Foundation blocks at the west abutment. Photo courtesy of FHWA/BGCThe contractor has also been hard at work installing micropiles for the bridge launch platform at the east abutment. Though there is not much to see at the surface, each of these micropiles (32 in all) will be drilled into the rock to a depth of 45 to 80 feet below grade. Into each drilled hole, the contractor will install either one or two steel casings (heavy wall steel pipes) and a threaded steel anchor bar with a diameter ranging from 1-3/4” inches to 2-1/2”, depending on the loads at each location. Each anchor bar will be bonded to the rock using cementitious grout pumped into the drilled hole.
Micropile installation at the east abutment. Photo courtesy of FHWA/BGCSpeaking of loads, the design loads for each of these micropiles varies from 80 to 325 kips (one kip is 1,000 pounds) in compression (downward force) and from 75 to 275 kips in tension (upward force). These high design loads are necessary to support the massive weight of the bridge as it is erected and shuttled across the landslide during the launch process.