Residual Shear Strength Determination of Overconsolidated Nespelem Clay.

摘要

Peaking operations of the Grand Coulee Dam Powerplants, Washington, could result in future downstream river fluctuations of up to 12 meters (38 ft) within a 24-hour period and trigger dangerous landslides. Much of the riverbank consists of old landslide deposits in varved, overconsolidated clays and silts. The residual shear strength of the clay was determined from drained, repeated (reversing) direct shear tests on slickensided or precut sliding surfaces under three different normal loads. Two different displacement rates were initially used. The residual strength, measured after large cumulative displacements, was used in slope stability analyses This report describes problems encountered during testing, the test procedure adopted, the fully automated direct shear apparatus and data recording system, results to date, and planned future research. In one of the downstream riverbank areas, a residual shear strength in the range a 10 degree to 13 degree (angle of internal friction) was confirmed by a back analysis of a recent slide.