Takuo Yamagami

A Limit Equilibrium Stability Analysis of Slopes with Stabilizing Piles

This paper presents a design method for slopes with a row of piles to enhance slope stability or to prevent slope failure. The basic idea of the method is to allow that two different slip surfaces can be assumed in upslope and downslope earth masses of the row of piles. Contrary to the conventional limit equilibrium procedure where a factor of safety is calculated for a given slip surface, in the present method forces acting on the stabilizing piles are estimated based on a given slip surface whose factor of safety is prescribed to ensure the slope stability. By assuming a slip surface in upper and lower earth masses respectively, the forces acting on the piles can be calculated from an existing limit equilibrium method with a prescribed value of the factor of safety. The Bishop method is employed, and a repeated trial procedure is used to find the most dangerous situation for the piles and the corresponding two critical slip surfaces in the upside and downside of the pile row. It may be understood that if the stabilizing piles are still sound under the most dangerous situation, then the slope will have, at least, the prescribed (target) factor of safety. In the proposed method, we clearly distinguish between forces which piles in a row can bear, i.e. the horizontal bearing capacity as passive piles, and forces which piles in a row should bear under the target factor of safety. The consideration in which the latter does not exceed the former makes possible a more rational design for stabilizing piles. The results of some examples illustrate the effectiveness of the proposed method.