Investigation of shear strength of prefailed overconsolidated high and low plastic clayey slopes with fast shearing

Abstract

Clayey soils may be investigated since the days of the beginning of the geotechnical science. However, the behaviour of the clays in different loading conditions and in different situations is still in investigation. This study is dealt with the prefailed soil slopes made with high or low plastic overconsolidated clays. After failure, thought of “soil strength reduces its residual strength” has found general acceptance and residual strength is applied to the calculations of the stability of prefailed slopes. In this point, the question comes to the minds; if the slope formed with clayey soil or more specifically, high or low plastic overconsolidated clays, what would be the difference in shear behaviour? That is the main point of this study. In the tests, Kaolin clay is used for low plastic and 50 % Kaolin + 50 % Bentonite in weight are used for high plastic clay samples. As testing steps; first, samples are overconsolidated, then sheared until their residual strengths and finally tested again in fast shearing. At the end of the 30 tests, the results are obtained as expected. High plastic samples gave lower strength values under the same normal stress; however, the interesting result was about residual strength and fast shear strength values. In general, fast shear tests, at least 21 days after prefailing, gave higher shear strength values than the residual ones.