Bearing failure modes of rock foundations with consideration of joint spacing

In this study, two main failure modes of jointed rock foundations consisting general shear failure and failure due to excessive deformation are discussed. For each of these two modes, the method of determining ultimate bearing capacity is presented and the effect of joint spacing is also examined. For the former mode, an upper bound method of limit analysis is employed, while for the latter one, distinct element numerical modeling is used to investigate the effect of joint spacing on the bearing capacity. The calculations are performed for a rock mass containing two orthogonal joint sets that the orientation angle of the first joint set is 15°, 30° and 45° to the horizontal, respectively. A non-dimensional parameter called “Spacing Ratio” (SRSR) is used to examine the effect of different joint spacing. This study shows that in the case of general shear failure mode, joint spacing does not have significant effect on the bearing capacity. In the failure mode induced by excessive deformation of the rock mass, for SR<30SR<30, increasing the SRSR results in decreasing the bearing capacity, however, for SR>30SR>30, the joint spacing does not significantly affect the bearing capacity.