Towards an In-depth Understanding of the Pile Installation Mechanism in Crushable Soils and the Post-installation Soil Ageing Effects

Description

The axial capacity of driven piles in crushable soils presents a high degree ofuncertainty for geotechnical engineers. The source of uncertainty comes from a lack of afull understanding of the mechanisms controlling penetration into the soil. Penetrationresistance is known to be a function of many variables including soil crushability, initialsoil density and stress level, soil gradation, pile diameter, and pile driven depth, etc. Dueto the inability to quantify the effects of these variables on the pile capacity, currentdesign methods adopted by the pile industry can be unreliable and unable to capture thebehavior observed in the field. This deficiency is critical for a metropolitan city likeHong Kong, where crushable soils as diverse as offshore skeletal carbonate sedimentsand highly weathered decomposed granites or volcanics are found.In this proposal, we propose a comprehensive investigation of the time-dependent loadcarrying capacity behavior of driven piles in crushable granular soils using a coupleddiscrete-continuum modeling approach with experimental calibration. The detailedmicromechanics underlying the pile-soil interaction will be handled by the DiscreteElement Method (DEM) while the wider region of foundation soil away from the pile willbe 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 thegrain-scale mechanisms that control the pile capacity under the influence of particlebreakage during pile installation and soil ageing after installation.The outcome of this research will be a significant advancement of knowledge of the pilecapacity behavior in crushable, coarse-grained soils in both short-term conditionsfollowing pile installation and long-term conditions following pile setup. The benefits ofthis research come from an improved understanding of the time-dependent pile capacitybehavior, especially of the processes, physics and mechanisms at the soil grain scale.This improved understanding will translate into an enhanced ability of engineers tomake more economic designs of pile foundations, particularly in incorporating critical,complex soil behavior such as grain crushing, interface friction degradation, soil creepand soil ageing. It is expected that the improved pile foundation designs will lead tomore construction cost savings in Hong Kong and worldwide in the future.?