Pearl Harbor Channel Underwater_ _ _ _ _ . . Waterline Crossing

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Consultant’s Role in Project

Fukunaga & Associates, Inc. (FAINC) served as the prime engineering consultant for the project, as well as the civil design engineer. As the prime consultant, FAINC handled all project management responsibility and coordination with the project manager Naval Facilities Engineering Command (NAVFAC) Pacific, the water system owner NAVFAC, Hawaii and the sub-consultant team.

Project Description

The primary water transmission main that serves Ford Island and the Pearl Harbor Naval Complex was over 65 years old. In 2006 the existing 24-inch water main supplying potable water to Ford Island and the Pearl Harbor Naval Shipyard was broken when a construction

Plume Over Waterline Break

vessel inadvertently dropped anchor on the pipeline. This incident revealed the vulnerability of this critical water supply line lying exposed on the bottom of the Pearl Harbor channel. The existing cast-iron waterline, installed in 1952 was also nearing the end of its service life. To address the vulnerability and age of this critical water supply, a new 24-inch fusible polyvinyl chloride (FPVC) water main was installed beneath Pearl Harbor utilizing a horizontal directional drilling procedure that has greatly improved the performance and reliability of the Navy’s water distribution system.

Pipe Roller Set Ups

Design challenges included varying subsurface conditions (soft sediment – hard rock), underwater crossing including a pull distance of over 3,500 linear feet, high thrust forces for fittings on large diameter pipes, and connection to existing major transmission mains. The applied method placed the pipe below the channel bottom, eliminating the vulnerability of a surface laid pipe, and avoiding environmental disturbances associated with conventional underwater pipe laying operations.

See Project Gallery for additional photos and descriptions.

Design Considerations

Among the primary considerations for the project was the need to improve the efficiency and reliability of the Navy’s Pearl Harbor water system. This project reduces the vulnerability of the waterline by placing it below the channel bottom, removing the chance of another breach due to surface vessel and/or underwater activities. The project also provides much needed carrying capacity as well as backup capability for the water system to maintain water service to all base activities.

The application of “trenchless” construction methods used in this project also resulted in minimal impact on the environment. Of specific concern was the underwater crossing work that may have caused significant disturbance to the sediments on the Harbor bottom. It was imperative that the Harbor and near shore waters not be contaminated with suspended sediment that may contain hazardous or toxic materials.

Fusible Polyvinyl Chloride (FPVC) Pipeline Prior to Installation

The pipeline materials used in the project were selected for their corrosion resistant properties, with the intent of providing maximum service life. Furthermore, serviceable items such as valves and expansion couplings are installed in concrete vaults that allow service and replacement without the need to excavate large areas, reducing future impacts on the surrounding areas.

Innovative Use of Existing Technologies and Materials

This Pearl Harbor Channel Underwater Waterline Crossing project demonstrated how existing technologies and innovative use of pipe materials can be extended beyond conventional applications to provide effective solutions. The choice of an innovative high-strength pipe material allowed the use of horizontal directional drilling without the need for a protective casing or more costly methods such as micro tunneling. The continuous 3,500 foot long pipe string was pulled through the under-channel bore hole in one day thereby limiting the effects on the existing residences and Naval operations in the area.

Complexity

Various design elements were considered as part of the modified HDD method, including vertical alignment for minimum pipe bend radius, pulling loads on the FPVC pipe string, and estimation of estuarine consolidation for the long term stability of the installed pipeline. Borehole stability, heave and hydro-fracture potential were assessed for various

Pipe Insertion Site

drilling fluid scenarios. Construction observations were also vital for project success, including offshore drill head navigation to insure proper bore hole alignment and eliminating high points in the smooth sweeping pipeline profile. Constant monitoring of pull loads was also required to avoid overstressing the pipe string, which could potentially permanently impair the pressure rating and longevity of the waterline.

Other key design parameters included ensuring adequate cover below the harbor mud line and avoiding existing utilities, bunkers, pile-supported docks, buildings and other structures. The design phase also required selection of appropriate work and staging areas in Pearl Harbor & Ford Island, where the entire fused pipeline could be laid out for the continuous pull-in.

Conclusion

FAINC and the design team were fully engaged in support of the project from inception, through development, and final completion, partnering with both the project manager (NAVFAC, Pacific) and the owner (NAVFAC, Hawaii). As with most projects the construction cost was a major concern. It was a significant challenge to meet project objectives within the available budget. For this project, the original programming documents had set the original budget at $11.29 million. The final bid was $10.04 million. Much of the cost savings can be attributed to the innovative design of the under channel pipeline crossing.

The greatest long-term benefits to the Navy will be enhanced system reliability. The new waterline will provide a reliable water supply to Ford Island that will support further development that will continue to transform the island into a vibrant commercial, visitor and operations center within Pearl Harbor.

The design team completed the project on time and within the design budget. The project was put out to bid on schedule in 2012, with construction commencing, also as scheduled, in 2013. The project was substantially completed in 2015.