FY01 MCON Project P-491 - Fukunaga & Associates, Inc.

Project Description

A key prerequisite for the Navy’s vision to develop Ford Island into a hub of commercial, residential and support activities within Pearl Harbor is the upgrade of the Island’s aging utility infrastructure. FY01 MCON Project P-491, Sewage Force Main, Ford Island to Pearl Harbor Naval Shipyard is the first of several infrastructure projects initiated by the P-491_1overall

Navy aimed to provide vital support of the proposed Ford Island development. The project, including a new force main and renovated pumping station, will provide the necessary wastewater transmission capacity needed to meet the anticipated increase in wastewater flows. The new force main will serve as the primary sewage conveyance route from the island, while the existing main will serve as a backup in the event of pipeline failure, or when system maintenance is required.

Most of the sewage force main was installed using horizontal directional drilling (HDD), a trenchless construction method involving precision drilling, reaming and pulling of the pipeline through a predetermined alignment. P-491_2 HDD was the most appropriate method for the installation of the pipeline across the Main Channel in Pearl Harbor where conventional underwater pipe laying would cause disruption of harbor operations and potential adverse environmental impacts by disturbing the Harbor’s bottom sediment, suspected of containing toxic material. HDD was also used on Ford Island to avoid disturbing historically significant sites from the December 7, 1941 attack, and through the Shipyard area where numerous utility and structural obstacles were present.

Background

With completion of the Admiral Clarey Bridge in 1998, the U.S. Navy’s Ford Island became readily accessible to visitors and future development. Later that year, the decommissioned battleship USS Missouri was permanently berthed at Ford Island, and officially opened as a memorial and museum honoring servicemen who fought for our country during World War II. These significant milestones are part of the Navy’s vision of developing Ford Island into a vibrant operations center, supplemental housing area and visitor/commercial attraction in Pearl Harbor. Along with the proposed growth, however, are the increased demands on the island’s utility infrastructure.

P-491_3 The Navy initiated several key infrastructure projects to provide vital support to the Ford Island Development. The first project is FY01 MCON Project P-491, Sewer Force Main, Ford Island to Pearl Harbor Naval Shipyard, and provides additional, “failsafe” wastewater transmission capacity with installation of over 6000 ft of 20-inch (OD) high-density polyethylene (HDPE) pipe. The project also include renovation of the main Ford Island wastewater pump station with installation of pumps capable of handling future demands.

Contribution to the Well-Being of People and Communities

The project provides enhanced wastewater transmission capabilities from Ford Island. This increased transmission capacity and system reliability allows the Navy to proceed with the P-491_4

Ford Island Development Plan. The Development Plan provides critically needed housing for Navy personnel, much needed economic revitalization to the area, and an opportunity for the Navy to showcase the historical significance of Pearl Harbor and its vital role in U.S.
military history.

Resourcefulness in Planning and Solving Design Challenges

The greatest challenge was installing the pipeline crossing under the 1200 ft wide and 50 ft deep Main Channel of Pearl Harbor. Major concerns were to avoid disrupting harbor operations, and restricting of the movements of Naval ships, key elements of our nation’s defense force. Construction equipment and activity within the Main Channel could impair harbor operations. Another concern was to minimize adverse water quality impacts that could potentially affect the ecosystem and recreational activities in adjacent near-shore waters. Sediments on the harbor bottom may be contaminated due to heavy industrial activity conducted within the facility in the past.

Another major challenge was to avoid damaging the numerous historical features on Ford Island, including World War II vintage buildings and significant physical features resulting from the December 7, 1941 attack that propelled the U.S. into World War II.

To meet these challenges, the design team and the Navy discussed options for the channel crossing. Major considerations included: impact on the environment, aesthetics, functional reliability, and preservation of the historical nature of this landmark. The selected solution was to install a new HDPE pipeline using HDD. The design called for drilling a 2000 ft long, 8-inch pilot hole across the Main Channel. The pilot hole would be 30 ft below the channel bottom, effectively preventing disturbance of the channel bottom. After the pilot hole was reamed and enlarged, a 20-inch HDPE pipe was pulled from Ford Island to the Shipyard. The use of HDD also preserved the historic features along the Ford Island waterfront.

The unprecedented length of the pull and tracking the drilling head 80 ft. below the ocean was especially challenging. The need to keep the Main Channel open ruled out the use of a large boat or barge to track the drill head as it crossed the channel. Instead, a tracking grid system installed by divers on the sea floor was used to monitor the position and depth of the drill head.

The new force main had to cross under the transport system used for moving the 500-ton Shipyard cranes. The challenge was to minimize down-time of the cranes, which were critical for shipyard operations. The Navy, design team and Contractor worked closely together to come up with an effective solution after it was discovered that the foundations deviated from details shown on record drawings.

P-491_7 Maintaining wastewater service on Ford Island during construction was a major goal for the project. An innovative sewage bypass plan was conceived that included high capacity, low head pumps to convey flows from the collection system into a portable wet well, and a second set of high head pumps to pump the wastewater into the existing force main across the channel.

Pioneering in Use of Materials and Methods

The use of HDPE pipe installed by HDD offered the following advantages:

HDPE is non-corrosive to both wastewater and seawater.
HDPE pipe was able to flex and curve around physical obstructions minimizing the need for fittings and other appurtenances that would have added cost to the project.
HDD caused minimal disruption of marine and on-land operations.
This was the first project to utilize HDD for a submarine crossing at Pearl Harbor.
The Main Channel crossing was the longest single-pull HDD installation to date using HDPE pipe.

Innovations in Construction

The use of HDPE pipe installed by HDD required several innovations in construction:

The use of HDD to install large diameter, heavy-walled HDPE pipe is relatively new to the industry. The tensile stresses developed while pulling the pipe through the borehole could potentially damage the HDPE pipe. The designers partnered with the drilling Contractor to carefully monitor the drilling and pull-back forces to ensure proper installation.
The ability to accurately install the submarine pipeline was critical to the project’s success. It was imperative that the drill head did not exit the ground and damage any of the historic features on Ford Island. With historic bomb craters located within 30 ft of the exit hole, the drill path needed to be accurately tracked at all times. A wire grid system laid on the sea floor allowed accurate tracking of the drill head path, and resulted in an exit hole within centimeters of the design point.

Impact on the Physical Environment

Application of HDD techniques resulted in minimal impacts on the physical environment.

No contaminated sediments were disturbed.
Dewatering and associated problems were avoided.
Handling and disposal of contaminated groundwater and excavated soil was minimized.
Significantly less construction-related disruptions were encountered compared with conventional, open trenching methods.
Disturbance of the numerous historical features along the pipeline alignment was avoided.

Beneficial Effects of the Project,
Including Aesthetic Value

Beneficial effects of the project include:

The reliability and capacity of the Ford Island wastewater collection system is greatly enhanced.
The Navy can proceed with its much-needed revitalization of Ford Island.