Indy’s Deep Rock Tunnel Project Progressing

By Jeff Griffin, Senior Editor | August 2012, Vol. 67 No. 8

By mid-year 2012, Morgan said Shea-Kiewit joint venture crews were excavating at the launch shaft location. Spoil has been removed, but rock from 100 to 283 feet below the ground surface must be removed, and a chamber large enough to accommodate the tunnel boring machine (TBM) must be opened. Installation of the slurry walls also is under way.

The tunnel will be dug by a massive Robbins 203-205 TBM tunnel boring machine (TMB) that will be approximately 350-feet long with trailing gear and weighs approximately 900,000 pounds. The machine produces 2.9 million pounds of thrust. Its cutting head will be 20-feet, 2-inches in diameter.

Construction details
The TBM came out of the ground last fall after completing a subway tunnel in New York City and currently is being rebuilt for the Indianapolis project in Mount Pleasant, PA. Nearly 75 semi-trailer truck loads will be required to get the machine to the Indianapolis project site. Delivery of the TBM is expected in September.

Once excavation of the tunnel begins, it is expected the machine will excavate approximately 100 feet per 24 hours -- actual production rates won’t be known until construction is under way.

A conveyor system will remove muck from the tunnel to the surface for hauling to an offsite location. It is estimated that approximately 1 million cubic yards of material will be removed from the tunnel during the project with as much as possible reclaimed for reuse.

Grippers will extend from the tunnel rib and propel the machine as it slides along the tunnel invert. The trailing gear runs on rails. Morgan said the trailing great provides the TBM’s means of production, including hydraulic equipment, power transfer, steering, rock bolts, strapping and various mechanical materials.

Alignment of the tunnel will be maintained by a PPS guidance system which automatically determines the exact position and driving direction of the TBM in three dimensional space and provides the operator with information necessary to keep the machine on course.

The tunnel will be braced when necessary as the machine moves forward, Morgan continued. It is expected the lining will begin when the TBM has advanced beyond the first utility shaft location, a distance of about 5,000 feet from the launch. The lining will be clear concrete, not containing rebar. The specified strength is 6,000 psi and will be installed via use of slip forms.

Because the launch shaft is located within a flood plain, Morgan said a part of the project is to extend an existing levee to protect the project site and pump station to be constructed later.