Numerical modelling of discrete pile rows for slope stability and generic guidance for design

Discrete (spaced) pile rows are an established method of improving slope stability, or ‘dowelling' an existing slip. The piles predominantly provide horizontal restraint to the potentially unstable mass of the slope. The method becomes more cost effective as the pile spacing increases, but there is also increasing risk that the soil will ‘flow' through the gap between piles, rather than arching across it. Two- and three-dimensional numerical analyses of a generic slope with piles at various locations are undertaken. A simple model of the stabilising force required for a given increase in factor of safety of the slope is then combined with a model of limiting pile row interaction to allow direct estimation of the effect of piles at a particular spacing ratio in improving the factor of safety.