Load-Spread Angles for Circular Footing on Two-Layered Soil System

Abstract

The paper presents an analysis of a uniformly loaded circular footing on two-layered soil system consisting of stiff layer overlying soft one. The variation of normal stresses with distance at the interface between the two layers is obtained using PLAXIS software for different modular (E1/E2) and relative thickness (h/a) ratios where E1and E2 are deformation moduli of the stiff upper and lower layers respectively, h –the thickness of the upper layer and a -the radius of the footing.  A Bell-curve is fitted to this variation of normal stresses with distance and integrated to estimate radial extents for different percentages of load transferred at the interface. The load spread angle defined as the ratio of extent of radial distance over which a prescribed percentage of loads is transferred to the thickness of the upper layer is obtained for different modular and relative thickness ratios and for different percentages of load. Load spread angle increases with increase in modular ratio, E1/E2 and with h/a1.  The load spread angle increases marginally for thickness ratio, h/a, greater than 2.0.