Failing Culverts Provide Niche For Innovative Contractors

January 2009 Vol. 64 No. 1
The picture above shows the 250 ton Tenbusch Jacking Unit that was used.

The Christiana Hospital and Helen Graham Cancer Center in Newark, DE, are located off Route 4. A local stream passes under the highway through a corrugated metal pipe (CMP) near the hospital.

The CMP, which has been in service for more than 20 years, was failing. The Delaware Department of Transportation (DelDOT) decided to replace the 48 inch CMP with a 54 inch reinforced concrete pipe.

Initially DelDOT considered lining the culvert, but instead opted to upsize the line with 54 inch reinforced concrete pipe installed by open cut construction. Tunnel and replace methods were initially disregarded since DelDOT did not have experience with such construction techniques. There were, however, serious concerns about whether open cut construction would work due to the soil conditions, high traffic volume and proximity to the hospital.

Eastern States Construction in Wilmington, DE, won the bid and immediately submitted a Value Engineering Proposal (VEP) to tunnel and replace the failing culvert. The VEP allowed for replacement without open cutting the roadway. Open-cut construction called for a three phase plan that included paving in the median and diverting traffic from one side of the highway to the other to keep traffic flowing at all times. The tunneling alternative also saved the DelDOT $130,000 over the open cut construction plan.

A work pit, located in the center median of Route 4, would be used to tunnel under the highway in both directions. The proposal was accepted and Eastern States Construction began the work.

Proper equipment

When Eastern States decided to submit a trenchless alternative, they called on Tenbusch Inc. to explore the cost and availability of appropriate equipment to handle the new 54-inch concrete pipe. Tenbusch supplied Eastern States Construction with a tunneling shield and a hydraulic jacking unit. The tunneling shield protected the men as they removed the existing corrugated metal pipe and excavated as necessary to accommodate the new concrete pipe. As the tunnel was excavated, the hydraulic jacking unit provided the necessary force to jack the 54 inch reinforced concrete pipe column under the roadway.

The contract gave Eastern States Construction 75 days to complete the project. Eastern States began construction on Sept. 21. The tunneling was finished with the new pipe installation complete on Oct. 11. The job took approximately 15 working days. The tunneling was performed at a rate of approximately eight feet per day.