A theoretical study on ground movement prediction for braced excavation in soft clay

Abstract

Braced excavation in urban areas requires control of ground movements as well as wall deflection. Previously interpolation from empirical database or numerical analysis by finite element method is used for estimation of ground settlement. But these methods are relatively complex and sometimes important assumptions are invalid at different situations. A design approach for calculating wall deflection and ground settlement is proposed by Bolton and Osman (2006) assuming the plastic deformation mechanism. Here, in this paper this design method is extended by presenting displacement profiles at different zones of the mechanism with different mathematical functions on the basis of ground settlement profile suggested by Peck (1969) and reported case study of Kolkata Metro Excavation (Som, 1991). From this deformation function incremental shear strain is calculated and average shear strain mobilized in each zone is expressed in term of maximum deflection. The conventional hyperbolic stress strain relationship is used to relate mobilized shear stress and shear strain. Finally, the total loss of potential energy is equated with the virtual work done by the soil within the deformed zone in order to develop an equation which may serve as a design tool for calculating ground surface movement and wall deflection at different stages of excavation at different depth.