EFFECTS OF ARTIFICIAL OVERCONSOLIDATION RATIOS ON THE SHEAR BEHAVIOUR AND SHEAR STRENGTH OF LANDSLIDE SOILS

The objective of the present study was to investigate whether the effects of overburden compression and overburden relaxation of normal stress conditions would have any influence on the soil samples as far as their shear behaviour is concerned. The effect of artificial overconsolidation ratios (OCR) on the drained shear behaviour and shear strength of a highly plastic clayey soil material and a loessic soil material has been discussed from an experimental point of view. The two soil materials were obtained from the slip surfaces of two landslides, namely Kamenose (Japan) and Miaowan (China). The slip surface materials were remoulded and consolidated from slurry and were subjected to drained shear tests. Four overconsolidation ratios (OCR 1, OCR 2, OCR 4 and OCR 6) were artificially created on the remoulded soil specimens and, subsequent to the overconsolidation, the specimens were sheared under constant effective normal stress in a ring shear apparatus. The overconsolidated specimens achieved peak strength at relatively lesser shear displacements in contrast to the normally consolidated specimens in the Kamenose soil. There was no significant difference in the horizontal shear displacement required to reach the maximum strength between the normally consolidated and overconsolidated specimens in the Miaowan soil. The fully softened shear strength and the residual shear strength showed stress dependency in the OCR 1 bloc of both soils. However, between the two soils, although dissimilar patterns of variation of these two shear strength parameters in the overconsolidated state compared to the normally consolidated state was evident, significant differences in residual shear strength attributable to overconsolidation were not found.