In the preparation of a trackway for a movable tail tower for pouring concrete for the spillway of the Lookout Point Dam, a trench 1500 feet long, 30 feet deep, and 100 feet wide was dug in a slope which shows signs of previous sliding. The waste material was placed on the downhill side of the cut. Following a period of exceptionally heavy rainfall the ground started to slump in two places on the hill. The lower slide was a short distance above the Southern Pacific railroad right of way and threatened the tracks. In an effort to control the slide the toe was cut away, with a resulting increase in slumping. Eventually the slide reached a point of equilibrium. The cause of the sliding is ascribed to overloading an already delicate state of balance followed by a period of excessive rainfall.
Figures & Tables
Engineering Geology Case Histories Number 1
Prepared for the Division on Engineering Geology of the Geological Society of America, Engineering Case Histories 1 includes 9 case histories ranging from the geology of the Queens Midtown Tunnel to the McNary Dam, Oregon.