ULTIMATE BEARING CAPACITY OF SHALLOW FOUNDATIONS IN JOINTED ROCKS

Abstract

In general the theories developed for soils were adopted to rocks without giving due weightage to their peculiar characteristics. Rocks were treated to be competent enough and very little attention was paid to them. It is very recently, the geotechnical engineering community realized that rocks especially jointed and weathered posed unique problem. They are highly anisotropic and the discontinuities present in them govern the engineering response. The problem becomes more severe if massive structures such as tall buildings, nuclear power plants, arch dams etc are constructed on the discontinuous rocks. The theoretical approaches were observed to be inadequate to define the strength behavior of rocks. Alternatively empirical equations were derived, which have no theoretical base; and are derived based on experience and extrapolating from laboratory results field investigations. In the present work a methodology as used by Singh and Rao (2004) and also given by Bell is taken into consideration and bearing capacity is computed through different strength criteria. This approach is based on the assumption that the rock under the footing will be under triaxial state. Two elements are considered by Bell one is just adjacent to the footing, which is called as a passive element, and the other is just under the footing called active element. Four strength criteria are chosen for estimating bearing capacity. They are Mohr-Coulomb criterion, Hoek-brown criterion, Singh & Rao criterion and Ramamurthy criterion. A comparative study is done by taking the four practical examples from the Hoek and brown, 1997. After the comparative study it is observed that the ultimate bearing capacity obtained through Hoek-Brown criterion giving the values close to the average values of ultimate bearing capacity obtained through the Singh and Rao criterion. Computer program are developed for computing the ultimate bearing capacity through different criteria.