Summary and DescriptionA new 24-inch (ID) high-density polyethylene water main was installed beneath Pearl Harbor utilizing an innovative directional drilling and underwater splicing procedure that has greatly improved the performance and reliability of the Navy’s water distribution system. The applied method avoided environmental disturbances associated with conventional underwater pipe laying operations.
The primary water transmission main that serves Ford Island and the Pearl Harbor Naval Complex is over 75 years old. Failure of this primary line exposes the existing and proposed developments on Ford Island and potentially the Pearl Harbor Naval Shipyard to extended water supply outages and possible interruption or impairment of essential activities within the Naval Complex. A new replacement line was programmed and installed as part of this project to improve the reliability of the water system serving Pearl Harbor. Fukunaga & Associates, Inc. was selected by the Naval Facilities Engineering Command Pacific (NAVFAC Pacific) to provide engineering services to design the new replacement waterline.
and the water system owner (NAVFAC, Hawaii). Subconsultants for the project included: URS Corporation of Honolulu— geotechnical engineers and HDD consultant, MK Engineers, Ltd.—Electrical Engineers, and SLSH, Inc.— Structural Engineers.The design process for this project included a Functional Analysis Concept Development (FACD) study that brought together all stakeholders associated with the project. Participants included the project owner – NAVFAC, Hawaii; the client – NAVFAC Pacific; and the design team. The FACD effort defined the project scope, and emphasized the need for a commitment from all participants to work together towards a successful project, meeting the owner/client objectives and keeping within the available funding and project schedule. The commitment was formalized in a Partnering Agreement that documented the project scope and basis of design. The Agreement was signed by representatives of the Owner, Client and Fukunaga & Associates, Inc.—the prime consultant for the design team. This spirit of partnership and commitment carried throughout the project development and implementation, resulting in a final product that met the owner’s objectives and exceeded the expectations of improved system performance.
The first, and potentially the most difficult and costly challenge, was the under channel crossing beneath Pearl Harbor. From shoreline to shoreline, the crossing would need to cover over 5,000 linear feet. It would not be possible to make this crossing in a single pull using conventional HDD methods with thermoplastic pipe.
Careful inspection of a bathymetric survey of the harbor bottom identified a distinct drop-off after a shallow shelf on the northeast shore of Ford Island. By using two separate bores, with one starting from the Ford Island side (Bore No. 2), exiting at the toe of the steep drop-off, and the second starting from the Halawa shore (Bore No. 1) exiting just past the navigation channel, a continuous, sweeping profile through the underwater splice would be possible without creating a high-point under the channel. (The design profile is illustrated in Figure 2.) The underwater splice was backfilled with clean, crushed aggregate and covered with an articulated concrete matting system. This was done to protect the pipeline, and also to provide ballast to keep the pipeline permanently anchored in place. Providing the proper ballast volume and weights for the pipeline were crucial to insure stability throughout the underwater installation process, as well as for the permanent installation.The remainder of the waterline network on Ford Island was installed utilizing both conventional HDD and open trench operations. In all, approximately 19,550 linear feet of pipeline was installed on Ford Island. The total project construction cost was $12.0 million, which was well below the estimated construction cost (ECC) program budget of $12.6 million.
This project demonstrates how existing technologies can be extended beyond conventional applications to provide effective solutions. The two bore horizontal directional drilling and pipe string method used in this project exceeded conventional single point bore applications. The two bore method allowed the installation of a pipeline twice the length expected under conventional HDD operations. Of course, the use of dive operations for the underwater splice connection was required; however, this underwater work was substantially less than would be required for typical underwater pipe laying construction.
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 waters not be clouded with suspended sediment that may contain hazardous or toxic materials. 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.
Borehole stability, and heave and hydro-fracture potential were assessed for various drilling fluid scenarios. Risk of consequential damage to the adjacent pile supported Admiral Clarey Bridge from potential hydro-fracture or borehole collapse was also evaluated using finite element analysis of combined pipe and bridge soil-structure interaction, confirming HDD to be the preferred solution as compared to underwater cut and cover (trenching) methods. Construction observations were also vital for project success, including offshore Tru-Tracker drill head navigation to insure proper borehole alignment, avoiding encroachment into the bridge foundation support zone 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. Surface barge staging operations, with an assist rig to provide support of the pipeline during the over water staging and pipe string insertion operations, were required. Also, dive operations for the final underwater splice connection were also required to complete the installation of the submarine line.
(NAVFAC, Hawaii), as formalized in the FACD effort. 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 ECC at $12.6 million. The final design construction cost estimate was $12.1 million, and the actual final construction cost was $12.0 million. Much of the cost savings can be attributed to the innovative design of the under channel pipeline crossing.The design team completed the project on time and within the design budget, earning a Certificate of Appreciation from the Navy for “outstanding design and engineering services, responsiveness and highest level of professionalism.” The project was put out to bid on schedule in 2002, with construction commencing, also as scheduled, in 2003. The project was substantially completed in 2005. The waterline was operational and ready to support several key Ford Island facilities including the National Oceanic & Atmospheric Administration Pacific Regional Center and Ship Operations Facility (under construction), the Pacific Warfighting Center (in design), and the Pacific Aviation Museum (under construction).