SCWA Vortex Tube Rehabilitation Project

Project Details

Auger Boring

  • 36-inch steel creek bypass pipeline
  • 215-foot crossing of Monterey Drive

Geotechnical Conditions

  • Hard sandy fat clay over andesite
  • Groundwater at casing invert
  • Loose sand/soft clay behind thrust block


  • Mitigate impacts to creek in work area
  • Constrained work areas
  • Difficult geotechnical conditions
  • Short construction season

Project Overview

As a subconsultant to BKF, Bennett Trenchless provided full design services for the auger bore installation of 215 feet of 36-inch steel pipeline under Monterey Drive.  The pipeline provided a bypass for dry-weather flows of Santa Rosa Creek to allow for rehabilitation of the existing parallel 96-inch vortex pipeline.  Trenchless construction was necessary to limit impacts to Monterey Drive, which is a major commuter thoroughfare located on an approximately 12-foot high embankment which paralleled the creek.  Bennett Trenchless conducted a feasibility study to determine appropriate trenchless methods, drafted trenchless technical specifications, provided drawing edits, and provided an estimate of construction cost and duration.   

Challenges on the project included mitigating construction impacts while working within the creek channel on both sides of the crossing, including a nearby fish ladder; challenging geotechnical conditions including a gravel/rock contact; low depth of cover on the jacking side resulting in reduced jacking capacity; protecting the concrete aprons on the embankment; and a compressed construction season in which to construct both the bypass pipeline, rehabilitate the existing pipeline, and create the gated bypass structure.  Coordination between the owner, the rehab team, and the trenchless team was critical in the project’s success.