GEOTECHNICAL INVESTIGATION REPORT 31 AUG 07.pdf

G e o t e c h n i c a l R e p o r t

BRAC Headquarters ANG and Readiness Center Addition

Project Number AJXF059145

Headquarters ANG Addition Project Number AJXF069112

Submitted to

National Guard Bureau, Andrews Air Force Base, Camp Springs, Maryland

August 31, 2007

Copyright 2007 by CH2M HILL, Inc.

Reproduction and distribution in whole or in part beyond the intended scope of the contract without the written consent of CH2M HILL, Inc. is prohibited.

WDC/346862.HQ i

Table of Content Acronyms and Abbreviations .........................................................................................................................iii

Introduction

1.1 Purpose and Scope

1.2 Limitations

1.3 Site Description

1.4 Project Description and Proposed Construction

Regional Geology

Subsurface Investigations

3.1 Historical Geotechnical Data

3.2 Design Phase Subsurface Investigation

3.3 Laboratory Testing

Subsurface Conditions

4.1 Stratification

4.1.1. STRATUM 1 (TYPE 1): FILL

4.1.2. STRATUM 2 (TYPE 2): COHESIVE SOIL

4.1.3. STRATUM 3 (TYPE 3): DENSE SAND

4.1.4. STRATUM 4 (TYPE 4): LOOSE SAND

4.1.5. STRATUM 5 (TYPE 5): COHESIVE SOIL

4.2 Groundwater Condition

4.3 Evaluation of Soil Properties

4.3.1. STRATUM 1 (TYPE 1): FILL

4.3.2. STRATUM 2 (TYPE 2): COHESIVE SOIL

4.3.3. STRATUM 3 (TYPE 3): DENSE SAND

4.3.4. STRATUM 4 (TYPE 4): LOOSE SAND

4.3.5. STRATUM 5 (TYPE 5): COHESIVE SOIL

4.3.6. SUMMARY

4.4 Evaluation of Soil Corrosivity

Seismic Considerations and Site Class

5.1 Liquefaction Potential

5.2 IBC 2006 Seismic Site Class

5.3 Seismic Design Parameters

Settlement Analyses

6.1 Settlement Analyses of Shallow Foundations

6.2 Settlement Analyses of Slabs on Grade

Deep Foundation Analyses and Design

7.1 Axial Load Capacity of Individual ACIP Piles

7.2 Alternate Foundation Types

7.3 Lateral Pile Group Analyses

Excavation Support Systems

8.1 Types of Excavation Support Systems

8.2 Lateral Earth Pressure

8.3 Sloped Excavation

Construction Considerations

9.1 Site Preparation

9.2 Site Fill

9.3 Backfill Under and Around Structures

WDC/346862.HQ ii

9.4 Trench Backfill

9.5 Groundwater Control

9.6 Settlement Control

9.7 Deep Foundations

9.7.1 PILE INSTALLATION

9.7.2 INTEGRITY TESTS

9.7.3 STATIC PILE LOAD TESTS

References

List of Tables 3-1 Summary of All Laboratory Tests Performed for BRAC Headquarters ANG and

Readiness Center Addition Project 3-2 Summary of Index Properties of All Silty or Clayey Soil Samples Tested 3-3 Summary of Modified Proctor and CBR Test Results 4-1 Correlated Engineering Properties of the Two Major Cohesive Soil Strata 4-2 Total and Effective Stress Shear Strength Parameters Obtained from CU Triaxial Test with Pore Pressure Measurements on Undisturbed Samples from Stratum 5 4-3 Recommended Range of Index, Consolidation, and Strength Properties of Various Soil

Strata 4-4 Summary and Evaluation of Corrosivity Testing Results of Samples from Strata 2 and 3 4-5 Summary and Evaluation of Corrosivity Testing Results of Samples from Stratum 5 5-1 Seismic Design Parameters for 2 Percent PE in 50 Years 6-1 Results from Settlement Analyses of Various Structures 7-1 Recommended Group Efficiency and Design Capacity of 18-inch Diameter 75-ft Long

ACIP Piles with Different Pile Spacing 8-1 Design Lateral Earth Pressure for Temporary Excavation Support Systems 8-2 Recommended Slope Ratios for Sloped Excavations

List of Figure 7-1 Design Capacity versus Pile Length of 18-Inch Diameter ACIP Piles to Support Column

Footings of the Buildings Based on Subsurface Conditions Indicated in Borings B1 Through B8 with a Group Efficiency of 0.8

List of Appendices A Boring Location Plan and Boring Logs B Laboratory Testing Results

BRAC HEADQUARTERS ANG AND READINESS CENTER ADDITION

HEADQUARTERS ANG ADDITION

GEOTECHNICAL REPORT ACRONYMS AND ABBREVIATIONS

WDC/346862.HQ iii

Acronyms and Abbreviations 1-D one-dimensional AASHTO American Association of State Highway and Transportation Officials ACIP augered cast-in-place piles AFB Andrews Air Force Base ASTM ASTM International ATV all-terrain vehicle bpf blows-per-foot CBR California bearing ratio CU consolidated-undrained FS factor of safety ft/sec feet-per-second GWT groundwater table HSA hollow-stem auger IBC International Building Code ID inside diameter ksi kips per square inch LL liquid limit LRFD load-and-resistance-factor MFM magnetic flow meter mg million gallons mgd million gallons per day MSL mean sea level N-value standard penetration test resistance NCEER National Center for Earthquake Engineering Research OCR over-consolidation ratio OD outside diameter pcf pounds per cubic foot PE probability of exceedance PI plasticity index PID Photo-ionization Detector PIR-A pile installation recorder for augered-cast piles PIT pile integrity test PL plastic limit PP pocket penetrometer ppm parts per million psf pounds-per-square-foot PVC polyvinyl chloride RPA resource protection area S/D center-to-center spacing to diameter ratio SPT standard penetration test SF square feet tsf tons-per-square-foot USCS Unified Soil Classification System USGS United States Geological Survey UU unconsolidated-undrained w (%) moisture content

WDC/346862.HQ 1

SECTION 1

Introduction

1.1 Purpose and Scope

This report presents geotechnical investigation results and recommendations for the proposed BRAC Headquarters ANG and Readiness Center Addition at the Andrews Air Force Base (AFB), in Camp Springs, Maryland. Geotechnical investigations were conducted to characterize subsurface conditions, to evaluate engineering properties of soils, to assess settlement and corrosion potential, and to develop recommendations regarding deep foundations, excavation support systems, and construction considerations for this project.

The geotechnical investigation scope included:

• Reviewing available geological information and geotechnical data from previous explorations

• Drilling 54 soil borings

• Conducting laboratory tests on representative soil samples

• Evaluating and analyzing drilling and laboratory testing data

• Developing geotechnical design and construction recommendations

• Preparing this geotechnical report

1.2 Limitations

This geotechnical report has been prepared in accordance with generally-accepted engineering practices. It is intended for the exclusive use of the National Guard Bureau for the proposed construction of the BRAC Headquarters ANG and Readiness Center Addition.

No other warranty, expressed or implied, is made.

Information contained in this report is limited, based on data obtained from boring logs and laboratory testing that show subsurface conditions only at the specific location and time investigated, and only to the depth penetrated. Subsurface conditions and groundwater levels at other locations or depths may differ from conditions occurring at investigated locations. The passage of time may also result in changed conditions at these locations. If, during construction, subsurface conditions are found to vary from those described in this report, geotechnical recommendations should be re-evaluated.

This report includes both factual and interpreted information. Factual information is defined as objective data based on direct observations, such as boring logs and laboratory testing results. Interpreted information or geotechnical engineering interpretation is based on the engineering judgment, correlation, or extrapolation from factual information. No warranties, explicit or implied, are provided for interpreted information.

GEOTECHNICAL REPORT 1 INTRODUCTION

WDC/346862.HQ 2

1.3 Site Description

The project site is bounded by Fechet Avenue on the north, and Pennsylvania Avenue on the west. On the south and east, the project limits are constrained by an existing Chesapeake Bay resource protection area (RPA) associated with the minor tributaries to Charles Branch.

The site slopes generally toward the south and east from a ridge along Fechet Avenue.

Much of the area where the two new buildings occupy is cleared of trees, with the exception of parking lot landscaping. Wooded areas also exist along the natural drainage paths toward the south and east of the site for the new buildings.

Overall project limits comprise approximately 30 acres. Site grade is generally flat in the areas of the existing parking lot south of building 3500 and of a few existing buildings along Ohio Drive, where it varies between an elevation of 275 and 277 feet, MSL. The site grade slopes more rapidly toward the south and east beyond these areas.

1.4 Project Description and Proposed Construction

The Air National Guard plans to construct a new addition to the existing HQ ANG Building (3500) at the Andrews Air Force Base (AFB). The addition is expected to consist of one 170,000-square-feet (SF), 4-story building and one 20,000-SF, 2-story building and is intended to house 605 employees. The proposed buildings will be constructed immediately south of the existing building 3500, between Pennsylvania Avenue and Ohio Drive.

In addition to the construction of the two buildings, parking lots, driveways, walkways, courtyards, storm sewers, and stormwater management ponds are also planned to be constructed to accommodate the addition.

WDC/346862.HQ 3

SECTION 2

Regional Geology

Andrews AFB is situated entirely within the Coastal Plain physiographic province. The geologic formations in the Coastal Plain physiographic province are sloping to the southeast at approximately one degree and thicken in the same direction. In the Andrews AFB area, the total thickness of these unconsolidated sedimentary soil deposits is approximately 1,300 feet (Hansen, 1972). The surface materials are Upland deposits, comprised mainly of sand and gravel with minor amounts of silt and clay. These surface deposits are underlain by various geologic formations, such as the Calvert clay, Nanjemoy formation, Marlboro clay, Aquia sand and clay, Brightseat and Monmouth formations, Magothy formation, Patapsco formation, Arundel formation, and Patuxent formation, in a descending order, until Precambrian crystalline basement rocks can be found (USAF, 2001).

WDC/346862.HQ 4

SECTION 3

Subsurface Investigations

The subsurface investigations for this project were performed in one phase between the 30% and 65% design. This investigation is termed “Design Phase Subsurface Investigation.” A total of 54 soil borings, designated B1 through B8, OH1 through OH8, OH10, OH10A, P1S through P6S, P1E through P12E, MP1 and MP2, and T1 through T14 were initially planned. Among these borings, only boring T9 was not actually drilled. Therefore, the total number of borings drilled is the same as initially planned. The boring location plan and all boring logs from this investigation are shown in Appendix A of this report.

In addition to the Design Phase Subsurface Investigation, historical geotechnical data, including boring logs, laboratory testing results, and geotechnical recommendations, from previous investigations/projects were also reviewed.

3.1 Historical Geotechnical Data

Available historical data reviewed as a part of the subsurface investigation included boring number 1 through 14, drilled by Schnabel Engineering Associates of Bethesda, Maryland in 1982 for the Air National Guard Support Center project and boring B-1 through B-4, drilled by Geomatrix, Inc. of Baltimore, Maryland in 2002 for the Air National Guard Readiness Center project. The locations of the 1982 borings were not available to us. The depth of these borings ranged between 5 and 35 feet. A total of 5 different soil strata were identified by these borings. They are: Stratum A: sandy and gravelly fill, Stratum B: stiff to hard silty clay and clayey silt, Stratum C: medium dense to very dense sand, Stratum D: very loose to medium dense sand, and Stratum E: soft to medium stiff silty clay and clayey silt. The groundwater table was located at a depth of 18 to 20 feet. The soil strata and groundwater level compare reasonably well with the data recently obtained for this project. In fact, Stratum A to E in the 1982 borings can be correlated to Soil Types 1 to 5, which are the designations used in this report to classify the subsurface soil materials.

The location plan and logs of the 2002 borings were attached to a memorandum prepared by Whitman, Requardt and Associates, LLP, which provided foundation recommendations for the Air National Guard Air Readiness Center Addition project. It appeared that the four borings drilled in 2002 were located to the northeast of the existing building 3500 for the Air Readiness Center Addition. The depth of these four borings ranged between 46.5 and 80 feet. Materials encountered in these borings were similar to those in the 1982 borings and the borings drilled for this project. The groundwater table was located at a depth of 26 to 28 feet, as shown in the boring logs. However, these readings are not comparable with other groundwater data obtained in 1982 and recently. The recommendations in this memorandum actually suggested a groundwater elevation of 258 feet, MSL, which is approximately 18 to 20 feet below the existing grade.

GEOTECHNICAL REPORT 3 SUBSURFACE INVESTIGATIONS

WDC/346862.HQ 5

3.2 Design Phase Subsurface Investigation

A total of 54 soil borings as discussed previously were drilled between August 29, 2006 and March 16, 2007, by Parratt-Wolff, Inc., of Hillsborough, North Carolina, under a subcontract to CH2M HILL. The borings in the open areas were drilled using truck-mounted drill rigs (CME-75 and Diedrich D-55) and the borings in the wooded areas were drilled using a drill rig (Diedrich D-90) mounted on a rubber-tired all-terrain vehicle (ATV). A CH2M HILL geotechnical engineer or geologist was on site at all times during soil boring activities, overseeing the drilling and sampling, and performing visual-manual classification of the soil samples (ASTM D2488) according to the Unified Soil Classification System (USCS)

(ASTM D2487).

In general, borings drilled during the Design Phase Subsurface Investigation were extended to a depth between 4 and 102 feet below existing grade. The shallow borings with a depth less than 30 feet were typically drilled with a 2-1/4-inch or 3-1/4-inch inside diameter (ID) hollow-stem auger (HSA). Standard Penetration Tests (SPTs) were performed using a standard 2-inch outside diameter (OD) split-spoon sampler driven 24 inches with an automatic hammer or a standard 140-pound hammer falling a distance of 30 inches, in accordance with ASTM D1586. The number of blows was recorded every 6 inches, and the sum of the numbers of blows required to drive the split-spoon sampler for the second and third 6-inch increments represents the N-value. In general, disturbed soil samples were continuously retrieved in the top 10 feet, and at 5-foot intervals thereafter to the bottom of borings. In some of the shallow borings, disturbed soil samples were continuously retrieved to the bottom of the borings. Pocket penetrometer (PP) tests were performed on disturbed silt and clay samples retrieved from the split-spoon sampler as an index test to estimate the unconfined compressive strength of the silt and clay samples. Undisturbed silt and clay samples were also obtained at selected locations using Shelby tubes, according to ASTM D1587. In addition, testing for contamination using the Photo-Ionization Detector (PID) was performed frequently on disturbed soil samples, due to the fact that historically various contaminants such as benzene, trichloroethene, and carbon tetrachloride, were encountered in groundwater in a parcel of land to the west of the project site. Most PID readings obtained in these borings are 0, showing that contamination is unlikely. These shallow borings were backfilled with soil cuttings after the 24-hour groundwater readings were taken. Boring T13, however, was backfilled with cement grout because possible contamination was discovered with a PID reading ranging between 0 and 7.2.

The eight deep borings, located within the footprints of the two buildings, with a depth greater than 30 feet were drilled using a “double-casing” technique, due to the contaminations encountered historically to the west of the project site. This precautionary technique is used to avoid any possible migration of contamination at shallower depths to deeper aquifers due to drilling. These borings were advanced using a 3-1/4-inch ID HSA to the Calvert formation, which consists of medium to high plasticity clay, at a depth of 35 to 40 feet below the existing grade. Disturbed soil samples in these borings were obtained continuously in the top 20 feet, and at 5-foot intervals thereafter to the bottom of the borings. SPT N-values, PP and PID readings were obtained in the same manner as of those shallow borings. After reaching the Calvert formation, the boreholes were re-drilled using an 8-1/4-inch ID HSA to the same depth. Inside the 8-1/4-inch ID HSA, a 6-inch diameter polyvinyl chloride (PVC) casing was installed and the annular space between the HSA and

WDC/346862.HQ 6

the PVC casing was grouted with cement grout while the HSA was retrieved. Groundwater readings were obtained after the installation of the PVC casing. Before drilling beyond this depth, a 4-inch diameter steel casing was installed to a depth of 5 feet below the tip of the PVC casing and the annular space between the PVC and steel casings was grouted with bentonite slurry. Rotary drilling with drilling mud was used to advance these deep borings (B1 through B8) to completion depths. Disturbed soil samples, SPT N-values, PP and PID readings were obtained at 5-foot intervals to the bottom of these borings. All PID readings obtained in these 8 borings are 0, showing that contamination is unlikely. However, for precautionary purposes, these borings were backfilled with cement grout upon completion.

3.3 Laboratory Testing

Laboratory tests including 17 natural moisture content tests, 13 Atterberg Limits tests, 24 particle size (sieve) analysis tests, 9 hydrometer tests, 1 one-dimensional (1-D) consolidation test, 2 sets of three-point consolidated-undrained (CU) triaxial tests with pore pressure measurements, 6 sets of California bearing ratio (CBR) tests, 9 Modified Proctor compaction tests, and 5 sets of corrosivity tests (including resistivity, pH, and chloride and sulfate concentrations) were performed on samples obtained from the borings drilled in the Design Phase Subsurface Investigation. The laboratory tests were generally performed in accordance with the ASTM International (ASTM) and U. S. Environmental Protection Agency (EPA) standards listed in Table 3-1. Results of these laboratory tests are presented in Appendix B. A summary of index properties (natural moisture content [w (%)], liquid limits [LLs], and plastic limits [PLs]) of all soil samples tested is presented in Table 3-2. A summary of the shear strength parameters obtained from CU triaxial tests with pore pressure measurements on undisturbed samples is presented in Table 3-3.

TABLE 3-1

Summary of All Laboratory Tests Performed for BRAC Headquarters ANG and Readiness Center Addition Project

Number of Tests Performed

Type of Test

Standard

17 Natural Moisture Content Test ASTM D2216

13 Atterberg Limits Test ASTM D4318

26 Particle Size (Sieve) Analysis Test ASTM D422, D1140

9 Hydrometer Test ASTM D422

1 1-D Consolidation Test ASTM D2435

2 CU Triaxial Shear Test ASTM D4767

6 CBR Test ASTM D1883

9 Modified Proctor Compaction Test ASTM D1557, D4718

5 Corrosivity Test (Resistivity, pH, Chlorides, and Sulfates) ASTM G57, ASTM D4972, EPA Method 300.0A

WDC/346862.HQ 7

TABLE 3-2

Summary of Index Properties of All Silty or Clayey Soil Samples Tested

Boring No.

Depth (ft)

Depth to GWT (ft)

Sample No.

SPT N-value (bpf)

Soil Type*

USCS

LL

PL

PI

w

LI

B1 5 19 S3 18 2 CL 32 16 16 15.4 -0.04

B2 43 18 Shelby Tube

Not applicable 5 CL 40 19 21 47.2 1.34

B7 51 19.5 S16 7 5 SC 64 31 33 53.5 0.68

B8 45 20 S15 4 5 CL 41 22 19 49.0 1.42

MP1 7 Dry** S4 34 2 CH - - - 16.6 - T4 3 Dry** S2 8 2 CL 40 17 23 19.9 0.13

T5 7 Dry** S3, S4, S5

Not applicable 2 and 3 ML and

GC - - - 13.1 -

T7 5 Dry** S3 33 2 CH - - - 16.7 - T8 5 Dry** S3 5 2 CL 32 13 19 13.4 0.02

OH5 5 Dry** S3 4 2 CL 47 22 25 16.9 -0.20

P5S 9 15 S5 5 5 CL 34 24 10 56.2 3.22

P5S 16 15 S6 7 5 CH - - - 45.5 -

OH10A 23 8 Shelby Tube

Not applicable 5 CL 38 24 14 34.5 0.75

P1E 5 14.5 S3 6 2 CL - - - 18 -

P7E 16 8 S6 4 5 CL 43 20 23 39.1 0.83

P12E 9 Dry** S4 4 5 ML 35 25 10 32.6 0.76

* Soil types are explained in Section 4 of this report.

** Dry at the bottom of soil boring

TABLE 3-3

Summary of Modified Proctor and CBR Test Results

Boring # Depth (ft) Soil Type Field

USCS

woptimum γd,max (pcf) CBR*

OH8 6 Type 2 ML 10.1 126.0 10.9

OH4 6 Types 2 and

CL, ML,

SP 13.4 121.2 9.9

P4E 6 Type 3 SP 7.9 134.9 2.3**

P1S 7.5 Type 2 CL 10.6 125.2 8.3

B4 6 Type 2 ML 11.7 122.6 6.9

OH2 7.5 Type 2 CL 12.4 123.0 11.7

P10E 5 Type 3 GW 8.6 131.2 -

P4S 6 Type 2 ML 12.1 118.8 -

T3 3 Type 2 CL-ML 15.2 112.0 -

* CBR is reported at 0.1 inch penetration and 95% modified proctor compaction.

**This CBR value is low probably due to test imperfections.

WDC/346862.HQ 8

SECTION 4

Subsurface Conditions

4.1 Stratification

Subsurface stratification of the site is generally similar, with some variations at different locations. The subsurface soil profile at the BRAC Headquarters ANG and Readiness Center Addition site can be classified into the following soil strata based on descriptions in the boring logs, where visual-manual classifications of soil samples are recorded.

• Stratum 1 (designated type 1): Fill, consisting of silty sand, sand, and gravel

• Stratum 2 (designated type 2): Cohesive Soil, consisting of brown and gray clayey silt, silt, silty clay, and clay

• Stratum 3 (designated type 3): Dense Sand, consisting of brown and gray silty sand, sand, and sand and gravel

• Stratum 4 (designated type 4): Loose Sand, consisting of brown and gray silty sand, clayey sand, and sand

• Stratum 5 (designated type 5): Cohesive Soil, consisting of brown and gray clay, silty clay, clayey silt, and silt

It should be noted that the boring logs present the change of soil strata using distinct breaks, while actual stratification changes gradually.

4.1.1. Stratum 1 (Type 1): Fill

Generally, 0 to 2 feet of fill, consisting of silty sand, sand, and gravel was encountered at some of pavement area (such as boring OH1). The SPT N-values vary from 8 to 17 blows-per-foot (bpf), with an average N-value of 13 bpf. The sandy fill varied from loose to medium dense.

4.1.2. Stratum 2 (Type 2): Cohesive Soil

The cohesive soil layer, consisting of brown and gray clayey silt, silt, silty clay, and clay, extends 6 to 14 feet below the bottom of fill or ground surface. The SPT N-values in this stratum range between 4 and 72 bpf, with an average N-value of 25 bpf. The unconfined compressive strength of the soil in this stratum, indicated by pocket penetrometer (PP) tests, ranges between 0.5 and 4.5 tons-per-square-foot (tsf), with an average unconfined compressive strength of 3.5 tsf. It should be noted that PP tests was performed on disturbed soil samples. The cohesive soil in this stratum is generally considered soft to hard.

4.1.3. Stratum 3 (Type 3): Dense Sand

The dense sand stratum consisting of brown and gray silty sand, sand, and sand and gravel, generally underlies Stratum 2, and extends 4 to 12 feet below the bottom of Stratum 2. The SPT N-values in this stratum range between 28 and 106 bpf, with an average of 42 bpf.

GEOTECHNICAL REPORT 4 SUBSURFACE CONDITIONS

WDC/346862.HQ 9

Boulder or cobbles may be present in this layer according to grinding sound occurs while advancing the auger. The density of this stratum ranged from medium dense to very dense.

4.1.4. Stratum 4 (Type 4): Loose Sand

The loose sand layer, consisting of brown and gray silty sand, clayey sand, and sand, generally underlies Stratum 3 and extends 10 to 17 feet below the bottom of Stratum 3, until it reaches the Cohesive Soil (Stratum 5). The SPT N-values in this stratum range between 2 bpf and 27 bpf, with an average of 15 bpf. The density of this stratum ranged from very loose to medium dense.

4.1.5. Stratum 5 (Type 5): Cohesive Soil

This stratum, consisting of brown and gray clay, silty clay, clayey silt, and silt, consistently underlies Stratum 4 in the 8 deep borings drilled in the footprints of the two buildings. This stratum is also encountered in some of the shallow borings, such as P5S, P7E, P12E, and OH10A. The brownish cohesive soil in this layer, with thickness of 5 to 10 feet, is generally sitting on the top of the grayish cohesive soils. The top of this stratum was encountered at a depth between 30 and 35 feet below the existing grade. The SPT N-values in this stratum range between 2 and 13 bpf, with an average of 7 bpf. The unconfined compressive strength of the soil in this stratum, indicated by PP tests, ranges between 0 and 2 tsf, with an average of 0.75 tsf. The soil in this stratum can be considered very soft to stiff.

4.2 Groundwater Condition

The groundwater table (GWT) during the drilling of deep borings (B-1 through B-8) was found at a depth between 18 and 20 feet below the existing grade. This GWT is at an elevation between 256.5 and 258.5 feet, with an average elevation of 257 feet. Several shallow borings, such as P3E, P4S, and P6S, indicated water table ranging between elevations 250 to 257 feet. Most of other shallow borings were dry within the extent of drilling.

4.3 Evaluation of Soil Properties

The engineering properties of various soil strata at the BRAC Headquarters ANG and Readiness Center Addition site, developed from subsurface investigations (borings) and laboratory tests, are discussed in this section. Some of these engineering properties were directly measured from laboratory, while other properties were interpreted based on published correlations or based on engineering judgments. Correlations of engineering properties of cohesive soils are generally made based on their index properties, i.e., LLs, PLs, and w (%).

WDC/346862.HQ 10

TABLE 4-1

Correlated Engineering Properties of the Two Major Cohesive Soil Strata

Boring

No.

Depth to Sample

(ft)

Depth to

GWT

(ft)

Sample

No.

SPT

N-value

(bpf)

Soil

USCS

LL

PL

PI

w

LI

φ'cv

(deg) σv'

(psf)

OCR2

OCR3

cu

(psf)

Cc

Cr

Cc

Cr

Cεα

B1 5 18 S3 18 Type 2 CL 32 16 16 15.4 -0.04 33 625 50.2 57.0 2686 0.20 0.03 0.22 0.04 0.002

T4 3 13 S2 8 Type 2 CL 40 17 23 19.9 0.13 30 375 45.4 42.1 1458 0.27 0.04 0.31 0.06 0.002 T8 5 - S3 5 Type 2 CL 32 13 19 13.4 0.02 32 625 40.3 40.7 2186 0.20 0.03 0.26 0.05 0.001

OH5 5 - S3 4 Type 2 CL 47 22 25 16.9 -0.20 30 625 93.4 148.7 6920 0.33 0.04 0.34 0.07 0.002

Average for Type 2 Type 2 - 38 17 21 16.4 -0.02 31 563 57 72 3312 0.25 0.03 0.28 0.06 0.002 B8 45 18 S15 4 Type 5 CL 41 22 19 49.0 1.42 32 3670 1.0 1.0 662 0.28 0.04 0.26 0.05 0.005

B2 43 18 Shelby Tube - Type 5 CL 40 21 19 45.4 1.28 32 3565 1.0 1.0 643 0.27 0.04 0.26 0.05 0.005

B7 51 18 S16 7 Type 5 SC 64 31 33 53.5 0.68 28 3986 1.0 1.0 925 0.49 0.06 0.45 0.09 0.005 P5S 9 15 S5 5 Type 5 CL 34 24 10 56.2 3.22 36 1125 1.0 1.0 165 0.22 0.03 0.14 0.03 0.006

OH10A 23 8 Shelby Tube - Type 5 CL 38 24 14 34.5 0.75 33 1789 1.0 1.0 289 0.25 0.03 0.19 0.04 0.003

P7E 16 8 S6 4 Type 5 CL 43 20 23 39.1 0.83 30 1421 1.0 1.0 277 0.30 0.04 0.31 0.06 0.004 P12E 9 - S5 4 Type 5 ML 35 25 10 32.6 0.76 36 1125 1.4 1.0 165 0.23 0.03 0.14 0.03 0.003

Average for Type 5 Type 5 - 42 24 18 44.3 1.28 32 2464 1.1 1.0 471 0.29 0.04 0.25 0.05 0.004 Note: 1: Based on correlation by Mitchell (1976) 2: Based on correlation by Stas and Kulhawy (1984) 3: Based on correlation by Wood (1983) 4: Based on correlation by Ladd et al. (1977)

5: Based on correlation by Terzaghi and Peck (1967) 6: Based on correlation by Wroth and Wood (1978) 7: Based on correlation by Mesri (1973)

WDC/346862.HQ 11

4.3.1. Stratum 1 (Type 1): Fill

The fill layer generally consists of silty sand, sand, and gravel, with SPT N-values ranging between 8 and 17 bpf. The drained friction angle of the sandy fill should be between 32 and 36 degrees, based on the N-values and Meyerhof (1956) correlations.

4.3.2. Stratum 2 (Type 2): Cohesive Soil

The cohesive soil of this stratum is generally brown and gray clayey silt, silt, silty clay, and clay. The average SPT N-values in this stratum is 25 bpf, which may indicate an undrained shear strength of 3000 psf according to the SPT correlation by Bowles (1988). The average unconfined compressive strength (qu) of the soil in this stratum is approximately 3.5 tsf from PP tests. The average correlated undrained shear strength (cu) of the soil in this stratum, based on Ladd et al. (1977), is approximately 3300 psf, as shown in Table 4-1. Considering these correlations, design undrained shear strength of the soil in this stratum is recommended to be between 2000 and 4000 psf. Drained friction angle of the soil in this stratum is at least 30 degrees, based on the correlation by Mitchell (1976).

Also based on the data presented in Table 4-1 and the correlations by Stas and Kulhawy (1984), and by Wood (1983), the soil in Stratum 2 is considered highly over-consolidated, with an OCR between 40 and 148. The compression and recompression indices (Cc and Cr) are estimated to be ranging from 0.2 to 0.34 and from 0.03 to 0.07, respectively, based on the correlations by Terzaghi and Peck (1967) and Wroth and Wood (1978). The secondary compression ratio (Cεα) was estimated to be ranging from 0.001 to 0.002 based on the correlation by Mesri (1973).

4.3.3. Stratum 3 (Type 3): Dense Sand

The dense sand stratum consists of brown and gray silty sand, sand, and sand and gravel.

The SPT N-values in this stratum range between 28 and 106 bpf, with an average of 42 bpf.

As a result, the estimated friction angle ranges between 38 and 46 degrees based on the correlation by Meyerhof (1956).

4.3.4. Stratum 4 (Type 4): Loose Sand

The soil in Stratum 4 is generally brown and gray silty sand, clayey sand, and sand. The SPT N-values in this stratum range between 2 bpf and 27 bpf, with an average of 15 bpf. As a result, the estimated friction angle ranges between 28 and 37 degrees based on the correlation by Meyerhof (1956).

4.3.5. Stratum 5 (Type 5): Cohesive Soil

Soil in this stratum is typically brown and gray clay, silty clay, clayey silt, and silt. The average SPT N-values in this stratum is approximately 7 bpf, which may indicate an undrained shear strength of 840 psf according to the SPT correlation by Bowles (1988). The average unconfined compressive strength (qu) of the soil in this stratum is approximately

0.75 tsf from PP tests. The average correlated undrained shear strength (cu) of the soil in this stratum, based on Ladd et al. (1977), is approximately 470 psf, as shown in Table 4-1. Two

WDC/346862.HQ 12

sets of 3-point consolidated undrained (CU) triaxial tests with pore pressure measurements were performed on samples obtained from Stratum 5. The total and effective stress shear strength parameters obtained from the CU triaxial tests are presented in Table 4-2. The two CU tests also provided 1200 psf and 1580 psf for the undrained shear strength under in-situ overburden pressure. Considering these testing data and correlations, design undrained shear strength of the soil in this stratum is recommended to be between 200 and 1200 psf.

Drained friction angle of the soil in this stratum is from 28 to 33 degrees, based on the correlation by Mitchell (1976).

One consolidation test, performed on an undisturbed sample from this stratum, provided compression and recompression indices (Cc and Cr) of 0.52 and 0.03, respectively. The secondary compression ratio (Cεα) and OCR from the consolidation test were 0.001 and 1.3, respectively. Also based on the data presented in Table 4-1 and the correlations by Stas and Kulhawy (1984), and by Wood (1983), the soil in Stratum 5 is considered normally consolidated, with an OCR of 1.0. Stratum 5 is generally located below the GWT. Based on the test and empirical correlations shown in table 4-1, the compression and recompression indices (Cc and Cr) are recommended to be ranging from 0.2 to 0.52 and from 0.03 to and 0.09, respectively. The secondary compression ratio (Cεα) is recommended to be ranging from 0.001 to 0.006.

TABLE 4-2

Total and Effective Stress Shear Strength Parameters Obtained from CU Triaxial Test with Pore Pressure Measurements on Undisturbed Samples from Stratum 5

Total Stress Effective Stress Unit

Sample from Boring B-5 (40 feet bgs) cu 616 c’ 456 psf φu 7 φ' 17.4 deg

Sample from Boring B-8 (43 feet bgs) cu 1286 c’ 1208 psf φu 1.7 φ' 4.9 deg

4.3.6. Summary

The index, consolidation, and strength properties of the soil strata at the project site were developed and summarized in Table 4-3 from in-situ and laboratory testing data and from published correlations, as discussed in the previous sections. The soil properties shown in Table 4-3 are representative range of the soil properties of specific strata, and are recommended for use in geotechnical engineering analyses and design with good engineering judgments because soil properties can vary significantly in the same stratum.

WDC/346862.HQ 13

TABLE 4-3

Recommended Range of Index, Consolidation, and Strength Properties of Various Soil Strata

Stratum 1 Stratum 2 Stratum 3 Stratum 4 Stratum 5

Property

Fill

(Type 1)

Cohesive Soil (Type

2)

Dense Sand

(Type 3)

Loose Sand

(Type 4)

Cohesive Soil

(Type 5)

Unit

Index Properties γ 120 130 130 115 110 pcf

W - 13-20 - - 33-56 %

LL - 32-47 - - 34-64 -

PL - 13-22 - - 20-31 -

PI - 16-25 - - 10-33 -

Consolidation Properties

Cc - 0.2-0.34 - - 0.2-0.52 -

Cr - 0.03-0.07 - - 0.03-0.09 -

Cεα - 0.001-0.002 - - 0.001-0.006 -

Strength Properties cu - 2000-4000 - - 200-1200 psf φu - 0 - - 0 deg c’ 0 0 0 0 0 psf φ' 32 – 36 30 – 33 38 – 46 28 – 37 28-33 deg

4.4 Evaluation of Soil Corrosivity

Corrosivity tests were performed on soil samples obtained from strata 2, 3, and 5. These tests included resistivity, pH, and concentrations of chlorides and sulfates. Results from the corrosivity tests are presented in Appendix B and are summarized and evaluated in Table 4- 4 and 4-5 for soil samples from Strata 2 and 3 and Stratum 5, respectively.

Based on the data shown in Table 4-4, the test results of samples from strata 2 and 3 indicated that the soil is considered non-corrosive based on resistivity measurements and concentrations of chlorides and sulfates. However, pH measurements showed that the soil is slightly to strongly acidic. Because corrosion of concrete is largely dependent on the concentration of sulfates, the tested samples from strata 2 and 3 are considered not corrosive to concrete materials. Also, in the range of pH 4 to pH 9, the corrosion rate of iron is relatively independent of the pH of the environment. Therefore, the samples from strata 2 and 3 are generally considered not corrosive.

On the contrary, the samples from stratum 5 are considered corrosive to both concrete and steel based on the data shown in Table 4-5. Especially, the sulfate contents of 3 out of 4 samples from this stratum are relatively high, which will likely attack concrete. Therefore, WDC/346862.HQ 14 sulfate resisting cement, such as cement with 25% pozzolanic material, e.g. Class F fly ashes, should be adopted for the concrete or grout used in deep foundations.

TABLE 4-4

Summary and Evaluation of Corrosivity Testing Results of Samples from Strata 2 and 3

Boring No. B2 B7 T2 T5

Test Sample Depth (ft) 10 4 4 7

7300 9215 9783 6622 Resistivity

Mildly Corrosive

Mildly Corrosive

Mildly Corrosive

Mildly Corrosive

Ohm-cm

7.3 5.2 5.3 5.1 pH

Neutral Severe Severe Severe

40 110 44 180 Chlorides

Threshold Threshold Threshold Threshold ppm

16 9 110 10 Sulfates

Negligible Negligible Negligible Negligible ppm

Overall Evaluation Not Corrosive

Not Corrosive

Not Corrosive

Not Corrosive -

TABLE 4-5

Summary and Evaluation of Corrosivity Testing Results of Samples from Stratum 5

Boring No. B3 B3 B5 B7

Test Sample Depth (ft) 48.5 58.5 40 43

660 279 665 285 Resistivity

Corrosive Very Corrosive Corrosive Very

Corrosive

Ohm-cm

6.4 1.5 1.7 1.5 pH

Moderate Severe Severe Severe

24 26 27 28 Chlorides

Threshold Threshold Threshold Threshold ppm

900 8200 5600 7100 Sulfates

Moderate Severe Severe Severe ppm

Overall Evaluation Corrosive Corrosive Corrosive Corrosive -

WDC/346862.HQ 15

SECTION 5

Seismic Considerations and Site Class

This section presents the testing and analyses conducted to evaluate the liquefaction potential of the soils and determine the 2006 International Building Code (IBC) seismic site class for this project site.

5.1 Liquefaction Potential

Liquefaction potential was evaluated using the procedures and recommendations in the Proceedings of the National Center for Earthquake Engineering Research (NCEER) Workshop on Evaluation of Liquefaction Resistance of Soils (Technical Report NCEER-97-0022), December 1997, and the Summary Report from the 1996 NCEER and 1998 NCEER/NSF Workshops on Evaluation of Liquefaction Resistance of Soils, in Journal of Geotechnical and Geoenvironmental Engineering, October 2001.

The liquefaction potential analysis design earthquake magnitude (M) and peak horizontal ground acceleration (amax/g) were determined using the probabilistic seismic hazard maps and data published on the United States Geological Survey (USGS) website (http://earthquake.usgs.gov/research/hazmaps/products_data/48_States/index.php).

The M and amax/g were determined to be 6.6 and 6 percent, with 2 percent probability of exceedance in 50 years.

Because of the presence of loose sand below the groundwater level, liquefaction potential was evaluated and the factor of safety against liquefaction was found to be greater than 1.5, which is considered acceptable.

5.2 IBC 2006 Seismic Site Class

The seismic site class was determined based on available subsurface information and Chapter 16 of the 2006 International Building Code (IBC 2006). The site was determined to be a Class E site according to Table 1613.5.2 in IBC 2006.

5.3 Seismic Design Parameters

The recommended seismic design parameters for this project are summarized in Table 5-1.

These parameters were developed using 2 percent probability of exceedance (PE) in 50 years.

GEOTECHNICAL REPORT 5 SEISMIC CONSIDERATIONS AND SITE CLASS

WDC/346862.HQ 16

TABLE 5-1

Seismic Design Parameters for 2 Percent PE in 50 Years

Design Parameter Value

Site Class E

Spectral acceleration for 0.2 sec period, SS 0.176 g

Spectral acceleration for 1.0 sec period, S1 0.063 g

Peak ground acceleration, PGA 0.06g

Site coefficient for 0.2 sec period, Fa 2.5

Site coefficient for 1.0 sec period, Fv 3.5

Design earthquake magnitude, Mw 6.6

WDC/346862.HQ 17

SECTION 6

Settlement Analyses

6.1 Settlement Analyses of Shallow Foundations

Settlement analyses were performed to determine whether shallow foundations, such as spread footings or mat foundations, can be used to support the columns of the proposed 4-story and 2-story buildings. The settlement analyses were performed using the method proposed by Schmertmann et al. (1978) for the immediate settlement and using the consolidation theory for the consolidation settlement.

For the settlement analyses of the spread footings supporting columns, an allowable bearing pressure of 3,000 psf was assumed to size the dimensions of the spread footings. Settlement analyses were then performed using the minimum dimensions of the spread footings that are required to result in a foundation bearing pressure less than 3,000 psf and using a bearing pressure of 3,000 psf. The minimum footing dimensions are 5 ft x 5 ft and 18 ft x 18 ft for the smallest and largest column loads. It is also assumed that the bottoms of the spread footings are embedded 3 feet below the existing grade.

For the settlement analyses of mat foundations, it is assumed that the mat foundation is rigid enough such that the bearing pressure under the mat foundation is uniform. The bearing pressure was determined by dividing the sum of all column loads and the weight of the mat foundation by the area of the mat foundation. The resulting bearing pressure of the mat foundation is approximately 1,800 psf. An equivalent dimension of 100 ft x 290 ft was assumed for the mat foundations of the buildings.

It is also assumed in the above analyses that no site fill will be placed underneath and immediately around the buildings. Therefore, settlement caused by site fill is negligible. The results of the settlement analyses are summarized in Table 6-1. As shown in Table 6-1, the magnitudes of settlement and differential settlement are excessive. Generally, a total vertical settlement of 1 inch and a differential settlement, in terms of distortion, of 1/500 are acceptable. Additionally, the minimum spread footing dimensions required to achieve a bearing pressure less than 3,000 psf at most column locations are greater than 10 feet by 10 feet. Therefore, it was determined that shallow foundations, such as spread footings and mat foundations, are not suitable to support the loads of the buildings in this project. Deep foundations, discussed in the next section, will be required for this project.

6.2 Settlement Analyses of Slabs on Grade

In addition to the settlement analyses of shallow foundations, settlement analyses of slabs on grade were also performed to determine whether slabs on grade can be used in conjunction with columns which are supported on deep foundations.

In these analyses, it was assumed that the equivalent dimensions of the slabs of the two buildings are 160 ft x 290 ft. The loadings consisted of a live load of 100 psf and the weight

GEOTECHNICAL REPORT 6 SETTLEMENT ANALYSES

WDC/346862.HQ 18

of the concrete slabs, which was assumed to be 5 inches thick. Additionally, in the equipment area inside the building, an equipment deadload of 250 psf was assumed over a slab of 30 ft x 120 ft in dimension. The resulting pressure on the subgrade ranged between 150 and 300 psf. The results of settlement analyses of slabs on grade are also summarized in Table 6-1. As shown in Table 6-1, the magnitudes of settlement and differential settlement are higher than the tolerated values. Therefore, slabs on grade are not suitable for this project. Structural slabs supported on deep foundations will be required.

TABLE 6-1

Results from Settlement Analyses of Various Structures

Structure and Foundation Type Immediate

Settlement*

(inch)

Consolidation

Settlement

(inch)

Total Settlement

(inch)

Differential

Settlement** (inch)

2 and 4-story Buildings 100 ft x 290 ft

Mat Foundation

3-5 8-10 11-15 5-8

922-kip Columns in the

4-story Building

18 ft x 18 ft

Spread Footing

1-3 1-3 2-6 N/A

600-kip Columns in the

2 and 4-story Buildings

14 ft x 14 ft

Spread Footing

1-2 1-2 2-4 N/A

360-kip Columns in the

2 and 4-story Buildings

11 ft x 11 ft

Spread Footing

0-2 0-1 0-3 N/A

2 and 4-story Buildings 160 ft x 290 ft

Slabs on Grade

0-1 1-3 1-4 0.5-2

4-story Building

Equipment Area

30 ft x 120 ft

Slabs on Grade

0-1 1-2 1-3 0.5-1.5

* Immediate settlement estimated using Schmertmann’s method is calculated assuming a 2-year period for it to occur.

** It is assumed that the settlement at the corner of the mat foundation is half of the settlement in the middle of the mat foundation. The differential settlement is calculated based on this assumption. Therefore, the differential settlement can be 5 to 8 inches over 150 feet, which corresponds to a distortion of 1/360 to 1/225.

***In additional to the above immediate and consolidation settlement, settlement from secondary compression as much as 6 inches can occur.

WDC/346862.HQ 19

SECTION 7

Deep Foundation Analyses and Design

As a result of the settlement analyses discussed in the previous section, both column footings and structural slabs of the 4-story and 2-story buildings in this project will be supported on deep foundations. Due to the proximity of new buildings to the existing building 3500, driven piles are not recommended for this project because of vibration and settlement potential related to installation of driven piles. Two types of deep foundation systems were considered in the design process. They are: augered cast-in-place (ACIP) piles, and drilled shafts. Axial and lateral load and capacity, installation cost, and construction considerations were evaluated in the design process to identify the most suitable deep foundation system for this project. It was determined that 18-inch diameter ACIP piles are the most suitable deep foundations to support the structural slabs and column footings for the buildings in this project.

7.1 Axial Load Capacity of Individual ACIP Piles

The design capacity and estimated pile lengths (or tip elevations) of the ACIP piles were obtained using the following methods. These methods are recommended by Zelada and Stephenson (2000) and Moss and Stephenson (2004) as the best methods to date to evaluate the capacity of ACIP piles in specific soil conditions.

• For ACIP piles in sand, the “modified” Reese and O’Neill (1988) method is used for side shear resistance

• For ACIP piles in sand, the “modified” Neely (1991) method is used for tip resistance

• For ACIP piles in clay, the API (2000) method is used for both side shear and tip resistance

The equations for unit tip and side shear resistance of ACIP piles in sand are summarized below:

qt= 1.7 N ≤ 75 tsf fs= β σ’v β= 1.2 – 0.108 z0.5 where 0.2 ≤ β ≤ 0.96 where:

qt: unit tip resistance in tsf

N: N-value in bpf fs: unit side shear resistance σ’v: average effective vertical stress in a layer z: depth to the mid-point of a layer in feet

GEOTECHNICAL REPORT 7 DEEP FOUNDATION ANALYSES AND DESIGN

WDC/346862.HQ 20

The equations for unit side shear and tip resistance of ACIP piles in clay are summarized below:

fs= α cu where α ≤ 1.0 α= 0.5 ψ-0.5 for ψ ≤ 1 α= 0.5 ψ-0.25 for ψ > 1 ψ= cu/σ’v qt= 9 cu where:

fs: unit side shear resistance cu: undrained shear strength in a layer σ’v: average effective vertical stress in a layer qt: unit tip resistance

Unit side shear and tip resistance are generally estimated using the friction angle and undrained shear strength of sand and clay, respectively, based on SPT N-values and pocket penetrometer readings. Meyerholf’s (1956) correlations were used to estimate the friction angle of sand based on the SPT N-values.

Site fill is minimal around the two buildings in this project. Generally, no more than 2 feet of site fill is expected in the area of the buildings. The top of pile (cut-off) elevation is within +/- 2 feet from the existing grade elevations. Therefore, downdrag force is not expected to impact the axial load capacity of the ACIP piles. Group efficiency, however, will have a significant effect on the capacity of piles arranged in a group, due to the close pile spacing planned for the 18-inch diameter ACIP piles supporting the column footings. The group efficiency is a function of the ratio between pile center-to-center spacing and diameter (S/D) and it is assumed to reduce the resistance of 18-inch diameter piles.

The ultimate capacity of a single pile is then calculated using the following equations:

Qult= Qs + Qt

Qs= η ∗ ∑ fs As

Qt= η ∗ qt At where:

Qult: ultimate capacity

Qs: side shear resistance

Qt: tip resistance η: group efficiency

As: side area of a pile section

WDC/346862.HQ 21

At: tip area of a pile

A factor of safety (FS) of 2.25 for axial capacity of piles is recommended for this project, based on the performance of pile integrity tests (PITs) and static load tests discussed in Section 9. Therefore, the design (or allowable) capacity can be determined as:

Qdgn = Qult/FS where:

Qdgn: design (or allowable) capacity

The design capacity of 18-inch diameter ACIP piles supporting column footings was estimated using the above procedure and subsurface conditions indicated in Borings B1 through B8. Group efficiency (η) of 0.8 was used in the analyses, based on a pile center-to-center spacing to diameter ratio (S/D) of 2.33. This group efficiency was determined based on the work performed by O’Neill (1983). The relationship between the design capacity and length of 18-inch diameter ACIP piles is shown in Figure 7-1. From this figure, it is determined that the design capacity of 18-inch diameter ACIP piles is 150 kips (75 tons) and 160 kips (80 tons) for 75-foot long piles and 80-foot long piles, respectively. Furthermore, the effect of pile spacing on design capacity was investigated for 18-inch diameter ACIP piles.

The results are summarized in Tables 7-1 and 7-2.

It is expected that the settlement of the top of 18-inch diameter ACIP piles at the recommended design capacity is less than ½ inch.

During static load tests, however, group efficiency will not impact the pile capacity.

Therefore, the minimum test load should be carried out to:

Qtest = (Qs + Qt)/η = Qult/η where:

Qtest: the minimum test load

During construction, it is recommended to install four test piles. Two of the four test piles will be 18-inch diameter and 75-foot long. Another two out of the four test piles will be 18-inch diameter and 80-foot long. One 75-foot long ACIP pile and one 80-foot long ACIP pile out of the four 18-inch diameter test piles are recommended to be loaded to failure or the maximum test load during static pile load tests, such that the ultimate capacity and unit side shear and tip resistance values can be back-figured from instrumentation discussed in Section 9. The minimum test loads for the 75-foot long and 80-foot long 18-inch diameter test piles calculated using the equation above are approximately 420 kips and 450 kips, respectively. Failures can occur prior to reaching the minimum test load or beyond this load.

In case that failures occur beyond the minimum test load, the test should be carried out to a maximum test load of 500 kips (250 tons) or failure, whichever occurs first. The maximum test load was established based on the structural capacity of the 18-inch diameter ACIP piles such that the maximum compressive stress in test piles does not exceed 50 percent of the unconfined compressive strength of the grout.

WDC/346862.HQ 22

It should be noted that the estimated pile lengths (or tip elevations) will be at least validated based on the static pile load test results. The results also present an opportunity to optimize (shorten) the pile length if the measured pile capacity is higher than the calculated capacity.

BRAC Headquarters ANG and Readiness Center Addition 18" Diameter ACIP Pile -…