This paper presents a technique to evaluate the effects of drilled piers on the stability of slopes. The model allows for construction sequences, interaction between pier displacements and soil movements, remolded areas around the piers, and weaker seams (if present) in the soil profile. Applications of the technique are presented, with emphasis on identifying and optimising the factors that control the performance of piers used for slope stabilisation. Three applications of the use of drilled piers for slope stabilisation were investigated: surcharge loading, excavation from a horizontal ground surface, and cut slope stabilisation. Several conclusions regarding slope-pier interaction can be drawn. Of prime importance is that the piers must be positioned at a point where relatively large displacements are expected to occur; the magnitude of these displacements determines how much stress will be mobilised against the pier. The balance between cohesive strength mobilised and frictional strength mobilised is important to the performance of the stabilising piers. Where upward movement is a prime component, the support offered by the piers becomes very indirect, providing added support through retention of confinement. The entire soil-structure interaction that occurs between the piers and soil mass must be considered when evaluating drilled piers for slope stabilisation -- not simply the added shearing resistance provided by the piers. The redirection of stresses throughout the soil can be either beneficial or detrimental to the final stability. On the basis of the analyses performed to date, the best applications of the piers seem to be in purely cohesive materials under loading conditions that can use the vertical resistance of the piers.
Samenvatting