Note: The following project description of the Hemlock Seawall Project is a portion of the approved Waterboard permit document for this project.
See entire document:  401 WQC 23-172 West Hemlock Street Seawall Repairs_combined-1

The Project Details

The seawall, between the 3900 and 3966 block of West Hemlock Street, spans horizontally and consists of 32 concrete panels (10 feet high by 10 feet wide) interspersed with 33 concrete pilasters (columns). Due to age and the surrounding marine environment, the structure is significantly deteriorated and requires repair and reinforcement. Overstress cracks to theconcrete panels and pilasters were observed in some sections due to exceedance of the seawall’s load-bearing capacity. Significant corrosion spalling was also observed on the corners of the pilasters and several panels exposed and corroded rebar. Without repairs, the structures will be damaged further over time and will need to be replaced. The repairs will prevent additional cracking, spalling, corrosion, and failure of the seawall and pilasters.

Project Activities
The project will cover 370 feet of seawall along West Hemlock Street. The work will repair 320 linear feet of concrete panels (0.5 inch thick), install 33 concrete pilaster jackets (six inches thick), and drive 12 steel H-piles into the channel to support the seawall during repair and construction.

The proposed work includes the following:

• The seawall will be stabilized with steel H-piles driven into the channel. The H-piles will bear the load of the seawall with timber blocks resting between the seawall and the Hpiles.
• Then the top two inches of concrete will be removed from the surface of the pilasters using lightweight, handheld, chipping tools.
• The pilasters will then be encased in a form. Reinforcing bars will be embedded between the form and pilaster. A marine, reinforced concrete, will be pumped through a hose into the form to create an external jacket, strengthening the pilasters.
• The H-piles and timber blocks will then be removed.
• A 0.5-inch-thick layer of weak or damaged concrete panels will then be removed through water blasting. The water blasting will span up to a height of eight feet.
• The seawall will be reinforced in between the pilasters with fiberglass, reinforced plastic (FRP) rods. The FRP rods will be embedded in slots that are cut into the wall.
• Prefabricated FRP panels will then be bonded to the seawall with a thin layer of epoxy and secured with screws.
• Cementitious mortar, consisting of aggregate and cement slurry, will also be sprayed from floating work platforms on sections of the seawall that were not installed with the FRP panels.

The concrete waste will be collected and placed in temporary covered enclosures, on a barge adjacent to the demolition area. At the end of each work period, waste from the work site will be transported offsite and be legally disposed.

The following vehicles and equipment will be used in waters during throughout the different phases of the project:

• Small work float platforms will be used in the active work area during construction activities to access seawalls from the water; and may be kept in the work area throughout the construction duration or removed daily based on the contractor’s means and methods. If removed daily, the float platforms would be transported off site to the contractor’s yard.
• A small work boat will be used to transport equipment, materials, some workers, and move docks if needed; transport to and from the site and between the work area and the site’s street loading zone; used during active construction in the active work area; and likely moored to an existing float at the street end when not in active use.

The pilasters repair work will occupy a total of 50 linear feet of space along the outside of the seawall and will be conducted in dry conditions during low tide. The seawall panel repairs will occupy 320 linear feet between the pilasters and will also be conducted in low tide, when practical.
The FRP panels and cementitious mortar will extend the seawall footprint by an inch (approximately 7 cubic yards).

Construction (including driving in and removing steel H-piles and timer blocks), repair work and staging of equipment, materials, and personnel will temporarily impact 0.25 acres of marine waters.

The new pilaster jackets, new FRP panels, and cementitious mortar will permanently impact 0.003 acres of marine waters.

Project activities are projected to start after issuance of the permits and last eight months with construction taking six months.

Note:
To read the entire approved Waterboard permit document see:   401 WQC 23-172 West Hemlock Street Seawall Repairs_combined-1

This page will contain schedule updates and information for residents to be impacted by this project.

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