DRILLED PIERS USED FOR SLOPE STABILIZATION (FINITE ELEMENT, REINFORCEMENT)
Abstract
Large diameter drilled piers discretely placed so that some clear space exists between the piers can take advantage of the arching action of the soil to form a continuous barrier. The drilled piers improve the stability of the slope in two ways: by transmission of the driving stresses to more stable foundation layers, and by redistribution of the stress patterns in the slope. A three dimensional model for slopes stabilized by drilled piers has been developed for this study. This model includes provisions for mesh generation, finite element analysis and stability analysis. The finite element analysis involves nonlinear soil behavior, construction sequences and remolded surfaces around the piers. A two dimensional, limiting equilibrium analysis uses the stress field output from the finite element model to estimate the factor of safety of the slope. A number of cases are explored to give insight into the slope/pier interaction mechanisms, and to evaluate the efficiency of the piers as retaining structures. Several conditions have been considered during the course of this study: surchange loading, excavation, cutslope and self weight loading. The soil arching was found to provide an effective barrier against soil movement even though the piers do not form a continuous wall. The piers added lateral support to a stresses slope as has been the commonly used situation of these piers in practice. However, a significant amount of soil support was also found to be provided in clay soils by the vertical support of the piers. Previous studies have found the piers to be ineffective if allowed to rotate. This study examines cases of piers firmly socketted in bedrock or stiff foundation materials. Other constraints, such as tiebacks and caps, which ease the structural demands on the piers, can also be modelled. In general, the effectiveness of the piers increases for increased pier stiffness, increased pier diameter and decreased pier spacing. The position of the piers in the slope can be related to the failure mode with a trade-off between overall stability and volume of the slide. In general, the optimum position of the piers is at the point of maximum displacement for the unreinforced case.
Degree
Ph.D.
Subject Area
Civil engineering
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