I-680 at Sabercat Road Sanitary Sewer Relocation Project
Union Sanitary District, California

The I-680 at Sabercat Road sanitary sewer in Fremont, California, is a 12-inch diameter vitrified clay pipe (VCP) gravity pipeline installed about 50 years ago by open-cut trenching.  A CCTV survey revealed that the existing pipeline was severely offset where it crossed the Hayward fault.  The pipeline was replaced using trenchless methods (tunneling) along a parallel alignment 30 feet north of the existing pipeline which allowed the existing pipeline to remain active during construction.  The new alignment is approximately 1,000 feet long, has a depth of cover varying from about 9 feet to 50 feet, and crosses under an 8-lane freeway and across the active Hayward fault line.  The replacement pipeline was designed as a 12-inch High Density Polyethylene (HDPE) carrier pipe inside a 48-inch steel casing installed by Tunnel Boring Machine (TBM) pipe jacking. The design also included a 35 feet deep drop manhole at the upstream end.  Construction began in mid-June 2013, and tunneling began in early August. The tunnel daylighted in late September 2013, and the project was completed in December 2013. Highlights of the project approach and execution included:

  • Protecting traveling public and avoiding costly emergency repairs
  • Selecting the alignments and construction methods to meet the unique project and site conditions
  • Keeping change orders low and project on schedule
  • Improving cost effectiveness with use of a pressure balance tunneling machine with allowed rubble to be cleared with no change orders required and no lost time in the schedule for the contractor
  • Providing environmental permitting, and CEQA documentation to address environmental concerns including proximity to two community creeks and the potential for locating pre-historic fossils

Industry Awards

  • California Water Environment Association (CWEA), San Francisco Bay Area Section 2014 Engineering Achievement Award