A-Line Relief Interceptor Phase 2A

Project Details

Earth Pressure Balance Pipejacking

  • 96-inch ID RCP gravity sewer
  • 3,000 feet in two drives (Record Length)


  • 72-inch ID RCP gravity sewer
  • 1,000 feet in two drives

Geotechnical Conditions

  • Soft to stiff fat clay, high groundwater


  • Traffic control in urban area
  • Very shallow grade
  • Flight path restrictions
  • Golf Course protection

Project Overview

As the trenchless subconsultant to Carollo Engineers Inc., Bennett Trenchless Engineers provided preliminary and final design services for the trenchless installation of 4,000 feet of 72- and 96-inch gravity sewer through a golf course and a congested urban area. In addition to reducing impacts to residents and businesses, challenges included coordination with the local airport, limited work areas at shaft locations, high groundwater levels, low earth cover, utility conflicts and limiting impacts to a high traffic bike trail.

Bennett Trenchless Engineers led the evaluation of shaft locations, staging areas, and trenchless construction methods. Bennett Trenchless Engineers also reviewed geotechnical information, and prepared cost estimates, pipe material recommendations, settlement evaluations and monitoring plan, specifications, and construction schedules. The construction methods selected for the final design were earth pressure balance pipejacking for the 96-inch pipeline, and microtunneling for the 72-inch pipeline. Bennett Trenchless also provided construction inspection for the trenchless components of this project. The project was completed within budget with no claims.