Time-Dependent Pile Capacity Behavior in Coarse-Grained Soils by A Coupled Discrete-Continuum Modelling Approach

The load-carrying capacity of driven piles in crushable, coarse-grained soils remains a topic with many uncertainties in geotechnical engineering. The source of uncertainty comes from a lack of a full understanding of the mechanisms that control pile penetration into the soil and pile setup with time after installation. Despite a significant amount of experimental work dedicated in this field, current design methods adopted by the pile industry may not be fully reliable and often have difficulties in capturing the behavior observed in the field. This deficiency is important for a metropolitan city like Hong Kong, where crushable soils such as highly weathered, decomposed granites or volcanics are found.In this proposal, we propose a comprehensive investigation of the time-dependent load-carrying capacity behavior of driven piles in crushable granular soils using a coupled discrete-continuum modeling approach with experimental calibration. The detailed micromechanics underlying the pile-soil interaction will be handled by the Discrete Element Method (DEM) while the wider region of foundation soil away from the pile will be modeled using the Finite Element Method (FEM) or Finite Difference Method (FDM). The major goal of the proposed research is to develop an in-depth understanding of the grain-scale mechanisms that control the pile capacity under the influence of particle breakage during pile installation and soil ageing after installation.The outcome of this research will be a significant advancement of knowledge of the pile capacity behavior in crushable, coarse-grained soils in both short-term conditions following pile installation and long-term conditions following pile setup. The benefits of this research come from an improved understanding of the time-dependent pile capacity behavior, especially of the processes, physics and mechanisms at the soil grain scale. This improved understanding will translate into an enhanced ability of engineers to make more economic designs of pile foundations, particularly in incorporating critical, complex soil behavior such as grain crushing, interface friction degradation, soil creep and soil ageing. It is expected that the improved pile foundation designs will lead to more construction cost savings in Hong Kong and worldwide in the future.