RESEARCH ARTICLE Bearing capacity of foundations on rock mass using the method of characteristics Amin Keshavarz 1 | Jyant Kumar 2 1 School of Engineering, Persian Gulf University, Bushehr, Iran 2 Civil Engineering Department, Indian Institute of Science, Bangalore, India Correspondence Jyant Kumar, Civil Engineering Department, Indian Institute of Science, Bangalore 560012, India. Email: jkumar@iisc.ac.in Summary The method of stress characteristics has been used for computing the ultimate bearing capacity of strip and circular footings placed on rock mass. The modi- fied Hoek‐and‐Brown failure criterion has been used. Both smooth and rough footing‐rock interfaces have been modeled. The bearing capacity has been expressed in terms of nondimensional factors N σ0 and N σ , corresponding to rock mass with (1) γ = 0 and (2) γ ≠ 0, respectively. The numerical results have been presented as a function of different input parameters needed to define the Hoek‐and‐Brown criterion. Slip line patterns and the pressure distribution along the footing base have also been examined. The results are found to com- pare generally well with the reported solutions. KEYWORDS bearing capacity, failure, foundations, Hoek‐Brown criterion, rocks, the method of characteristics 1 | INTRODUCTION The determination of the bearing capacity of footings on rocks forms an important issue especially while (1) laying foundations on weak rocks, (2) estimating the ultimate tip resistance of piles placed on rocks, and (3) designing dams' foundations. As compared with foundations in soils, only limited studies seem to have been available in literature to compute the bearing capacity of foundations on rock mass. Serrano and Olalla used the Hoek‐and‐Brown (HB) failure criterion to compute the ultimate bearing capacity of strip footings placed on a weightless rock medium. 1 Serrano et al also used the modified HB criterion to evaluate the bearing capacity of a strip footing placed on a weightless rock medium. 2 By using the original HB criterion, Yang et al performed a lower‐bound limit analysis to compute the bear- ing capacity of a strip footing placed on a weightless rock medium. 3 Merifield et al used the limit analysis in combi- nation with optimization and finite elements to compute the ultimate bearing capacity of strip footings on rock mass. 4 In this analysis, the modified HB failure criterion was used to compute the ultimate bearing capacity. By using the original and modified HB failure criteria, Zhou et al applied the slip line method to calculate the bearing capacity of strip footings placed on rock mass. 5 Clausen used the standard displacement‐based elastoplastic finite element approach to compute the ultimate bearing capacity of circular footings laid on rock mass. 6 Chakraborty and Kumar evaluated the ultimate bearing capacity of circular footings on rock mass by using the lower‐bound theorem of the limit analysis. 7 In this work, the modified HB failure criterion was used but by assuming a constant value of the expo- nent, a = 0.5, which provides an overestimation of the bearing capacity for lower values of the geological strength index (GSI). Keshavarz et al used the method of stress characteristics to evaluate the seismic bearing capacity of strip footings placed over rock mass. 8 The study was, however, based on the original HB failure criterion, and moreover, it did not consider a formation of a nonplastic wedge, which invariably occurs for a rough footing base. As compared with available solutions for strip footings, not many theories seem to be existing for finding the bearing capacity of Received: 9 September 2016 Revised: 11 July 2017 Accepted: 26 September 2017 DOI: 10.1002/nag.2754 542 Copyright © 2017 John Wiley & Sons, Ltd. Int J Numer Anal Methods Geomech. 2018;42:542–557. wileyonlinelibrary.com/journal/nag