This paper focuses on a numerical study using the universal distinct element, to investigate settlement behavior of two strip footings with close spacing resting on a rock mass obeying the modified Hoek–Brown failure criterion. The perfectly rough strip footings are considered to be resting on a modified Hoek–Brown material. The material is assumed to exhibit perfect plasticity, obeying an associated flow rule. The effect of various parameters such as geological strength index (GSI), m for intact rock (mi), intact rock uniaxial compression strength (σci), and clear spacing between footings on the settlement behavior of closely spaced footings has been determined. For different clear spacing (S) between two footings, values of the settlement ratio (ζδ) were determined; where ζδ is defined as ratio of settlement of single footing at failure in presence of other footing of a given width (B) to that of a single isolated footing having the same width. The maximum value of (ζδ) occurs at space between S/B = 0.5 to 1.0. The results have been compared with those available in the literature.
In order to accommodate structural details or to limit footing loads, often footings place quite close to each other. In such cases, due to the interference of failure zones, bearing capacity and load-settlement behavior of footings are different from an isolated footing condition. Therefore, the interaction between adjacent footings is of great practical significance. Stuart 1962 studied the interference effect on the ultimate bearing capacity of two nearby strip footings theoretically by considering the limit equilibrium method, which could be considered as the pioneering work in this area.
Several experiments have also been carried out by various researchers (Das and Larbi-Cherif 1983; Saran and Agarwal 1974; West and Stuart 1965) to study the interference effect of two footings. The obtained results generally show lower efficiencies than those predicted by the theoretical analysis of Stuart 1962. The interference effect of two closely spaced footings on sand has been studied theoretically by various researchers (Griffiths et al. 2006; Kumar and Ghosh 2007a; Kumar and Ghosh 2007b; Kumar and Kouzer 2008). (Mabrouki et al. 2010) used finite difference code, FLAC, to evaluate the influence of interaction between two nearby shallow strip footings on the ultimate bearing capacity. The obtained results were in good agreement with those presented by (Hazell 2004). Hazell used the method of characteristics and experimental modeling to study the interaction between a pair of parallel shallow rough and smooth strip footings on sand.