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Title: The effect of rate of displacement on measuring the residual strength of clays
Authors: Harvard University.
LaGatta, Daniel P.
Keywords: Bearpaw shale
London clay
Residual shear strengths
Rotation shear tests
Soil testing
Soil mechanics
Publisher: U.S. Army Engineer Waterways Experiment Station.
Engineer Research and Development Center (U.S.)
Description: Contract Report
Abstract: Rotation shear tests were performed with a rotation shear device, developed for the purpose of measuring residual shear strengths of clays and clay shales on 2 mm thick annular specimens of remolded Bearpaw shale and remolded London clay. Rates of displacement in comparative tests, expressed in peripheral velocities of the annular specimens, were 2.8 x 10⁻¹, 5.6 x 10⁻², 5.6 x 10⁻³, and 5.6 x 10⁻⁴ cm per min. Results of this limited investigation indicated the following: (A.) rates of displacement in the range tested have a negligible effect on the residual shear strength of remolded Bearpaw shale; residual friction angles varied generally from 3.5 to 4.0 deg; and (B.) the residual angle of internal friction of the London clay increased from about 7.5 deg at the slowest rate of displacement of 5.6 x 10⁻⁴ cm per min to 9.2 deg at the fastest rate of 2.8 x 10⁻¹ cm per min. It was found difficult to make readings when the test was performed at the fastest rate, and it was considered that in testing London clays a rate of displacement of 5.6 x 10⁻² cm per min was acceptable, since it caused the residual strength to be only about 8 percent higher than that for the lowest rate, and because at this rate of displacement, the test could be performed in one working day.
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