Modelling the seismic performance of root-reinforced slopes using the Finite Element Method

This paper investigates the seismic performance of rooted granular slopes using dynamic finite-element analysis, validated against recently published centrifuge test data. The importance of selecting suitable strength parameters to represent soil response within a strain-hardening constitutive model was demonstrated and the simulations suggested that any boundary effects introduced through the use of the equivalent shear beam container in the centrifuge are negligible and can be represented by a semi-infinite lateral boundary condition. Using the validated model, a parametric study investigated the effects of different rooted soil properties on the performance of slopes of different heights. Vegetation was effective in reducing deformations at the crest of slopes of modest height, although the benefit reduced as slope height or soil apparent cohesion increased. The effectiveness was significantly affected by the extent of the root system, but only moderately sensitive to root cohesion, and insensitive to stiffness or damping of the rooted soil. Plant species possessing deep and extensive root systems are therefore recommended for seismic stabilisation rather than those with the strongest roots. For modelling purposes, it is sufficient to be able to quantify only the strength of the rooted soil and its area of influence. The magnitude of improvement from vegetation in terms of decreasing seismic permanent slip was also found to be insensitive to the construction method used (i.e. compacted/uncompacted embankment or cutting) for drained granular slopes.