INSTALLATION OF POST-TENSION ANCHORS IN THE WILDERNESS –MORE THAN JUST DRILLING AND GROUTING

摘要

Rush Creek Meadows Dam, a 50-foot high concrete arch dam located at 9,500 feetrnelevation on the eastern slope of the Sierra Nevada, was evaluated for stability for thernProbable Maximum Flood (PMF). While the dam section proved to be stable, the spillwayrnsection was not. After several refinements to the analysis failed to demonstrate stability,rnSouthern California Edison (SCE) made the decision to install post-tensioned grouted anchors.rnDrilling and installing anchors at the dam presented several challenges. Located in arnU.S. Forest Service Wilderness area, transportation to and from the dam was limited to foot orrnanimal. Helicopter flights were strictly limited to equipment too heavy or bulky to transport byrnmule. Remoteness of the site required building a camp to support the work crews around thernclock. Strict environmental controls were required to protect the stream and surrounding area.rnAlmost from the start, weather patterns were shifting toward winter conditions, with snow andrncold on the horizon.rnSCE’s contractor used percussion drilling to create the boreholes for the anchors, evenrnthough the spillway section was relatively thin. Several of the holes failed water testing,rnrequiring consolidation grouting and redrilling. With freezing temperatures and mixingrnproblems, grout curing setbacks occurred. The tension-testing and lock-off loading wererncompleted with several feet of snow on the ground and winter storms looming.rnSCE and its contractor completed the installation of the ten post-tensioned anchors inrn74 days. The project required over 200 mule trips and 86 helicopter flights to deliver andrnretrieve materials, supplies, and personnel.