C. Olalla

Ultimate bearing capacity of rock masses

Abstract The determination of the ultimate bearing capacity of spread foundations on rock masses has traditionally been considered taking into account previous experience, using empirical criteria or applying local or national codesAR1]. This paper defines a methodology for bearing capacity quantification based on the Hoek and Brown rock failure equations and by applying the characteristics method for resolving the differential equation systems which govern the stress field. Reference is made to the works of both Sokolovskii [3] and Serrano [4] in solving the plasticity problem. Three different regions of the characteristic lines are considered, two of which are of the Karman type, the third being of the Prandtl type. The boundary conditions defined by the external load system and the geometrical configuration are incorporated, allowing for a closed form solution. In this paper, gravity rock masses will not be considered. Therefore, the required data are: the type of rock, the uniaxial compressive strength of the intact rock and the Bieniawski classfication (RMR parameter). To facilitate an overall understanding of the procedure, and example problem is solved showing how the initial data are used and illustrating the intermediate steps involved.

Analytical Bearing Capacity of Strip Footings in Weightless Materials with Power-Law Failure Criteria

AbstractSokolovskii’s method of characteristics is extended to provide analytical solutions for the ultimate load at the moment of plastic failure under plane-strain conditions of shallow strip foundations on weightless rigid-plastic media with a noncohesive power-law failure envelope. The formulation is made parametrically in terms of the instantaneous friction angle, and the key idea to obtain the bearing capacity is that information can be transmitted from the free surface (where external loads are known) to the contact plane of the foundation. The methodology can consider foundations adjacent to a slope, external surcharges at the free surface, and inclined loads (both on the slope and on the foundation). Sensitivity analyses illustrate the influence on bearing capacity of changes in the different geometrical parameters involved. An application example is presented and design plots are provided, and model predictions are compared with results of bearing capacity tests under low gravity.