Report1_Subsurface Investigation Report.pdf

REPORT ON SUBSURFACE INVESTIGATIONS AND

FOUNDATION RECOMMENDATIONS

PROPOSED I-95 DEFENSE ACCESS ROAD RAMP FROM THE

FORT BELVOIR NORTH AREA (FORMERLY ENGINEERING

PROVING GROUNDS), FORT BELVOIR

SPRINGFIELD, VIRGINIA

by

Haley & Aldrich, Inc.

McLean, Virginia for

Parsons Washington, D.C.

File No. 31555-003 1 June 2011 i

1 June 2011 File No. 31555-003

Parsons 100 M Street, SE Suite 1200 Washington, DC 20003-3515

Attention: Stephen C. Walter, P.E.

Subject: Report on Subsurface Investigations and Foundation Recommendations

Proposed I-95 Defense Access Road Ramp from the Fort Belvoir North Area (formerly Engineering Proving Grounds)

Fort Belvoir Springfield, Virginia

Ladies and Gentlemen:

We are pleased to submit herewith our final report entitled “Report on Subsurface Investigations and Foundations Recommendations, Proposed I-95 Defense Access Road Ramp from the Fort Belvoir North Area (formerly Engineering Proving Grounds), Fort Belvoir, Springfield, Virginia.” This report has been prepared in accordance with our Supplemental Agreement 1 dated 24 March 2009 to our original Subconsultant Agreement dated 23 May 2007 and your subsequent authorization.

The purpose of this study was to evaluate the subsurface soil and groundwater conditions at the proposed site and develop recommendations for the design and construction of the foundations for the proposed new ramp into Fort Belvoir North Area from I-95. The main features of the study are summarized in the Executive Summary with the details presented in the text of the report.

It has been a pleasure to work with you on this project. If you have any questions or require additional information, please do not hesitate to contact us.

Sincerely yours, HALEY & ALDRICH, INC.

David A. Schoenwolf, P.E.

Senior Vice President

G:\Projects\31555-Parsons\003-DAR Ramps\100% Design\February 2011 PS&E Report\Complete report\2011-0601-HAI-Formal Report-F.doc

Haley & Aldrich, Inc.

7926 Jones Branch Dr.

Suite 870 McLean, VA 22102

Tel: 703.336.6200 Fax: 703.356.4699

HaleyAldrich.com i

EXECUTIVE SUMMARY

A new ramp is proposed to connect the existing I-95 northbound HOV flyover ramp from the Fort Belvoir North Area (formerly Engineering Proving Grounds (EPG)) at Fort Belvoir in Springfield, Virginia. This report presents the results of our subsurface and laboratory testing program and summarizes the results of our geotechnical engineering evaluations and foundation recommendations for the proposed ramp.

The proposed alignment runs east to west connecting the new South Spine Road within the EPG to the existing northbound I-95 HOV flyover ramp. The alignment crosses through an undeveloped forested region located east of the EPG, through the Capitol Building Supply yard, and over Route 617 (Backlick Road) and the southbound general purpose and HOV lanes of I-95. In general, the existing site grades vary from approximately El. 199 at the eastern end of the alignment within the EPG into the steep creek ravine of Field Lark Branch, where the grades steeply drop to the creek bottom at El. 162, and then increase to El. 221 near the middle of the proposed alignment, and then gradually decrease to El. 217 at the western end near the existing northbound flyover ramp of I-95.

Recent and previous subsurface explorations at the site revealed a man-placed FILL stratum of variable thickness in the building supply yard which extends west to Field Lark Branch. The FILL is underlain by a sequence of laterally varied and interbedded RESIDUAL SOIL, consisting of sand and clay layers overlying DECOMPOSED ROCK and BEDROCK.

West of Field Lark Branch, however, TERRACE DEPOSITS were encountered above RESIDUAL SOIL similar to those described above. Beneath the RESIDUAL SOIL (where penetrated), DECOMPOSED ROCK was encountered. The DECOMPOSED ROCK gradually grades to more competent BEDROCK described as Gneiss and Phyllite.

Phase I construction consists of a roadway embankment, four abutments and two piers. At the western end of the alignment there are two sections of Mechanically Stabilized Earth (MSE) walls separated by a single bridge span crossing over Field Lark Branch. East of this area is a section to be constructed at approximately the existing ground surface, a section supported on the north side by an MSE wall and a sloped embankment on the south, and then another bridge consisting of two abutments and two piers. On the east side of the alignment the roadway connects to an existing pier supported ramp. Phase II involves construction of a north/south trending embankment ramp supported by parallel MSE walls on the east side of I-95 and the removal of one of the Phase I Piers. The bridge spanning the Field Lark Branch is designed to have semi-integral abutments. The west abutment of the I-95 crossing at Backlick Road will have a stub abutment.

Slope stability, settlement, and bearing capacity analyses were performed at critical design sections along the embankment length. Our analyses indicate that over-excavation, ground improvement and pile support is necessary to have embankment settlement within acceptable limits and to maintain slope stability.

Due to the consistency of the near surface soils and in consideration that the new ramp will be structurally connected to the existing northbound I-95 flyover ramp, which is founded on a deep pile foundation, it is recommended that deep foundations be used to support the piers and abutments of the new I-95 overpass.

Deep foundations for these structures should consist of HP12X53 pile sections installed at a minimum center-to center spacing of 2.5 times the pile diameter. Axial capacity analyses indicate that the pile sections should be driven to end-bearing on rock with tip levels at approximately El. 130 to El. 112 to achieve their factored axial capacity of 268 kips. Downdrag forces at the abutment adjacent to Backlick Road will reduce the factored axial capacity to 142 kips/pile.

ii

For the East and West Field Lark Branch Abutments, axial capacity analyses indicate that the pile sections should be driven to end-bearing on rock with tip levels at approximately El. 145 for both abutments to achieve their factored axial capacity of 268 kips.

Subgrade improvement recommendations for the MSE wall between Sta. 601+89+35 to Sta. 602+39 include over-excavation, subgrade compaction, and backfill with compacted select granular backfill to the MSE wall subgrade. Between Sta. 602+39 to Sta. 602+87, at the West Field Lark Branch Abutment, ground improvement recommendations include over-excavation to the top of the decomposed rock stratum and backfill with lean concrete to the MSE wall subgrade. It is recommended that the East Field Lark Branch Abutment be supported on a pile supported concrete pad. It is recommended that the approach embankment be load balanced using Geofoam lightweight fill for slope stability purposes.

Vibro-Concrete Columns (VCC) are recommended to support the embankment between Sta. 605+75 and 609+88.83. The VCCs would be overlain by a GLT Platform. The VCC should have a minimum 18 in.

diameter shaft with a 36-inch diameter crown at the top and 24 inch diameter bulb at the bottom and should extend to at least El. 170.

TABLE OF CONTENTS

Page

EXECUTIVE SUMMARY i LIST OF TABLES v LIST OF FIGURES v

1. INTRODUCTION 1

1.1 General 1

1.2 Purpose and Scope 1

1.3 Elevation Datum/Coordinate System 1

1.4 Limitations 1

2. FIELD AND LABORATORY INVESTIGATIONS 3

2.1 Previous Test Borings 3

2.1.1 Original Bridge Test Borings (1990) 3

2.1.2 Previous Design Borings (2008) 3

2.2 Recent Test Borings 3

2.3 Cone Penetrometer Testing 4

2.4 Laboratory Testing 5

3. SITE AND SUBSURFACE CONDITIONS 6

3.1 Site Conditions 6

3.2 Regional Geology 6

3.4 Groundwater 8

4. GEOTECHNICAL ENGINEERING DESIGN RECOMMENDATIONS 9

4.1 General 9

4.2 Proposed Connector Ramp Construction 9

4.3 Ramp Piers and Abutment Foundation Support Recommendations 10

4.3.1 Pile Axial Capacity and Pile Group Layout 10

4.3.2 Pile Group Lateral Deflections 12

4.3.3 Pile Design Criteria 12

4.4 Approach Embankment Foundation Design Recommendations 13

4.4.1 Embankment Support Options 13

4.4.2 MSE Wall Analysis Methodology 15

4.4.3 MSE Embankment Between Sta. 601+90.85 and Sta. 602+79.67 17

4.4.4 MSE Embankment Between Sta. 603+92.50 and Sta. 605+80 21

4.4.5 MSE Embankment between Sta. 605+80 and Sta. 609 +90 25

4.4.7 Embankment Fill Monitoring 28

4.5 Sand Filter Structure 31

4.6 Utilities 32

4.7 Phase II Construction 32

5. CONSTRUCTION CONSIDERATIONS 33

5.1 General 33

5.2 Temporary Excavation Support 33

TABLE OF CONTENTS

(Continued)

Page iv

5.3 Dewatering 33

5.4 Fill Materials and Placement Procedures 34

5.5 Construction Monitoring 34

TABLES

FIGURES

APPENDIX A - Recent Test Borings APPENDIX B - Previous Test Borings APPENDIX C - Laboratory Test Results APPENDIX D - Drawings Prepared by Parsons APPENDIX E - Engineering Analyses v

LIST OF TABLES

Table No. Title

I Summary of Subsurface Explorations

II Summary of Laboratory Testing

III Summary of External Stability Analyses – Sta. 601+91 (embedded)

IV Summary of External Stability Analyses – Sta. 602+40 (embedded)

V Summary of External Stability Analyses – Sta. 602+51 (embedded)

VI Summary of Slope Stability Analyses for MSE Walls – Sta. 602+79.67

(embedded)

VII Summary of Bearing Resistances – Field Lark Branch West Approach

VIII Summary of External Stability Analyses – Sta. 604+45 (embedded)

IX Summary of Slope Stability Analyses for MSE Walls – Sta. 603+92.50

(embedded)

X Summary of Bearing Resistances – Field Lark Branch East Approach

XI Summary of External Stability Analyses – Sta. 609+82

XII Summary of Settlement Analyses – Sta. 609+82

XIII Summary of Bearing Resistances – Backlick Road West Approach

XIV Settlement Monitoring Guidelines (embedded)

XV Summary of Settlement Monitoring Requirements (embedded)

XVI Summary of Proposed MSE Wall Settlement Monitoring (embedded)

XVII Summary of AASHTO Test Methods (embedded)

LIST OF FIGURES

Figure No. Title

1 Project Locus

2A Exploration Location Plan vi

2B Exploration Location Plan

3 MSE Cross Section

1. INTRODUCTION

1.1 General

This report presents the results of subsurface investigations and provides design recommendations for the proposed construction of a new access ramp to an existing flyover ramp on I-95 from the Engineering Proving Ground (EPG) at Fort Belvoir. As shown on Figure 1, “Project Locus,” the project site is located in Springfield, Virginia, between the new South Spine Road within the EPG site and the northbound HOV flyover ramp on I-95. This new ramp is approximately 1,300 ft long and will cross (from west to east) an undeveloped area east of the EPG and west of the storage yard of Capitol Building Supply, the Capitol Building Supply storage yard, Route 617 (Backlick Road), and the southbound general purpose and HOV lanes of I-95. The Federal Highway Administration (FHWA), in cooperation with the U.S.

Army – Fort Belvoir and the Virginia Department of Transportation (VDOT), is preparing for the construction of the new connector ramp that is proposed in support of the nationwide Base Realignment and Closure (BRAC) program, which calls for relocating 8,500 employees of the National Geospatial- Intelligence Agency to the EPG site by 2011.

The work summarized herein has been coordinated with Parsons of Washington, D.C., Project Engineer.

The Owner is the Federal Highway Administration – Eastern Federal Lands Highway Division.

1.2 Purpose and Scope

The purpose of this study was to evaluate the subsurface conditions in the vicinity of the proposed connector ramp location and to provide geotechnical recommendations for foundation design. The foundation recommendations include considerations for the bridge crossings and support of the proposed roadway embankment. To achieve this objective, Haley & Aldrich, Inc. (Haley & Aldrich) planned and executed a subsurface exploration program consisting of 19 test borings and four Cone Penetrometer Tests (CPT) to define the subsurface soil and groundwater conditions at the site.

To determine the engineering properties of the soils at the site, a laboratory test program was performed in conjunction with the subsurface exploration field program. Engineering analyses were then conducted to determine the appropriate foundation types for the proposed bridge abutments, piers and embankment supported roadway. The results of our field and laboratory investigations and engineering studies have been summarized in this report.

1.3 Elevation Datum/Coordinate System

The elevations on the roadway plans are referenced to the NAVD 1988 Vertical Datum and are in feet.

The project coordinate system is referenced to the Virginia State Plane Coordinate System. Therefore, consistent with the project design, the elevations and boring locations in this report are also referenced to the same vertical datum and coordinate system, respectively.

1.4 Limitations

This Report was prepared pursuant to Supplemental Agreement 1 dated 24 March 2009 between Parsons and Haley & Aldrich, Inc. (Haley & Aldrich). All uses of this Report are subject to, and deemed acceptance of, the conditions and restrictions contained in the Agreement. The observations and conclusions described in this Report are based solely on the Scope of Services provided pursuant to the Agreement. Haley & Aldrich has not performed any additional observations, investigations, studies or other testing not specified in the Agreement. Haley & Aldrich shall not be liable for the existence of any condition the discovery of which would have required the performance of services not authorized under the Agreement.

This Report is prepared for the exclusive use of Parsons and the Federal Highway Administration, Eastern Federal Lands Highway Division in connection with design and construction of the new access ramp to I- 95 from the Engineering Proving Ground (EPG) at Fort Belvoir. There are no intended beneficiaries other than Parsons and the Federal Highway Administration, Eastern Federal Lands Highway Division. Haley & Aldrich shall owe no duty whatsoever to any other person or entity on account of the Agreement or the Report. Use of this Report by any person or entity other than Parsons and the Federal Highway Administration, Eastern Federal Lands Highway Division for any purpose whatsoever is expressly forbidden unless such other person or entity obtains written authorization from Parsons and the Federal Highway Administration, Eastern Federal Lands Highway Division and from Haley & Aldrich. Use of this Report by such other person or entity without the written authorization of Parsons and the Federal Highway Administration, Eastern Federal Lands Highway Division and Haley & Aldrich shall be at such other person's or entity's sole risk, and shall be without legal exposure or liability to Haley & Aldrich.

Use of this Report by any person or entity, including by Parsons and the Federal Highway Administration, Eastern Federal Lands Highway Division, for a purpose other than for design and construction of the new access ramp to I-95 from the Engineering Proving Ground (EPG) at Fort Belvoir is expressly prohibited unless such person or entity obtains written authorization from Haley & Aldrich indicating that the Report is adequate for such other use. Use of this Report by any person or entity for such other purpose without written authorization by Haley & Aldrich shall be at such person's or entity's sole risk and shall be without legal exposure or liability to Haley & Aldrich.

This report reflects site conditions observed and described by records available to Haley & Aldrich as of the date of report preparation. The passage of time may result in significant changes in site conditions, technology, or economic conditions which could alter the findings and/or recommendations of the report.

Accordingly, Client and any other party to whom the report is provided recognize and agree that Haley & Aldrich shall bear no liability for deviations from observed conditions or available records after the time of report preparation.

Use of this Report by any person or entity in violation of the restrictions expressed in this Report shall be deemed and accepted by the user as conclusive evidence that such use and the reliance placed on this Report, or any portions thereof, is unreasonable, and that the user accepts full and exclusive responsibility and liability for any losses, damages or other liability which may result.

Haley & Aldrich, Inc. performed geotechnical engineering services for this project. The assessment of oil or hazardous materials at the site was excluded from our scope of work. Investigating the presence of mold or other biological pollutants at the site, the characterization of excavated soil or groundwater which will be generated as a result of the planned construction activity, or assessment of the impact that contamination or pollutants could have on the proposed construction, or the development of criteria or procedures to minimize the growth of mold or other biological pollutants in or near any structure was also excluded from our scope of work.

2. FIELD AND LABORATORY INVESTIGATIONS

2.1 Previous Test Borings

2.1.1 Original Bridge Test Borings (1990)

In 1990, six test borings were drilled as shown on the contract drawings by Howard Needles Tammen & Bergendorf (HNTB) of Alexandria, Virginia, for design of the existing flyover ramp over I-95. Copies of the logs for these borings were provided to Haley & Aldrich by Parsons. The locations of these borings are shown on a boring location plan in Appendix B along with copies of the boring logs. Those test borings that are closest to the proposed access ramp are shown on Figure 2A.

As indicated on the logs, the borings were drilled to depths of 71.5 to 81.5 ft below ground surface.

2.1.2 Previous Design Borings (2008)

In October of 2008, 11 test borings (designated as 95RP-01 to 95RP-08 and HOV-01 to HOV-3) were drilled by Froehling & Robertson, Inc., for the design for the proposed South Loop Road HOV and I-95 Ramps within Fort Belvoir Engineering Proving Ground. Copies of the logs and boring location plan for these borings were provided to Haley & Aldrich by Parsons, and are included in Appendix B, Previous Test Boring Logs. Those test borings that are located closest to the proposed access ramp are shown on Figure 2B.

As indicated on the test boring logs, all the borings were drilled to a depth of approximately 20 ft below existing ground surface.

2.2 Recent Test Borings

Haley & Aldrich conducted a subsurface exploration program at the project site during the periods 1 to 6 April 2009, 22 to 29 April 2009, and 21 to 23 December 2009, to obtain subsurface soil and groundwater information for engineering evaluations. The program consisted of drilling 19 test borings, designated 09BH-01 through 09BH-15, including 09BH-5A, 09BH-6A, 09BH-8A, 09BH-11A, 09BH-13A. Test boring 09BH-12 was eliminated from the proposed exploration program due to site accessibility issues.

The locations of the test borings are shown on Figures 2A and 2B, “Exploration Location Plan.” Borings 09BH-01 through 09BH-05 are located within the VDOT Right-of-Way of I-95 and Backlick Road;

borings 09BH-06 through 09BH-11 and 09BH-15 are located within the lot currently occupied by Capitol Building Supply; and borings 09BH-13 and 09BH-14 are located in the privately owned property located between the EPG and Capitol Building Supply’s lot. The as-drilled locations were determined in the field by Haley & Aldrich using a Trimble GeoXT GPS unit. The ground surface elevations of the borings were determined by Haley & Aldrich by interpolating between ground surface elevation contour lines shown on a topographic plan prepared by Parsons. The locations and elevations of the explorations should be considered accurate only to the degree implied by the method used.

Fifteen (15) of the borings (Borings 09BH-01 through 09BH-04 and 09BH-06 through 09BH-15) were drilled using a truck-mounted CME-55 drill rig. The remaining four test borings (09BH-05, 09BH-13, 09BH-13A, 09BH-14) were drilled using a track mounted CME-45 ATV drill rig. All of the test borings were drilled by GeoServices Corporation of Forestville, Maryland. A Haley & Aldrich representative was present in the field to monitor the borings and log the soil conditions encountered.

The test borings were drilled to depths ranging from 18.6 ft to 100.3 ft below ground surface; a summary of the subsurface investigations is shown in Table I with the logs of recent test borings in Appendix A.

All test borings, except 09BH-05A and 09BH-08A, were advanced using 3-1/4-in. inside diameter (I.D.)

hollow stem augers. Borings 09BH-05A and 09BH-08A were advanced using 4-1/4-in. I.D. hollow-stem augers. A summary of the soil sampling procedures is provided below.

Split-spoon samples were typically obtained at approximately 2.5-ft-depth intervals for the upper

10 ft of the borings, and at 5 ft depth intervals thereafter. The standard penetration resistance was determined at each sample level by counting the number of blows required to drive a standard split-spoon sampler (1-3/8-I.D.) a distance of 18 in. into undisturbed soil under the impact of a 140 lb hammer free-falling 30 in. The number of blows required to advance the sampler was recorded for each 6-in. interval. The standard penetration resistance N-value is determined by summing the number of blows required to advance the sampler the last 12 in. of the 18-in.

sampling range. Note that borings 09BH-5A, 09BH-6A, 09BH-8A and 09BH-11A were auger-drilled without sampling to 20.5, 80, 21.5 and 64.5ft below the ground surface, respectively. It should be noted that the N-values shown on the test boring logs were not corrected for energy and rod length.

A Type “U” sampler (2-3/4-in. I.D.; 3 -1/4-in. O.D.) was used to obtain large diameter samples of the Residual soils at selected depths in borings 09BH-05A and 09BH-08A. The penetration resistance was determined at each sample level by counting the number of blows required to drive the sampler a distance of 18 in. into undisturbed soil under the impact of a 300-lb hammer free-falling 30 in. The number of blows required to advance the sampler was recorded for each 6-in.

interval.

Rock coring was performed in test borings 09BH-6A, 09BH-11A and 09BH-13A. A 5-ft length of NX core was obtained in each of these borings.

Borings 09BH-05A and 09BH-08A were drilled specifically for the retrieval of soil samples using a Type “U” sampler. This sampler allows for the retrieval of relatively undisturbed samples of coarse grained soils for direct shear testing in the laboratory. In both of these locations, the borings were advanced to the target depth without sampling.

Samples recovered from the borings were taken to Haley & Aldrich’s office for further evaluation. Some of these samples were subsequently selected for laboratory testing.

2.3 Cone Penetrometer Testing

On 21 December 2009, In-Situ Soil Testing, L.C. performed two cone penetrometer tests at the site. Two Cone Penetration Tests (CPT) were performed, labeled 09CP-1 and 09CP-2; two attempts were made for 09CP-1 before achieving a suitable depth. The first two attempts met with refusal at depths of 26.7 and

4.3 ft. Finally, a third attempt was successful and a depth of 30 ft was achieved. 09CP-2 penetrated to a depth of 62.8 ft. The locations of the CPTs are shown on Figures 2A and 2B. The results of the CPT tests are included in Appendix A.

2.4 Laboratory Testing

A laboratory soil testing program was performed to determine soil classification and for correlation of engineering properties. Laboratory tests were performed on selected samples of soils recovered from borings. Testing consisted of geotechnical index tests including moisture content, Atterberg Limits, Grain Size Analyses, a California Bearing Ratio test, and a modified Proctor compaction test. Soil strength testing performed included direct shear tests. Corrosivity testing included pH test testing, soil resistivity, Magnesium content, Chloride content, Ammonia Nitrogen content, percent Sulfur, redox potential versus H2, percent solids, Sulfate content, and neutral extraction Sulfide. The geotechnical laboratory tests were performed in general conformance with applicable ASTM procedures. Corrosivity testing was performed in accordance with applicable EPA testing procedures. Results of laboratory testing are included in Appendix C. In addition, a summary of the test results is provided in Table II.

3. SITE AND SUBSURFACE CONDITIONS

3.1 Site Conditions

The proposed new flyover ramp will extend between the new South Spine Road within the EPG site and the existing northbound HOV flyover ramp on I-95. It will be structurally connected to the northbound HOV flyover ramp. The new ramp is approximately 1,300 ft long and will cross (from west to east) an area of undeveloped forested land located east of the EPG and west of the supply yard of Capitol Building Supply, the Capitol Building Supply yard, Route 617 (Backlick Road), and the southbound general purpose and HOV lanes of I-95 in Springfield, Virginia, as shown in Figures 2A and 2B.

Topographically the existing ground surface along the proposed alignment is relatively flat-lying and level, except in the area of undeveloped forested land where the alignment crosses over Field Lark Branch. The ground surface level gradually undulates between El. 198 and 201 from the west end of the alignment at Sta. 601+57.19 to the western edge of the Field Lark Branch ravine at Sta. 601+77. From Sta. 601+77 to Sta. 603+35 the ground surface slopes downward toward the Field Lark Branch. The Field Lark Branch bottoms out at El. 162, and then steeply increases in grade to El. 219 at Sta. 604+75. From the eastern edge of the ravine at Sta. 604+75 to the east end of the alignment at Sta. 613+22.84, the ground surface level generally slopes downward from El. 221 to 217.

3.2 Regional Geology

The site lies on the geologic Fall Line separating the Coastal Plain alluvial deposits from the Piedmont Geologic Province. Geologic references indicate that the site is underlain by Terrace Deposits and Residual Soils derived from weathering of the parent bedrock which includes metamorphic rocks such as Phyllite, Gneiss and Schist. Generally, the test borings at the site indicate a thin layer of coastal plain soils above residual deposits. The Coastal plain deposits at the site are comprised of the Terrace Deposits above the Residual Soils consisting primarily of sand with varying amounts of silt and clay.

Terrace Deposits are alluvial deposits that are Pliocene in age and are described as gray to yellow-brown, thick to thin-bedded, well-rounded cobble and pebble gravel interbedded with quartzose sand, silt and clay. This stratum occurs as widespread, sheet-like fluvial deposits about 30 ft thick forming a nearly level upland terrace. Saprolite overlies the Piedmont crystalline rocks west of the Fall Line and overlaps a wedge of Cretaceous Potomac Formation to the southeast.

The Residual Soils were encountered below the Terrace Deposits on the west side of Field Lark Branch and below a thick layer of FILL soils on the east side of Field Lark Branch. These deposits are described as varicolored sand and silt with interbedded layers of lean clay. Below the residual soils is decomposed rock and then bedrock. The bedrock at the site consists of Phyllite, Gneiss and Schists of the Piedmont Geologic Province.

3.3 Subsurface Conditions

Descriptions of the soil conditions encountered during the subsurface exploration program conducted at the site are provided below in order of increasing depth below ground surface. Refer to the test boring logs in Appendix A for specific descriptions of soil samples obtained from the borings. The boring logs and related information depict subsurface conditions only at the specific locations and at the particular time designated on the logs. Soil conditions at other locations may differ from conditions occurring at the boring locations. In addition, the passage of time may result in a change in the soil conditions at these boring locations.

FILL – Below the ground surface, there is a stratum of man-placed FILL primarily described as red-brown, brown, orange, and gray loose to very dense silty SAND (SM), and soft to hard sandy CLAY (CL). Wood, rootlets, gravel, asphalt and organics were observed in the soil samples. This stratum was encountered in 11 of the 13 test borings performed. It was not encountered in the test borings drilled west of Field Lark Branch (09BH-13, 09BH-13A and 09BH-14). Where encountered, it was fully penetrated by all borings. Within the VDOT right-of-way, the FILL thickness ranged in depth from 2.5 to 7.5 ft. In the Capitol Building Supply yard, the FILL thickness ranged from 27 to 57 ft thick.

It should be noted that in boring 09BH-04, which was drilled in the center median of the VDOT right-of-way, at the ground surface, a 3-in.-thick asphalt layer over a 9-in.-thick Portland cement concrete pavement was encountered. Below the shoulder-roadway surface at this location, there is a BASE COURSE consisting of medium dense well-graded fine to coarse SAND with some gravel. At this location the BASE COURSE was 12 in. thick.

TERRACE DEPOSITS - In borings 09BH-13, 09BH-13A and 09BH-14, TERRACE DEPOSITS exist below a 0.3 ft thick layer of topsoil. The TERRACE DEPOSITS are primarily described as orange, loose to medium dense clayey SAND and clayey SAND with gravel. This layer of soil ranged in thickness from 3.7 to 5.7 ft.

RESIDUAL SOIL – Below the FILL and TERRACE DEPOSIT, there is a stratum of natural soil primarily described as orange-white, gray and tan loose to very dense silty SAND (SM), and medium stiff to hard sandy CLAY (CL). Many of the SAND samples from this stratum were micaceous in nature and some samples were observed to have relict structure of the underlying rock, which is indicative of saprolite. This stratum was encountered in all borings, except boring 09BH-11. When encountered, it was only fully penetrated by test borings 09BH-01, 09BH-02, 09BH-03, 09BH-05, 09BH-06, 09BH-6A, 09BH-13, 09BH-13A, and 09BH-14. Layers of stiff to hard CLAY were encountered in the residual stratum in seven of the 13 borings. The CLAY layers were encountered between approximate El.182 and 178 in borings 09BH-06 and 09BH-07;

between El. 179 and El. 174 in borings 09BH-04 and 09BH-05; between El. 170 and El. 163 in boring 09BH-01; between El. 165 and El. 154 in borings 09BH-01, 09BH-02, 09BH-03, and 09BH-04; and between El. 135 and El. 125.5 in borings 09BH-03 and 09BH-04.

DECOMPOSED ROCK – Below the FILL in boring 09-BH-11 and the RESIDUAL soil stratum in the borings where the RESIDUAL stratum was fully penetrated, there is a stratum of decomposed / highly weathered rock (HWR) recovered as soil and primarily described as gray-white, white-tan, and blue green silty SAND (SM) and sandy SILT (ML). This stratum was encountered in borings 09BH-01, 09BH-02, 09BH-03, 09BH-05, 09BH-06, 09BH-6A, 09BH-13, 09BH-13A, 09BH-14 and 09BH-15.

BEDROCK – A 5-ft-long rock core was obtained in borings 09BH-6A, 09BH-11A and

09BH-13A. The rock underlying the site is described as light gray GNEISS, soft to very hard, slightly to highly weathered, medium grained with low to moderate angle joint discontinuities. In the bottom of the rock core run in boring 09BH-06A a 1.6 ft length of dark brown to black PHYLLITE, soft, moderately weathered with moderately dipping discontinuities was recovered.

The percent recovery ranged from 98 to 100 percent with the RQDs ranging between 37 to 92 percent.

3.4 Groundwater

Groundwater was encountered in all of the original borings drilled in 1990, varying from El. 170.8 to El. 199.7 ft. Groundwater was encountered in three (3) of the eleven (11) borings drilled by Froehling & Robertson, Inc., in 2008, and varied between El. 168 and El. 180.3.

Groundwater was encountered during drilling of the recent borings 09BH-01, 09BH-02, 09BH-03, 09BH- 05, 09BH-06, 09BH-6A, 09BH-08, 09BH-11, 09BH-11A, 09BH-13 and 09BH-13A. The depth to groundwater was observed to range from 11.4 to 70.5 ft below the ground surface, corresponding to approximately El. 161.6 to El. 169.5. However, at boring 09BH-05 the groundwater was encountered at a depth of 70.5 ft below ground surface (El. 146.9), and at a depth of 69.9 ft below the ground surface in boring 09BH-06 (El.145). In test boring 09BH-11 the groundwater was encountered at 66.8 ft below the ground surface (El. 147.7).

Groundwater level readings were obtained in borings 09BH-06A, 09BH-11A and 09BH-13A 24 hours after the completion of the test borings. These readings indicate groundwater levels ranging between El.

164.1 and El. 154.8 in December of 2009.

It should be noted that water level readings have been made in drill holes at times and under conditions stated in the boring logs. The above discussed observations were made during drilling of the test borings.

However, it must be noted that fluctuations in the level of the groundwater may occur due to the variations in season, rainfall, temperature, and other factors not evident at the time measurements were made and reported herein.

4. GEOTECHNICAL ENGINEERING DESIGN RECOMMENDATIONS

4.1 General

Recommendations presented herein are based on the proposed ramp layout and anticipated structural loadings and configurations provided by Parsons at the time of this writing. Any future project revisions that affect the geotechnical design should be reviewed by Haley & Aldrich for continued applicability.

The analyses and recommendations presented herein have been performed in accordance with the 2008 Interim Revisions to the AASHTO LRFD Bridge Design Specifications, Customary U.S. Units, 4th Edition, 2007. The Vibro-Concrete Column/GLT Platform design was performed in accordance with British Standard Code of Practice for Strengthened/Reinforced Soils and Other Fills (BS 8006:1995).

4.2 Proposed Connector Ramp Construction

The proposed connector ramp will be approximately 1,300 ft long and 30 ft wide (face-to-face of curbs).

The western project limits are at Sta. 601+49 and the eastern limits at Sta. 613+22.63. The project includes bridges, at-grade roadway, and embankments fully or partially supported by MSE walls. The MSE walls range in height from approximately 8 to 40 ft (extending up to 30 ft above the existing ground surface).

From Sta. 601+49 to Sta. 601+89.35 the ramp will be supported by a low embankment with side slopes down to existing grade.

From Sta. 601+89.35 to Sta. 602+79.67 the ramp will be supported by two parallel MSE walls and a north/south orientated MSE abutment wall (MSE Walls 1, 2 and 3). The northern-most wall (Wall 1) is taller than the southern wall (Wall 2) because the embankment traverses the side of a hill. (Refer to Appendix D Sheet D06). MSE Wall 3 starts and ends at Sta. 602+50.85, extending around three sides of the embankment in a “U” shape.

A single span bridge structure (Structure No. B603) extends between Sta. 602+71.00 (measured from the back wall of the abutment) and Sta. 604+01.17, crossing over the Field Lark Branch. This bridge will be supported on semi-integral abutments within the MSE supported embankments. (Refer to Appendix D Sheet R-03).

On the east side of Field Lark Branch, the bridge abutment and approach is supported by parallel MSE walls extending from Sta. 603+92.50 to 604+73.82 (MSE Walls 4 and 5). As the embankment extends up the steep side slope of Field Lark Branch, the MSE walls get shorter until the ramp is at approximately existing grade (Refer to Appendix D Sheet D07). MSE Wall 6 starts and ends at Sta. 604+21.32, extending around three sides of the embankment in a “U” shape.

From Sta. 604+73.82 to Sta. 605+99.35, the ramp will be constructed at approximately existing grade (Refer to Appendix D Sheet D07).

Between Sta. 605+99.35 and Sta. 609+23.53, the ramp will be an earthen embankment supported on the north side by an MSE wall (Wall 7) and on the south by 2H:1V (horizontal to vertical) side slopes extending down to existing grade. On the north side of the embankment Wall 7 continues from Sta.

609+23.53 to Sta. 609+59.35. On the south side of the embankment Wall 8 extends from Sta. 609+23.53 to Sta. 609+63.35. Wall 9 is a “U” shaped wall that wraps around the abutment (Abutment A for the bridge that crosses the I-95 right-of-way). It begins on the north side at Sta. 609+59.35 and continues around to the south side, terminating at Sta. 609+63.35. Abutment A is a stub abutment located within the MSE supported embankment that will be located just west of Backlick Road. This abutment is also referred to in this report as the Backlick Road abutment (Refer to Appendix D Sheets D07, D08, and D09).

Between Sta. 609+81.42 and Sta. 613+12.10, a three span bridge structure (Structure No. B602) will cross the I-95 corridor, including Backlick Road and I-95. At Sta. 613+12.10 the new connector ramp will connect to the existing I-95 northbound HOV flyover ramp. The back wall of the Backlick Road Abutment is at Sta. 609+81.42. Pier 1 is at Sta. 611+39.17, Abutment B is at Sta. 612+89.40, and Pier 2 is at Sta. 613+09.81. Abutment B does not support a differential soil loading during its Phase I service life, but will support a differential soil loading when Phase II is constructed (Refer to Appendix D Sheet R- 102).

In a future phase of the project (Phase II), Pier 2 and a pier supporting the existing ramp structure will be removed and Abutment B and a parallel MSE wall will support a future north/south trending ramp supported by MSE walls. (Refer to Appendix D Sheets R-104 and R-127D).

Parsons provided axial and lateral pile loading information for the Service, Strength and Extreme Event limit states for structures associated with the I-95 Crossing (Abutment A at Backlick Road), Abutment B, Pier 1 and Pier 2 and for the Field Lark Branch Crossing Abutments. The loading information provided was considered in developing pile support recommendations and was used as input data for lateral deflection and moment capacity analyses. Engineering analyses are included in Appendix E.

4.3 Ramp Piers and Abutment Foundation Support Recommendations

The following pile group layouts were provided by Parsons for the abutments and piers.

Abutment A at Backlick Road – 2x6 pile group (total of 12 piles);

Pier 1 – two-4x4 pile groups (total of 32 piles);

Abutment B – 3x21 pile group (total of 63 piles);

Pier 2 – four-2x2 pile groups (total of 16 piles);

Field Lark Branch Crossing Abutments – one 11-pile group (one row of 5 piles, one row of 6 piles) for each abutment;

Specific pile design recommendations are discussed below.

4.3.1 Pile Axial Capacity and Pile Group Layout

I-95 Right-of-Way

The density and compressibility of the near surface soils are such that founding the bridge structure that traverses I-95 and Backlick Road on spread footings bearing at relatively shallow depths below the ground surface is not technically feasible. The settlement of piers founded on spread footing foundations would likely be greater than 1 in. In addition, as previously discussed, since the new ramp will be connected to an existing flyover structure that is founded on pile foundations, the differential settlement between the new ramp and existing flyover would be significant. Therefore, it was concluded that the bridge piers and abutments of this new structure should be supported on deep foundations in order to reduce the potential for significant differential settlements.

In order to reduce the potential construction-related effects on the existing flyover structure, and to support the design loads provided by Parsons, it is recommended that the ramp abutments and piers be supported on deep foundations consisting of end-bearing HP12x53 steel H-piles driven to refusal on or in the bedrock stratum.

Pile capacity computations were performed following AASHTO-LRFD using subsurface information from the field exploration program. The axial factored capacity of an H-pile end-bearing in rock is controlled by the structural capacity of the pile section. For an HP12x53 pile section (considering 1/16” corrosion allowance), Grade 50 steel, and using a resistance factor of 0.50, the factored axial capacity is 268 kips.

Piles should be driven to refusal (defined as 20 blows for less than 1 in. of penetration) into DECOMPOSED ROCK or BEDROCK. Where dynamic testing is performed during driving, the pile should be driven to a CAPWAP nominal capacity of 596 kips (end-of-driving or beginning-of-restrike).

The west bridge abutment of the I-95 crossing will be designed as an ordinary stub abutment.

Therefore, the west approach to the I-95 crossing will be designed as an embankment supported with MSE walls. Due to the 30 ft. thick deposit of FILL soil underlying the embankment, it is recommended at the west approach embankment of the I-95 Crossing be supported on Vibro- Concrete Column (VCC) elements as described in subsequent sections of this report. The VCC elements are designed as end bearing elements and are assumed to transfer the embankment load to soils beneath the tips of the elements. Based on the expected subsurface conditions at this location, the soils at depth beneath the VCC elements are expected to experience settlement in response to the embankment loads. In addition, the VCC elements themselves are expected to experience some amount of elastic compression in response to the embankment loads. The combination of settlement of the bearing soils beneath the VCC elements and elastic compression of the VCC elements is expected to impart frictional downdrag loads on the piles supporting the Backlick Road abutment (Abutment A). The factored downdrag load on foundation piles at Abutment A is estimated to be 126 kips/pile assuming that the portion of the piles extending above the Load Transfer Platform is encased in a friction breaking sleeve (a corrugated steel shell can be used as the sleeve). After MSE wall construction, the annular space between the sleeve and the steel H-pile should be backfilled with sand. Therefore, the net factored axial capacity of the piles in Abutment A is 142 kips/pile (268 kips -126 kips).

Field Lark Branch Crossing

The density and compressibility of the FILL, TERRACE, and RESIDUAL soil deposits that exist in the vicinity of the Field Lark Branch crossing are such that founding this bridge structure on spread footings bearing at relatively shallow depths below the ground surface is not technically feasible. The settlement of piers founded on spread footing foundations would likely be greater than 1 in.

In order to reduce the potential construction-related settlements and to support the design loads provided by Parsons, it is recommended that the bridge abutments be supported on deep foundations consisting of end-bearing HP12x53 steel H-piles driven to refusal on or in the rock stratum.

Pile capacity computations were performed following AASHTO-LRFD using subsurface information from the field exploration program. The axial factored capacity of an H-pile end-bearing in rock is controlled by the structural capacity of the pile section. For an HP12x53 pile section (considering 1/16” corrosion allowance), Grade 50 steel, and using a resistance factor of 0.50, the factored axial capacity is 268 kips.

Piles should be driven to refusal (defined as 20 blows for less than 1 in. of penetration) into DECOMPOSED ROCK or BEDROCK. Where dynamic testing is performed during driving, the pile should be driven to a CAPWAP nominal capacity of 596 kips (end-of-driving or beginning-of-restrike).

The Field Lark Branch crossing will be designed as a semi-integral abutment bridge with abutment support piles sleeved through the embankment fill soils (a corrugated steel shell can be used as the sleeve). After construction of the MSE wall supported embankment, sand is placed in the annulus between the steel sleeve and the H-pile. Based on the isolating effect of the sleeves, the expected bearing conditions beneath the embankment fill soils and the embankment support recommendations contained herein, the abutment support piles at the Field Lark Branch crossing are not expected to be subject to downdrag loads.

A portion of the approach embankment at the Field Lark Branch east abutment is to be constructed on a pile supported reinforced concrete pad (refer to Drawing D07 in Appendix D).

It is recommended that these piles also be driven to refusal in DECOMPOSED ROCK or BEDROCK as described above. As a result the soils beneath the concrete pad will be subject to minimal load increase and are not expected to experience significant settlement or impart frictional downdrag forces on the piles supporting the reinforced concrete pad.

4.3.2 Pile Group Lateral Deflections

The lateral load behavior of pile groups was evaluated using the software program FB-MultiPier.

The pile cap was assumed to be rigid and the pile-to-cap connection was assumed to be fixed.

Service loads provided by Parsons were applied to the pile cap and corresponding deflections were calculated. The influence of MSE wall boundaries on the lateral capacity of the piles for the Field Lark Branch and Backlick Road abutments was considered using P-multipliers. For Pier 1, Pier 2, and Abutment B pile group interaction was considered using P-multipliers.

The calculated lateral deflections at the cap level are shown below:

Abutment A at Backlick Road – transverse: 0.24 in.; longitudinal: 0.05 in.

Pier 1 – transverse: < 0.05 in.; longitudinal: < 0.05 in.

Abutment B – transverse: < 0.05 in.; longitudinal: < 0.05 in.

Pier 2 – transverse: < 0.05 in.; longitudinal: 0.18 in.

Field Lark Branch Crossing Abutments – transverse: 0.66 in.; longitudinal: 0.49 in.

It is our understanding that the loads provided by Parsons for Abutment B above are for Phase I.

4.3.3 Pile Design Criteria

The estimated pile tip bearing elevations are as follows:

Abutment A at Backlick Road – 2x6 pile group (total of 12 piles); El. 130 Pier 1 – two-4x4 pile groups (total of 32 piles); El. 112 Abutment B – 3x21 pile group (total of 63 piles); El. 123 Pier 2 – four-2x2 pile groups (total of 16 piles); El. 123

Field Lark Branch Crossing Abutments – one 11-pile group (one row of 5 piles, one row of 6 piles) for each abutment; El. 145 for both abutments

Pile design should also take into consideration the following:

The minimum center-to-center spacing of the piles should be no less than 30 in. or 2.5 pile diameters.

The distance from the side of any pile to the nearest edge of the pile cap should not be less than 9 in. The tops of the piles should be embedded into the pile cap at least 12 in.

after all damaged sections of the pile have been removed. If the piles are attached to the pile cap with reinforcing steel, then the pile embedment can be reduced to 6 in.

The steel H-piles should be fitted with steel driving shoes to reduce the potential for damage to the pile due to hard driving.

For the end-bearing H-piles, we recommend that dynamic testing with signal matching analysis be performed in order to confirm the axial capacity. For the two Field Lark Branch abutments, we recommend performing dynamic tests with signal matching on at least three (3) piles total. For Abutments A and B and Piers 1 and 2 for the I-95 crossing, we recommend performing dynamic tests with signal matching on at least four (4) piles total. For the Field Lark Branch and I-95 crossings, we recommend that the dynamic testing be distributed in such a way that at least one pile is tested at each pier and abutment location.

4.4 Approach Embankment Foundation Design Recommendations

4.4.1 Embankment Support Options

As discussed above, the proposed ramp will be supported on new embankments fully or partially supported by MSE walls within the limits of the following stations:

Sta. 601+89.35 to Sta. 602+79.67 Sta. 603+92.5 to Sta. 604+73.82 Sta. 605+99.35 to Sta. 609+88.83

From Sta. 601+89.35 to Sta. 602+79.67, the embankment is underlain by loose to medium dense clayey sand of the TERRACE DEPOSITS overlying RESIDUAL SOIL consisting of loose to dense silty sand and medium stiff to hard clay.

Between Sta. 603+92.5 and Sta. 609+88.83, the new embankment segments are underlain by man-placed FILL of varying thicknesses (between 27 and 57 ft thick). The FILL generally consists of loose to very dense silty sand and soft to hard sandy clay intermixed with varying amounts of construction debris.

The consistency/density of the natural soils between Sta. 601+89.35 and Sta. 602+79.67 is such that these soils cannot support the proposed embankment and MSE walls without significant post-construction settlement and/or stability concerns.

Between Sta. 603+92.5 and Sta. 609+88.83, the FILL appears to have been placed in an uncontrolled manner and includes deleterious material. Without any documentation to the contrary, it must be assumed the FILL was placed with little to no compaction. There is a significant risk to the future satisfactory performance of the MSE wall supported embankments if founded directly on this uncontrolled FILL soil. Ground improvement of the existing FILL or structural support of the proposed embankments is, therefore, recommended in some areas to reduce the potential for post-construction settlement and enhance the performance of the bearing soils that support the ramp embankment and MSE walls. Two ground improvement and one structural support schemes were considered as described below.

Option 1 – Deep Dynamic Compaction

Deep Dynamic Compaction (DDC) involves the repeated dropping of a heavy weight (the tamper, which weighs on the order of 6 to 20 tons) on the surface of the FILL using a crawler crane.

Tampers are typically dropped from heights of 40 to 80 ft. The repeated application of the high energy impact causes deep compaction in the soil mass. The impact energy produced by dropping the tamper is a function of the tamper weight and the height of the fall.