With post-tensioning and grouting now complete on the west abutment (photo below), focus returns to the east abutment, where the contractor is starting installation of the vertical ground anchors that will be drilled through the top of the abutment blocks deep into the rock below.
Completed post tensioning and grouting on the west abutment. Photo courtesy of BGC Engineering/FHWA
Each of the 22 ground anchors at the east abutment will consist of a minimum 5-inch diameter hole drilled 40 feet below the bottom of the abutment block. Into each drilled hole, the contractor will insert a 1-3/4” diameter threaded steel bar that will extend from the bottom of the hole up above the top of the abutment blocks. After placement of the threaded bar into the hole, the contractor will fill the drilled holes with cementitious grout; this grout (once cured) will both bond the anchor to the rock and help protect the steel from corrosion. After the grout has cured, the contractor will install a heavy steel washer (16 inches in diameter and 2-7/8” thick) over each anchor within matching circular recesses cast in the top of the abutment blocks. With the washers in place, massive steel nuts will be installed on the exposed threaded ends of each anchor and torqued until the tension created in the anchor rods reaches the “lock-off” load of 118,500 pounds. The combined tension in all 22 anchors will act to pull the abutment downward onto the surface of the rock with a total force of over 2.6 million pounds, firmly anchoring the abutment and allowing it to safely support the bridge.