Coupled hydro-mechanical modelling of open-ended driven piles in chalk under impact hammering

The reliable prediction of axial bearing capacity is challenging for offshore, port, bridge or other structures founded on piles driven in chalk – a fine-grained, highly fissured and brittle carbonate rock. While high strain dynamic load testing is routinely used to monitor pile resistances during driving or after a set-up period, conventional one-dimensional signal matching techniques yield non-unique solutions from these data and cannot adequately model wave propagation or complex soil-structure interaction. This study considers hydro-mechanically coupled finite element simulations of impact hammering on open-ended piles in chalk, using measured force-time history from dynamic sensors mounted near pile head as an input. Valuable insights are gained by comparing FE model's predicted shaft displacement and driving resistances with results from the signal matching analysis and field data. This work highlights the potential of FE approaches to capture more accurately the important changes in chalk properties, excess pore pressures and time-dependent axial resistances generated by either continuous percussive driving or single re-strike hammer blows. • Coupled hydro-mechanical FE modelling can simulate dynamic responses of open-ended piles in chalk under impact driving. • Zoning approach has been employed to reflect the percussive damage in chalk; each chalk zone calibrated against lab and in-situ tests. • Puttified chalk near the pile yields plastically and governs response, while fractured and intact zones remain elastic. • FE modelling versus signal matching show benefits of capturing local stress, stiffness and excess pore pressures.