Timber Cove Culvert Replacement 04-3G7404

Project Details

Pipe Ramming

  • 108-inch steel casing for culvert
  • 88-foot crossing under Route 1

Geotechnical Conditions

  • Fill from road construction
  • Active water flow

Challenges

  • Severely restricted work areas
  • Steeply sloped terrain
  • Short construction window
  • Minimize traffic impacts

Project Overview

As a subconsultant to WRECO, Bennett Trenchless provided design services for the trenchless replacement of an existing 48-inch culvert beneath US Route 1 along the Northern California coast for Caltrans. The original CMP culvert was installed on a steep grade under a hairpin turn in the road along a steep section of the coast, resulting in high velocity flows. The invert of the culvert was completely deteriorated and the culvert diameter was too small to pass large debris during storm events. Although the culvert was only about 90 feet long, open-cut methods could not be used due to the lack of a convenient detour around the remote project location. In addition, Caltrans required that the pipe be upsized to 108-inch to reduce the frequency of debris removal at the upstream end. Increasing the culvert diameter significantly reduced the depth of cover beneath the roadway, increasing the risk of settlement. The existing culvert was installed at the same time as the road was constructed. No geotechnical borings were drilled, but the ground conditions at the crossing site were anticipated to be debris from the road construction, increasing the likelihood of cobbles and boulders.

Bennett Trenchless conducted a feasibility evaluation of the trenchless crossing. Due to severe work area restrictions and a two-month construction window, pipe ramming was selected as the recommended construction method. Bennett Trenchless developed a pipe ramming (non-standard) specification for Caltrans as this project was the first time Caltrans had used pipe ramming. Bennett Trenchless also conducted settlement analysis, provided drawing mark-ups, and provided engineering services during construction.

Line 210 A,B,C Replacement Project at Cordelia Valve Lot

Project Details

HDD

  • 16- and 24-inch gas transmission lines
  • Twin 1,000-foot bores

Guided Boring

  • Twin 400-foot crossings of I-80
  • Single 225-foot crossing of I-680

Geotechnical Conditions

  • Stiff clay and dense silty sand

Challenges

  • Caltrans crossings
  • Protection of numerous major utilities
  • Restricted work areas
  • Abandoned foundations

Project Overview

As a subconsultant to GTS, Inc., Bennett Trenchless provided trenchless design assistance on the relocation of three large PG&E gas transmission lines, 16- to 24-inches in diameter. The relocation of the existing lines was required due to modifications to the I-680/I-80/SR-12 Interchange. The design required twin guided boring crossings of I-80, twin HDD crossings of I-680, and a single guided boring crossing of I-680. Bennett Trenchless conducted a trenchless feasibility analysis to determine the most appropriate methods for the crossings, evaluated potential bore alignments, estimated settlement and hydrofracture risks, conducted pipe stress calculations for the HDD bores, prepared technical specifications and drawings.

Challenges included restricted work areas for all of the crossings, numerous major existing utilities, abandoned foundations near the exit point, lenses of loose sand beneath the highway, and crossing beneath 30-inch and 39-inch diameter water mains. Profiles and alignments were chosen to manage settlement and hydrofracture risk to the interstates and utilities, and a settlement monitoring program was designed to protect Caltrans and private facilities. The project was completed within budget and schedule with no claims.