Allowable Bearing Capacity of Strip Footings on Jointed Rock Masses: A Reliability Based Approach

Basha, B Munwar and K, Chandrakanth and Moghal, A A B (2015) Allowable Bearing Capacity of Strip Footings on Jointed Rock Masses: A Reliability Based Approach. In: International Foundations Congress and Equipment Expo, 17-21 March, 2015, San Antonio, Texas, USA.

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Abstract

In this paper, a reliability analysis is presented to compute the allowable bearing capacity of shallow strip footing resting on jointed rock masses. The rock is assumed to follow the non Hoek-Brown failure criterion. Vertical loading case is considered in the analysis. In this study, the Bell’s approach has been used for the computation of ultimate bearing capacity. Jointed rock mass properties generally vary from location to location and also may change with time. Additional uncertainties may arise due to the laboratory estimation of the in situ rock properties. The conventional deterministic analysis based on the factor of safety concept in the estimation of bearing capacity fails to properly account variability. The variability is systematically incorporated in the bearing capacity calculations using reliability based design optimization (RBDO). In this study, the orientation, spacing, and strength parameters of discontinuities are considered to be random variables. Allowable bearing capacity is computed by considering the variability associated with the discontinuity orientation (θ1), rock material frictional angle (ør), and discontinuity frictional angle (øj), uniaxial compressive strength of intact rock (σci) and joint spacing (S). The graphs are plotted for the discontinuity orientation of joints in rock mass against allowable bearing capacity for the target reliability index (β) = 3.

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