90th South Crossing — Nix Construction

Tunnel Bore

**90TH SOUTH I-15 CROSSING**

INNOVATIVE PLANS AND JOBSITE SURPRISES

The requirements were challenging: Bore an eighth-of-a-mile tunnel, place 5’ diameter casing under 10 lanes of Interstate highway and a railroad main line, along with a tricky traverse through a low-elevation drainage area. Not a simple undertaking, to say the least.

In the low-ground area, conventional tunneling methods wouldn’t be possible, but the CH Nix team had an innovative solution in mind: Backfill the low-ground excavation with flowable fill material, allowing the bore machine to accurately cut an open trough through that area, and still stay on-line. The technique was so unusual that few tunnel crews would attempt such a thing, let alone imagine they could succeed at it. But the CH Nix team forged ahead.Midway through the low-ground area, an unexpected concrete drainage system was uncovered. It would need to be demolished and removed to allow the bore to continue on line, and the resulting delays and displacement of soil could cause issues. For the CH Nix team, this was all just business as usual. Their clever technique worked perfectly. 680 feet of steel casing was successfully punched through the soil to construct the tunnel that would house the new sewer expansion. The new pipeline was set and secured in the tunnel, and then tied into the trunk line without a hitch. Once again, another challenging mission accomplished by the CH Nix team.