C8006_Stabilize_Failed_Bulkhead_-_Design_&_Build_Report_April_2017.pdf

UNITED STATES COAST GUARD

CIVIL ENGINEERING UNIT, RM 2179

1240 EAST NINTH STREET

CLEVELAND, OH 44199-2060

Coast Guard Contract No. HSCG83-16-C-PCR238

DESIGN/BUILD ENGINEERING REPORT

FINAL REPORT

ENGINEERING SERVICES FOR STABILIZE FAILED BULKHEAD

AT

U.S. COAST GUARD CUTTER DILIGENCE MOORINGS

P/N 8502724

WILMINGTON, NC

APRIL 2017

PREPARED BY:

10201 FAIRFAX BLVD. SUITE 530

FAIRFAX, VA 22030

TEL: 703.691.4841

STABILIZE FAILED BULKHEAD

AT

U.S. COAST GUARD CUTTER DILIGENCE MOORINGS

ON

CAPE FEAR RIVER

WILMINGTON, NORTH CAROLINA

DESIGN/BUILD ENGINEERING REPORT

FINAL REPORT

APRIL 2017

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 35-07321.04

i

CONTENTS

1. Introduction and Purpose

2. Executive Summary

2.1. Site Description and Scope

2.2. Observations and Repairs

2.3. Changes in Site Conditions and Scope Modifications

3. Description of Waterfront Facilities

3.1. Sheet Pile Bulkhead

3.2. Utilities and Site Features

4. Inspection Methodology

4.1. Assessment of the Bulkhead

4.1.1. Pulse-Echo Testing of Tie Rods

4.1.2. Tracer-Dye Inspection to Identify Causes of Water Flow into Excavation

5. Conditions Observed

5.1. Bulkhead Conditions

5.1.1. Steel Sheet Pile – Repair Area A

5.1.2. Wale Connection Bolts and Plates – Repair Area A

5.1.3. Wale Channels – Repair Area A

5.1.4. Tie-Rods – Repair Area A

5.1.5. Repair Area B

5.2. Geotechnical and Hydraulic Observations

6. Repairs Completed

6.1. Repair Area A

6.1.1. Structural Repairs

6.1.2. Drainage and Site Improvements

6.2. Repair Area B

6.2.1. Structural Repairs

6.2.2. Drainage and Site Improvements

ii

CONTENTS (CONT.)

Appendix A – Photographs

Appendix B – Inspection Measurements and Observations

Appendix C – Pulse-Echo Tie-Rod Test Results

Appendix D – Description of Project Approach

Appendix E – As-Built Drawings iii

LIST OF PHOTOGRAPHS

Photograph 1 Overall of Repair Area A after Excavation, Looking South.

Photograph 2 Overall of Wale Assembly in Repair Area A after Excavation, Looking South.

Photograph 3 Exposed Wale in Repair Area A.

Photograph 4 Typical Wale Condition in Repair Area A.

Photograph 5 Coating Failure and Minor Corrosion with Scaling on Wale at Station 5+15.

Photograph 6 Failed Wale Connection Bolts and Vertical Separation Between Wale and Bolt Holes at Station 5+17, Repair Area A.

Photograph 7 Horizontal Separation at Station 5+18 Between Wale and Bolt Holes, Repair Area A.

Photograph 8 Typical Tie-Back Nut and Plate Washer Condition, Repair Area A.

Photograph 9 Under-engaged Tie-back Nut at Station 5+18, Repair Area A.

Photograph 10 Deformed Tie-back Rod at Station 5+09, Repair Area A.

Photograph 11 Gouges in Tie-Back Rod at Station 5+00, Repair Area A.

Photograph 12 Typical Pile Cap Construction, Repair Area A.

Photograph 13 Typical Pile Cap and Sheet Pile Condition, Repair Area A.

Photograph 14 Site Flooding Following Hurricane Matthew, Looking Northwest.

Photograph 15 Site Flooding Following Hurricane Matthew, Looking South.

Photograph 16 Void in Repair Area B, Following Partial Slab Removal, Looking Northwest.

Photograph 17 Void Below Slab in Repair Area B, Looking North.

Photograph 18 Wale and Tie-Back Condition in Repair Area B.

Photograph 19 Overall of Repair Area A, Following Bolt Replacement and Shim Installation.

iv

Photograph 20 Replacements Bolts Between Station 5+18 and Station 5+26, Repair Area A.

Photograph 21 Repair Area A, Following Initial Backfill Placement of Crushed Stone Aggregate, Repair Area A.

Photograph 22 Replacement Storm Water Pipe Behind Bulkhead in Repair Area A

Photograph 23 Repair Area A, Prior to Repaving.

Photograph 24 Repair Area A and Concrete Cap, Following Repaving.

Photograph 25 Replacement Bolts Just North of Retaining Wall, Repair Area B.

Photograph 26 Steel Sheet Pile Plug to Stop Water Infiltration at Station 4+65, Repair Area B.

Photograph 27 Filter Fabric Placement Prior to Backfilling, Repair Area B.

Photograph 28 Repair Area B Following Backfilling and Prior to Repaving.

1. INTRODUCTION AND PURPOSE

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, finding the wharf to be in fair to poor condition and recommending load restrictions on the operational wharf and park area. Collins completed various follow-up services, including discrete test pits for inspection of the wale and anchor wall system, and design of immediate repairs to a small section of the wall that failed in 2013. In September 2016, a major failure in the wall occurred, resulting in the top of the wall deflecting up to two feet outward toward the river, and a large sinkhole forming behind the bulkhead. The sinkhole and wall failure occurred along an 80-ft length of the bulkhead, extending from Station 4+75 to Station 5+55.

The purpose of this project was to design and construct an emergency repair to stabilize the failed portion of the bulkhead to prevent further deflection, and restore the site features affected by the wall failure.

Collins was a subconsultant to G.M. Hill for the United States Coast Guard (USCG) Civil Engineering Unit (CEU) Cleveland in the design of bulkhead repairs, with the construction completed by Inland Construction and Engineering, Inc. The project manager for CEU Cleveland was Lt. Kevin Noll at (216) 808-2064, and the site representative for CEU Cleveland was Mr. Tom Sledge. The point of contact for the City of Wilmington Engineering Division was Mr. Mike Naklicki at (910) 619-5538.

In addition to the inspection findings and repair discussion, this report also includes field measurements and inspection findings, pulse-echo test results on the exposed tie-rods, as-built drawings of the repairs, and representative photos from the inspection and during construction.

2. EXECUTIVE SUMMARY

2.1. Site Description and Scope

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+75, while the area between Stations 4+75 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.

The scope of this project was to provide design/build services for repairs to stabilize the failed portion of the bulkhead within the work limits from Station 4+75 to 5+55. The project approach consisted of excavating the area behind bulkhead, inspecting the tie-back system and determining the mode of failure, designing and completing repairs to stabilize the bulkhead, backfilling and improving draining behind the failure area, reconstructing the concrete bulkhead cap, and restoring the site by repaving and replacing/reinstalling site features as directed by the Coast Guard and City of Wilmington.

2.2. Observations and Repairs

The inspection of the tie-back system revealed that the wall failure occurred at the connection between the steel sheet pile and internal steel wale, which was a result of a combination of corrosion induced section loss to the wale connection bolts, and excess hydrostatic pressure behind the bulkhead due to a failed stormwater drain pipe. A total of thirty-four connection bolts were determined to be failed from Station 4+90 to 5+40 as of November 15, 2016. With the exception of the failed bolts and concrete cap that was damaged due to the wall deflection, the bulkhead and anchor system components were observed to be in satisfactory condition at the time of inspection on November 11, 2016 and November 15, 2016, and suitable for reuse.

The wall stabilization methodology consisted of jacking the wale back into vertical alignment with the existing connection holes, and installing replacement bolts and plate washers to reconnect the wale to the steel sheet pile. Once the wale was reconnected, the soil between the sheet pile and wale was jetted and the replacement bolts tensioned to pull the sheet pile back into alignment. The sheeting was pulled to the maximum extent practical, with pressure treated timber shims installed to provide positive bearing between the sheet pile and wale. After the shims were installed and final tensioning completed on the wale connection bolts, the excavation was backfilled and the site restored. To improve drainage behind the bulkhead, crushed gravel with a filter fabric lining was used as the primary backfill, performing as a traditional French drain. Additionally, the existing storm water drain pipe penetrating the bulkhead and associated catch basin were replaced, and the site was regraded to establish positive drainage away from the face of the bulkhead and into the storm water system.

2.3. Changes in Site Conditions and Scope Modifications

After excavation had commenced and prior to inspection of the wale and tie-back system, the project was impacted by Hurricane Matthew as it made landfall in Wilmington on October 9th, 2016. Following the hurricane, a dam was released upstream subjecting the project site to heavy flooding with record water levels. The river levels peaked on October 17th with extreme water levels lasting through the end of the month. Due to the flooding, work was delayed until water levels returned to normal. Work was restarted on October 31st, with the wale system exposed for inspection on November 9th.

During repairs to the wale the following week, it was observed that substantial water and fine soils were infiltrating the work area from under the retaining wall that separates the operational and non-operational areas of the bulkhead, located adjacent to the repair area. During the investigation of the source of the water, two open bolt holes were observed in the sheet pile at Station 4+70. A large void was also observed beneath the slab adjacent to the bulkhead, extending from Station 4+25 to Station 4+75 in the operational area of the bulkhead. The void was likely initiated from Hurricane Matthew-related flooding at the site, during which fine soils were transported into the open excavation. The voids below the slab then progressively grew during daily tidal fluctuations.

Because the water infiltration and fine soils entering the repair area significantly impacted and delayed the work, a contract modification was obtained to repair the bolt holes, prevent additional water infiltration into the excavation, fill the void, and restore the site by repaving and replacing/reinstalling site features. For the purpose of this report, Repair Area A will refer to the initial contracted repair area between Station 4+75 and 5+55, and Repair Area B will refer to the additional repair area between Station 4+25 and 4+75.

3. 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+75 and the non-operational bulkhead is located south of Station 4+75 to Station 7+47.

The operational area includes a 23-ft. wide asphalt covered wharf that services the DILIGENCE, with the deck located at 9.7 ft. above Mean Low Water (MLW). From Station 4+15 to 4+75, the wharf behind the operational area is composed of a concrete slab. The landside edge of the operational wharf is retained by a cantilevered concrete retaining wall, and access to the wharf is gained via concrete ramps, located on the north and south ends of the operational area. The non-operational area of the bulkhead is covered with asphalt pavers running from the face of the bulkhead and North Water Street, with the deck located at 6.4 ft. above MLW. At Station 4+75, there is a concrete retaining wall and handrail that runs perpendicular to the bulkhead, separating the operation and non-operational areas. The non-operational area is leased to the City of Wilmington as waterfront parkland.

3.1. Sheet Pile Bulkhead

The bulkhead was constructed in 1965 and extends 747 ft along the Cape Fear River in the north/south direction. MZ-38 steel sheet piles were used to construct the bulkhead from Stations 0+00 to 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. 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 3.1 lists the measured sheet pile lengths and the lengths called for on the as-built drawings. A 17 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, with expansion joints at 40-ft. spacing.

Table 3.1 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. between Stations 0+00 and 4+91 and at 9 ft. 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, 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, 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 wales and 12 in. by 10 in timber chocks. 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., with similar chocks and wales as Station 0+00 to 4+91.

3.2. Utilities and Site Features

There are various mooring fittings, utilities, and site features located along the wharf; for the purpose of this report, only features within the limits of work are include in the discussion.

A 9-in. diameter steel double-bitt is located at Station 4+90 and at Station 4+65, both supported by 9-ft. x 4-ft. concrete foundations on timber piles. Additionally, a 36-in. steel cleat is located at Station 5+25, supported by a 3-ft x 3.5-ft concrete foundation on timber piles.

At Station 4+80, three utility lines run perpendicular to the bulkhead from North Water Street. The utility services, consisting of an 8-in. fire suppression pipe, a 3-in. domestic water pipe, and a 3-

in. forced-sewer main, penetrate the bulkhead and run across the bottom of the Cape Fear River to service the USS North Carolina Battleship. At Station 5+10, a 12-in. storm water pipe runs perpendicular to the bulkhead from North Water Street to its outfall through the bulkhead.

Approximately 20 ft. behind the bulkhead, a catch basin is connected to the 12-in. storm drain, with an 8-in. storm pipe running from the catch basin to the south, parallel to the bulkhead.

At Station 4+85, approximately 30 ft. behind the bulkhead, a sanitary sewer manhole with an 8-

in. service feeds the manhole from North Water Street. Based on information obtained from the City of Wilmington, the manhole is abandoned.

An electrical panel is at the corner of the retaining wall at Station 4+72 approximately 20-ft. behind the bulkhead, with conduits running east to North Water Street, and west to a light pole at Station 4+76.

Additionally, there are various planters, a pedestrian barrier along the face of the bulkhead, benches, and a fountain adjacent to North Water Street that are located within the limits of work.

4. INSPECTION METHODOLOGY

4.1. Assessment of the Bulkhead

Following excavation completed by the contractor to expose the wale in Repair Area A, Collins completed a visual and tactile inspection of the bulkhead components within the repair limits. At each tie-rod location, calipers and non-destructive testing methods were utilized to determine remaining steel section of the sheet pile and wale components, and pulse-echo testing was completed on the tie rods to determine if any discontinuities or significant defects were present. A copy of the Project Approach for the Emergency Repairs is provided in Appendix D.

A total of seven tie-rods and forty-two wale connection bolts were exposed in Repair Area A between Station 4+85 to 5+45, exposing the entire limits of wall failure which extended from 4+90 to 5+40. Excavation for inspection was completed to an approximate depth of 1.5 ft. below MLW, extending back from the face of bulkhead approximately 6-8 ft. to allow for inspection of the complete wale system.

In Repair Area B, following removal of the existing concrete slab and mooring fitting foundation to expose the full limits of the void, excavation was completed between Station 4+65 to 4+75 to expose the bolts holes in the sheet pile that appeared to be the primary cause of water infiltration.

A total of two tie rods and ten wale-connection bolts were exposed for inspection. Because the bulkhead failure mode was determined to be at the wale connection and no significant defects or discontinuities were observed in the tie rods in Repair Area A, pulse echo testing was not performed in Repair Area B.

4.1.1. Pulse-Echo Testing of Tie Rods

FDH, Inc. of Raleigh, NC performed pulse-echo and bending wave dynamic testing on all of the exposed tie rods in Repair Area A 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. A copy of FDH’s test report is provided in Appendix C.

4.1.2. Tracer-Dye Inspection to Identify Causes of Water Flow into Excavation

After the full extents of the void was exposed in Repair Area B, water infiltration was observed coming into the excavation from further north along the bulkhead, in addition to that entering through the bolt holes. To help determine water infiltration limits, tracer dye is placed in ports along the bulkhead north of Repair Area B, and the excavation area observed for die entering, indicating potential source locations for the water infiltration.

5. CONDITIONS OBSERVED

5.1. Bulkhead Conditions

With the exception of the failed wale connection bolts, which are discussed further in this section, the structural components of the bulkhead were generally in satisfactory condition, with only minor deterioration observed. The steel tie rods, wale channels, and plate washers were coated in coal tar or bitumen pitch, which was typically 50% to 90% intact, with isolated locations of increased coating loss generally observed at the tie-rods. Where the coating was failed, the underlying steel had minor surface corrosion, however no significant section loss was observed.

5.1.1. Steel Sheet Pile – Repair Area A

The steel sheet pile coating was typically 75%-90% intact, with increased coating loss near MLW.

In areas of coating loss, the exposed steel had minor surface corrosion with no significant section loss. Moderate corrosion was observed at the interlocks, and discrete rust nodules approximately 1 in. to 2 in. in diameter were observed randomly throughout the sheet pile. Ultrasonic thickness measurements revealed section loss in the steel ranging from 0% to 7%.

5.1.2. Wale Connection Bolts and Plates – Repair Area A

The wale connection bolts were failed from Station 4+90 to 5+40. Some of the failed bolts were recovered for inspection, which revealed elongation in the bolts and resultant tensile failure, abetted by corrosion-induced section loss. Between Stations 4+90 and 4+80 and 5+40 and 5+50, the bolts and washers were intact and when struck with a hammer appeared securely fastened.

Moderate corrosion was observed on the exposed portions of the bolts still secured to the wale.

The coating was typically intact on the plate washers, with no significant deterioration or section loss observed.

5.1.3. Wale Channels – Repair Area A

The coating on the wale was typically 75% to 90% intact, with minor surface corrosion on underlying steel and localized areas of advanced coating loss and moderate corrosion. Steel thickness measurements indicated less than 5% section loss to the channels.

The steel wale was displaced up to 16 inches vertically from Station 4+90 to Station 5+30, due to the self-weight of the wale being unsupported as a result of the bolt failures. The steel wale had no signs of overstressing or buckling in the web or flanges. At Station 5+25, the top flange had one localized area where the interior top flange was displaced approximately 1/2 in. over a length of 3 in.; however, it appears that the deformation was a result of impact damage from either initial construction or excavation and does not significantly affect the capacity of the wale.

5.1.4. Tie-Rods – Repair Area A

The steel tie-rods were in satisfactory condition and acceptable for reuse. The results from the pulse-echo testing is provided in Appendix C. 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 that the discontinuities found during the tests were the tie rod turnbuckles. The coating was typically 50% to 75% intact, with minor surface corrosion on the exposed steel. Ultrasonic thickness measurements indicated less than 3% section loss in the tie-rods. The tie-rod located at Station 5+00 had multiple 2 in. long gouges up to 1/4 in. wide, and the tie-rod was slightly displaced vertically approximately 3 ft.

from the wale, with approximate 2 in. of vertical displacement of a length of 4 ft. At Station 5+09 the tie-rod was displaced vertically approximately 4 in. over a length of 8 ft. It appeared that the tie-rods were displaced during excavation; however, based on stress-strain interaction and results of the pulse-echo testing, the structural integrity of the tie-rod was not compromised. The tie-rods were straightened as tensile loads were applied when the wale was reconnected.

5.1.5. Repair Area B

Upon excavation to expose the void limits and wale assembly for inspection, the steel tie-rods, wale assembly, and sheet pile were observed to be in satisfactory condition and suitable for re-use, with the exception of two missing wale connection bolts where the remnant bolt holes in the sheeting caused water infiltration. The sheet pile condition was consistent with the other areas of the bulkhead, with approximately 50-75% coating loss and minor corrosion on the exposed steel and interlocks. The wale, tie-rods, and plate washers had 25-50% coating loss, with light corrosion on exposed steel and no significant section loss observed. The wale-connection bolts still intact appeared securely connected when struck with a hammer.

5.2. Geotechnical and Hydraulic Observations

The excavated material at the site and existing backfill generally consisted of generally soft clayey organics overlaid with a 2-3 ft. layer of fine-grained backfill. Water levels in the excavations were relatively consistent with water levels in the river, with minor drawdown delays observed during falling tides.

Following the events of Hurricane Matthew during initial inspection and repairs, excessive water infiltration was observed coming from the north from underneath the retaining wall, bringing significant amounts of fine grained soils into the excavation. Upon further investigation, water was observed coming through the sheet pile via two remnant bolts holes just north of the retaining wall.

After removal of the slab and excavation to access the remnant bolts holes, it was determined that additional water infiltration was occurring as the water was channeling along the underside of the wale from the north and into the excavation. To better understand the source of the water, tracer dye was poured into existing ports in the operational area north of Repair Area B. No tracer die was detected coming into the excavation, indicating that the water was likely infiltrating through the bulkhead within the limits of Repair Area B.

6. REPAIRS COMPLETED

The following provides a description of the repairs completed, including the original scoped repairs to stabilize the failed portion of the bulkhead in Repair Area A, as well as the additional repairs completed in Repair Area B. A copy of the As-built drawings detailing the repairs are included in Appendix E.

6.1. Repair Area A

6.1.1. Structural Repairs

The structural repair approach to stabilize the failed portion of the bulkhead consisted of jacking the wale back into alignment with the bolt holes, replacing failed wale connection bolts, and pulling the sheet pile back to the maximum extent practical by jetting the backfill and tension the wale connection bolts. All components not suitable for re-use or not able to be recovered, were replaced to match the existing design, with the exception of using hot-dipped galvanized (HDG) components instead of plain steel for additional corrosion protection.

Replacement bolts consisted of 7/8 in. diameter ASTM A307 all-thread rod, and exterior plate washers consisted of HDG 3 in. x 6 in. x 5/8 in. plate washers. Interior plate washers were recovered from the excavation and re-used. During the process of pulling the sheet pile back into alignment, the threads on the all-thread rods were stripped during tensioning of the replacement bolts. As a result, 7/8 in. diameter steel threaded rebar was used in place of the all-thread rod at a total of eight locations due to the rebar’s higher thread strength. Although the rebar has a higher yield stress than the all-thread rod and therefore is structurally adequate, to maintain similar load path capacities with the original design, all rebar bolts were replaced with all-thread rod prior to finalizing repairs at the direction of the Coast Guard.

Due to the soil compaction behind the sheet pile resulting from the outward wall movement during the failure, an attempt to pull the sheet pile completely back to the original alignment would bend the sheets, increase flexural stress on the sheet pile, and increase wale system loads. Therefore, the sheet pile was only pulled back to the maximum extent possible using incremental loading and limiting sheet pile deformations. To maintain a positive connection between the wale and sheet pile, a combination of 4x4 and 2x4 pressure treated timber shims were utilized in between the wale and sheet pile at each bolt connection.

Once the bulkhead was stabilized, the excavation was filled to a minimum of 4 ft. above the wale with compacted #57 crushed stone aggregate, lined with filter fabric, and then overlaid with fine-grained compacted backfill. The site was brought to the finish grade with a 9-in. thick layer of compacted aggregate base course (ABC), and 3 in. of bituminous asphalt pavement. Prior to repaving, a reinforced concrete cap was placed on the top of the bulkhead to match the existing, with the exception of a varying width to help aesthetically mask the deflected sheet pile shape along the top of the bulkhead.

6.1.2. Drainage and Site Improvements

The existing 12 in. diameter reinforced concrete drainage pipe that had failed behind the bulkhead was removed and replaced with a 12 in. high-density polyethylene (HDPE) pipe, extending from the face of the bulkhead back approximately 20 ft. to the catch basin. The HDPE pipe was determine to be the best alternative as a replacement pipe as it has excellent resistance to corrosion, was readily available, and provides the structural and performance criteria required to replace the existing pipe. The concrete catch basin the pipe extends to the bulkhead from was replaced in-kind.

To improve drainage behind the bulkhead, the #57 stone was used as the primary backfill to essentially serve as a large French drain. After the crushed stone backfill was placed, the repair area was observed to be very well draining, with no significant tidal lag observed during falling tides. Additionally, drain outlets were cast into the concrete bulkhead cap to match the existing, and the pavement was installed to pitch away from the bulkhead face and into the catch basins for improved drainage of storm water runoff.

During construction a sanitary sewer manhole was discovered approximately 30 ft. behind the bulkhead, at approximately Station 4+85. The top of the manhole was located 2 in. below the existing grade and had been previously covered by the asphalt pavers. After confirming with the City of Wilmington that the manhole was abandoned, the manhole was knocked down sufficiently below grade to maintain minimum cover for subgrade placement and paving, filled in, and paved over per the direction of the Coast Guard.

After all drainage improvements and backfilling was completed, the entire limits of the excavation and areas disturbed from construction were compacted and paved to restore operations of the site as a pedestrian walkway and city park.

6.2. Repair Area B

6.2.1. Structural Repairs

The structural repairs completed in Repair Area B consisted of replacing the two missing bolts with 1 in. diameter HDG ASTM F1554 Grade 105 ksi threaded rod, with HDG exterior plate washers to match the existing, and reinstalling the existing interior plate washers which were recovered from the excavation. The original wale connection bolts in the operational area of the bulkhead were 1 1/8 in diameter; however, HDG ASTM A307 rods were not readily available in this size. Therefore, the smaller diameter ASTM F1554 threaded rod was determined to be most suitable replacement available, as the bolts have significantly higher yield stress to meet the required strength of the original bolts.

Once the bolts were replaced, the excavation was lined with filter fabric and backfilled with compacted #57 crushed stone aggregate. The final finish grade was established with a 9-in. layer of ABC and 3 in. of bituminous asphalt pavement.

6.2.2. Drainage and Site Improvements

As the northern area of Repair Area B did not include structural repairs and only included filling the existing void, a steel sheet pile and filter fabric plug was installed at Station 4+60. The purpose of the plug was to seal off the working excavation areas and inhibit water infiltration and migration of fines. The plug consisted of driving 12-ft. long steel sheet pile perpendicular to the bulkhead, extending from the wale back approximately 5 ft. from the face of the bulkhead. A concrete tremie seal was provided where the sheet pile intersected the bulkhead, and filter fabric filled with crushed stone aggregate was placed on either side of the sheet pile. Once the water infiltration was minimized, the entire excavation and void in Repair Area B was lined with filter fabric and backfilled.

In order to access the void, the existing concrete slab and brick facing against the bulkhead was removed in the area of work. In lieu of in-kind replacement, the concrete slab removed was replaced with bituminous pavement, and the brick facing replaced with a cast-in-place concrete facing. The grading of the bituminous pavement was also improved to slope away from the face of the bulkhead back into the storm water catch basins.

Respectfully submitted, COLLINS ENGINEERS, INC.

Elizabeth C. Burkhart, P.E.

Coast Guard Program Manager

Originated by:

Zachary D. Jenkins, P.E., S.E.

A-1

APPENDIX A – PHOTOGRAPHS

A-2

Photograph 1 Overall of Repair Area A after Excavation, Looking

South.

Photograph 2 Overall of Wale Assembly in Repair Area A after

Excavation, Looking South.

A-3

Photograph 3 Exposed Wale in Repair Area A. Note typical wale and sheet pile condition.

Photograph 4 Typical Wale Condition in Repair Area A.

A-4

Photograph 5 Coating Failure and Minor Corrosion with Scaling on

Wale at Station 5+15. Note bottom wale splice.

Photograph 6 Failed Wale Connection Bolts and Vertical Separation

Between Wale and Bolt Holes at Station 5+17, Repair Area A. Note bolt holes plugged with timber shims.

A-5

Photograph 7 Horizontal Separation at Station 5+18 Between Wale and Bolt Holes, Repair Area A.

Photograph 8 Typical Tie-Back Nut and Plate Washer Condition, Repair Area A.

A-6

Photograph 9 Under-engaged Tie-back Nut at Station 5+18, Repair

Area A. Nut tightened during repairs.

Photograph 10 Deformed Tie-back Rod at Station 5+09, Repair Area A.

A-7

Photograph 11 Gouges in Tie-Back Rod at Station 5+00, Repair Area A.

Photograph 12 Typical Pile Cap Construction, Repair Area A.

A-8

Photograph 13 Typical Pile Cap and Sheet Pile Condition, Repair

Area A.

Photograph 14 Site Flooding Following Hurricane Matthew, Looking

Northwest.

A-9

Photograph 15 Site Flooding Following Hurricane Matthew, Looking

South.

A-10

Photograph 16 Void in Repair Area B, Following Partial Slab

Removal, Looking Northwest.

Photograph 17 Void Below Slab in Repair Area B, Looking North.

A-11

Photograph 18 Wale and Tie-Back Condition in Repair Area B.

A-12

Photograph 19 Overall of Repair Area A, Following Bolt

Replacement and Shim Installation.

A-13

Photograph 20 Replacements Bolts Between Station 5+18 and Station

5+26, Repair Area A.

Photograph 21 Repair Area A, Following Initial Backfill Placement of

Crushed Stone Aggregate, Repair Area A.

A-14

Photograph 22 Replacement Storm Water Pipe Behind Bulkhead in

Repair Area A.

Photograph 23 Repair Area A, Prior to Repaving.

A-15

Photograph 24 Repair Area A and Concrete Cap, Following

Repaving.

Photograph 25 Replacement Bolts Just North of Retaining Wall, Repair Area B.

A-16

Photograph 26 Steel Sheet Pile Plug to Stop Water Infiltration at

Station 4+65, Repair Area B.

Photograph 27 Filter Fabric Placement Prior to Backfilling, Repair Area B.

A-17

Photograph 28 Repair Area B Following Backfilling and Prior to

Repaving.

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APPENDIX B – INSPECTION MEASUREMENTS AND OBSERVATIONS

C2

REPAIR AREAS

INSPECTION LOCATION PLAN

B1

INSPECTION PLAN

A1

SECTION AT TIE-BACK

A2

SECTION AT WALE BOLT

A1

A3

SHEET PILE ELEVATION

A2

A3

C-1

APPENDIX C – PULSE-ECHO TIE ROD TEST RESLTS

Dispersive Wave Propagation Testing of Existing Tie Rods within a Sheet Pile Tieback System

Report Prepared for Collins Engineering, Inc.

Site Name: USCG Cutter Diligence Moorings N Water St. - Wilmington, NC

Lat: 34.23635 Lon: -77.95006

FDH Project Number 16PWFV1450

FDH Velocitel, Inc.

6521 Meridien Dr.

Raleigh, NC 27616

T: (919)755-1012 F: (919) 755-1031 www.fdhvelocitel.com

12/1/2016

Reviewed By:Prepared By:

Rakesh Anthony Khan, PE Engineering Manager

Engineering Investigative Services

Brennon Jarrett Fuqua, PMP, EI Project Manager

Engineering Investigative Services

2 Nondestructive Testing Report Collins Engineering, Inc.

12/1/2016

6521 Meridien Drive Raleigh, NC 27616 Ph: (919)755-1012 Fax: (919)755-1031 info@fdhvelocitel.com

TABLE OF CONTENTS

EXECUTIVE SUMMARY…………..………………………………………………..

Scope of Work The FDH Velocitel Testing Methodology

DISCUSSION………………………………………………………………………….

GENERAL COMMENTS/LIMITATIONS….………………………………………..

APPENDIX…………………………………………………………………………….

Site Layout Sample Test Results

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EXECUTIVE SUMMARY

Dispersive Wave Signal Analysis:

Prepared By: Reviewed By:

David Milligan Laura Guy Signal Analyst Manager – Signal Analyst Nondestructive Testing Services Nondestructive Testing Services

FDH Velocitel 6521 Meridien Drive – Raleigh, NC 27616 Tel: (919)755-1012 Fax: (919)755-1031

Client: Collins Engineering, Inc.

Project Location: N. Water Street - Wilmington, NC

Investigated Element: Sheet Pile Tie Rod

No. of Tie Rods Investigated: Seven (7)

Scope of Work

Field crews from FDH Velocitel (FDHV) performed a nondestructive Dispersive Wave investigation of the tie rods for the above mentioned mooring in Wilmington, NC. All the rods were tested utilizing impact echo (IE) techniques. These tests were conducted to collect data used for determining the rods’ overall, in-situ length and location of discontinuities greater than 1/3 rod diameter. The data acquired was transmitted to FDHV’s offices in Raleigh, NC where it was post-processed and analyzed. Contained herein are the results from this analysis.

The FDHV Testing Methodology

FDHV’s method of Impact Echo records the dispersive waves produced by a hand-held impact device with accelerometers (gages) that are temporarily mounted directly adjacent to the impact area. The waves created by the blow propagate throughout the rod and are recorded as they return on a digital storage oscilloscope. The data is then analyzed by digital signal processing techniques using special software designed by FDHV. This analysis permits computation of the time needed for a select group of waves to travel from the gages to the end of the rod and back.

The rod’s length is then computed from the product of the assumed compressive wave speed and measured wave time.

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DISCUSSION

The computed tie rod lengths shown below in Table 1 are considered to be from the exposed tie rod end to the first joint. The values shown in Table 1 are averages from the data collected in the field at each rod. If there is a break, fracture, deterioration, or some other significant material anomaly in the rod, a strong return would be found on the record at the approximate location of the apparent damage. The computed length then would be the distance from grade to the location of such a material anomaly.

Table 1: Computed Average Tie Rod Lengths

Rod Test Method Overall Length Reflection (ft.)

1 IE 34.9

2 IE 34.5

3 IE 27.7

4 IE 29.1

5 IE 27.8

6 IE 27.9

7 IE 30.6

The site is situated beyond the wharf area. Rod 1 is the northernmost part of the site pit, while Rod 7 is the southernmost.

Tie rods at the site, beyond the wharf area, have a total design length of between 55 and 66 feet, plus the width of the concrete anchor, per the drawing provided by your office (Drawing No.

107817, Sheet 6 of 13, dated 12/30/64). Tests indicate a joint at approximately half the design length, which most likely represents the location of a single turnbuckle. This turnbuckle is shown but not dimensioned on the provided drawing.

Example data is provided in the Appendix for each tie rod tested. Note that the lengths shown on the sample data and the lengths in Table 1 are not equivalent. The data illustrates the nature of energy propagation in each rod from one of several tests run on that rod. The average length from tests is presented in the table above

In summary, testing suggests that a single discontinuity is present in each rod, and this discontinuity is most likely associated with coupling at a turnbuckle. Additionally, visual observation of tie rods within site pits did not indicate signs of significant corrosion or distress.

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GENERAL COMMENTS/LIMITATIONS

Professional judgments are incorporated into this report. These are based on our evaluations of field information gathered, on our understanding of the characteristics of the project, and on our experience and capabilities using dispersive wave propagation methods. We do not guarantee performance of this project in any respect, only that our work and judgments rendered meet the standard of care of our profession.

Wave propagation testing uses the fact that wave energy is mechanically generated and allowed to travel up and down the rod’s length. Wave reflections, used for thickness or depth computations, are caused by energy encountering either the bottom of the timber, voids, fractures, breaks, deterioration/corrosion, or varying material properties. If such areas are present, a strong return would be found on the record at the approximate location of the apparent interface. The computed length then would be the distance from the grade to the location of such a material anomaly.

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Appendix

U S CG CU T T ER DIL IGEN CEM O O R IN G – S A M P L ES IGN A L S

(N O T AL L DAT A P R O VIDED)

Figure1.P lotofm easuredsignalfrom Im pactEchotestingonAnchor1 w iththenotedinitial im pactandreturnreflectionfrom theturnbucklehavingbeenoutlined.

Figure2.P lotofm easuredsignalfrom Im pactEchotestingonAnchor2 w iththenotedinitial im pactandreturnreflectionfrom theturnbucklehavingbeenoutlined.

Figure3.P lotofm easuredsignalfrom Im pactEchotestingonAnchor3 w iththenotedinitial

Figure4.P lotofm easuredsignalfrom Im pactEchotestingonAnchor4 w iththenotedinitial

Figure5.P lotofm easuredsignalfrom Im pactEchotestingonAnchor5 w iththenotedinitial

Figure6.P lotofm easuredsignalfrom Im pactEchotestingonAnchor6 w iththenotedinitial

Figure7.P lotofm easuredsignalfrom Im pactEchotestingonAnchor7w iththenotedinitial

D-1

APPENDIX D – DESCRIPTION OF PROJECT APPROACH

D-2

Project Approach for Collins Engineers, Inc.’s Engineering Services, except as noted:

1. Provide a project approach for the field inspection and design of repairs to the existing structure between Stations 4+80 and 5+50.

2. Ensure coordination of construction activities with the City of Wilmington.

3. Provide the following design details:

a. Provide a specification and detail for restoration of the paved and unpaved surfaces, including backfill, after completion of the inspection.

b. Provide repair design details for anticipated wale to steel sheet connection.

c. Provide a design detail to replace the broken storm water drain line.

d. Provide a design detail to provide additional drainage at the bulkhead, such as by installing prefabricated drains in the sheet piles or a French drain behind the bulkhead.

e. Provide a concrete bulkhead cap design to replace the existing.

4. Review the construction contractor’s plan for the excavation, stabilization, and realignment of the bulkhead section.

5. Photograph and identify areas of subsidence along the length of the topside and cap.

6. Monitor and document the excavation to uncover the wale and tie-rod connection to the sheet piles between Station 4+80 and 5+50. Excavation will be continued to at least 1 ft below the bottom of the wale. Tie rod to wale connections will also be exposed.

7. Provide the following:

a. Photographs of conditions at the wale connections

b. Visual inspection of the exposed tie rod including remaining diameter, surface deterioration or corrosion, and the integrity of the connection to the wale or anchor wall

c. Visual and D-meter (non-destructive) inspection of the wale and connections including the condition of bolts and channels, remaining section, and surface deterioration or corrosion

d. Visual and (D-meter) non-destructive inspection of the sheet pile section and the anchor wall including remaining section and surface deterioration or corrosion

e. Pulse echo (non-destructive) testing of the anchor rods at the excavated end to determine remaining area of the tie rod and the location of discontinuities in the tie rod. (by Collins’ subconsultant)

8. Determine if the repair design detail provided is adequate for the repair of the failure of the bulkhead. If failure mode is not limited to the wale to steel sheet connection, notify the Contracting Officer of changed conditions, and provide the design detailing of a suitable repair method.

9. Monitor and document the repair installation to ensure that it is suitable. Provide engineering guidance to troubleshoot problems related to the repair and realignment of the bulkhead section.

D-3

10. Provide as-built drawings that document the work performed at the site under this contract. Drawings will be sealed by a professional engineer.

11. Provide draft and final engineering reports documenting the work performed at the site.

The report will be sealed by a professional engineer.

E-1

APPENDIX E – AS-BUILT DRAWINGS

MARCH 2017

HALF-SIZE DRAWINGS - SCALE ACCORDINGLY