5.0 0.1 --- --- 3.2 29.1 --- --- 4 28

19B-02 33.34 50.0 0.1 3.5 29.8 --- --- --- --- 4 29

19B-02A 33.42 5.0 0.1 --- --- 3.8 29.6 --- --- 4 29

19B-03 25.55 40.0 0.2 3.0 22.6 --- --- --- --- 3 23

19B-04 26.83 40.0 0.3 2.0 24.8 --- --- --- --- 2 25

19B-05 30.58 4.0 0.2 --- --- 2.7 27.9 --- --- 3 28

19B-06 23.90 40.0 0.5 11.0 12.9 --- --- --- --- 4 20

19B-07 22.22 40.0 0.3 12.0 10.2 --- --- --- --- 4 18

19P-01 34.61 10.0 0.3 3.0 31.6 --- --- --- --- 6 29

19P-02 31.31 10.0 0.2 7.0 24.3 --- --- --- --- 4 27

19P-02A ~31 4.0 0.2 --- --- 2.7 28.3 --- --- 3 28

19P-03 23.10 10.0 0.3 --- --- --- --- --- --- 5 18

19P-04 21.43 10.0 0.2 6.0 15.4 --- --- --- --- 6 15

19P-05 24.42 10.0 0.3 --- --- --- --- --- --- 3 21

P-4 ~26 10.0 1.0 1.5 24.5 --- --- --- --- --- ---

19SW-01 23.56 15.0 0.1 14.0 9.6 --- --- 7.6 16.0 9 15

19SW-02 21.21 15.0 0.1 4.0 17.2 --- --- 4.0 17.2 4 17

19SW-03 ~19 9.0 0.2 --- --- 7.6 11.4 --- --- 3 16

19PZ-01 28.70 15.0 --- --- --- --- --- 3.8 24.9 --- ---

19PZ-02 23.20 15.0 --- --- --- --- --- 5.2 18.0 --- ---

19PZ-03 21.50 15.0 --- --- --- --- --- 7.0 14.5 --- ---

Note: 1All referenced elevations are with respect to the datum NAVD88.

The following subsurface strata were observed within the test borings in the vicinity of proposed building area:

• Surficial soil – Surficial soil was encountered in all test borings to a depth of approximately 0.5 feet. However, depths of organic rich materials are likely greater than the observed surficial soil thicknesses in the wooded areas of the proposed facility and may be up to approximately one foot.

• Upper Alluvial Sand – Loose to medium dense alluvial sand with varying amounts of silt and clay (SP, SP-SM, SM, SC) was encountered beneath the surficial soil to approximate El. 15 in the north side of the building and the thickness gradually declines to zero feet on the south side. N60 (corrected for hammer energy) ranged from 0 to 36 blows per foot (bpf) with an average of 9 bpf. These soils are gray to dark gray, light gray, light brown, brown to dark brown and red-tan in color.

• Alluvial Clay – Beneath the upper alluvial sand, alluvial lean clay (CL) was encountered with the top elevations approximately at El. 15 on north side of the building to El. 26 on the south side. N60 ranged from 0 to 19 bpf with an average of 4 bpf, indicating the consistency of the clay to be primarily soft. These soils are gray to dark gray, tan, tan-gray, red-brown, orange-brown and brown in color.

• Lower Alluvial Sand – Beneath the alluvial clay, loose to medium dense sand with varying amounts of silt and clay content (SP, SP-SM, SM, SC) was encountered with the top elevations approximately at El. -14 on north side of the building to El. -3 on the south side. N60 ranged from 8 to 36 bpf with an average of 16 bpf. These soils are tan, gray to dark gray and dark green-gray in color.

Based on the laboratory results, the maximum dry density in the upper five feet of subgrade soils varied from approximately 104.6 to 117.5 pounds per cubic foot (pcf) with an average of 109.4 pcf when tested in accordance with ASTM D698 (Standard Proctor energy). The optimum water content of the on-site soils in the upper five feet varied between 10.7 and 15.3 percent with an average of 13.5 percent.

The in-situ moisture content of the existing near-surface subgrade soils (upper five feet) were generally found to be, on average, approximately five percent above optimum moisture content within the project site. A subsurface diagram near the proposed building is presented on Figure A-5 of Appendix A.

Expansive Soils Expansive soils are characterized by their ability to undergo significant volume changes (shrink or swell) due to variations in moisture content. Changes in soil moisture content can result from precipitation, landscape irrigation, utility leakage, roof drainage, perched groundwater, drought, or other factors. Expansive soils may result in unacceptable settlement or heave of structures or concrete slabs on grade.

The soils observed in our exploratory borings in the upper 10 feet within the building footprint on the north side were primarily granular soils and the soils in the south side were few feet of granular soils and primarily firm to stiff lean clay with plasticity index greater than 15 in the upper 10 feet.

The lean clays below 10 feet depth are in a very soft to soft consistency. Therefore, soils within the upper 10 feet of the proposed building location on the north side are not considered expansive.

Laboratory test results for borings in the south side of the building and south eastern area of the project site (parking lot and stormwater management facilities) indicate plasticity index greater than 15, therefore in accordance with Section 1803.5.3 of the International Building Code (2018), soils in the south and southeastern area of the project site may be considered expansive, and may exhibit volume change when exposed to varying moisture conditions.

Corrosion Potential A corrosion test was performed on a composite sample (depths between 1 to 4 feet bgs) from Borings 19B-01, 19B-02, 19P-02, and 19SW-01. The test results indicate the soil exhibited non-detectable amount of sulfate, a minimum resistivity of 41,800 ohms-centimeter (ohm-cm), chloride was not detected, and a pH level of 5.5. Based on the guidelines established the Portland Cement Association (1988), the subsurface soils at the site are not considered corrosive towards concrete or steel. The test results are included in Appendix C.

Chemical-Analytical Results HDR collected one composite soil sample from a depth of one to four feet bgs at exploration locations 19B-01, 19B-02, 19P-02, and 19SW-01 to characterize soil quality. Laboratory analyses were performed for total petroleum hydrocarbons (TPH) gasoline-range organics (GRO) and diesel-range organics (DRO) using solid waste method SW846 8015C, leaching potential of the 8 RCRA metals using EPA Methods 6010D and 7470A (mercury only) with 1311 extraction, and volatile organic compounds (VOCs) using SW846 8260B. The results of laboratory analyses, as shown below in Table 7-2, were qualified with either a U or J flag indicating that the results were either not detected above the reporting limit or estimated below the reporting limit, with one exception. The concentration of TPH-DRO (C10-C28) was 3.26 ppm. This may indicate additional soil in this area may have to be excavated, disposed of in accordance with federal, state, and local requirements; and, be replaced with clean fill during construction. Table 7-2 summarizes the test results.

Table 7-2: Summary of Chemical-Analytical Test Results

Tested Analyte Result (ppm)

Benzene 0.0023

Toluene 0.017

Ethylbenzene 0.0023

Xylene 0.007

TPH-GRO (C6-C10) 3.5

TPH-DRO (C10-C28) 3.26

Arsenic 0.05

Barium 0.084

Cadmium 0.10

Chromium 0.050

Lead 0.020

Mercury 0.00053

Selenium 0.050

Silver 0.020

The details of testing are included in Appendix C.

Subsurface Water

Subsurface water levels were measured in the test borings at the time of drilling. Water was introduced into the boreholes as part of the drilling process used to advance the borings. Drilling fluid may have impacted water level measurements or made it harder to visually observe the transition to depths below water during drilling. Temporary piezometers were installed in 19SW- 01 and 19SW-02, 19PZ-01, 19PZ-02 and 19PZ-03.

Boring logs contained in Appendix B of this report, depict the subsurface water level elevations observed in the test borings and temporary piezometers and the estimated seasonal high-water elevations. Additionally, GETS remobilized to the project site to evaluate static water levels at five hand auger locations (near 19B-01, 19B-02, and 19P-02 and two new locations, 19B-05 and 19SW-03). As presented in Section 7.1, the 48-hour water readings indicate water levels within the building pad were observed as high as approximate El. 25 (19PZ-01) to as low as approximate El. 18 (19PZ-02). The proposed finished floor elevation is 27.5 feet.

Explorations proximal to the stormwater management facility footprint (19B-06, 19B-07, 19PZ-02, 19PZ-03, 19SW-01, 19SW-02, and 19SW-03) had observed subsurface water elevations as high as approximate El. 18 (19PZ-02) to as low as approximate El. 14.5 (19PZ-03). Within the four explorations specifically completed for the stormwater management facilities (19PZ-03, 19SW- 01, 19SW-02, and 19SW-03), the seasonal high water table was interpreted as high as approximate El. 17 to as low as approximate El. 15. A subsurface diagram at the stormwater management facilities is presented on Figure A-6 of Appendix A, and depicts the observed and interpreted subsurface water conditions.

The observed groundwater depths and approximate elevations and the estimated seasonal high-water depths and elevations are presented in Table 7-1. Subsurface water levels may be anticipated to fluctuate due to precipitation, season, temperature, site grading, drilling methods, and other factors that may be different from the prevailing conditions at the time HDR completed its subsurface investigation.

8.0 ANALYSES AND RECOMMENDATIONS

The following sections describe the geotechnical analyses completed to support the design of planned facilities. HDR analyzed shallow foundations for the proposed building facility. Based upon our evaluation of the soils and geologic information, the proposed project is feasible for construction from a geotechnical standpoint provided the recommendations presented in this report are incorporated into the design of the project. Prior to foundation construction, earthwork activities should be performed as outlined in Section 9.0 of this report. The following sections outline HDR’s geotechnical recommendations for the design and construction of the proposed project.

Assignment of Geotechnical Soil Design Parameters In order to conduct the required geotechnical analyses, HDR assigned geotechnical design parameters for each soil stratum within the subsurface of the footprint of the north and south corners of the building, each of which had a separate stratigraphy.

For settlement and bearing capacity evaluation, HDR assigned soil parameter values for unit weight, shear strength, compressibility, and stress history. The unit weight, drained friction angle, and cohesion were developed from SPT N60 and laboratory test correlations. The consolidation test result determined consolidation parameters such as compression ratio (CR), recompression ratio (RR), and preconsolidation pressure (P’c) for the clay layers.

Table 8-1 and Table 8-2 summarize the geotechnical design stratigraphy and parameters developed for our analyses of the north (cut side) and south (fill side) portions of the building pad, respectively.

Table 8-1: Summary of North End (Cut Side) Design Stratigraphy and Geotechnical Parameters

Stratum Modeled

Depth, ft 1,2

N60 Range (average) blows/ft

Unit Weight (pcf)

Drained Friction Angle (degrees)

Cohesion (psf)

CR3 RR4

P’c5

(ksf)

Upper Alluvial Sand

0 to 9 0 to 36 (9) 110 32 -- -- -- --

Alluvial Clay

9 to 39 0 to 19 (4) 105 -- 600 0.25 0.03 3.0

Lower Alluvial Sand

39 to 50 8 to 29 (15) 120 32 -- -- -- --

1 Modeled depth has been selected to conservatively represent the stratigraphy influencing the settlement analysis.

2 The foundation bearing grade modeled at El. 25.5, which corresponds to the deepest ‘strip footing’ bearing elevation.

3CR = cc/(1+e0) = Compression Ratio 4 RR = cr/(1+e0) = Recompression Ratio 5 P’c = Preconsolidation Pressure

Table 8-2: Summary of South End (Fill Side) Design Stratigraphy and Geotechnical Parameters

Stratum Modeled

Depth, ft1,2

N60 Range (average) blows/ft

Unit Weight (pcf)

Drained Friction Angle (degrees)

Cohesion (psf)

CR3 RR4

P’c5

(ksf)

Alluvial Clay

0 to 27 0 to 17 (5) 105 -- 600 0.25 0.03 3.0

Lower Alluvial Sand

27 to 50 8 to 36 (17) 120 32 -- -- -- --

1 Modeled depth has been selected to conservatively represent the stratigraphy influencing the settlement analysis.

2 The foundation bearing grade modeled at El. 25.5, which corresponds to the deepest ‘strip footing’ bearing elevation.

3CR = cc/(1+e0) = Compression Ratio 4 RR = cr/(1+e0) = Recompression Ratio 5 P’c = Preconsolidation Pressure

Shallow Foundations Strip footings (for structure walls) and spread footings (at PEMB columns) are proposed for the building. Based on the anticipated loading and soil conditions encountered, it is our opinion that shallow foundations are feasible for the building provided the recommendations in this report are followed.

The proposed finished floor elevation is EL. 27.5 feet NAVD 88 with an interior slab subgrade as low as El. 26.5 (FFE = 27.5, 6 inch slab, and 6 inches of capillary barrier). The expected maximum frost penetration in the project area is zero inches. HDR completed our analyses assuming a bearing elevation for strip footings as deep as El. 25.5 and for column footings as deep as El.

22.5 NAVD 88.

In our analyses, we anticipate a minimum embedment depth of 2.0 feet with clay in direct contact with the bottom of the foundation based on conditions depicted in borings 19B-03, 19P-03, and

19B-06. This model is considered conservative and encompasses the range of potential foundation sizes and bearing depths. Water was considered to exist at the bearing level.

HDR determined the ultimate bearing capacity of the foundation soils utilizing an internally developed Excel spreadsheet for standard bearing capacity calculations using the methods developed by Meyerhoff and Vesic, and referenced in NAVFAC 7.02 Chapter 4. Based on HDR’s calculations the foundations for the proposed building may be supported on shallow spread footings with an allowable bearing capacity (Ultimate Bearing Capacity/Factor of Safety = 2.5 or

Bearing Capacity Resistance Factor = 0.4) of approximately 1,400 pounds per square foot (psf), as determined by the critical case of a 26-inch wide turn-down strip footing.

HDR evaluated settlement of shallow foundations in accordance with Chapter 5 of the NAVFAC

7.01 Soil Mechanics Design Manual. HDR analyzed shallow continuous strip and square footings for the various proposed sizes using an internally developed spreadsheet. Service loads at strip-footing supported walls are expected to be 1.4 ksf (3 kips per linear foot for a 2.2 feet wide strip footing). PEMB column service loads are anticipated to be approximately 26 kips, with service bearing pressures less than approximately 500 psf.

Settlement calculations were based on these anticipated loads, as well as the stratigraphy and design parameters presented in Table 8-1 and Table 8-2.

The critical analytical case is for the southern portion of the building footprint where the footings will bear at or closer to the top of the clay layer relative to the northern portion. Figure 8-1 summarizes HDR’s recommendations to limit bearing pressures to either remain below the allowable bearing capacity or to limit calculated settlements to less than one inch. Calculations indicate the primary consolidation settlement to be all recompression settlement and is expected to happen during the construction.

Figure 8-1: Summary of Recommended Limited Bearing Pressures

Note: The allowable bearing pressures are controlled by foundation settlement except for the first two points of the strip footing which is controlled by bearing capacity.

Differential settlement between support locations is anticipated to be less than 0.5 inches. In addition to the foundation elements, the concrete floor slab settlement was analyzed for post-construction condition due to the new fill placement on the existing subgrade. The new fill placement of approximately 2 to 4 feet is considered in the analysis based on the existing ground elevations of El. 26 ft to El. 23 ft from the middle portion of the building footprint to the south side.

Under this loading scenario, we expect the primary consolidation settlement could be as high as

2 inches with post construction settlement of less than 0.5 inches. The time rate of settlement calculations indicate a 60 day waiting period is required after the fill placement for a primary consolidation settlement to end. Therefore, a 60 day waiting period is recommended after the fill placement and before the slab and the foundation construction.

Example settlement calculations are presented in Appendix D. The global stability of the building foundation was also investigated considering the proximity of the foundation elements to the stormwater basin on the south side. The global stability analysis do not indicate any global stability issues for both short term and long term conditions. The global stability analysis is included in

Appendix D.

Sliding Resistance

Sliding resistance of cast-in-place concrete foundations elements in contact with the near-surface sand soils or approved structural fill may be designed using a friction factor of 0.40 per Table 1 of

NAVFAC 7.02-63. If additional resistance is required and cannot be provided by shear between the base of the foundation and the subgrade soils, passive earth pressure may be utilized if the zone providing resistance is protected from future disturbance/removal. Passive earth pressure resistance may be applied using an equivalent fluid unit weight of 160 pcf, which is based on the upper sand alluvium parameters presented in Table 8-1 (’=32 degrees, =110 pcf) and a 40% reduction factor to address strain compatibility.

Seismic Site Classification and Design Parameters To reduce the effects of ground motions produced by regional seismic events, seismic design should be performed in accordance with ASCE 7-16 and IBC 2018. Based on information obtained from our geotechnical investigation, published geologic literature and maps, it is our opinion that the project site could be classified as Site Class E, Soft Clay Soil.

However, it is our understating that the design seismic event will have a short period (less than

0.5 second), as such, the proposed structure may be designed using Site Class D, Stiff soil. The seismic site classification should be considered for the seismic analysis of the proposed structural improvements at the project site per the applicable building codes.

Design CBR

The California Bearing Ratio (CBR) values of the near-surface subgrade soils are summarized in

Table 8-4 for relative compactions of approximately 99 and 97 percent of the maximum dry density obtained from the Standard Proctor value, determined by ASTM D 698.

The near-surface subgrade soils, within the upper five feet bgs, encountered during our field exploration were generally comprised of granular material (silty sand, poorly graded sand, and poorly graded sand with silt) on the north side and generally comprised of fine grained material

(lean clay) and granular material (clayey sand) on the south side with the exception at boring 19B-

04. CBR testing based on ASTM D1883 was performed on two recovered bulk samples.

Table 8-3: Subgrade Support Characteristics

Boring Depth (feet)

Soil Type Maximum Dry Density (pcf) 1

Optimum Moisture

Content (%) 1

CBR Prepared Relative Compaction and Moisture (%) 2 CBR Value 3

19P-03 0.25-2 SC-SM 109.1 15.3 99.1 and 19.7 7.7

19SW-02 0-10 SP-SM 106.9 13.6 97.0 and 17.0 17.3

1 Maximum dry density and optimum moisture determined by ASTM D 698.

2 CBR sample preparation condition.

3 CBR values are based on laboratory curves for 0.1-inch penetration.

Based on CBR test results and encountered soils, a design CBR of 5, which corresponds to a k-value of approximately 150 pounds per square inch/inch, was selected for the existing on-site near-surface soils with an average relative compaction of approximately 95 percent of the maximum dry density, + 3% of optimum moisture content obtained from the Standard Proctor value, determined by ASTM D 698. If soil deflects (“pumps”) during excavation and proof-rolling operations, the recommendations in Section 9.2 shall be followed prior to backfilling. The soil below the proposed pavement surface should be prepared to the criteria contained in Table 5-1 of Unified Facilities Criteria (UFC) 3-250-01 subgrade compaction requirements.

Pavement Design Flexible (light- and heavy-duty asphalt) and rigid pavement (concrete) are expected to be used in the parking lots, entrance road, dumpster enclosures, and laydown/loading areas, respectively.

The truck turn-around loop is proposed to be an aggregate pavement. Recommended pavement sections presented below were developed using UFC 3-250-01. Numerous variables, in addition to the subgrade and traffic, affect the ultimate performance of a pavement. These include, but may not be limited to drainage, material type/quality, construction staging and planned maintenance.

We understand the facility will delay application of the final recommended surface course (2” of NCDOT S9.5C) up to 2 years after initial construction. Pavement performance prior to the placement of the final surface course can be negatively impacted if heavy truck traffic loading is significant.

Heavy duty asphalt is proposed to be used at the main access road and aggregate pavement at the truck loop. Heavy duty concrete is anticipated at the rear of the building in the laydown and staging area. Based on discussions with the project team, vehicles expected to impact these pavement areas include:

Light Duty Pavement (POV)

• Passenger Vehicles – 300 passes per day

• Fire Truck – 4 passes per year

Heavy Duty Pavement (Access Road, Truck Loop and Transition to POV Parking)

• Passenger Vehicles – 300 passes per day

• Fire Truck – 4 passes per year

• WB-67 TT (Truck 5-Axle) – 2 passes per week

• Garbage Truck – 2 passes per week

• Shipping Container Delivery (M1074 Load System) – 10 operations (two loaded passes each) per week

Heavy Duty Concrete (Laydown Area and Forklift Operations)

• Fire Truck – 4 passes per year

• WB-67 TT (Truck 5-Axle) – 2 passes per week

• Garbage Truck – 2 passes per week

• Shipping Container Delivery (M1074 Load System) – 10 operations (two loaded passes each) per week

• Genie GTH Forklift – 10 operations (one loaded pass each) per week

Pavement design period is 25 years. The recommended pavement thicknesses were evaluated based on a CBR value of 5 for the on-site soils re-compacted to at least 95% of the maximum dry density obtained from the Standard Proctor value, determined by ASTM D 698 and within +3% of optimum moisture, as well as a 12-inch overexcavation and backfilling with geotextile and select material. The following sections provide our recommendations for each pavement type anticipated for the project.

Asphalt Concrete Pavement for Parking Lots and Roads

Passenger vehicles were considered to be the main type of vehicle where light duty asphalt is proposed to be used. Therefore, for light duty asphalt applications, we recommend a pavement section consisting of 2” of asphalt concrete (2” NCDOT S9.5C) over 6 inches of aggregate base (NCDOT ABC aggregate). The design recommendation for light duty is based on the assumption that the fire truck access is about 2 to 3 times over a 25-year period. If the access is more than the assumed, it is recommended that the parking lot loop road be designed to be heavy duty pavement. Aggregate base course, ABC, should meet the ABC gradation outlined in Table 1005- 1 of the 2018 NCDOT Standard Specifications for Roads and Structures (NCDOT Specs).

For heavy duty pavement areas, we recommend a final flexible pavement section consisting of 4 inches of asphalt concrete (2” of NCDOT S9.5C over 2” of I19.0C) over 6 inches of aggregate base (NCDOT ABC aggregate) material. We understand the final 2” of surface course may not be placed on the I19.0C for up to two years after construction completion. While this reduced section may perform adequately for this short period of time, it may also be adversely impacted, requiring repair prior to final overlay and incur additional cost. This should be considered during planning.

Subgrades must be prepared in accordance with Section 8.6.5.

Aggregate Truck Loop Pavement

The truck turn-loop is planned to be an aggregate pavement. For this area, we recommend a 4 inch top aggregate course of NCDOT Class II, Type 1 Select Material (minimum PI = 4) overlying 6 inches of NCDOT ABC supported by prepared subgrade as described in Section 8.6.5.

Portland Cement Concrete Pavement

Portland Cement Concrete (PCC) pavements will be used in the laydown/loading area behind the building, dumpster enclosures, and may be used in other areas subjected to heavy traffic loads.

PCC pavement thickness was estimated using a 28-day compressive strength of concrete of at least 4,000 psi, a minimum 28-day flexural strength of 650 psi, and a subgrade k-value of 150 pci.

Joint and dowel designs including type, spacing, and diameter for PCC pavement should be in accordance with the UFC 3-250-01. Expansion joints in the PCC pavement should be saw cut as soon as the concrete has hardened sufficiently to avoid excessive raveling (typically 4-8 hours depending on environmental conditions and admixtures used).

Based on the soil conditions encountered at the site and per the pavement analysis, we recommend the PCC pavement have a minimum nominal thickness of 6 inches and underlain by 6 inches of aggregate base course, meeting the ABC gradation as outlined in Table 1005-1 of the NCDOT Specs. The upper 12 inches of subgrade shall be over-excavated and replaced with a woven geotextile with the minimum properties as presented in Table 8-5, overlain by imported select material subbase (minimum CBR=20) compacted to 100% of the maximum dry density per ASTM D698. The design recommendation is based on the assumption that the fire truck access is about 2 to 3 times over a 25-year period. If the access is more than the assumed, it is recommended that the PCC thickness of concrete loading area to be 7 inches.

Consideration for All Pavements

The pavement sections provided above are contingent upon the following recommendations being implemented during construction:

• Subgrade soils should be in a stable, non-deflecting (non-pumping) condition at the time the aggregate base materials are placed and compacted. The upper 12-inches of the subgrade soil must be over-excavated and replaced with a woven geotextile, with the minimum properties depicted in Table 8-5, overlain by imported Select Material (minimum CBR=20) compacted to 100% maximum dry density per ASTM D698.

Table 8-5: Minimum Physical Requirements for Subgrade Stabilization Geotextile

Property Units Acceptable Values Test Method

Wide-Width Tensile, Ultimate lbs/ft 2,500 ASTM D4595

Wide-Width Tensile, 5% Strain lbs/ft 1,250 ASTM D4595

Grab Strength lbs 260 ASTM D4632

Seam Strength lbs 1,250 ASTM D4632

Puncture lbs 1,000 ASTM D6241

Trapezoidal Tear lbs 110 ASTM D4533

Flow Rate gal/min/ft2 40 ASTM D4491

Permittivity sec-1 0.05 ASTM D4491

Apparent Opening Size US Sieve (mm) 40 ASTM D4751

Ultraviolet Degradation percent 50 at 500 hours ASTM D4355

• All aggregate materials should be compacted to at least 100 percent of the Maximum Dry

Density obtained from the Standard Proctor value, determined by ASTM D 698. Adequate drainage (both surface and subsurface) should be provided such that the subgrade soils and aggregate base materials are not allowed to become saturated.

• Asphalt concrete and aggregate materials should conform to the NCDOT Specifications.

Floor Slabs

Floor slabs should be designed for a subgrade modulus of 150 pci based on correlation with the adopted design CBR value of 5, which is characteristic of the near-surface soils and controlled structural fill. As there is a potential for subsurface water within five feet of the FFE, we recommend the slab be underlain by a minimum of six inches of free-draining open graded aggregate meeting the gradation requirements for No. 57 stone as outlined in Table 1005-1 of the NCDOT Specs. Aggregate should be placed over an approved vapor barrier.

Site Drainage Foundation, pavement, and slab performance depends greatly on proper drainage conducting runoff water offsite. This drainage should be maintained both during construction and over the intended life of the project. The ground surface around structures should be graded such that water drains rapidly away from structures without accumulating or ponding. The required surface gradient is dependent upon the landscaping type.

Under Building Pad and Other Areas of Elevated Water

Water levels within the building pad area were noted as high as El. 28 (based on End of Drilling Water Reading) as presented in Table 7-1, which is above the planned finished floor elevation of

27.5. The long-term water readings indicate water levels within the building pad were observed as high as El. 25 (19PZ-01) to as low as El. 18 (19PZ-02). Additional areas of the site may also encounter elevated water levels associated with static or perched conditions that may fluctuate over the course of the design life. To reduce the impact of water on the planned foundations and subgrade, we recommend installing permanent underdrains within the building footprint and other areas where the expected water levels may be within three feet of finished grade.

Near surface soils classify as poorly graded sand (SP), sand with silt (SP-SM), and silty sand (SM). Based on the results of the field permeability test and range of permeability associated with similar of soils, HDR estimates a permeability ranging from 10-4 to 10-5 cm/s (0.28 to 0.028 ft/day) to these soils in order to understand the sensitivity of the underdrain to the encountered conditions.

Based on the approach presented in Figure 4-3 and 4-5 of UFC 3-220-05 (2004), we calculate flows of approximately 200 ft3/day. We recommend sub-slab drain placement approximately every 25 feet (transverse to the building long-axis) running parallel to the long-axis (north to south) while avoiding column lines. Sub-slab drains should be a minimum of 2.5-feet wide and extend to a depth of 3.0-feet below the planned finished floor elevation or greater and graded to drain. Exterior “French drains” should be placed around the perimeter of the building to a depth equal to or greater than the bearing elevation of the turndown slab. Exterior drains should be placed no more than 5 feet beyond the edge of footing line.

All underdrains shall be constructed using filter fabric (Mirafi 140N or equivalent) wrapped, open graded aggregate meeting the gradation requirements for No. 57 stone as outlined in Table 1005-1 of the NCDOT Specs. Slotted HDPE pipe (4-inch minimum diameter) should be centered in the underdrain laterally and have at least six inches of aggregate between the geotextile fabric and the pipe invert. Lower permeability soils consisting of clayey sand (SC) or lean sandy clay (CL) should be placed above the fabric wrapped No. 57 aggregate to a depth of 0.5 feet to help or grade should be sloped away from the building to prevent surface water infiltration into the French drain system. All collected water should be either day-lighted or directed into the planned storm water drainage system.

Stormwater Management Facilities

The observed water level depths at the proposed SWM facilities ranged from 4 to 14 feet (between approximate El. 17 to El. 10) and the estimated seasonal high water table (SHWT) depth ranged from 3 to 9 feet (between El. 17 to El. 15). Boring 19SW-02 indicated high subsurface water and SHWT elevation, at El. 17, which is at proposed bottom of basins. Therefore, we recommend the facilities be lined and use a sand filter to prevent potential subsurface water intrusion. A combination of french drains and underdrains should be utilized to control potential impacts associated with a perched condition if deemed appropriate to facility function.

General Considerations

We recommend landscape planters not be located adjacent to buildings and pavement areas;

however, if they are, we recommend that they be properly drained. Drought resistant plants, with minimum watering requirements are recommended for planters immediately adjacent to structures. No raised planters should be installed immediately adjacent to structures unless they are damp-proofed and have a drainpipe connected to an area drain inlet. Planters should be built such that water draining from them will not seep into the foundation areas or beneath slabs and pavement. Additionally, waterproofing the slab and walls is highly recommended.

Roof water should be directed to fall on hardscape areas sloping to an area drain, or roof gutters and downspouts should be installed and routed to area drains.