141 / 2024-03-02 03:20:30

Normalisation of excess water pressure in CPTU under partially drained conditions: cavity expansion method

piezocone penetration test,partially drained effect,rate effect,CPTU,cavity expansion

Excess water pressure (EWP) measured by piezocone penetration tests (CPTU) may be significantly affected by the partially drained effect and this effect is captured in this paper by a hydro-mechanical coupled solution for cavity expansion under partially drained conditions. The mechanical behaviour of soils is modelled by the elastoplastic Tresca model and water flow within porous soils is assumed to obey Darcy’s law. Two partial differential equations (PDEs) are established in the elastic and plastic zones, respectively, transforming the cavity expansion analysis into a typical Stefan problem with moving boundary conditions. Then the PDEs are solved by the variable transformation method and validated by comparison with finite element results. Based on the new solution, a novel normalised penetration rate is defined considering the rigidity index of soils, with which a unique backbone curve for CPTU is found. Finally, the backbone curve is compared with a database consisting of 109 in-situ experimental tests, 101 centrifuge modelling tests, and numerical simulation results. The proposed solution may provide a useful theoretical tool for interpreting the consolidation coefficient of fine-grained soils from the penetration stage of multi-rate CPTU, which can enhance the interpretation reliability for CPTU dissipation tests.