ECI – Engineers Construction

ECI’s Middlebury Tunnel Project was highlighted in the May 2018 edition of Trenchless Technology.  This early work package contract included construction of the deep stormwater conveyance tunnels for the upcoming railroad tunnel project.  The three 60-inch-diameter tunnels in rock  conditions were launched from a 40-ft-dia by 35-ft-deep launch shaft constructed in the heart of busy downtown Middlebury.  The drives ranged from 140 to 152 feet long.  The rock consisted of marble with an unconfined compressive strength of up to 20,000 psi.  The third drive extended through the hard rock and into a mixed face and then a soft clay over the last 20 feet.  ECI used a Robbins Motorized Small Boring Unit (SBU) tunneling machine with hard-rock disc-cutter tooling.  The SBU is mounted at the front of steel casings which are jacked forward with an auger boring machine from inside the launch pit.  The electrically motorized SBU head rotates as the steel casing transfers the applied jacking force from the auger boring machine system.  The operator is inside the SBU-M and uses a laser-guided target to stay on line and grade.  Steering is achieved by slight adjustments to the articulated forward shield.  The tunnel is permanently lined by the trailing steel casing connected with permalok snap-on joints.  This project used a 42-in-dia polypropylene corrugated steel pipe as the main carrier with annular grout fill.

Trenchless Technology Magazine:  https://trenchlesstechnology.com/eci-robbins-sbu-m-three-hard-rock-crossings-vermont/prettyPhoto/0/

ECI’s involvement in the project will continue into the next phase of the railroad tunnel construction anticipated to start up this summer and completion in 2020.

VTrans Project Website:  https://vtrans.vermont.gov/projects/middlebury

Robbins Company SBU-M Bochure:  https://www.therobbinscompany.com/wp-content/uploads/2010/08/SBU-M-spec-sheet-2009_metric.pdf