Effect of Interference on Ultimate Bearing Capacity of Strip Footings Resting on Reinforced Clay Overlying Sand

Abstract

The prevailing studies on the bearing capacity of shallow foundations show the tendency of relying on a hypothesis of an isolated footing resting in a homogeneous soil mass. In practice, the soil is seldom homogeneous, and heterogeneity increases with the area of consideration. In addition to the non-homogeneous nature of the soil, the footing also may not be isolated due to various reasons like very rare availability of good construction sites and rapid urbanization coupled with the shortage of land. However, these studies are ineffective when the closely placed footings encountered at shallow depths of a multi-layered soil mass. In the present study, a numerical investigation is carried out to evaluate the effect of interference on the ultimate bearing capacity of two closely placed identical surface strip footings resting over two-layered soil (weak soil overlying on a strong soil) mass subjected to a vertical concentric load using the finite element package, PLAXIS 3D. The granular soil (sand with relatively higher stiffness) is considered as strong soil, whereas the soft soil is considered as a weak soil. The analysis is carried out for various ratios of clear spacing to the footing width (s/B) ranging from 0.5 to 6 by varying first layer thickness (H) as B–5B @B. Based on the analyses of results, the critical spacing (s_cr) and significant depths (H_s) were observed as 3B and 2B. The increment in ultimate bearing capacity ceases after these spacing and depth for weak soil overlying strong soil mass system. Also, with the inclusion of reinforcement, the critical spacing (s_cr) was observed as 1.5B.