Effect of Interference on Ultimate Bearing Capacity of Strip Footings Resting over Multi-Layered Reinforced Soil

Abstract

The prevailing studies of bearing capacity for shallow foundations have a tendency to rely on the hypothesis of an isolated footing in a homogeneous soil mass. In practice, footing may not be isolated due to heavy loads and the non-availability of good construction sites,rapid urbanization coupled with the scarcity of land)and the soil may not be homogeneous throughout its thickness. However, these studies are not sufficient and become ineffective in the cases where the footings are placed closely in multilayered soil mass encountered at shallow depths. The limitation of bearing area caused the insufficient bearing capacity to carry the working load, which in turn can take care of by incorporating the reinforcement.The effect of reinforcement is hence included in the current study to overcome the limitation of insufficient bearing capacity. In the current study, a numerical investigation is carried out using the finite element package(PLAXIS 3D)to evaluate the ultimate bearing capacity of two closely spaced surface strip footings resting on two-layered soil(strong soil overlying on a weak soil and vice versa)mass subjected to a vertical load at the center of the footings. The numericalanalysis is carried out in a test tank of size 2m*0.37m*0*65m(L*B*H)on the footing with dimensions 36cm*7cm*2.5cm(L*B*t)and modeled by a plate element.The granular soil is considered as strong soil whereas the soft soil is considered as a weak soil. A clear spacing to the footing width ratio(s/B)of0.5;1;1.5;2;3;4;5;6 with varying first layer thickness(H)from 1B to5B is considered in the analysis. In homogeneous soils, comparison of results obtained in current study with the results of Kumar and Bhoi(2009) experimental investigation also presented. Based on the analyses of results, the critical spacing(scr) and depths (Hcr) were observed as 1B,3B and3B,2B as there is no further increment in ultimate bearing capacity after these spacing and depth for strong soil overlying weak soil and weak soil overlying strong soil mass systems respectively. with inclusion of reinforcement, the critical spacing (scr) is obtained as 0.5 B and 1.5B in strong soil overlying weak soil and weak soil overlying strong soil respectively.