Randall Essex, Executive VP, Director of Professional Excellence & Practices, Mott MacDonald, will present a case history on the Lake Thistle Emergency Drainage Project. The free webinar, presented by the UCA of SME Young Members committee. The webinar is scheduled for Wednesday, Aug. 31, at noon Eastern.
A 25 million cubic yard mudslide formed an un‐engineered, 225‐ft high dam across a river canyon near Spanish Fork, Utah. The mass of montmorillonite, judged the sixth largest landslide in the history of North America, completely blocked the flow of the Spanish Fork River, and formed a 60,000 acre‐foot, 200‐ft deep lake. The impounded run‐off completely engulfed the town of Thistle, situated one-half mile upstream of the slide, and submerged the town beneath 175 ft of water.
A team of engineers and engineering geologists was retained to design and engineer an emergency system to drain the lake as quickly as possible, and provide a permanent diversion for the river around the slide‐dam. The system included a 2,230‐ft long, 13‐ft wide drill‐and‐blast rock tunnel, a 16‐ft diameter, 180‐ft deep shaft, a bulkhead and twin valves at the base of the shaft to control lake water discharge, and a sequentially deepened channel excavation between the lake and the shaft.
About the speaker: Essex holds a B.S. in Geomechanics from the University of Rochester, two master degrees from the University of California, Berkeley, and is a Professional Engineer in five states. He has authored over 40 technical papers and is the principal author of the 2007 ASCE Guidelines document “Geotechnical Baseline Reports for Construction.” He is the current U.S. Representative to the International Tunnelling Association and was recently awarded the prestigious Golden Beaver Award for Engineering.
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