Geotechnical Report by GET Solutions.pdf

RESCUE SWIMMER TRAINING FACILITY

USCG AVIATION TECHNICAL TRAINING CENTER (ATTC)

AT

US COAST GUARD SUPPORT CENTER

ELIZABETH CITY, NORTH CAROLINA

PROJECT NO: 32-X3617

February 26, 2010

Geotechnical Report

UNITED STATES COAST GUARD

FACILITIES DESIGN & CONSTRUCTION CENTER

(FDCC)

5505 ROBIN HOOD ROAD

SUITE K

NORFOLK, VIRGINIA 23513-2413

Frick Building 437 Grant St., North Mezzanine Pittsburgh, PA 15219 Phone: (412) 201-4900 Fax: (412) 201-2338 www.kimballcorp.com

REPORT OF SUBSURFACE INVESTIGATION AND

GEOTECHNCIAL ENGINEERING SERVICES

Rescue Swimmer Training Facility USCG Support Center

Pasquotank County, North Carolina

G E T PROJECT NO: EC09-278G

December 16, 2009

Prepared for

L. Robert Kimball & Associates 437 Grant Street

North Mezzanine – Frick Building Pittsburgh, PA 15219

ATTN: MR. Keith Williams

Prepared by

GET Solutions, Inc.

504 E. Elizabeth Street Ste. 2, Elizabeth City, NC 27909 ♦ Phone 252-335-9765 ♦ Fax 252-335-9766 info@getsolutionsinc.com

December 16, 2009

TO: L. Robert Kimball & Associates 437 Grant Street North Mezzanine – Frick Building Pittsburgh, PA 15219

Attn: Mr. Keith Williams

RE: Report of Subsurface Investigation and Geotechnical Engineering Services Rescue Swimmer Training Facility USCG Support Center Pasquotank County, North Carolina GET Project No: EC09-278G

Dear Mr. Williams:

In compliance with your instructions, we have completed our Subsurface Investigation and Geotechnical Engineering Services for the referenced project. The results of this study, together with our recommendations, are presented in this report.

Often, because of design and construction details that occur on a project, questions arise concerning subsurface conditions. G E T Solutions, Inc. would be pleased to continue its role as Geotechnical Engineer during the project implementation.

We trust that the information contained herein meets your immediate need, and we would ask that you call this office with any questions that you may have.

Respectfully Submitted, G E T Solutions, Inc.

Gerald W. Stalls Jr., P.E.

Senior Project Engineer NC Reg. #034336

Camille A. Kattan, P.E.

Principal Engineer NC Reg. # 014103

Copies: (3) Client

504 East Elizabeth Street; Suite 2 Elizabeth City, NC 27909 Phone: (252)335-9765 Fax: (252)335-9766 info@getsolutionsinc.com

Preliminary Report of Subsurface Investigation and December 16, 2009 Geotechnical Engineering Services Rescue Swimmer Training Facility USCG Support Center Pasquotank County, North Carolina GET Project No: EC09-278G i

EXECUTIVE SUMMARY

The project site is located along the south (relative to plan north) side of the main entrance roadway to the USCG Support Center, in Pasquotank County, North Carolina.

More specifically, it is our understanding that the proposed development is located south of the Aviation Technical Training Center (ATTC). The construction at the site is planned to consist of building a new 51,000 square foot training facility and other associated site infrastructure components. A brief description of the anticipated characteristics of the new structure is presented below:

Single story structure with a mezzanine level for office space.

Pre-cast concrete wall and/or structural steel frame design.

Shallow foundation design with maximum anticipated wall and column loads ranging from about 2 to 12 klf and 70 to 293 kips, respectively.

The structure will include the construction of a cast-in-place concrete training pool and submersion pool with a maximum depth ranging from about 13 to 15 feet, respectively.

A proposed dunking pool for submerged equipment simulation will include the installation of a steel frame crane to support the submerged equipment. This crane will be supported by a deep foundation independent of the building and/or ground level slabs. Maximum foundation loads associated with the crane were reported to be on the order of about 275 kips.

Finish floor elevation of the structure is proposed to be 8 feet MSL, which is located slightly above the existing grade elevations. Accordingly, cut and/or fill operations are not expected to exceed 1 to 2 feet in order to establish the design grade elevations.

First floor to consist of slab-on-grade construction with distributed loads of about 150 pounds per square foot (psf).

Our field exploration program included four (4) recently completed 50- to 60-foot deep SPT borings drilled by G E T Solutions, Inc. within the footprint of the proposed structure. Additionally, a total of three (3) 40-foot deep previously completed SPT borings as well as one (1) previously completed 100-foot deep CPT Sounding was performed during the project’s initial feasibility study and included in our evaluations for foundation design recommendations for the newly proposed building location. A brief description of the natural subsurface soil conditions is tabulated on the following page:

Rescue Swimmer Training Facility USCG Support Center Pasquotank County, North Carolina GET Project No: EC09-278G ii

Note (1) SPT = Standard Penetration Test, N-Values in Blows-per-foot Note (2) BTD = Boring Termination Depth

The groundwater level was recorded at the boring locations and as observed through the wetness of the recovered soil samples during the drilling operations. The initial groundwater table was measured to occur at depths ranging from 6 to 7 feet below existing site grades at the boring locations, which corresponded to an elevation ranging from 0.2 to 0.9 feet MSL. A groundwater monitoring well was installed at the location of borings B-7 and B-7B and 24-hour groundwater readings were noted to indicate a static water level of about 5 feet below existing grades, which corresponded to an elevation of

1.9 feet MSL.

The following preliminary evaluations and recommendations were developed based on our field exploration and laboratory-testing program:

Field testing program during construction to include, subgrade proofrolling, compaction testing, foundation excavation observations for bearing capacity verification, test and production pile monitoring, pile load testing, and/or vibration monitoring. All other applicable testing, inspections, and evaluations should be performed as indicated in the North Carolina State Building Code (2006 International Building Code with North Carolina Amendments) and/or UFC (Unified Facilities Criteria).

An estimated cut depth ranging from approximately 4 to 9 inches will be required to remove the existing concrete pavements as well as the topsoil and associated root mat, where encountered.

AVERAGE

DEPTH (Feet)

STRATUM DESCRIPTION

RANGES OF

SPT(1) N-

VALUES

0.0 to 0.33 Topsoil TOPSOIL; Boring B-6 only 0.0 to

0.46 – 0.75 Pavement Concrete Pavement; Not encountered at boring B-6

0.33 – 0.67 to

2 – 6 I

Lean CLAY (CL) to Fat CLAY (CH) with varying amounts of sand; Not encountered at the location of boring B-3 4 to 11

2 – 6 to

BTD(2)

II

SAND with varying amounts of silt and/or clay (SP, SP-SM, SM, SC-SM, SC)

2 to 61 to

18 - 23

IIA

SILT (ML) and/or Sandy Lean CLAY (CL) borings B-3, B-5, B-6, and B-9

Rescue Swimmer Training Facility USCG Support Center Pasquotank County, North Carolina GET Project No: EC09-278G iii

The subgrade evaluation procedures should include a series of test pit excavations to further evaluate these soils and to substantiate their suitability to remain in-place.

Some subgrade improvements should be anticipated within the construction areas (undercutting and backfilling with select fill) as a result of the potential for the cohesive subgrade soils (SAND; SC, CLAY; CL, CH) to become unsuitable/unstable.

Building shallow foundations designed using a net allowable bearing capacity of 2,000 psf (18-inch embedment, 24-inch width). Shallow foundation embedment depths for the building should not extend below a depth of 3 feet beneath finished grades (5 feet MSL). Foundation bearing elevations below 5 feet MSL may result in excessive settlements exceeding that noted below.

Estimated post-construction total and differential settlements for the buildings up to 1-inch and ½-inch, respectively.

Due to a proposed pool depth of about 13 to 15 feet, the pool slabs and wall foundations are anticipated to have a bearing elevation coinciding with, or directly above very soft CLAY and/or very loose SAND layers encountered at the boring locations. Accordingly, the pool slabs, walls, and associated submersion crane should be supported by deep (pile) foundations. Additionally, the slab and/or wall areas are anticipated require a 12 to 18 undercut and backfill with the use of No.

57 stone in order to provide temporary support to the cast-in-place slabs, pile caps, and/or grade beams. Design of the pool walls and foundations should include the influence of lateral loads as contributed by the building shallow foundations.

Proposed structure should be designed based on a site seismic classification of “D”, based on the results of the 100-foot deep CPT boring, our experience in the project area, and the requirements provided in provided in the North Carolina State Building Code (2006 International Building Code with North Carolina Amendments) section 1615.1; Table 1615.1.1.

This summary briefly discusses some of the major topics mentioned in the attached report. Accordingly, this report should be read in its entirety to thoroughly evaluate the contents.

TABLE OF CONTENTS

EXECUTIVE SUMMARY.............................................................................................. i

1.0 PROJECT INFORMATION

1.1 Project Authorization

1.2 Project Description

1.3 Purpose and Scope of Services

2.0 FIELD AND LABORATORY PROCEDURES

2.1 Field Exploration

2.2 Laboratory Testing

3.0 SITE AND SUBSURFACE CONDITIONS

3.1 Site Location and Description

3.2 Site Geology

3.3 Subsurface Soil Conditions

3.4 Groundwater Information

4.0 EVALUATION AND RECOMMENDATIONS

4.1 Clearing and Grading

4.2 Subgrade Preparation

4.3 Structural Fill and Placement

4.4 Suitability of On-Site Soils

4.5 Shallow Foundation Design Recommendations

4.6 Shallow Foundation Settlements

4.7 Shallow Foundation Excavations

4.8 Building Floor Slabs

4.9 Bellow Grade Structures

4.10 Pool Design Recommendations

4.11 Pile Foundation Design Recommendations

4.12 Pile Group Settlement

4.13 Test Piles

4.14 Dynamic Testing – Pre-Stressed Concrete Piles

4.15 Establishing Pile Driving Criteria

4.16 Allowable Driving Stresses

4.17 Hammer Types and Energies

4.18 Driven Pile Installation Monitoring

4.19 Adjacent Structures

4.20 Seismic Evaluation

TABLE OF CONTENTS - CONTINUED

5.0 CONSTRUCTION CONSIDERATIONS

5.1 Drainage and Groundwater Concerns

5.2 Site Utility Installation

5.3 Excavations

6.0 REPORT LIMITATIONS

APPENDIX I BORING LOCATION PLAN

APPENDIX II BORIING LOCATION SURVEY

APPENDIX III BORING LOGS

APPENDIX IV GENERALIZED SOIL PROFILE

APPENDIX V SUMMARY OF CPT SOUNDING

APPENDIX VI CONSOLIDATION TEST RESULTS

APPENDIX VII CLASSIFICATION SYSTEM FOR SOIL EXPLORATION

Report of Subsurface Investigation and Geotechnical Engineering Services December 16, 2009 Rescue Swimmer Training Facility USCG Support Center Pasquotank County, North Carolina GET Project No: EC09-278G

1.0 PROJECT INFORMATION

1.1 Project Authorization

G E T Solutions, Inc. has completed our subsurface investigation and geotechnical engineering services for the proposed USCG Rescue Swimmer Training Facility project located along the east side of the main entrance roadway of the USCG Support Center in Pasquotank County, North Carolina. The Geotechnical Engineering Services were conducted in general accordance with G E T Solutions, Inc. Proposal No. PEC09-218G, dated September 10, 2009. Furthermore, these services were provided in conjunction with our previously completed feasibility study reported on the date of September 17, 2007 (GET Project No. EC07-278G). Authorization to proceed with the Geotechnical Engineering Services was received from Mr. Keith Williams with L. Robert Kimball and Associates, on the date of November 17, 2009 in the form of the signed “Work Authorization” sheet included with our original proposal.

1.2 Project Description

The construction at the site is planned to consist of building a new 51,000 square foot training facility and other associated site infrastructure components. At this time it is our understanding the project will not include the construction of any storm water management ponds. Additionally, the only pavement construction that will be required is the replacement of the portion of the existing rigid pavement that will be removed to facilitate construction of the proposed building as well as an asphalt over-lay of the adjacent existing rigid pavements.

The proposed structure will consist primarily of a single story pre-cast concrete building supported by shallow foundations with a training swimming pool, a submersion training pool, and a mezzanine level for office space. The swimming pool will be approximately 165 feet in length, 70 feet in width, and will range in depth from about 5 to 13 feet. The submersion training pool will be about 60 feet in length, 38 feet in width, and about 15 feet in depth and include an associated steel frame crane to support the submerged equipment. Maximum foundation loads associated with the crane were reported to be on the order of about 275 kips.

The design building loading conditions noted in the RFP were indicated to result in maximum wall and column loads ranging from about 2 klf to 12 klf and 70 kips to 293 kips, respectively.

The first finished floor of the building will be constructed as a slab-on-grade member with its distributed loads not expected to exceed about 150 pounds per square foot and a proposed finished floor elevation (approximately 8 feet MSL) located slightly above the existing site grade elevations. Existing site elevations encountered at the boring locations determined by Albemarle and Associates, Ltd were noted to range from about 6.22 to 7.75 feet MSL (NAVD 88). Accordingly, cut and/or fill operations necessary to establish the design grade elevations are not expected to exceed about 1 to 2 feet.

USCG Support Center Pasquotank County, North Carolina GET Project No: EC09-278G

If any of the noted information is incorrect or has changed, please inform G E T Solutions, Inc. so that we may amend the recommendations presented in this report, if appropriate.

1.3 Purpose and Scope of Services

The purpose of this study was to obtain information on the general subsurface conditions at the proposed project site. The subsurface conditions encountered were then evaluated with respect to the available project characteristics. In this regard, engineering assessments for the following items were formulated:

1. General assessment of the soils revealed by the borings performed at the proposed development.

2. General location and description of potentially deleterious material encountered in the borings that may interfere with construction progress or structure performance, including existing fills or surficial/subsurface organics.

3. Soil subgrade preparation, including stripping, grading, and compaction.

Engineering criteria for placement and compaction of approved structural fill material.

4. Construction considerations for fill placement, subgrade preparation, and foundation excavations.

5. Feasibility of utilizing a shallow foundation system for support of the proposed structure. Design parameters required for the foundation systems, including foundation sizes, allowable bearing pressures, foundation levels, and expected total and differential settlements.

6. Development of driven pile design criteria for the proposed pool slabs, pool walls, and dunking (submersing) crane foundations including pile types, pile embedment depths and the associated allowable capacities, and estimated settlements.

7. Development of soil design parameters including active, passive, and at rest earth pressure coefficients to be used in design of the below grade walls.

8. Seismic site classification provided based on the results of the previously completed 100-foot deep CPT sounding performed at the project site during the previously referenced Feasibility Study scope of services as well as our experience with similar projects located in the vicinity of the site.

USCG Support Center Pasquotank County, North Carolina GET Project No: EC09-278G

The scope of services did not include an environmental assessment for determining the presence or absence of wetlands or hazardous or toxic material in the soil, bedrock, surface water, groundwater or air, on or below or around this site. Any statements in this report or on the boring logs regarding odors, color, unusual or suspicious items or conditions are strictly for the information of the client. Prior to development of this site, an environmental assessment is advisable.

2.0 FIELD AND LABORATORY PROCEDURES

2.1 Field Exploration

In order to access the subsurface soils beneath the existing pavements and to perform the required borings, a total of three (3) 6-inch diameter cores were performed at the location of the borings B-7 through B-9. Subsequently, in order to explore the general subsurface soil types and to aid in developing associated foundation design parameters, a total of four

(4) 50- to 60-foot deep Standard Penetration Test (SPT) borings (designated as B-6 through B-9) were drilled by G E T Solutions, Inc. within the limits of the proposed structure. The recently completed borings were performed in conjunction with, and labeled consecutively with the previously completed borings associated with the project’s feasibility study reported on the date of September 17, 2007 (GET Project No. EC07-278G).

Accordingly, the borings performed during our initial feasibility study for the proposed project (B-2, B-3, and B-5), which were previously located within the vicinity of the newly proposed building location, are included herein. Additionally, the previously completed CPT sounding (CPT-1) is included herein. Whereas, the remaining borings performed during the initial feasibility study identified as B-1 and B-4 are not provided as they were not performed within the newly established limits of the proposed structure.

Standard Penetration Tests were performed in the field in general accordance with ASTM D 1586. The tests were performed continuously from the existing ground surface to depths of 10 feet, and at 5-foot intervals thereafter. The soil samples were obtained with a standard 1.4” I.D., 2” O.D., 30” long split-spoon sampler. The sampler was driven with blows of a 140 lb. hammer falling 30 inches. The number of blows required to drive the sampler each 6-inch increment of penetration was recorded and is shown on the boring logs. The sum of the second and third penetration increments is termed the SPT N-value.

A representative portion of each disturbed split-spoon sample was collected with each SPT, placed in a glass jar, sealed, labeled, and returned to our laboratory for review.

Two (2) thin-walled tube samples were obtained from the very loose strata, by hydraulically pressing a 3-inch outside diameter Shelby tube into the soils. Specifically the tube samples were obtained at the location of borings B-6 and B-8 at depths of 15 to 17 feet below the existing site grades. The tubes were sealed to prevent moisture loss and returned to the laboratory for extraction, classification and consolidation testing.

USCG Support Center Pasquotank County, North Carolina GET Project No: EC09-278G

Following the exploration procedures, the borings were backfilled with a neat cement grout mix in accordance with NCDENR requirements, excluding the two (2) locations where groundwater monitoring wells were installed. As an exception, a groundwater monitoring well was installed at the location of boring B-7 as well as at the location of B-7B, which was performed solely to measure draw-down during flow rate testing. More specific information regarding boring locations and depths is provided in the following table (Table I – Boring Schedule).

Table I – Boring Schedule

GPS Coordinates Boring

Number

Boring

Depth

(feet)

Boring

Surface

Elevation

(ft MSL)*

Boring Location Description Latitude ** Longitude**

B-2 40 INA

Approximately 50 feet South and 20 Feet West of the Northwest Building Corner 36° 15.859 76° 10.915

B-3 40 INA

Approximate Northeast Corner of Rescue

Training Swimming Pool 36° 15.891 76° 10.889

B-5 40 INA

Approximately 120 feet East and 5 feet South of the Northwest Building Corner 36° 15.888 76° 10.908

CPT-1 100 INA

Approximately 5 feet West and 5 feet South of the Northwest Building Corner 36° 15.877 76° 10.917

B-6 50 7.75 Approximate Southwest Building Corner 36° 15.854 76° 10.900

B-7 60 6.93 Approximate Center of Pool 36° 15.880 76° 10.894

B-8 60 6.69 Approximate Center of the Proposed Crane

Foundation 36° 15.897 76° 10.877

B-9 50 6.22 Approximate Northeast Building Corner 36° 15.909 76° 10.890

* = Surface elevations were based on the topographic information provided by Albemarle and Associates, Ltd

(NAVD 88).

** = GPS coordinates were established with the use of hand held devices for B-2, B-3, and CPT-1 and are considered preliminary. GPS coordinates provided for B-6 through B-9 were determined from the NC state plane coordinates determined by Albemarle and Associates, Ltd. (NC Grid NAD 83; 2001).

The boring locations were established and identified in the field by G E T Solutions Inc.

personnel by measuring from existing landmarks. The approximate boring locations are shown on the attached “Boring Location Plan” (Appendix I) which was developed based on the site plan provided to G E T Solutions, Inc. by L. Robert Kimball and Associates.

Following the drilling procedures, the recently completed boring locations were surveyed by a NC licensed Professional Land Surveyor to determine existing site grade elevations and NC state plane coordinates for each boring location. The results of these surveying services are provided in Appendix II.

USCG Support Center Pasquotank County, North Carolina GET Project No: EC09-278G

2.2 Laboratory Testing

Representative portions of all soil samples collected during drilling were sealed in glass jars, labeled and transferred to our laboratory for classification and analysis. The soil classification was performed by a Geotechnical Engineer in accordance with ASTM D2488.

Sixteen (16) representative soil samples were selected and assigned to laboratory testing, which will include natural moisture, -#200 sieve wash, and/or Atterberg Limits testing and analysis, in order to corroborate the visual classification. These testing procedures were not completed at this time. However, following their completion they will be included in our final report and the results will be provided in the following table (Table II – Laboratory Test Results) and will be presented on the “Boring Log” sheets (Appendix II), included with this report.

Table II - Laboratory Test Results

Boring No.

Sample Type

Depth (Feet)

Natural Moisture

Passing

#200

Atterberg Limits

(LL/PL/PI)

USCS

Classification

B-2 SS 2-4 23.1 69.8 41/21/20 CL

B-2 SS 13-15 24.0 44.0 Not Tested SM

B-3 SS 23-25 23.9 3.8 Not Tested SP

B-3 SS 38-40 21.6 6.2 Not Tested SP-SM

B-5 SS 13-18 29.8 67.7 36/20/16 CL

B-6 SS 13-15 34.8 70.9 29/23/6 ML

B-6 ST 15-17 24.7 84 28/25/3 CL

B-7 SS 2-4 21.7 62.8 Not Tested CL

B-7 SS 6-8 18.8 26.5 Not Tested SM

B-7 SS 8-10 23.9 3.5 Not Tested SP

B-7 SS 13-15 32.3 47.5 Not Tested SC-SM to SC

B-8 SS 2-4 25.0 64.6 Not Tested CL

B-8 SS 13-15 26.7 40.8 Not Tested SM w/clay to

SC-SM

B-8 ST 15-17 33.4 60 29/22/7 CL

B-9 SS 4-6 20.3 54.6 33/20/13 CL

B-9 SS 13-15 32.7 65.4 31/23/8 CL

SS = Split Spoon Sample ST = Shelby Tube Sample

USCG Support Center Pasquotank County, North Carolina GET Project No: EC09-278G

Two (2) one-dimensional consolidation tests were performed on specimens from the Shelby tube samples obtained at the location of Borings B-6 and B-8 at depths of 15 to 17 feet beneath the existing site grades. The consolidation tests were performed at our Virginia Beach laboratory in general accordance with ASTM D 2435. A representative specimen from each of the Shelby tubes was also subjected to natural moisture content, Atterberg Limits, and -#200 sieve testing. A summary of the consolidation test results is presented in the following table (Table III) and the comprehensive results are provided in Appendix VI.

Table III - Consolidation Test Results (Shelby Tube Samples)

Boring No.

Depth (ft)

Natural Moisture

Overburden Pressure

(tsf)

Pre consolidation Pressure Pc (tsf)

Cc Cr eo

B-6 15-17 24.7 0.65 1.15 0.08 0.01 0.676

B-8 15-17 33.4 0.65 1.50 0.17 0.01 0.918

3.0 SITE AND SUBSURFACE CONDITIONS

3.1 Site Location and Description

The project site is located along the south side (relative to plan north) of the main entrance roadway to the USCG Support Center, in Pasquotank County, North Carolina. More specifically, it is our understanding that the proposed development is located south of the Aviation Technical Training Center (ATTC). The proposed construction area was observed to consist primarily of existing concrete pavements with an isolated grass covered area.

Existing grade elevations determined by Albemarle and Associates, Ltd at the recently completed boring locations generally ranged from about 6.22 to 7.75 feet MSL (NAVD 88).

Furthermore, the site was visually estimated to be relatively level with less than 1 to 2 feet of change in elevation in 50 linear feet.

The project site is bordered to the west and north by existing structures (Building No. 6 and No. 4) followed by the main entrance roadway for the USCG Support Center, to the south and east by a combination of existing concrete pavement taxi-ways, concrete paved runway, and grass covered areas.

USCG Support Center Pasquotank County, North Carolina GET Project No: EC09-278G

3.2 Site Geology

The project site lies within a major physiographic province called the Atlantic Coastal Plain.

Numerous transgressions and regressions of the Atlantic Ocean have deposited marine, lagoonal, and fluvial (stream lain) sediments. The regional geology is very complex, and generally consists of interbedded layers of varying mixtures of sands, silts and clays.

Based on our review of existing geologic and soil boring data, the geologic stratigraphy encountered in our subsurface explorations generally consisted of marine deposited sands, silts and clays.

3.3 Subsurface Soil Conditions

The results of our recently and previously completed soil test borings at this site indicated that the existing concrete pavements encountered at the coring/SPT boring and/or CPT locations ranged from approximately 5.5 to 8 inches in thickness. Underlying the existing concrete materials, the typically occurring Aggregate Base Course (ABC) materials were not encountered. Topsoil encountered at the location of boring B-6, where concrete pavement was not encountered, was noted to be approximately 4-inches in thickness.

More detailed information regarding the surficial material types and thicknesses are provided in the table below:

Table IV: Summary of Surficial Materials

Core / Boring No.

Core / Boring Location Topsoil

Thickness (in.)

Concrete Pavement Thickness

(in.)

B-2 Approximately 35 feet West/Southwest of the

Northwest Building Corner N/A 7

B-3 Approximately 7 feet North/Northwest of the Center of the North Building Wall Line N/A 8

B-5 Approximately 120 feet East and 5 feet South of the Northwest Building Corner N/A 9

CPT-1

Approximately 30 feet North/Northwest of the

Northwest Building Corner N/A 7

B-6 Approximate Southwest Building Corner 4 N/A B-7 Approximate Center of Pool N/A 5.5

B-8 Approximate Center of the Proposed Crane

Foundation N/A 5.5

B-9 Approximate Northeast Building Corner N/A 6.75

USCG Support Center Pasquotank County, North Carolina GET Project No: EC09-278G

Beneath the existing concrete pavements and/or TOPSOIL the subsurface soils encountered at the boring locations were consistent at the boring locations, to their explored depths, and were arranged in a two (2) layer configuration. More specifically, the subsurface soils consisted of a soft to stiff CLAY with varying amounts of silt and sand (CL, CH) underlain by very loose to very dense SAND (SP, SP-SM, SM, SC-SM, SC) with varying amounts of silt and clay. The shallow subsurface Cohesive soil deposits (CLAY;

CL, CH) were not encountered at the location of boring B-3. Additionally, deeper subsurface deposits of very soft SILT (ML) and/or Sandy Lean CLAY (CL) were encountered at the locations of boring B-3, B-5, B-6, and B-9 at depths of about 13 feet below existing grades and extended to a depths ranging from about 18 to 23 feet.

The subsurface description is of a generalized nature provided to highlight the major soil strata encountered. The records of the subsurface exploration are included in Appendix II (Boring Log sheets) and in Appendix III (Generalized Soil Profile), which should be reviewed for specific information as to the individual borings. The stratifications shown on the records of the subsurface exploration represent the conditions only at the actual boring locations. Variations may occur and should be expected between boring locations. The stratifications represent the approximate boundary between subsurface materials and the transition may be gradual.

3.4 Groundwater Information

The groundwater level was recorded at the location of borings B-2, B-3, B-5, and B-6 through B-9 as observed through the wetness of the recovered soil samples during the drilling operations. The initial groundwater table was measured to occur at depths ranging from 6 to 7 feet below current grades at the boring locations. Based on the site topography information provided by Albemarle and Associates, Ltd. (NAVD 88), the encountered groundwater level corresponds to an elevation generally ranging from about 0.2 to 0.9 feet

MSL

The boreholes were backfilled upon completion for safety considerations. As such, the reported groundwater levels may not be indicative of the static groundwater level.

However, two (2) groundwater monitoring wells were installed at the location of boring B-7 and B-7B. The static groundwater level encountered following a period of 24-hours after the monitoring wells were installed was noted to occur at a depth of 5 feet below the existing site grade elevations, which corresponds to an elevation of 1.93 feet MSL.

Shallow perched groundwater levels are anticipated to occur throughout the site as a result of potential restrictive SAND (SC) and/or CLAY (CL, CH) soil layers, which were encountered throughout the site at depths extending from below the surficial concrete pavements and/or topsoil to depths ranging from 4 feet to 6 feet.

USCG Support Center Pasquotank County, North Carolina GET Project No: EC09-278G

Groundwater conditions will vary with environmental variations and seasonal conditions, such as the frequency and magnitude of rainfall patterns, as well as man-made influences, such as existing swales, drainage ponds, underdrains and areas of covered soil (paved parking lots, sidewalks, etc.). Seasonal groundwater fluctuations of 3 to 4 feet are common in the project’s area; however, greater fluctuations have been documented. We recommend that the contractor determine the actual groundwater levels at the time of the construction to determine groundwater impact on the construction procedures.

4.0 EVALUATION AND RECOMMENDATIONS

Our recommendations are based on the previously discussed project information, our interpretation of the soil test borings and laboratory data, and our observations during our site reconnaissance. If the proposed construction should vary from what was described, we request the opportunity to review our recommendations and make any necessary changes.

4.1 Clearing and Grading

The proposed construction area should be cleared by means of removing the existing concrete pavements as well as the topsoil and associated root mat, where encountered. It is expected that a cut ranging from approximately 4 to 9 inches below existing grades will be required to remove the majority of the existing pavements and/or surface organic soils.

This cut is expected to be deeper in isolated areas to remove deeper deposits of concrete pavements and/or organic soils, which may become evident during the clearing. It is recommended that the clearing operations extend laterally at least 5 feet beyond the perimeter of the proposed construction areas.

Following the initial clearing, the resulting exposed subgrade will generally be comprised of CLAY (CL, CH) and/or SAND (SM, SC) containing an appreciable amount of fines.

Accordingly, combinations of excess surface moisture from precipitation ponding on the site and the construction traffic, including heavy compaction equipment, may create pumping and general deterioration of the bearing capabilities of the surface soils.

Therefore, undercutting to remove loose/soft soils in isolated areas should be expected.

The extent of the undercut will be determined in the field during construction based on the outcome of the field testing procedures (subgrade proofroll). In this regard, and in order to reduce undercutting, care should be exercised during the grading and construction operations at the site.

Furthermore, inherently wet subgrade soils combined with potential poor site drainage make this site particularly susceptible to subgrade deterioration. Thus, grading should be performed during a dry season if at all possible. This should minimize these potential problems, although they may not be eliminated. The project’s budget should include an allowance for subgrade improvements (undercut and backfill with structural fill or aggregate base in the building and pavement areas).

USCG Support Center Pasquotank County, North Carolina GET Project No: EC09-278G

4.2 Subgrade Preparation

Following the clearing operation, the exposed subgrade soils should be densified with a large static drum roller. After the subgrade soils have been densified, they should be evaluated by G E T Solutions, Inc. for stability. Accordingly, the subgrade soils should be proofrolled to check for pockets of loose material hidden beneath a crust of better soil.

Several passes should be made by a large rubber-tired roller or loaded dump truck over the construction areas, with the successive passes aligned perpendicularly. The number of passes will be determined in the field by the Geotechnical Engineer depending on the soils conditions. Any pumping and unstable areas observed during proofrolling (beyond the initial cut) should be undercut and/or stabilized at the directions of the Geotechnical Engineer.

Following the proofroll and approval by the engineer, it is recommended that the newly exposed subgrade soils be compacted to a dry density of at least 95 percent of the Modified Proctor maximum dry density (ASTM D1557), as tested to a depth of at least 12 inches.

4.3 Structural Fill and Placement

Following the approval of the natural subgrade soils by the Geotechnical Engineer, the placement of the fill required to establish the design grades may begin. Any material to be used for structural fill should be evaluated and tested by G E T Solutions, Inc. prior to placement to determine if they are suitable for the intended use. Suitable structural fill material should consist of sand or gravel containing less than 20% by weight of fines (SP, SM, SW, GP, GW), having a liquid limit less than 20 and plastic limit less than 6, and should be free of rubble, organics, clay, debris and other unsuitable material.

All structural fill should be compacted to a dry density of at least 95 percent of the Modified Proctor maximum dry density (ASTM D1557). In general, the compaction should be accomplished by placing the fill in maximum 10-inch loose lifts and mechanically compacting each lift to at least the specified minimum dry density. A representative of G E T Solutions, Inc. should perform field density tests on each lift as necessary to assure that adequate compaction is achieved.

Backfill material in utility trenches within the construction areas should consist of structural fill (as previously above), and should be compacted to at least 95 percent of ASTM D1557.

This fill should be placed in 4 to 6 inch loose lifts when hand compaction equipment is used.

Care should be used when operating the compactors near existing structures to avoid transmission of the vibrations that could cause settlement damage or disturb occupants. In this regard, it is recommended that the vibratory roller remain at least 25 feet away from existing structures; these areas should be compacted with small, hand-operated compaction equipment.

USCG Support Center Pasquotank County, North Carolina GET Project No: EC09-278G

4.4 Suitability of On-site Soils

The subsurface CLAY (CL, CH) and/or SAND (SC, SC-SM, and SM with clay) soils encountered at the boring locations do not appear to meet the criteria recommended in this report for reuse as structural fill, but may be used as fill within green areas. However, the SAND (SP, SP-SM, and SM) soils may be suitable for reuse as structural fill. Further classification testing (natural moisture content, gradation analysis, and Proctor testing) should be performed in the field during construction to substantiate the suitability of excavated soils for reuse as fill within construction areas.

4.5 Shallow Foundation Design Recommendations - Building

Provided that the recommended earthwork construction procedures are properly performed, the proposed structure can be supported by shallow spread footings, bearing over firm natural soil or well compacted structural fill material. The footings can be designed using a net allowable soil pressure of up to 2,000 pounds per square foot (psf).

In using net pressures, the weight of the footings and backfill over the footings, including the weight of the floor slab, need not be considered. Hence, only loads applied at or above the finished floor need to be used for dimensioning the footings.

In order to develop the recommended bearing capacity, the base of the footings should have an embedment of at least 18 inches beneath finished grades, and wall footings should have a minimum width of 24 inches. As an exception, all shallow foundations should have a maximum footing embedment depth of 3 feet below finished grades.

Deeper footing embedment depths will result in excessive settlement magnitudes beyond that indicated in Section 4.6 of this report. In addition, isolated square column footings are recommended to be a minimum of 3 feet by 3 feet in area for bearing capacity consideration. The recommended 18-inch footing embedment is considered sufficient to provide adequate cover against frost penetration to the bearing soils.

4.6 Shallow Foundation Settlements - Building

It is estimated that, with proper site preparation, the maximum resulting post construction settlement of the building foundations should be up to 1 inch. The maximum differential settlement magnitude is expected to up to ½-inch between adjacent footings (wall footings and column footings of widely varying loading conditions).

As previously stated in Section 4.5 of this report, the shallow footing embedment depths for all foundations should not exceed a depth of 3 feet, which corresponds to an elevation of about 5 feet MSL. Footing embedment depths below an elevation of 5 feet MSL are anticipated to experience excessive settlement magnitudes.

The settlements were estimated on the basis of the results of the field penetration tests as well as our consolidation test results. Careful field control will contribute substantially towards minimizing the settlements.

USCG Support Center Pasquotank County, North Carolina GET Project No: EC09-278G

4.7 Shallow Foundation Excavations - Building

In preparation for shallow foundation support, the footing excavations should extend into firm natural soil or well compacted structural fill. All foundation excavations should be observed by G E T Solutions, Inc. At that time, the Geotechnical Engineer should also explore the extent of excessively loose, soft, or otherwise unsuitable material within the exposed excavations. Also, at the time of footing observations, the Geotechnical Engineer may find it necessary to perform hand auger borings or use a hand penetration device in the bases of the foundation excavations.

If pockets of unsuitable soils requiring undercut are encountered in the footing excavations, the proposed footing elevation should be re-established by means of backfilling with “flowable fill”, an open graded washed stone (such as No. 57 stone or equivalent), or a suitable structural fill material compacted to a dry density of at least 95 percent of the Modified Proctor maximum dry density (ASTM D 1557), as described in Section 4.3 of this report. This construction procedure will provide for a net allowable bearing capacity of 2,000 psf.

Immediately prior to reinforcing steel placement, it is suggested that the bearing surfaces of all footings be compacted using hand operated mechanical tampers, to a dry density of at least 95% of the Modified Proctor maximum dry density (ASTM D 1557) as tested to a depth of 12 inches, for bearing capacity considerations. In this manner, any localized areas, which have been loosened by excavation operations, should be adequately re-compacted.

Soils exposed in the bases of all satisfactory foundation excavations should be protected against any detrimental change in condition such as from physical disturbance, rain or frost. Surface run-off water should be drained away from the excavations and not be allowed to pond. If possible, all footing concrete should be placed the same day the excavation is made. If this is not possible, the footing excavations should be adequately protected.

4.8 Building Floor Slabs

The building floor slabs may be constructed as slab-on-grade members provided the previously recommended earthwork activities and evaluations are carried out properly. It is recommended that the ground floor slab be directly supported by at least a 4-inch layer of relatively clean, compacted, poorly graded sand (SP) or gravel (GP) with less than 5% passing the No. 200 Sieve (0.074 mm). The purpose of the 4-inch layer is to act as a capillary barrier and equalize moisture conditions beneath the slab.

USCG Support Center Pasquotank County, North Carolina GET Project No: EC09-278G

It is recommended that all ground floor slabs be "floating". That is, generally ground supported and not rigidly connected to walls or foundations. This is to minimize the possibility of cracking and displacement of the floor slabs because of differential movements between the slab and the foundation. Slab-on-grade post construction settlements should be limited to ½-inch or less.

It is also recommended that the floor slab bearing soils be covered by a vapor barrier or retarder in order to minimize the potential for floor dampness, which can affect the performance of glued tile and carpet. Generally, use a vapor retarder for minimal vapor resistance protection below the slab on grade. When floor finishes, site conditions or other considerations require greater vapor resistance protection; consideration should be given to using a vapor barrier. Selection of a vapor retarder or barrier should be made by the Architect based on project requirements.

4.9 Below Grade Structures:

In order to reduce the magnitude of lateral loads being applied to below grade walls and to promote positive water drainage, it is recommended that a granular backfill be placed directly behind the retaining wall and extend laterally back from the wall a minimum distance of five feet. These granular soils should be a relatively clean, free draining granular material (sand) classified as SP-SM or better, containing less than 12 percent passing the No. 200 sieve (0.074 mm). The compaction of the select backfill soils behind the walls should be 95 percent of the Modified Proctor maximum dry density (ASTM D1557). The soils in this zone should not be over-compacted. In order to minimize the potential for wall damage due to excessive compaction, hand operated mechanical tampers should be used to compact the granular materials. Heavy compaction equipment should not be allowed within five feet of the retaining wall.

With regard to the design of the structure’s walls to resist lateral earth pressures, the estimated soil design parameters provided in the following table (Table V) can be used:

USCG Support Center Pasquotank County, North Carolina GET Project No: EC09-278G

Table V – Below Grade Structures Soil Design Parameters

Earth Pressure Coefficient On-Site

Natural CLAY

(CL, CH)

On-Site Natural SAND

(SP, SP-SM,

SM, SC)

Select Backfill

SAND (SP,

SP-SM)

Total Moist Unit Weight (Ww; lbs/ft3)

120 120 110

Coeff. of At-Rest Soil Pressure (Ko)

0.91 0.50 0.50

Coeff. of Passive Soil Pressure (Kp)

1.19 3.00 3.00

Coeff. Of Active Soil Pressure (Ka)

0.84 0.33 0.33

Angle of Internal Friction ()

5 30 30

Cohesion (c; psf) 400 0 0

Retaining walls should be sized with considerations given to the hydrostatic pressures.

These pressures should assume the water table to occur near the ground surface. Also, the wall’s foundation (base) should be sized by the Structural Engineer, in order to enhance wall stability (sliding, overturning, and bearing capacity).

4.10 Pool And Submersion Crane Design Recommendations

The proposed pools will bear in approximately 4 to 6 feet of very soft CLAY/SILT, which would result in potentially excessive settlements and associated cracking and leaks in the event that shallow foundations are implemented. Accordingly, it is recommended that the pools’ slabs and its associated walls and/or submersion crane be supported by a deep foundation system. It is anticipated that the pool slab and walls will require an over-excavation depth of about 12 to 18 inches, which should be backfilled with the use of an open graded stone (such as #57 stone or equivalent) in order to provide temporary support of the cast-in-place slabs and grade beams. Additional recommendations for pile foundations are provided in Sections 4.11 through 4.21 of this report.

Also, the pool wall and foundation designs should take into account the lateral loads as contributed by the shallow foundations of the building that are in close proximity and within the influence zone of the pool walls.

USCG Support Center Pasquotank County, North Carolina GET Project No: EC09-278G

4.11 Pile Foundation Design Recommendations

For this project, it is our opinion that driven12-inch square pre-cast concrete piles will be most economical of the driven pile options to support the proposed pools’ slabs and associated walls. Alternative recommendations for round timber piles have also been provided. We conducted pile capacity analyses using static formulas with coefficients recommended by Geoffrey Myerhoff and George Sowers. The analyses include the contributions of shaft friction and end bearing to the pile capacity. The piles are expected to derive the majority of their capacity from shaft friction and end bearing in the deeper sand layer at the depths presented in Tables II and III on the following page of this report.

The piles are generally expected to derive the majority of their capacity from end bearing, which will be contributed by medium dense to dense sand layers at a depth of approximately 35 to 40 feet below existing grades. These depths correspond to an elevation ranging from about -27 to -34 feet MSL. Our individual pile axial capacity estimates versus pile embedment lengths and tip elevations are tabulated on the following page (Table VI – Pile Capacities).

Table VI – Pile Capacities

Pile Type & Dimensions

Installation Method

Pile Embedment Depth (ft) *

Pile Tip Elevation

(ft. MSL)*

Allowable Capacity in

Compression (tons)

Allowable Capacity in

Tension (tons)

Allowable Lateral

Capacity (tons) **

12” Square Prestressed

Precast Concrete

Driving 30 to 35 -27’ to -34’

MSL

50 8 3.0

* The pile foundation depths noted above are generally anticipated to be uniform throughout the proposed construction areas at a depth of about 35 to 40 feet below existing grades (tip elevation of about -27’ to -34’ MSL).

** Lateral capacity computed for a lateral load applied at free pile butt level, at ground level for a maximum butt deflection of ½ inch. Batter piles would enhance stability.

The noted pile embedment depths and pile tip elevations are required to achieve the allowable capacities. Any reduction in the length of embedment will correspond to a reduction in the allowable design capacity, unless otherwise directed by the geotechnical engineer after the pile-testing program.

USCG Support Center Pasquotank County, North Carolina GET Project No: EC09-278G

In order to minimize the reduction in capacity due to group action of the piles, it is recommended that the piles be installed with a center-to-center spacing of at least 3 feet.

The driven piles should be advanced with an impact hammer to their design tip elevations.

If for some reason during construction, pile “refusal” is encountered before piles reach their design tip elevation, the Geotechnical Engineer should be retained to review field records and reports before assuming the pile can adequately support the design capacity. If the pile driving hammer is not properly matched to the pile type, size, and subsurface conditions, it may reach practical refusal before the pile reaches the design tip elevation, or the required capacity.

The subsurface soils at the project site consist predominately of loose to dense SAND (SP- SM, SM). The natural granular soil materials typically exhibit time-dependent strength characteristics, consequently shaft friction and end bearing support tend to increase from initial installation through a process termed “soil setup”. Essentially, the dynamics of driving piles through these materials will cause excess pore pressures to develop, thereby decreasing driving resistance during initial pile installation. The pile capacities developed during driving are usually much lower than the design values. However, once driving is complete these excess pore pressures dissipate with time (and soil setup occurs) and the bearing capacity of the pile increases.