© The authors and ICE Publishing: All rights reserved, 2015.Slopes excavated in stiff clay are prone to delayed and brittle failure. These slopes are widespread across the rail and road networks in the United Kingdom. The use of a row of discrete vertical piles is an established method, sucessfully used to remediate failure of existing slopes and to stabilise potentially unstable slopes created by widening transport corridors. This paper will challenge the assumptions made in current design procedures for these piles, which treat the pile only as an additional force or moment and simplify soil/pile interaction. Two dimensional plane-strain finite element analyses were performed to simulate the excavation of the slope in an overconsolidated clay and the interaction of vertical piles within the slope. A nonlocal strain softening model was employed for the stiff clay to reduce the mesh dependency of the solution. This model controls the development of strain by relating the surrounding strains to the calculation of strain at that point, using a weighting function. A variety of different failure mechanisms developed depending on pile location and length. The variability of the pile and slope interaction that was modelled suggests that an oversimplification during design could miss the critical failure mechanism or provide a conservative stabilisation solution. Given the prevalence of stiff clay in the UK transport infrastructure, increased capacity requirements and the age of slopes in this material, an informed and more realistic design of stabilisation piles will become increasingly necessary.