DBM Rehabilitates Idaho Railroad Bridge Overpass

Job Location: SR 10 MSE Wall Repair, Soda Springs, ID

Project Owner: Idaho Department of Transportation (IDT)

Project Description: DBM Contractors Inc. recently completed a $2.5 million rehabilitation of the SH-34 Railroad Bridge Overpass in Soda Springs, Idaho.

DBM was contracted by the Idaho Transportation Department (ITD) to reinforce one of the nation’s first “true” mechanically stabilized earth (MSE) bridge abutments after years of unanticipated corrosive roadway salt treatments rotted away existing steel soil reinforcing strips. The three-month project was completed in late December 2002, on time and under budget.

To retain the existing lateral earth pressures, DBM installed a new permanent earth retention system, which incorporated a series of horizontal crosstie anchors at the approach walls, anchored soldier piles at the abutments and a reinforced shotcrete fascia. The horizontal crossties were used to connect the “back-to-back” MSE approach walls. The soldier piles had three rows of sharply inclined tieback anchors, which provided lateral support. The final element, a shotcrete fascia, provided connectivity to the entire system.

Elevations between the crossties and existing grade varied from two to 20 feet. To address this challenge, DBM modified a standard excavator by removing the digging bucket and replacing it with a drill unit. With a reach of nearly 20 feet, DBM used it to install the horizontal crossties from existing grade and from the top of the roadway. At the abutments, to overcome height constraints below the bridge deck and restrictions imposed by Union Pacific rail traffic, the design included cutouts in the bridge deck that coordinated with the existing bridge girders. Soldier piles and tiebacks at the abutment were installed from the bridge deck through the cutouts.

Soda Springs is located in the Cascade foothills, posing the challenge of temperatures below those suitable for placing and curing shotcrete. To combat the cold weather, DBM designed a scaffolding system that was protected with plastic sheeting and contained a heating system that monitored and maintained a constant temperature of 60 degrees Fahrenheit.

Other contractors who worked with DBM on this project were: Air-Placed Concrete Specialists, shotcrete subcontractor and Amerigo, Inc., traffic control subcontractor.

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