Application of coupled hydro-mechanical CEL method for variable rate cone penetration analysis

Rate-dependent soil resistance is widely concerned in offshore cone penetration and structure installation analyses, particularly in ‘problematic’ intermediate silts and calcareous soils in which hard driving (or refusal) and self-weight fast penetration could occur. Advanced numerical analysis capable of modelling large-deformation penetration problems can provide significant insights into rate-dependent soil drainage and shearing resistance behaviour, complementing field or model scale experimental observations and theoretical analyses. The Coupled Eulerian-Lagrangian (CEL) method is widely recognised as a robust approach for large-deformation analysis. However, the method is primarily limited to total stress analysis, restricting its application in effective stress and consolidation problems in saturated soils. This paper reports on the implementation and application of a coupled hydro-mechanical CEL method in modelling cone penetration of variable rates in dense fine silica sands. Predictions of cone resistance profiles were made with a conventional Mohr-Coulomb model and an advanced hypoplastic soil model and then validated against centrifuge experiment results. It is found that cone penetration in dense dilatant fine sand is dependent on the advancing rate, with resistances increasing substantially as the response transitions from partially drained to fully undrained conditions as quantified with normalised penetration velocity. The overall pattern of dilation-induced resistance increase can be interpreted within a drainage framework in which an opposite trend may be expected for contractive soils. The coupled CEL method has significant potential for improving the theoretical understanding and design practice for a wide range of offshore penetration and installation problems.