BEARING CAPACITY OF SHALLOW FOUNDATIONS ON ROCK SLOPES: AN EXPERIMENTAL STUDY

Abstract

Bearing capacity of Shallow foundations on jointed blocky rock mass is greatly influnced by the presence of joints. Orientation of joints, their roughness and joint spacing are the major controlling factors in the assessment of bearing capacity of footings on jointed rocks. Most of the research carried out so far has been devoted to isotropic rock condition. Very few studies have been reported on the bearing capacity of jointed rock mass where, the mass is considered as anisotropic in nature. The applicability of methods for predicting the bearing capacity, which treat the rock mass as an isotropic medium is doubtful. Recently two methodologies have been suggested for foundations on anisotropic blocky rock mass, namely those given by: Prakoso and Kulhaway(2004); Singh and Rao(2005). In the present study, an attempt has been made to investigate the Bearing capacity of foundations on jointed blocky rock mass through bearing capacity tests under plane strain condition. Plaster of Paris mixed with sand has been used as a model material. Specimens of rock mass, having various joint orientations were assembled and the footing was placed at different edge distances. These specimens consisted of two joint sets. Joint set I was continuous and was inclined at an angle of 00 with horizontal and joint set I was orthogonal to joint set 1 and was stepped. From the laboratory experiments, it was found that the predominant failure mode was. the shearing and splitting below the base of the footing. It was also observed that bearing capacity was affected by joint orientation, edge distance and stepping. Although the primary objective of the study has been to suggest an approach for assessing the bearing capacity of shallow foundations, an attempt has been made to numerically simulate the experimental findings from the afore-mentioned experimental programme. The bearing capacity predicted by the UDEC model was low as compared to that obtained from experimental programme for all the cases. The model is able to capture the failure mode to some extent as observed in the laboratory tests