Bearing Capacity of Strip Footing Due to Nearby Existing Footing on Hoek–Brown Rock Mass

In practice, strip footings are often constructed very close to one another either newly built or old footings due to limitations of space. To the authors’ knowledge, there is no research on the interference effect of strip footing due to an old footing lying on a rock mass. The present study’s goal is to examine the interference effect of a footing caused by an asymmetrical existing footing close by. A detailed parametric study is carried out for parameters such as the distance at which the old footing is located, the width of the old footing, and parameters like GSI and mi using finite element limit analysis (FELA). The result of this study is given in terms of efficiency factor (ξ), which is the ratio of a footing’s bearing capacity when there are existing footings close by to that of an isolated footing. The size of the existing footings greatly influences the new footing at close spacing but as the spacing of the footings is increased, the interference effect also dies out, and eventually, at enough spacing the footings behave as isolated footings. It was found that for larger existing footing the value of ξ is inversely proportional to the spacing of the footings while for smaller existing footing, the value of ξ initially increases up to some extent and then decreases. Two types of failure mechanisms were observed, where one extends to the side edge of the old footing and the other passes beneath the old footing.