C8006_Site_Inspection_Report_-_Collins_Oct_2013.pdf

UNITED STATES COAST GUARD

CIVIL ENGINEERING UNIT, RM 2179

1240 EAST NINTH STREET

CLEVELAND, OH 44199-2060

Coast Guard Contract No. HSCG83-13-J-PCR121

SITE INSPECTION AND PRELIMINARY DESIGN

FINAL REPORT

ENGINEERING SERVICES FOR PRELIMINARY DESIGN FOR

BULKHEAD REPAIRS

AT

U.S. COAST GUARD CUTTER DILIGENCE MOORINGS

P/N 5200971

WILMINGTON, NC

OCTOBER 2013

PREPARED BY:

10201 FAIRFAX BLVD. SUITE 530

FAIRFAX, VA 22030

TEL: 703.691.4841

SITE INSPECTION AND PRELIMINARY DESIGN FOR BULKHEAD REPAIRS

AT

U.S. COAST GUARD CUTTER DILIGENCE MOORINGS

ON

CAPE FEAR RIVER

WILMINGTON, NORTH CAROLINA

SITE INSPECTION AND PRELIMINARY DESIGN

FINAL REPORT

OCTOBER 2013

PREPARED FOR:

UNITED STATES COAST GUARD

CIVIL ENGINEERING UNIT CLEVELAND

PREPARED BY:

COLLINS ENGINEERS, INC.

10201 FAIRFAX BLVD., SUITE 530

FAIRFAX, VA 22030

(703) 691-4841

COLLINS PROJECT 35-07321

i

CONTENTS

1. Introduction

2. Executive Summary

3. Purpose and Scope of Report

4. Description of Waterfront Facilities

4.1. Sheet Pile Bulkhead

4.2. Wharf

5. Inspection Methodology

5.1. Three-Dimensional Acoustical Scan of the Bulkhead

5.2. Topographic Survey and Site Utility Investigation

5.3. Inspection Pit Assessment of the Bulkhead

5.4. Pulse-Echo Testing of Tie Rods

5.5. Geotechnical Observations of the Excavation Pits

5.6. Tracer-Dye Inspection to Identify Causes of Water Flow into Inspection Pits

6. Record of Conditions Observed During Field Work

6.1. Acoustic Scan Observations and Analysis

6.2. Bulkhead Conditions

6.2.1. Inspection Pit 1 – Non-Operational Area

6.2.2. Inspection Pit 2 – Non-Operational Area

6.2.3. Inspection Pit 3 and 4 – Non-Operational Area

6.2.4. Inspection Pit 5 –Operational Area

6.2.5. Inspection Pit 6A –Operational Area

6.2.6. Inspection Pit 7A –Operational Area

6.2.7. Inspection Pit 8A –Operational Area

6.3. Anchor Wall Conditions

6.4. Tie Rod Testing Results

6.5. Geotechnical Observations in the Inspection Pits

7. Preliminary Design Alternatives for Bulkhead Repairs

7.1. Introduction

ii

7.2. Concept 1: Welding Steel Cover Plates and Replacing Wale Bolts

7.2.1. Concept Summary

7.2.2. Physical Operational Considerations

7.2.3. Environmental Permitting Considerations

7.2.4. Constructability and Cost Considerations

7.3. Concept 2: Bonding FRP Sheets and Replacing Wale Bolts

7.3.1. Concept Summary

7.3.2. Physical and Operational Considerations

7.3.3. Environmental Considerations

7.3.4. Constructability and Cost Considerations

7.4. Concept 3: Casting a Concrete Facing and Replacing Wale Bolts

7.4.1. Concept Summary

7.4.2. Operational Considerations

7.4.3. Environmental Considerations

7.4.4. Constructability and Cost Considerations

7.5. Concept 4: Driving New Sheet Piles, Drilling New Tie Rods, and Installing New Wales

7.5.1. Concept Summary

7.5.2. Operational Considerations

7.5.3. Environmental Considerations

7.5.4. Constructability and Cost Considerations

7.6. Concept A: Driving New Piles and Connecting to the Existing Anchor Wall

7.6.1. Concept Summary

7.6.2. Physical and Operational Considerations

7.6.3. Environmental Considerations

7.6.4. Constructability and Cost Considerations

7.7. Concept B: Driving New Sheet Piles in Front of the Existing Anchor Wall (Operational Area Only)

7.7.1. Concept Summary

7.7.2. Physical and Operational Considerations

7.7.3. Environmental Considerations

iii

7.7.4. Constructability and Cost Considerations

7.8. Combined Preliminary Design Alternative Estimated Cost and Construction Duration 22

7.9. Concepts Considered and Not Developed

8. RECOMMENDATION

Appendix A – Acoustical Imaging Drawings

Appendix B – Emergency Site Inspection Protocol

Appendix C – Inspection Measurements and Observations

Appendix D – Photographs

Photograph 1 View of Inspection Pit 2, Looking North from Station 6+40. This Photograph Shows the Typical Inspection Pit in the Non-Operational Area.

Photograph 2 View of the Wale to Sheet Pile Wall Connection at Station 6+34. This Photograph Shows the Typical Condition in the Non-Operational Area.

Photograph 3 View of the Tie Back Connection to the Wale at Station 5+30. This Photograph Shows the Typical Condition in the Non-Operational Area.

Photograph 4 View of the Concrete Cap at Station 6+22. This Photograph Shows the Typical Cap Condition at the Site.

Photograph 5 View of the Missing Plate-Washers at Station 7+05. The Wale and Sheet Pile Wall were Not Connected at this Location.

Photograph 6 View of the Separation Between the Wale and Sheet Pile Wall Looking South from Station 5+39.

Photograph 7 View of the 5.5 in. Horizontal Gap between the Wale and the Sheet Pile Wall (Missing Bolts) at Station 5+55.

Photograph 8 View of the Wale to Sheet Pile Wall Connection at Station 5+62. As- Built Drawings Call for 0.875 in. Diameter Bolts, But 0.5 in. Diameter Bolts were Measured.

Photograph 9 View of Test Pit 8A, Looking North from Station 1+12. This Photograph Shows the Typical Inspection Pit Layout in the Non- Operational Area Along the Bulkhead.

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Photograph 10 View of the Wale to Sheet Pile Wall Connection at Station 2+48. This Photograph Shows the Typical Condition in the Operational Area.

Photograph 11 View of the Tie Back Connection to the Wale at Station 1+82. This Photograph Shows the Typical Condition in the Non-Operational Area.

Photograph 12 View of the Sink Hole at the Inspection Pit 8A Location Prior to Excavation, North of Station 1+08.

Photograph 13 View of the Sink Hole Depth Measurement at Station 1+00.

Photograph 14 View of a 1.25 in. Gap Measured Between the Top Channel and the Sheet Pile Wall, North of Station 1+02.

Photograph 15 View of 10.7 Degree Rotation Measured at the Wale at Station 1+02.

Photograph 16 View of Water Migration and Flow into Pit 8A at Station 1+02.

Photograph 17 View of Test Pit 6B, Looking North from Station 2+62. This Photograph Shows the Typical Inspection Pit Layout in the Non- Operational Area Along the Bulkhead.

Photograph 18 View of the Tie Rod Connection to the Anchor at Station 2+48. This Photograph Shows the Typical Condition.

Photograph 19 View of the Exposed Tie Rod on the West Side of the Anchor Wall at Station 2+48. This Photograph Shows the Typical Condition.

Appendix E – Dynamic Tie Rod Testing Report

Appendix F – Geotechnical Field Notes

Appendix G – Repair Details

Appendix H – Preliminary Design Drawings for Bulkhead Repairs

Appendix I – Preliminary Specification Sections for Bulkhead Repairs

Appendix J – Preliminary Environmental Permitting Review

Appendix K – Preliminary Cost Estimates for Bulkhead Repairs

Appendix L – Preliminary Design Calculations for Bulkhead Repairs

1. INTRODUCTION

The USCGC Diligence (Diligence) moorings are located on a bulkhead on the Cape Fear River waterfront in Wilmington, NC. The north end of the bulkhead is an operational area for the Diligence, while the area to the south is leased to the City of Wilmington as parkland. Over the life of the wharf, numerous settlement and sinkholes have been identified and repaired. Collins Engineers, Inc. (Collins) performed a site inspection of the facility and a load rating analysis of the bulkhead walls in 2012. The wharf was found to be in fair to poor condition and load restrictions were placed on the operational wharf and park area. In December 2012, a major sinkhole and cracking of the concrete cap occurred in the non-operational bulkhead wall near Station 5+50. Additional sinkholes have been found since December 2012, which initiated the current inspection and development of preliminary design alternatives to repair of the facility.

The purpose of this project was to provide a site inspection of the Diligence bulkhead, to make temporary repairs to the structure, where possible, to stabilize the wall in the area around Station 5+50, and to develop preliminary design alternatives for bulkhead repairs. Inspection pits were excavated at locations along the wharf and the anchor wall to expose and inspect wales, tie-backs and portions of the anchor wall. During the inspection, temporary repairs to the bulkhead were made that included replacing missing bolts, washers, and nuts to reconnect the wale to the sheet pile sections. Information collected during the site inspection was used to develop preliminary design alternatives for bulkhead repair. A recommended design alternative has been selected based on operational, environmental, cost and constructability considerations.

Collins was a subconsultant to Michael Baker Jr., Inc. for the United States Coast Guard (USCG) Civil Engineering Unit (CEU) Cleveland in the inspection and preliminary design of bulkhead repairs for this facility. The point of contact at CEU Cleveland was Mr. Raymond Pipak, P.E. at

(216) 902-6227, and the points of contact at the Diligence were ENS Devin Quinn and LT Todd DeVries at (910) 815-4528. Additional points of contact for the project included Mr. Mike Naklicki from the City of Wilmington Engineering Division at (910) 619-5538 and Mr. Richard Oates from the Federal Courthouse at (910) 515-7854.

2. EXECUTIVE SUMMARY

The Diligence moorings are located on a bulkhead on the Cape Fear River waterfront in Wilmington, NC. The structure consists of a tied-back steel sheet pile bulkhead with a concrete cap. The operational moorings are located between Stations 0+00 and 4+76, while the area between Stations 4+76 to 7+47 is leased to the City of Wilmington as parkland. The entire area is open to the public and is adjacent to walkways along the Cape Fear Riverfront.

Over the life of the wharf, numerous settlement problems have been identified and repaired. In December of 2012, a major sinkhole and cracking of the concrete bulkhead cap occurred near Station 5+50 in the non-operational area. Additional sinkholes have been found since that time.

The purpose of this project was to provide a site inspection of the Diligence bulkhead, to make temporary repairs to stabilize the structure near Station 5+50, and to develop preliminary design alternatives for bulkhead repairs. Inspection pits were excavated at eight locations along the wharf and three locations along the anchor wall to expose and inspect wales, tie-backs, and portions of the anchor wall. Prior to backfilling, temporary repairs to the bulkhead were made that included replacing missing bolts, washers, and nuts to reconnect the wale to the sheet pile walls. Results from the site inspection were used to develop preliminary design alternatives for bulkhead repairs. A recommended design alternative has been selected based on operational, environmental, cost, and constructability considerations.

The tie rods and wales, as well as the tie rod connections at both the wale and the anchor wall, were typically in good condition at the time of inspection and are suitable for reuse. The condition of the wale-to-sheet pile section connections varied. Some connections were sound, while in other connections the bolts were elongated or missing. Prior to backfilling, missing bolts were replaced to stabilize the wall in the areas that were excavated. Notable migration of water through the bolt holes was typical at locations where bolts were either elongated or missing.

Localized portions of the sheet pile sections in the operational area were in fair to poor condition in the splash zone. Heavy organic debris, which was typically wedged between fender system and bulkhead, as well as marine growth and corrosion by-products, previously obscured the extent of the deterioration. Use of tracer dyes and the intensive removal of debris, marine growth, and corrosion by-products near mean high water exposed additional active penetrations in the wall.

The concrete surfaces of the anchor walls appeared sound with no visible cracks or spalling. The concrete anchor walls in two of the three excavations had measured rotations of between 2 and 4 degrees toward the water.

Several repair alternatives were identified to address deficiencies in the existing bulkhead. Each repair alternative addressed the following major deficiencies:

1. Section loss on the sheet pile walls near the splash zone along the length of the bulkhead.

2. Missing and distressed wale to sheet pile wall connections along the length of the bulkhead wall.

3. Insufficient capacity of the anchor wall along the length of the bulkhead.

Four sheet pile wall repair alternatives and two anchor wall repair alternatives were selected for preliminary analysis and design. The design alternatives were evaluated based on operational, environmental, cost and constructability considerations. The recommended preliminary design alternative, identified in this report as Concept 3-B, involves the following repairs:

1. Excavating to replace all of the bolts connecting the wale to the sheet pile walls.

2. Demolishing the existing concrete cap and cleaning the existing sheet pile walls to 3 ft below mean low water (MLW).

3. Casting a new concrete cap and concrete facing to 3 ft below MLW.

4. Driving new sheet piles in front of the existing anchor wall from Stations 0+00 to 4+76.

5. Driving new piles and casting concrete pile caps in front of the existing anchor wall from

Stations 4+76 to 7+47.

The concrete facing will also allow for installation of pneumatic or foam filled fenders instead of the current timber fender system along the bulkhead. Operations will be affected by the construction, which could be phased to allow the Diligence to be home ported during construction. This option also offers the most cost effective repair of all the design alternatives, with a total estimated construction cost of $2,504,000, including site demolition. Excluded from this cost are utilities, fender systems and site restoration, which are specifically excluded from our scope of work.

3. PURPOSE AND SCOPE OF REPORT

The purpose of this project was to provide a site inspection of the Diligence bulkhead, to make temporary repairs to stabilize the structure near Station 5+50, and to develop preliminary design alternatives for bulkhead repairs. The scope of work for the site inspection included a three dimensional acoustic scan of the entire waterfront structure; excavation of test pits to uncover and inspect the wale and tie rod connections at selected locations; pulse-echo testing to determine tie rod lengths; and, a tracer-dye inspection of the bulkhead in the operational area to trace the source of water infiltration into the inspection pits. Temporary repairs to the bulkhead made during the inspection included replacing missing bolts, washers, and nuts to reconnect the wale to the sheet pile sections in the non-operational area. The scope of work for developing preliminary design alternatives included the development of three conceptual designs to rehabilitate and stabilize the structure.

Results from the site inspection included in this report are images from the acoustical scan, field measurements from the site inspection, repairs made to the structure, pulse-echo test results, observed geotechnical conditions and discussion of the site conditions. Preliminary design alternatives for bulkhead repairs are presented along with a discussion of the pros and cons of each design, and as well as the rehabilitation alternatives that were not considered.

4. DESCRIPTION OF WATERFRONT FACILITIES

The Diligence moorings are located along the Cape Fear River in downtown Wilmington, NC at 109 North Water Street. The waterfront portion of the facility consists of a 747 ft long, tied-back steel sheet pile wall with a concrete cap and a timber fender system. The operational area is located on the north end of the facility between Stations 0+00 and 4+76 and the non-operational bulkhead is located south of Station 4+76 to Station 7+47. The operational area includes a 23 ft wide asphalt covered wharf that services the Diligence. The non-operational area is leased to the City of Wilmington as waterfront parkland. The entire facility is open to pedestrian access when the Diligence is not home ported. Mooring fixtures and utilities for the vessel are installed on the wharf, which is accessed by two concrete ramps located at Stations 0+10 and 4+70 of the operational bulkhead. Refer to Appendix B for a set of as-built drawings included in the site inspection protocol.

4.1. Sheet Pile Bulkhead

The bulkhead was constructed in 1965 and extends 747 ft along the Cape Fear River in the north/south direction. There is a 23 ft return on the north end of bulkhead at Station 0+00 and a 15 ft return on the south end of the bulkhead at Station 7+47. MZ-38 steel sheet piles were used to construct the bulkhead from Stations 0+00 and 4+91. The piles are reinforced with 3/8 in.

thick by 4 in. wide steel plates welded to the inner and outer flanges of the MZ-38 sheets.

Construction documents indicate that the plates were designed to extend between -10 ft and -31.5 ft (MLW), which is consistent with Collins’ field observations. Between Stations 4+91 and 7+47, the bulkhead is constructed of MZ-27 sections. Sheet pile length tests, performed in Collins’ 2012 inspection, determined that the steel sheet piles were not driven to the design tip length indicated in the as-built drawings. Table 4.1.1 lists the measured sheet pile lengths and the lengths called for on the as-built drawings. A 19 in. deep by 24 in. wide reinforced concrete cap is cast on to the steel sheet pile wall along the entire length of the facility. The top of the concrete cap acts as a curb for the wharf and has expansion joints spaced approximately 39 ft to 40 ft on center.

Table 4.1.1 Measured Sheet Pile Lengths (Top of Cap)

Station Measured Length As-Built Drawing

Length

0+10 58 ft 69 ft

2+10 62 ft 69 ft

4+05 68 ft 74 ft

5+45 58 ft 60 ft

7+10 50 ft 60 ft

The steel sheets are anchored by tie rods connected to a continuous double steel channel wale and a continuous concrete pile-supported anchor wall. Tie rods and anchor wall piles are spaced at 6 ft centers between Stations 0+00 and 4+91 and at 9 ft centers between Stations 4+91 and 7+47. Tie rods are typically centered 1 ft above MLW at the sheet pile wall. The concrete anchor wall between Stations 0+00 and 4+91 wall is 2.5 ft wide by 4 ft deep supported on one 30 ft long vertical H-pile and one 30 ft long H-pile battered at 7:12 toward the wharf. The waterside face of the concrete anchor wall in this area is located approximately 66 ft behind the sheet pile wall.

Between Stations 4+91 and 7+47, the concrete anchor wall is 2.17 ft wide by 4 ft deep and is supported on one 30 ft long vertical and one 30 ft long battered steel H-pile. The waterside face of the concrete anchor wall in this area is located approximately 56 ft behind the sheet pile wall;

however, the spacing gradually decreases south of Station 6+90 when the anchor wall moves into Water Street.

A timber fender system protects the entire length of the bulkhead. Between Stations 0+00 and 4+91, the fender system consists of 12 in. diameter timber piles spaced at 6 ft centers with 12 in.

by 12 in. timber chock. Four timber camels are installed in front of the fender system. Between Stations 4+91 and 7+47 the fender system consists of 12 in. diameter timber piles spaced at 12 ft centers with 12 in. by 12 in. timber chock.

4.2. Wharf

The operational wharf is 24 ft wide and is asphalt-paved between Stations 0+00 and 4+76. The landside edge of the operational wharf is retained by a cantilevered concrete retaining wall supported by compacted soil and 15 ft long timber piles spaced at 12 ft centers. Access to the wharf is gained via concrete ramps, located on the north and south ends of the operational area.

The wharf supports the mooring hardware for the Diligence, which consists of three 4 ft double bitts, nine 3 ft cleats, and two 3 ft bollards. All of the hardware is founded on independent pile-supported concrete foundations. Three utility wells and an electrical panel were also located on the wharf. South of Station 4+76, the non-operational wharf has asphalt pavers over a sand base.

5. INSPECTION METHODOLOGY

5.1. Three-Dimensional Acoustical Scan of the Bulkhead

Collins performed a three-dimensional acoustical scan of the bulkhead to record pre-excavation conditions below the waterline. The intent was also to identify major defects, such as significant damage, bowing, or movement of the sheet pile wall near the mudline.

The scans were performed on August 24 through 26, 2013 using BlueView scanning equipment.

Data obtained during the scans was post-processed to create a three-dimensional underwater model of entire waterfront bulkhead. Drawings created from the model of the acoustical scan at 50 ft stations are provided in Appendix A of this report.

5.2. Topographic Survey and Site Utility Investigation

McKim and Creed, Inc. of Wilmington, NC provided a topographic survey and a site utility engineering (SUE) investigation in May of 2013. The survey of the monuments, which were installed in August 2012, was compared to the original survey to identify movement of the concrete cap. The SUE investigation was used to determine appropriate locations for the investigation pits, as well as to determine bulkhead rehabilitation design options. Results from the topographic survey and SUE were submitted separately to CEU Cleveland in June 2013.

5.3. Inspection Pit Assessment of the Bulkhead

Inland Construction & Equipment, Inc. (Inland) of Panama City, FL provided construction support during the excavation of the inspection pits. Inland provided personnel and equipment to dewater, excavate, replace missing wale connection bolts, and backfill each of the inspection pits. Collins performed a visual inspection of the elements and connections, performed non-destructive testing on the steel sections, and measured the remaining sections of the wales, tie rods, sheet pile wall, concrete anchor wall, and all bolted connections. A copy of the Project Approach for the Site Inspection of the Diligence moorings is provided in Appendix B.

Eleven inspection pits were excavated with locations chosen in both the operational and non-operational areas. Locations were also chosen to ensure that areas of subsidence as well as areas with no visible subsidence were evaluated. The pits were numbered 1 to 8 from south to north.

Where inspection pits were excavated at both the bulkhead and the anchor wall, the bulkhead pit was numbered and identified as A; while the correlating inspection pit at the anchor wall was identified as B (e.g. pits 7A and 7B). Eight pits – 1, 2, 3, 4, 5, 6A, 7A, and 8A – were excavated adjacent to the bulkhead and were centered on Stations 6+95, 6+22, 5+51, 3+53, 2+52, 1+84, 1+02, respectively. Pits 3 and 4 were originally planned to be separate, but were combined during the inspection work to avoid site utilities. The location of Pit 8A was changed prior to excavation to coincide with a newly-formed sink hole. Three inspection pits were excavated at the anchor wall, including 6B, 7B, and 8B, centered at Stations 2+52, 1+85, and 0+90 respectively.

All inspection pits were typically 18 ft long and 8 ft wide and exposed a minimum of three tie rods in each pit. Inspection pits adjacent to the bulkhead were excavated to a depth of 9 ft, exposing the bottom of the wale, which also exposed the entire diameter of the tie rod section.

The pits at the anchor wall were excavated to a depth of 7 ft, which exposed the entire diameter of the tie rod section and the plate washers.

5.4. Pulse-Echo Testing of Tie Rods

FDH of Raleigh, NC performed pulse-echo and bending wave dynamic testing on all of the exposed tie rods in the inspection pits during the site inspection. The purpose of this assessment was to identify discontinuities in the tie rods and identify any deficiencies in the rods that exceeded one-third of the rod diameter FDH’s test report is provided in Appendix E.

5.5. Geotechnical Observations of the Excavation Pits

S&ME of Wilmington, NC made geotechnical observations of the excavation pits during the site inspection. Field notes from the geotechnical observations are included in Appendix F.

5.6. Tracer-Dye Inspection to Identify Causes of Water Flow into Inspection Pits

Excessive water flow into the pits was observed during the excavation of the pits in the operational area. As a result, a tracer dye inspection was performed to identify the source of the water. Diluted dye was forced into the areas affected by flow and the migration of the dye observed. The dive team mobilized for the inspection identified previously unobserved deterioration to the sheet piles that was obscured by heavy organic debris, marine growth, and corrosion by-products. After clearing the debris and cleaning several areas of marine growth and corrosion by-products, several penetrations through the bulkhead were identified. At these locations, D-meter readings were performed on the sheet pile surfaces around the holes to determine remaining thicknesses.

6. RECORD OF CONDITIONS OBSERVED DURING FIELD WORK

6.1. Acoustic Scan Observations and Analysis

Images from the acoustic scan show that the channel depth varies and the channel bottom slopes away from the bulkhead. The most severe channel bottom slope was located in the operational area between Stations 1+00 and 4+00. The as-built drawings indicate that the sheet pile wall design depth in the operational area was equal to 25 ft at a distance of 10 ft from the wall.

Analysis of the acoustic scan images indicates that the original design depth occurs at distances ranging approximately between 3 ft and 8 ft between Stations 1+00 and 4+00. To account for the observed channel slope, the channel depth used in the structural calculations was increased to 28 ft to 30 ft for the preliminary repair designs in the operational area. The channel bottom also sloped away from the bulkhead in the non-operational area. However, the observed depths were less than the 20 ft design depth shown in the as-built drawings. Refer to Appendix A for acoustic scan images of the bulkhead.

Section analysis of the acoustic scan images shows that the sheet piles along the bulkhead were not plumb. To quantify out-of-plumbness, the horizontal and vertical distance between the face of the sheet pile at the channel bottom and at the waterline were measured to calculate sheet pile slope. Table 6.1.1 lists the sheet pile slope at selected stations. Negative slope indicates horizontal movement of top of the wall toward the river. The sheet piles at Stations 1+50 to 4+00 and 5+50 to 7+00 had measured slopes ranging between –1 degree and –3 degrees. Top-of-bulkhead wall movement correlates with the migration of the bulkhead anchor system. This finding is consistent with Collins’ 2012 site observations and geotechnical analysis of the anchor wall. The sheet piles at Stations 0+50, 1+00 and 4+50 had measured slopes ranging between 1 and 2 degrees. Positive sheet pile slope at these stations could be caused by installation tolerance or local pile bending.

Department of Defense (DOD) steel sheet pile specifications allow up to 0.25 in. per ft out-of-plumbness when installing new sheet piles, or a 1.2 degree slope. Most of the measured sheet piles slopes do not meet current DOD specification tolerances. The slope of the existing sheet piles adds eccentric axial loading, which causes additional bending moments in the wall. The additional moment caused by eccentricity should be small relative to those caused by horizontal earth pressure and will be addressed during the final bulkhead repair design.

Table 6.1.1 Measured Sheet Pile Rotation from Vertical

Station Slope 1 (Deg)

Station

Slope 1 (Deg)

0+00 0 4+00 -1.0 0+50 2.0 4+50 1.0 1+00 2.0 5+00 0 1+50 -1.5 5+50 -2.0 2+00 -2.0 6+00 -1.5 2+50 -2.5 6+50 -1.0 3+00 -2.0 7+00 -1.5 3+50 -3.0

1. Slope is measured from vertical. Negative slope indicates horizontal movement of the top of the wall toward the river.

6.2. Bulkhead Conditions

The tie-rod to wale connections were typically in good condition at the time of inspection. The steel tie rods, wale channels, and plate washers were coated in coal tar or bitumen pitch and had minor surface corrosion at locations where the coating had flaked off. Tie rod thicknesses were measured greater than or equal to the diameters called out on the as-built drawings, including the coating. The plate washer sizes for the tie-rods and wales in pits 1, 2, 3, and 4 matched the as-built drawings with thickness losses less than 1%. The plate washer sizes in pits 5, 6A, 7A, and 8A had measured thicknesses equal to 1.25 in., but the as-built drawings called for 1.5 in. thick plate washers. All other plate washer dimensions were consistent with the as-built drawings. The reduction of the tie rod plate washers’ thickness was analyzed and should not affect the connection capacity. The wale channels dimensions were consistent with those indicated on the as-built drawings. Channel thickness measurements showed typical web section losses of less than 5% and negligible flange section losses. The top channel of the wale observed to be separated from the sheet pile wall in pits 5, 6A and 8A. This channel flanges were not bent and the section was not distressed, so bolt bending or elongation was the most likely cause of the separation. Refer to Appendix C for field observations and measurements and Appendix D for typical photographs of the site inspection.

The exterior flanges of the sheet piles in the areas with penetrations that were identified during the tracer dye inspection were in fair to poor condition in the splash zone between -2 ft and +8 ft MLW. Heavy organic debris was typically wedged between the timber camels, fender system, and steel sheet piles. After removal of the debris and extensive cleaning of the marine growth and corrosion by-products from the sheet pile sections, localized holes and deep pitting were visible on some of the sheet piles at and below MLW. The size and location of holes varied at each inspection location but remained consistent with previously identified and current subsidence levels. Refer to Appendix C for field observations and measurements.

Construction of the concrete cap was typically not consistent with the as-built drawings. Support angles were placed on the top of the sheet piles but were not cast into the concrete cap. Refer to Photograph 4 in Appendix D for a typical view of the concrete cap.

6.2.1. Inspection Pit 1 – Non-Operational Area

Inspection pit 1, located adjacent to the bulkhead, was 23 ft long and 8 ft wide, and was sited between Stations 7+06 and 6+83. The tie rods, wale channels, and plate washers were typically in good condition, and the inner flanges of the sheet piles were typically in satisfactory condition in inspection pit 1 at the time of inspection. The web of the top channel had measured losses of up to nine percent, the lowest measured reading off all tested locations. Two wale bolts were fractured at Station 7+05. The existing plate washers from the fractured bolts were recovered, and the connections were repaired using 0.875 in. diameter 36 ksi threaded rods. Water migrated freely through the bolt holes until the connection was repaired with the new threaded rod. All other tie rod to wale connections and wale to sheet pile connections in the pit were secure at the time of the inspection. Refer to Figures C-2 and C-3 in Appendix C for field observations and measurements and Photographs 2 through 3 in Appendix D for typical wall anchorage conditions. Refer to Photograph 5 in Appendix D for a view of the fractured bolts near Station 7+05.

6.2.2. Inspection Pit 2 – Non-Operational Area

Inspection pit 2, located adjacent to the bulkhead, was 27 ft long and 8 ft wide, and was sited between Stations 6+35 and 6+08. The tie rods, wale channels, and plate washers were typically in good condition, and the inner flanges of the sheet piles were typically in satisfactory condition in inspection pit 2 at time of the inspection. The tie rod to wale connections and the wale to sheet pile connections were secure at all locations in the pit at the time of the inspection. Minimal water percolated into inspection pit 2 during the inspection. Refer to Figures C-4 and C-5 in Appendix C for field observations and Photographs 2 through 3 in Appendix D for typical wall anchorage conditions.

6.2.3. Inspection Pit 3 and 4 – Non-Operational Area

Inspection pits 3 and 4, located adjacent to the bulkhead, were combined into one 48 ft long and 8 ft wide pit, which was sited between Stations 5+75 and 5+27. A wale to sheet pile connection failure was the apparent cause of the 6 ft long by 2 ft wide by 2 ft deep sink hole that was identified near Station 5+50 in December of 2012. At the time of the inspection, eight wale bolts were missing over a length of 24 ft between Stations 5+60 and 5+36. A gap up to 5.5 in. wide was measured between the wale and the sheet pile wall. The wale bolts were connected to the sheet pile wall south of Station 5+60 and north of Station 5+36, but the flanges of the wale were separated from the wall by up to 0.75 in. Additionally, 0.5 in. diameter bolts were identified at the two connections south of Station 5+60 where 0.875 in. bolts were called for in the as-built drawings. River water typically migrated through all bolt holes missing bolts and along the north corner of inspection pit 4 near Station 6+08. A previously identified broken storm drain near Station 5+05 was the probable source of water infiltration into inspection pit 4 near the north end. Prior to backfilling, the wale was reconnected to the sheet pile wall using the repair detail shown in Appendix G. Refer to Photographs 6 and 7 in Appendix D for photographs of the wale to sheet pile connection failure and Photograph 8 for 0.5 in. diameter bolts.

Other than the identified wale bolt failures, the tie rods, wale channels, and plate washers were in good condition, and the inner flanges of the sheet piles in inspection pits 3 and 4 were in satisfactory condition at the time of inspection. Refer to Figures C-6 through C-9 in Appendix C for field observations and measurements.

6.2.4. Inspection Pit 5 –Operational Area

Inspection pit 5, located adjacent to the bulkhead, was 18 ft long and 8 ft wide, and was sited between Stations 3+62 and 3+44. The tie rods, wale channels, and plate washers were in good condition, and the inner flanges of the sheet piles were in satisfactory condition at the time of inspection. The wale bolts were connected to the sheet pile wall, but the top wale flanges were separated from the wall by 0.75 in. from Station 3+62 to Station 3+44. Local flange bending or other distress of the wale channel at the point of separation was not observed. Bolt bending or elongation was the most likely the cause of the top flange separation. Minimal water percolated into inspection pit 5 during the inspection. Refer to Figures C-10 and C-11 in Appendix C for field observations and measurements and Photographs 10 through 11 in Appendix D for typical wall anchorage conditions.

6.2.5. Inspection Pit 6A –Operational Area

Inspection pit 6A, located adjacent to the bulkhead, was 21 ft long and 8 ft wide, and was sited between Stations 2+62 and 2+41. While inspection pit 6A was being excavated, a void was identified under the cleat foundation at Station 2+64, south of inspection pit 6A. A significant amount of water infiltrated inspection pit 6A from the southwest corner during mid and high tide.

During the tracer dye inspection, two holes were found in the sheet pile wall at Stations 2+67 and 2+64, located approximately 7 in. below MLW. The holes were located on the exterior sheet pile wall flange corners and were measured 12 in. by 4 in. in size at Station 2+67 and 4 in. by 2 in. at Station 2+65. These holes were the probable cause of material loss under the cleat. An additional hole was observed from inside the inspection pit on the exterior north corner of the sheet pile wall at Station 2+48.

The tie rods, wale channels, and plate washers were in good condition, and the inner flanges of the sheet piles at inspection pit 6A were in satisfactory condition at the time of the inspection.

The wale bolts were connected to the sheet pile wall, but the flanges of the wale were separated from the wall by 0.75 in. from Station 2+62 to Station 2+41. Local flange bending or other distress of the wale channel at the point of separation was not observed. Bolt bending or elongation was the most likely the cause of the top flange separation. Refer to Figures C-12 and C-13 in Appendix C for field observations and measurements and Photographs 10 through 11 in Appendix D for typical wall anchorage conditions.

6.2.6. Inspection Pit 7A –Operational Area

Inspection pit 7A, located adjacent to the bulkhead, was 18 ft long and 8 ft wide, and was sited between Stations 1+93 and 1+75. The tie rods, wale channels, and plate washers were in good condition, and the inner flanges of the sheet piles were in satisfactory condition at the time of inspection. A significant flow of water infiltrated the inspection pit near Station 1+82. During the tracer dye inspection, three holes were identified in the sheet pile wall at Stations 1+89, 1+85 and 1+83, located between MLW and 2 ft below MLW. The holes were located on the exterior sheet pile wall flange corners and were measured 5 in. by 2 in. in size at Station 1+89, 10 in. by 3

in. at Station 1+83 and 6 in. by 4 in. at Station 1+79. The hole at Station 1+83 was 4 in. by 2 in.

in size that increased once corrosion by-product was removed with a hammer during tracer dye inspection. Refer to Figures C-14 and C-15 in Appendix C for field observations and measurements and Photographs 10 through 11 in Appendix D for typical wall anchorage conditions.

6.2.7. Inspection Pit 8A –Operational Area

Inspection pit 8A, located adjacent to the bulkhead, was 20 ft long and 8 ft wide, and was sited between Stations 1+12 and 0+92. A 6 ft long by 2 ft wide by 4.33 ft deep sink hole was identified at Station 1+05 after the inspection team mobilized at the site. The location of inspection pit 8A, originally planned for a more northward location, was relocated to excavate around the sinkhole. A significant flow of water infiltrated the inspection pit near Station 1+02.

During the tracer dye inspection, seven holes were identified in the sheet pile wall between Stations 1+13 and 0+98, located between MLW and 12 in. below MLW. The holes were located on the exterior sheet pile wall flange corners and were typically measured 8 in. by 4 in. in size.

The largest hole was 14 in. by 4 in. at Station 1+11 and the smallest hole was 1 in. by 1 in. at Station 1+85.

The tie rods, wale channels, plate washers, and inner flanges of the sheet piles were in good condition at the time of inspection. The wale bolts were connected to the sheet pile wall, but the flanges of the wale were separated from the wall by 1.0 in. from Station 1+12 to Station 0+92.

The top channel had a measured rotation of 10.7 degrees down and away from the water. Local flange bending or other distress of the wale channel due to wale rotation and flange separation was not observed. Bolt bending or elongation was the most likely the cause of the top flange rotation and separation. Refer to Figures C-16 and C-17 in Appendix C for field observations and measurements. Refer to Photographs 12 and 13 for pictures of the sinkhole, Photograph 14 for a picture of the gap between the wale and sheet pile, Photograph 15 for the wale rotation measurement, and Photograph 16 in Appendix D for a view of water flowing into inspection pit 8A.

6.3. Anchor Wall Conditions

Inspection pits 6B, 7B, and 8B, located in the parking lot, were all approximately 24 ft long by 8 ft wide. Inspection pits 6B, 7B, and 8B were excavated between Stations 2+62 and 2+41, 1+93 and 1+75, and 1+02 and 0+78, respectively. The tie rod connections to the anchor walls were all in good condition at the time of inspection. Steel anchorage components were coated in coal tar or bitumen pitch, and the tie rod threads were wrapped in a protective fabric that was breaking apart. Plate washer thicknesses were measured, and no notable section losses were identified. All other dimensions were equal to or greater than the design thickness, including the coating.

Concrete surfaces were struck with a hammer and were sound without observable cracks or spalling during the inspection. Inspection pit 6B had noticeable water infiltration from the southeast corner of the pit during the inspection. The concrete anchor walls in inspection pits 7B and 8B had measured rotations of 4 degrees and 2 degrees, respectively, toward the water. The observed anchor wall rotation indicates the wall was not sufficiently embedded into the existing soil strata, which is consistent with the geotechnical investigation documented in Collins’ 2012 inspection report. Refer to Figure C-18 through C-20 for field observations and measurements and Appendix D photographs 17 through 19 for typical conditions in inspection pits 6B, 7B, and 8B.

6.4. Tie Rod Testing Results

The results from the analysis of test data obtained in the inspection pits are provided in Appendix E. Current testing methods are sensitive enough to identify a discontinuity or an inclusion greater than one-third of the tie rod diameter. Test results indicated that the lengths of all the discontinuities were approximately equal to half of the tie rod design lengths indicated on the as-built drawings. This indicates the discontinuities found during the tests were the tie rod turnbuckles. Based on the observed tie rod coating and field measurements, the tested tie rods did not have significant area loss or identifiable discontinuities and should be acceptable for reuse in the rehabilitation design.

6.5. Geotechnical Observations in the Inspection Pits

The observed geotechnical conditions in the inspection pits were consistent with those described in S&ME’s 2012 Geotechnical Engineering Report. Descriptions of the soil strata are provided in the inspection pit observations provided in Appendix C, and S&ME’s Geotechnical Field Notes are provided in Appendix F. Typical observed conditions in both the operational and non-operational areas were as follows: 4 to 12 in. of asphalt or asphalt pavers over 6 to 12 in. of compacted stone followed by silty sand with mixed aggregates down to the wales and anchor wall. Inspection pits 1, 2, 3, and 4 had a layer of filter fabric and grout-injected fabric from site modifications in 1999. All of the inspection pits were backfilled and compacted in layers of stone and sand. The inspection pits along the bulkhead wall were lined with filter fabric prior to backfilling. Filter fabric was also placed 1 ft below grade in the parking lot, followed by compacted stone and 4 in. of asphalt topping.

7. PRELIMINARY DESIGN ALTERNATIVES FOR BULKHEAD REPAIRS

7.1. Introduction

The bulkhead inspection identified deficiencies in the steel sheet piles, the wale to sheet pile connections and the anchor wall, which can be repaired to rehabilitate the bulkhead. Steel sheet piles had heavy pitting and holes in the steel sheets from 2 ft below MLW to 1 ft below the concrete cap. Below this elevation, Collins’ 2012 underwater inspection measured less than 1% steel sheet pile flange losses and 6% average web losses. The steel sheet piles can therefore be repaired in the splash zone to rehabilitate the bulkhead. Bolts connecting the wale to the steel sheet piles are missing or in distress, but the wale channels, tie rods and tie-rod connections are in good condition and can be reused to rehabilitate the bulkhead. Measurements indicated that the anchor wall rotated toward the river in pits 7B and 8B. However, the concrete wall, steel tie rods and connection hardware are in good condition and can be reused to rehabilitate the anchor wall.

Several repair alternatives were identified to address deficiencies in the existing bulkhead. Each repair alternative addresses the following deficiencies identified during the site inspection:

1. Section loss, heavy pitting, and holes through the sheet pile walls from 2 ft below MLW to 1 ft below the concrete cap along the length of the bulkhead.

1. Missing and distressed wale to sheet pile wall bolt connections along the length of the bulkhead wall.

2. Insufficient capacity of the anchor wall along the length of the bulkhead.

Four sheet pile wall repair concepts and two anchor wall repair concepts were selected for preliminary analysis and design. Repair concepts that were evaluated but not selected for preliminary design are discussed in Section 0. The preliminary design alternatives provided in this report are:

Sheet Pile Wall Repairs:

Concept 1: Welding steel cover plates to the existing sheet pile walls from 1 ft below the cap to 3 ft below MLW and replacing bolts to reuse the existing wale.

Concept 2: Bonding fiber reinforced polymer (FRP) sheets to the existing sheet pile walls from 1 ft below the cap to 3 ft below MLW and replacing bolts to reuse the existing wale.

Concept 3: Casting a concrete facing with an integral curb to the existing sheet pile walls to 3 ft below MLW and replacing bolts to reuse the existing wale.

Concept 4: Driving new sheet piles, drilling new tie rods, and installing new wales.

Anchor Wall Repairs:

Concept A: Driving new piles in front of the existing anchor wall.

Concept B: Driving new sheet piles in front of the existing anchor wall (operational area only).

Preliminary design drawings, outline specifications, environmental permitting review, cost estimates, construction schedules, and structural calculations for each of the alternatives are provided in Appendices H through L.

7.2. Concept 1: Welding Steel Cover Plates and Replacing Wale Bolts

7.2.1. Concept Summary

Concept 1 involves removing the existing timber fender system and cleaning the existing sheet piles from below the existing concrete cap to 3 ft below MLW. Steel bent plates, 0.5 in. thick, will then be field welded to the exterior flanges and webs of the sheet pile sections along the length of the wall. The area behind the wall will be excavated to expose the existing wale to allow replacement of the wale to sheet pile bolts and plate washers. The excavation cut will be lined with filter fabric and backfilled with select structural fill and stone, compacted in layers.

Passive cathodic protection will be installed on to the existing sheet piles along the entire length of the bulkhead.

The existing concrete cap will be demolished and replaced and a new timber fender system will be installed. Existing cleats and bits will be salvaged, cleaned, recoated, and reinstalled on new pile-supported foundations. A timber fender system similar to the existing system will be reinstalled. Asphalt will be repaved across the width of the wharf along the 476 ft operational area. Paving will not be replaced in the non-operational area as the City of Wilmington has a plan to reconstruct the existing park.

7.2.2. Physical Operational Considerations

Concept 1 will repair the existing bulkhead wall to extend the service life of the structure and will address settlement issues along the operational wharf. The repairs in Concept 1 will not alone increase the strength of the sheet pile wall, but will increase the allowable uniform live load capacity of the operational wharf when evaluated in combination with the anchor wall repair concepts outlined in Sections 7.6 and 7.7.

Portions of the operational wharf will not be in service during the construction of Concept 1.

Steel plate installation will limit waterfront access to the moorings during construction.

Excavating, dewatering, and other construction activities will occupy the operational wharf and at least one of the access ramps, which will also limit access and operational capabilities during construction.

7.2.3. Environmental Permitting Considerations

Concept 1 will maintain the current alignment of the bulkhead wall and therefore will not encroach into the public trust waters. This type of construction will be considered maintenance and repair per NC codes 113A-103 5(b) (5), and as a result, a Coastal Area Management Act (CAMA) permit will not be required. Federal projects are exempt from State permitting but would typically be applied for in support of public perception.

7.2.4. Constructability and Cost Considerations

Concept 1 has an estimated construction cost of approximately $1,100,000 for work along the bulkhead only. The estimated construction duration for this concept will be approximately 1 year, which includes site demolition and restoration. Construction for this concept will require staging to provide access to the wharf, which will be limited when excavating to replace wale bolts. A working platform and divers will be required to clean the existing bulkhead and weld sheeting on the exterior face of the existing sheet piles.

7.3. Concept 2: Bonding FRP Sheets and Replacing Wale Bolts

7.3.1. Concept Summary

Concept 2 is similar to Concept 1 and will also involve removing the existing timber fender system and cleaning the existing sheet piles from below the existing concrete cap to three feet below MLW. Fiberglass reinforced polymer (FRP) sheets will be bonded to the existing sheet pile wall to reinforce the existing steel sheets. The area behind the bulkhead will be excavated to expose the existing wale to allow replacement of the wale to sheet pile bolts and plate washers.

The excavation cut will be lined with filter fabric and backfilled with select structural fill and stone, compacted in layers. Passive cathodic protection will be installed along the entire length of the bulkhead.

The existing concrete cap will be demolished and replaced, and a new timber fender system will be installed. Existing cleats and bits will be salvaged, cleaned, recoated, and reinstalled on new pile-supported foundations. A timber fender system similar to the existing system will be reinstalled. Asphalt will be repaved across the width of the wharf along the 476 ft operational area. Paving will not be replaced in the non-operational area as the City of Wilmington has a plan to reconstruct the existing park.

7.3.2. Physical and Operational Considerations

Similar to Concept 1, Concept 2…