Slope Stability Analysis Considering Tiebacks and Other Concentrated Loads : Informational Report

Abstract

The krantz, ranke-oestermayer, French code of practice, broms, littlejohn, ostermayer, and finite element methods for determining the internal and overall stability of tied back and anchored structures are reviewed. Details are given of the development and implementation of the load distribution method (ldm) contained in the slope stability program, stabl4. The ldm, based on limiting equilibrium, attempts to account for the diffusion of stresses throughout a soil mass caused by a tiedback load by distributing the load to the potential failure surface, and hence all slices of the sliding mass, rather than accounting for the applied load only on the slice on which it acts. The distribution of the load to the failure surface, the distribution of normal and tangential stresses, and the restrictions on load distribution are discussed. The stress distribution used in the ldm assumes that the problem conforms to a semi-infinite elastic half-space; parametric studies were undertaken to test this assumption. These studies investigated the effect of point of application on the factor of safety, load inclination versus factor of safety, load magnitude versus factory of safety, and the effect of multiple tieback structures on the factor of safety. The studies showed that the ldm generally gives reasonable results, but at large applied loads and for some slope models, the method may not yield conservative solutions. Applications of the ldm include uniform line loads, distributed loads, braced excavations, buried tiedback structures, reinforced earth walls and fabric reinforced walls. It is especially useful for assessing the stability of tiedback structures used for landslide control, and can be used to determine the length, inclination, and load of tiebacks required for slope stabilisation. A brief discussion of the implementation of the mainframe computer program, stabl4, on the IBM microcomputer, pcstabl4, is presented. The addition of spencer's method of slices to the stabl program and the development of the linear approximation method (lam), which determines the factor of safety of spencer's method of slices while avoiding problems with non-convergence, are discussed. Spencer's method is contained in stabl5 and pcstabl5, and satisfies complete equilibrium and is capable of transferring the load from one slice to another through the interaction of the interslice shear and normal side forces. It is therefore well suited to the analysis of slopes and retaining walls subjected to tieback loads since it distributes the load from a tieback between slices.