Stability of Natural Slopes in Sensitive Clay

Failures of natural slopes in sensitive clays often retrogress leaving a characteristic crater which is wider than the opening In the slope. Two actual failures of this type that occurred near Ottawa, Canada are described and compared with stable slopes in the same general area. One of the failures occurred several hundred years ago but changes in ground water conditions since failure appear to have increased the stability of adjacent slopes in that area. The second failure, in an area of active sliding, occurred in 1963. In each case the required strength for stability under various ground water conditions has been computed and compared with measured values. It is concluded that an effective stress analysis of these slopes yields satisfactory results if tests are conducted in the working stress range and ground water conditions are carefully measured.