THE INFLUENCE OF GRANULAR CALCAREOUS PARTICLES ON THE RESIDUAL SHEAR-STRENGTH OF FULLER EARTH CLAY

Decalcification is proposed as a cause of the continued movement obser ved in many natural and engineered slopes in calcareous mudrock format ions. It is deemed that such movement may potentially occur as granula r calcareous particles, which otherwise maintain high residual shear s trengths, are leached from shear surfaces within slipped masses, chang ing the mode of residual shear from transitional to sliding. Measureme nts of the residual shear strengths of 42 natural samples taken throug h the Fuller's Earth succession near Bath over a range of effective no rmal stresses emphasize the curved nature of many failure envelopes. T he results demonstrate that the threshold between the two modes of she ar occurs at approximately 25% calcite content. Fuller's Earth Clay wi th more than 25% calcite content is thus prone to significant decrease s in residual shear strength upon partial or total decalcification.