BEHAVIOUR OF SHALLOW FOUNDATIONS ON JOINTED ROCK MASS

Abstract

Design of shallow foundations is one of the most important steps in the construction of many common structures. Many times a foundation has to withstand eccentric-inclined loads i.e. foundations of retaining walls, transmission towers. embankments etc. Also, many a times foundations are needed to be laid on jointed rock mass, whose behaviour is hard to predict due to their non-homogeneity. In the present study, the complete behaviour of strip footing resting on isotropic jointed rock mass is being investigated using the Pressure- sett leme nt characteristics considering the footing to be rigid and a non-linear elasto plastic rock mass behaviour. An extensive parametric study have also been carried out by varying the load eccentricity and inclination for different geological strength index values (i.e. 10, 20, 30, 40 and 50) of rock mass to arrive at some explicit non-dimensional correlations for obtaining ultimate bearing capacity, settlement and tilt of the footing subjected to eccentricinclined loading. Finite element methodology in conjunction with modified Hock-Brown criterion for rock mass has been used to analyze the behaviour of rock mass-footing system. Double tangent method as discussed by Lutenegger and Adams (1998) has been used for estimating the ultimate bearing capacity. The results obtained for ultimate bearing capacity in terms of bearing capacity factor N 0 in the present study agree well with those of Kulhawy and Carter (1992) and Serrano et al. (2000). The non-dimensional correlations for determination of footing settlement under eccentricinclined load requires knowledge of settlement of footing subjected to central vertical load, which can be evaluated using conventional methods present in the literature. The non-dimensional correlations obtained are found to be dependent on eccentricity to width ratio and inclination of load.