Current studies of bearing capacity for shallow foundations tend to rely on the hypothesis of an isolated footing. In practice a footing is never isolated; it is mostly in interaction with other footings. This paper focuses on a numerical study to evaluate the ultimate bearing capacity for two interfering strip footings resting on a rock mass in which the strength can be described by the generalised Hoek–Brown failure criterion. This criterion is applicable to intact rock or heavily jointed rock masses that can be considered homogeneous and isotropic. The material is assumed to exhibit perfect plasticity and obeys an associated flow rule. The effects of Hoek–Brown parameters including GSI, mi, and σci were studied and the corresponding results are presented. For different clear spacing (S) between the footings, values of the efficiency factor (ξ) were determined; where ξ is defined as the ratio of the failure load for an interfering new footing of a given width (B) to that of a single isolated footing having the same width. The maximum value of (ξ) occurs at spaced between S/B = 0.5 to 1.0. The results have been compared with those available in the literature.


Evaluating the ultimate bearing capacity of rock masses is essential for important projects like dams and bridges. Closely spaced footings may occur on rock masses in the form of pier foundation and grillage footing. Close spacing lead to permit higher loads than can be bore by similar isolated footings. The ultimate bearing capacity of two interfering strip footings resting on cohesionless soil have been studied theoretically (Kumar, & Gosh, 2007; Kumar, & Kouzer, 2008; Stuart, 1962). Results revealed when two strip footings approached closely enough, failure zones affect each other and ultimate bearing capacity significantly increased.

In order to study the effect of the interference of two footings, a number of experiments have also been carried out by various researchers (Das, & Larbi-Cherif, 1983; Stuart, 1962). Recently Mabrouki et al. (2010) conducted series of numerical computing using the finite difference code FLAC to evaluate the influence of the interaction between a pair of shallow strip footings on the ultimate bearing capacity. Due to the unit weight component, available experimental and numerical studies revealed that the ultimate bearing capacity increases by the interference of the other footing.

Important studies have been carried out to assess ultimate bearing capacity of rough strip footing rest upon rock masses (Imani et al., 2011; Merifield et al., 2006; Saada et al., 2008; Sutcliffe et al., 2004; Yang, & Yin, 2005). Nevertheless, no study was devoted to the assessment of bearing capacity of two interfering foundations resting on a generalised Hoek–Brown material. In this context, the works of coauthor seem to be among the pioneer contributions in the domain.

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