SNI FOCUS HDD ENGINEERING

 

San Nicolas Island (SNI) Fiber Optic Communications Undersea System (FOCUS) HDD Engineering, Undersea Cable, Stabilization and Repair

Brief Description

San Nicolas Island, California, is a major Navy research and development test site. Data and communications between SNI and the mainland at Point Mugu are provided by a redundant ring configuration of two fiber optic cables, called FOCUS (Fiber Optic Communications Undersea System). The cables were originally installed in 1992. The original shore cable protection system at SNI consisted of single armor cable pulled inside a 1.1-kilometer-long, five-inch outside diameter (OD) length of commercial drill pipe anchored to the sandstone seafloor (one conduit for each cable), out to a water depth of approximately 11 meters. Beyond the conduit pipe, the cable was surface-laid on the seafloor.

One of the cables failed at the shore end on SNI because of exposure to open ocean waves and inadequate protection of the cable at the surf zone. An underwater inspection in 2003 showed that the other cable was seriously deteriorated and likely to fail soon. This would leave the SNI test site with only a limited bandwidth, unsecure microwave communications system with sometimes questionable reliability. SST was tasked to replace both of the SNI FOCUS shore ends with new cables that were landed with horizontal directionally drilled bores. In addition to providing substantially improved protection to the cables exposed to Pacific Ocean waves, HDD allowed landing the cables at a Snowy Plover nesting site without causing any environmental impacts, since the bores were about 30 ft below grade.

 

Drilling the HDD Shore Bypass

The environmental permit obtained for the project provided for only a single bore. Therefore, it was necessary to find a HDD solution that would accommodate the two replacements and one spare cable in a single bore hole. A trade study showed that using a single bore with multiple cables in the conduit provided substantial cost savings over multiple bores and would meet the environmental requirements. The project brought three cables (two FOCUS shore ends and a spare) ashore through a single bore and conduit. This was the first time this had been done.

 

Terrestrial Cable Installation

The FOCUS terrestrial cable operations included the installation of approximately 11.2 kilometers of cable in new and existing conduits on SNI.