Finite element modelling of rock‐socketed piles

Rock socketed piles have a number of features which differentiate them from other types of piles. The generally stubby geometry leads to more even distribution of capacity between shaft and base. However, the low ratio of pile modulus to rock modulus leads to high compressibility and this, coupled with a tendency for the load transfer response along the shaft to exhibit strain-softening, gives rise to an overall response where the shaft capacity may be fully mobilized, and potentially degraded, before significant mobilization of base load. The paper presents results of finite element analyses of the response of rock-socketed piles, with particular attention to the shaft response with and without intimate base contact. The shaft interface uses a model, developed from principles of tribology, that includes dilation (and strain-hardening) prior to peak shaft friction, followed by strain-softening at larger displacements. The results of the study are shown to be consistent with field measurements, and to capture effects of the absolute pile diameter on the peak shaft friction. It is also shown that intimate base contact mitigates significantly the degree of strain-softening of the shaft response.