3 - Steel Plate Damage Prevention Work Plan rev5 4 Example.pdf

Steel Plate Damage Prevention Work Plan

EXAMPLE

Port Jersey

New York and New Jersey Harbor

Steel Plate Damage Prevention Work Plan

Contents:

Introduction ............................................................................................................................... Page 2

A. Location of Plates & Scope of Work… .................................................................................. Page 2

B. 3rd Party Before Dredging & After Dredging Surveying and Remote Sensing… .................. Page 2

C. Dredge Description & Specifications ..................................................................................... Page 3

D. X CY “Level Cut” Environmental Cable Arm Bucket Description & Specifications ............... Page 3

E. Clamshell Dredge, Bucket & Spud Positioning ..................................................................... Page 3

F. Guidelines & Methodology for Digging over Steel Plates… .................................................. Page 4

G. Monitoring Progress by Hydrographic Survey .......................................................................Page 5

H. Defining “Disturbance” & Plan to Reposition Disturbed Plates… ........................................ Page 6

I. THE CONTRACTOR Communication with USACE & PVSC… ............................................ Page 7

J. Attachment 1 - Survey Specification

K. Attachment 2 - Dredging Bucket position closing line relative to edge / lip of the steel plate (typical drawing)

Introduction

THE CONTRACTOR will maintain a proficient quality control system to ensure that the work performed under the referenced contract meets contract requirements incorporated within the plans and specifications. All work will be subject to inspection before acceptance to ensure compliance with the terms of the contract. This document is intended to provide information regarding the method THE CONTRACTOR intends to use while digging over the top of the Passaic Valley Sewerage Commission (PVSC) Tunnel protective steel plates.

A. Location of Plates & Scope of Work

THE CONTRACTOR has knowledge of the location of the steel protective plates over the top of the Passaic Valley Sewerage Commission (PVSC) Tunnel that crosses under Port Jersey. THE CONTRACTOR will be referencing the As-Built locations of every plate as received from the USACE (S-PJ-4 Steel Plate Installation As-Built Drawings attached to solicitation) to plan the digging procedures in this area.

The plates are 30ft x 4ft x 0.4ft (5in). The allowable gap between the plates was 0.33ft, except in the rock area. The top of the plates was to be placed between an elevation of -52.0ft and -52.5ft. The tilt of each plate had to be less than 2%, with less than 9.6% confidence interval. The ramp of each plate must be less than 1%. To accommodate changes, the contractor placed half-sized plates (i.e., 15ft x 4ft x 0.4ft). The total number of plates is four hundred and twenty nine. Of these four hundred and thirteen are full size plates, and sixteen are half-size plates.

The contract requires clearance to grade of -50.0ft elevation within the Acceptance Section defined in the provided Project Plans. Throughout this document, Design Depth refers to THE CONTRACTOR’s target digging depth as designed to meet contracted water depth obligations based on survey results. Given the proximity of Grade to the steel plates, for digging purposes THE CONTRACTOR defines initial Design Depth as 50.0ft below USACE MLLW.

B. 3rd Party Before Dredging & After Dredging Surveying and Remote Sensing

THE CONTRACTOR has hired HYDROGRAPHIC SURVEYOR (hereby known as E4Sciences) to perform hydrographic and remote sensing surveys before and after dredging. E4Sciences is familiar with this work site and qualified to perform this role. They were the third party surveyor responsible for Quality Assurance during the original contract to place the steel plates in 2011-2012.

E4Sciences will perform sub-bottom reflection seismology as the best approach for mapping the plates under the sediments. The seismic signal will penetrate the sediment and reflect off the top of the plates to profile their position in xyz. Successive profiles of each plate will determine their relative and absolute locations.

The error in the absolute locations will be determined by comparison with the orthosonographs and multibeam in the areas where the plates are exposed. E4Sciences expects the horizontal error to be driven by the error of the RTK positioning elements and geometric spreading in the measurements. Repeat sampling of the sediment (for temperature measurements to determine speed of sound) and use of known benchmarks will improve overall accuracy.

E4Sciences’ Before Dredging (BD) survey results will be promptly made available to the USACE. This pre-construction BD survey will be what subsequent surveys of the plates are compared to in determining if THE CONTRACTOR disturbed any plates in the course of the dredging process. E4Sciences will perform a post- construction After Dredging (AD) survey with the same equipment and by the same methods as the BD survey.

E4Sciences estimates that its BD measurements of the plates will be accurate within +/- 1.5ft horizontally and +/- 0.3ft vertically and its AD measurements will be accurate within +/- 0.3ft horizontally and +/- 0.2ft vertically. Please see Attachment 1 for a breakdown of these estimates.

C. Dredge Description & Specifications

THE CONTRACTOR will use the (Typical Mechanical Clamshell DREDGE) to dig in Port Jersey. Clamshell dredges are floating platforms that house a heavy-duty cycle crane that uses a wire rope suspended bucket to excavate the sea bottom. The dredge locates itself in position during dredging operations by lowering retractable spuds to the sea bottom. Excavated material is loaded into barges (scows) for transportation by tugs to a disposal area. Clamshell dredges are equipped with positioning programs that allow the operator to accurately place the dredge, spuds, and buckets.

The Dredge hull dimensions are X ft by X ft by X ft with a draft of X ft. It operates bucket sizes between 12 and 50 cubic yards and digs in depths up to X ft. It has a X ft long boom with a X ft swing radius. The total installed power is X hp. The dredge is maneuvered with the assistance of a tending Tug Boat. It also walks itself forward with a walking spud in the rear of the dredge. See Attachment 2 for dredge dimension drawings.

D. X CY “Level Cut” Environmental Cable Arm Bucket Description & Specifications

The DREDGE will be equipped with a “Level Cut” X cubic yard, level cut environmental bucket for digging in Port Jersey. The bucket has no teeth and sides that overlap when closed to minimize spillage and turbidity. This bucket weighs X lbs in air (X lbs in water). The bucket has a near-square footprint of X ft length open x X ft wide. The bucket has a hoist wire, closing wire, and tag line attached. The bucket depth, bucket position, closing speed, closing force, and open / close status are all monitored and adjusted for digging requirements.

The 30CY Cable Arm Level Cut bucket is designed to penetrate no more than 6-inches deeper than the bucket’s initial elevation at the start of closing. This feature will be verified visually and before dredging begins by closing the bucket above the water surface. The tolerance will be measured by repeating the same test above the deck of the dredge. Please see attachment 3 for schematic and specifications of the bucket and its level cut feature.

E. Clamshell Dredge, Bucket & Spud Positioning

The DREDGE is equipped with a dredge positioning program that allows the operator to see in real time the position of the dredge, bucket, and spuds relative to the permanent features of the work area. This program is interfaced with multiple sensors and GPS antennas that monitor location, heading, swing angles, boom angles, bucket depth, and a bucket open / closed sensor. These parameters allow the operator to accurately position the dredge, bucket, and spuds during digging operations. All critical measurements are taken from detailed mechanical drawings of the dredge and verified physically. Each sensor is calibrated before any dredging operations begin.

Overall Horizontal Control of Dredge Position

The DREDGE is equipped with a Trimble XXX Modular Receiver. The Trimble XXX uses all currently available satellite signals including GLONASS, L1, L2 and the GPS modernized L2C code. A nearby base station will transmit Real Time Kinematic correction signals, which will improve the position on the dredge and survey vessel to sub-centimeter accuracy. This system is interfaced with a Windows-based computer that allows the operator to view the dredge position relative to permanent fixtures (such as the steel plates, designated no spud zones, shorelines, etc.).

A pre-check of the horizontal location given by the dredge’s positioning system will be performed prior to any dredging activities. During the check, land-based surveying equipment will be used to determine the horizontal position of the dredge, spuds and bucket. This check will be performed by an independent licensed surveyor, using a land-mounted Total Station to determine the relative positions of the bucket, spuds and

GPS positioning antennas. These will be compared to positions given by the dredge’s positioning system to establish that all horizontal positioning parameters are correct.

Local Horizontal Control of Bucket Position

The DREDGE’s positioning system integrates sensors and offsets to determine the horizontal location of the bucket at all times. The known, measured geometry of the dredge deck and crane, a heading gyro as well as swing and boom angle sensors interface with the GPS positioning described above to locate the horizontal position of the boom tip and bucket below.

Spud Positioning

The DREDGE’s positioning program monitors the location of each of the three dredge spuds that are raised and lowered via the use of dedicated on board electric winches. This program integrates the heading gyro on board and known offsets to each spud from the GPS antenna. In addition to the land-based survey check described above, spud position will be verified by hydrographic survey as an additional quality control. The operator monitors the position of all three spuds to avoid lowering any of them within designated “No Spud” Zones”. When working in Port Jersey, the “No Spud Zone” shown to the operator will be the 90-foot wide corridor defined by the 30-foot wide steel plates plus an additional 30-foot buffer zone to its east and west.

Water Level Recorder – Herrin Design Tide System + RTK Tide Gauge

An electronic water level gauge (manufactured by Herrin Design) and adjacent tide board will be installed on a permanent, protected bulkhead approximately 1500 feet from the work area. The electronic gauge measures and transmits live water elevation as it changes with tidal currents. The electronic water level system provides real-time data for logging on board the dredge and survey vessel. The system uses a pressure transducer reading that is correlated to the elevation of the water surface at the time. This electronic water level is calibrated to known tide levels and adjusted to correspond to the project datum, USACE MLW. The adjacent board is used to keep the electronic gauge calibrated throughout the project via daily checks.

Additionally, an RTK tide gauge will be installed on board the dredge to provide sub-decimeter tidal accuracy at the dredge’s location. This tide gauge uses a pressure transducer installed over the side of the deck to measure freeboard in combination with an RTK-aided GPS receiver mounted nearby. With known offsets between the two, THE CONTRACTOR tracks the local elevation of the water surface throughout the project.

This redundancy serves as a check on the nearby Herrin Design Tide System described above.

Local Vertical Control of Bucket Position

To calculate the relative vertical position of the bucket to the water elevation, the dredge’s hoisting wire drum is equipped with revolution counters that measure the amount of wire paid in or out. This sensor provides live readings to the operator and observers (as well as a digital record) of the local vertical position of the bucket relative to the water surface. When calibrated and interfaced with the dredge positioning system and the Water Level Recording Devices described above, this gauge provides the depth of the bucket in the project datum, USACE MLW. As a redundancy, the hoisting wire will be marked, in two foot increments, from 50.0ft (Design Depth) to 58.0ft (Design Depth plus maximum expected tide of 8.0ft). In the event of extreme tides, extra markings will be incorporated as necessary.

F. Guidelines & Methodology for Digging over Steel Plates

When digging over the plates, THE CONTRACTOR will work within the following guidelines to ensure that the dig plan does not cause damage to or displacement of the plates.

Horizontal and Vertical QC Checks and calibrations will ensure equipment is positioned correctly and buckets are placed accurately.

Monitor the dig depth immediately after commencing dredging with hydrographic survey and at least two times per day thereafter to ensure work complies with Contract Plans and Specifications.

Monitor spud placement to ensure no spud is lowered over the top of the plates. Establish a “No

Spud Zone” to include the position of the plates plus a 30ft buffer to their east and west, to be incorporated into the background drawing on the positioning computer.

Lower open bucket to the water level to calibrate the bucket depth gauge to the tide value.

Lower bucket at a speed of 2 linear feet per second until stopping at the depth of 40ft prior to lowering bucket to Design Depth.

Resume lowering bucket at a speed of 1 linear foot per second until Design Depth so as to not cause possible excessive penetration of the bucket into the material above the plates.

Dig with the Bucket parallel to the steel plates to avoid picking up a plate.

Place Bucket in a way as to not allow the closing line to fall in line with an edge / lip of the steel plate. This will ensure the closing bucket lip does not push on the edge of the plate if it were to come into contact..

Bucket to be closed at a deliberate, controlled closing speed (targeting a ten-second close time) to reduce the chance of moving a plate if the bucket lip were to come into contact.

Monitor closing wire amp meter when closing the bucket to identify any spike in closing force that might correspond with a collision with a plate.

Put map (S-PJ-4 As-built drawings from solicitation to be checked against E4Sciences’ BD survey) of plates into background drawing so operators will see where buckets are placed in reference to the known existing location of the plates.

Utilize Bucket Depth Alarm in the Clamshell Positioning Computer to notify operator if the bucket is deeper than Design Depth prior to closing.

G. Monitoring Progress by Hydrographic Survey

THE CONTRACTOR will conduct its first conditional surveys upon removal of the first buckets taken and at least two times per day thereafter to monitor results. THE CONTRACTOR uses a multibeam sonar system to map the work area and monitor dig depths and locations with horizontal accuracy of +/- 0.3ft and vertical accuracy of +/- 0.1ft. Such surveys allow engineers to assess how the dredge is digging and inform any corrective actions needed. The following equipment will be calibrated and maintained daily and regularly checked against the results provided by E4Sciences and the USACE.

Multibeam Sonar

The SONAR MODEL is a shallow water multibeam system. It is designed for high resolution mapping in depths up to 300 meters. The SONAR MODELoperates at 200kHz, and is mounted at the head of the survey vessel, deployed via bow-mounted hydraulics. When not in use, the transducer is stored above the water line. The main features of this system are:

Swath Coverage: X degrees Equi-Distant and X degrees Equi-Angle Beam size longitudinal and width: X degree and X degree Depth resolution X mm Sweeps per second: X per second.

Navigation / Data Collection / Processing System

This Navigation / Data Collection / Processing System is PC-based Windows software by MANUFACTURER for planning and conducting hydrographic surveys. MANUFACTURER’S MB Max program is used for editing and publishing the survey data. Together, the programs provide hydrographic survey, channel setup, online navigation, data acquisition, data editing / tide correction, channel volume computations, channel cross sections, bathymetric plots and TIN modeling routines. These programs produce about 5 to 10 multi-beam fixes per 1ft2 and all of the other sensor data to output a corrected XYZ data set. Further, a binned data set is formed on a 3ft x 3ft or 5ft x 5ft grid (depending on the project and / or USACE specifications). The reduced sized, binned data set is easily managed and used for cross sections, batmaps and TIN volumes.

Heading, Heave, Pitch, & Roll Sensor – (MANUFACTURER)

The HDMS system is an inertial navigation system that provides heave, pitch, roll, and heading information to the multibeam system. System components include a control computer, Inertial Measurement Unit (IMU), and dual GPS antennas. The GPS antennas are used for position, heading and aid the IMU in determining the heave, pitch, and roll of the vessel. The system has a roll / pitch accuracy of 0.035 degrees, true heading accuracy RMS of 0.05 degrees, and a heave accuracy RMS of 5% of heave amplitude or 5 cm. The output of the system is supplied to the Reson system for correction of all sounding data.

RTK Receivers – MANUFACTURER

The Real Time Kinematic (RTK) positioning system consists of an MANUFACTURER Receiver receiving atmospheric corrections via radio-modem link (TDL 450H) to a base station. The receiver provides the positioning data to the Reson 7125 SV2 and is capable of providing real-time DGPS or RTK-OTF positions to sub-centimeter accuracy. The units track positions of up to 22 satellites and will be set in a mode that will not output positions if no RTK corrections are received. These receivers transmit NMEA-0183 position messages and QC data to the Reson 7125 at the rate of 5Hz. The GPS antenna with a ground plate is mounted close to the Reson 7125 transducer at the bow at about 3 meters above the water line. This is used to maximize the viewable sky, and minimize multi-path effects. The radio-modem antenna (TDL 450H) receiving RTCM messages for corrections, is mounted at another elevated location on the boat to ensure the best reception and greatest range.

Speed of Sound Sensor – Odom Digibar Pro

The Digibar uses a “sing-around” transducer to measure the actual sound velocity in the water column.

Factors such as water salinity and temperature are taken into account using this method. The samples are transmitted to the Reson 7125 for use in correcting sounding data. A new sound velocity profile is taken every two hours and / or tidal current direction change and / or new survey area. The observed sound velocities are logged in a daily survey log and electronically in the navigation / data collection system.

H. Defining “Disturbance” & Plan to Reposition Disturbed Plates

As discussed in Section B, once all material has been removed below the targeted project depth of 50.0ft E4Sciences will conduct an independent After Dredging (AD) inspection of the work area to determine if any steel plate has been disturbed during the dredging process. This AD inspection is to be performed using the same equipment, procedures and quality control measures as the Before Dredging (BD) inspection which will have established the condition of the plates before the start of work.

A plate will be considered disturbed if, as measured by the BD and AD inspections, its horizontal or vertical position is shown to change by a value greater than the established disturbance tolerance. The disturbance tolerance is defined as +/- 1.8ft in any horizontal direction and +/- 0.5ft in elevation. These tolerances are calculated by summing the BD and AD measurement accuracy tolerances established by E4Sciences discussed above and justified in Attachment 1.

If a plate is determined to have been disturbed, the following steps will be taken to relocate the plate to its BD location (within the AD inspection measurement accuracy defined for the equipment in use: +/- 0.3ft H and +/-0.2ft V):

Underwater divers will remove any remaining sedimentation from the surface of the plate using a handheld airlift dredging device. The diver will visually determine when the plate is clear of overburden before proceeding to the next step. If limited visibility underwater restricts the diver’s ability to determine that the plate is clear, multibeam survey will be employed as well.

Once the plate is determined to be cleared of overburden, an underwater welder will weld four padeyes to the plate, one to each corner of the plate (inset six inches from each edge) allowing for symmetrical rigging to keep the plate level upon repositioning. Once rigged, the crane operator will reposition the plate with the assistance of the dredge’s positioning software and divers acting as signalman via voice communication from below.

A monitor located in the crane operator’s cab will indicate the location for placement of the plate. The plate will be positioned over the design location and the plate will be lowered into place. Rotation of the plate into correct alignment is accomplished using tag lines from the shackles at the padeyes. The plates already in place will assist the divers to accurately guide the plate to its final location. Once the plate has been set on the bottom, divers will release the shackles from the padeyes. A confirmation survey will be performed by E4Sciences. Upon confirmation of the plate’s correct final position, the padeyes will be removed during a final dive.

In the event that the plate cannot be returned to its original location by such means, the bed layer of gravel below the plate will require levelling or otherwise adjusting. In that event, the plate will be lifted to the deck of the dredge. Once the plate has been removed divers will clean and level the original location of the displaced plate. Once the gravel bed is clear an inspection can take place by multibeam survey and any irregularities in the gravel bed will be further corrected by divers. Once survey reveals a level gravel bed at the desired elevation, the plate will be relocated by the means described above.

I. THE CONTRACTOR Communication with USACE & PVSC

Prior to any dredging, THE CONTRACTOR will provide the USACE a bathymetric map of the latest survey of the work area. Also, THE CONTRACTOR will notify Eric Granholm and James McCarthy at PVSC at least 24 hours prior to beginning work, at the start of each day dredging is performed and upon completion of work.

On the first day of work, THE CONTRACTOR will complete all calibrations. After the first set of buckets is removed, THE CONTRACTOR will survey the results to confirm the resulting water depth. The results of this first conditional survey will be shared with the USACE to demonstrate that the bucket is not disturbing material beyond the designed vertical depth or horizontal coordinates.

Attachment 1: E4Sciences Measurement Accuracy for Sub-bottom Profiling

EXPOSITION OF ACCURACY AND PRECISION OF E4SCIENCES’ SURVEY PROCEDURES

The determination of displacement of the plates horizontally or vertically relative to the locations in the as-built drawings will be accomplished by high-definition mapping. The mapping of the after-dredging configuration will be straightforward as the combination of multibeam, side-scan orthosonographs, and sub-bottom reflection seismology would provide repeatable accuracy of 0.2ft vertically and 0.3ft horizontally below the sediment. The challenge in the mapping project is to determine the before-dredging configuration of the plates. In the before-dredging state, the plates will be under a variable thickness of silt. The mapping of the before-dredging configuration will be challenging as the combination of multibeam, side-scan Orthosonographs, and sub-bottom reflection seismology would provide repeatable accuracy of 0.3ft vertically and 1.5ft horizontally at best.

We have as-built drawings and as-built imaging. We have side-scan images taken after the Sandy event.

Our strategy is to (a) image the plates in the current before-dredging state in May, (b) compare to the as-built drawings, and (c) image the after-dredging configuration. The major concern is the limitation in the accuracy of the measurements in the before-dredging mapping.

It is crucial to determine if at any time (a) the elevation of the plates reaches above -52.0ft MLW or (b) the plates have been horizontally displaced more than 1ft. The long axis displacement is limited to 4inches and the normal to axis displacement allows for several feet of displacement, therefore 1ft is adequate to determine the horizontal displacement. The vertical measurement is the difficult part to meet.

The methods include sub-bottom reflection seismology that will see through the sediment to the top of the plates. The numbers we give here below are for the before-dredge survey. The after-dredge survey specifications are better, 0.2ft vertically and 0.3ft horizontally

Sub-bottom reflection seismology (10kHz)

Penetration ~10ft Horizontal accuracy ~ ±1.5ft with dGPS (3ft) Vertical accuracy ~ ±0.3ft Vertical precision ~ ±0.2ft

Side-scan orthosonograph

Penetration ~0.1ft Horizontal accuracy ~ ±0.3ft Vertical accuracy ~ N.A.

Multibeam bathymetry

Penetration ~0.1ft Horizontal accuracy ~ ±0.25ft Vertical accuracy ~ ±0.1ft

Magnetic field

Horizontal accuracy ~ ±5ft Vertical accuracy ~ N.A.

By correlating the measurements, e4 estimates that:

Penetration ~10ft Horizontal accuracy ~ ±1.5ft (3ft) Vertical accuracy ~ ±0.3ft Vertical precision ~ ±0.2ft