Abstract:

Although cone penetration test (CPT) is an in-situ test method to obtain conventional geotechnical properties accurately, CPT data cannot be directly linked to macro constitutive model parameters. The principal reason is that the comprehensive studies on the macro-micro penetration mechanism. Based on the cylindrical (cone) cavity expansion theory, a macro and micro coupling simulation method for the CPT process is established. Firstly, based on the cavity expansion theory, the relationships among the cone resistance, sleeve friction and the cavity limit pressure are derived. Secondly, the numerical triaxial compression tests with the same dimensions on the Shanghai ②₁ silty clay in the shallow bearing layer are performed by both the maco and the micro simulation methods. The conversion formulas that relate the macro perfectly elastoplastic model (i.e., Mohr-Coulomb model) parameters to the micro linear parallel-bond model parameters have been proposed and implemented in the commonly used commercial software FLAC^3D. The macro-micro conversion formulas are validated by the CPT data on Shanghai ②₁ silty clay and  = 5 \* GB3 ⑤_1-1 gray clay. Finally, the discrepancies between the theoretical solution, numerical modelling results and the CPT measurements of cone resistance, sleeve friction and cavity limit pressure on the Shanghai ②₁ silty clay are analyzed from a macro perspective. The distribution of soil displacement and the contact force chain are presented and discussed from the micro perspective. The discrepancies between the theoretical solutions and the CPT measurements of the cavity limit pressure, cone resistance and sleeve friction are 1.30%, 0.45% and 0.77%, respectively. The discrepancies between the macro and micro coupling simulation results and the CPT measurements of the cavity limit pressure, cone resistance, sleeve friction and pore pressure are 9.68%, 2.99%, 9.19% and 8.42%, respectively. It indicates that the macro and micro coupling numerical modelling results are not only in agreement with the cavity expansion theory-based theoretical solutions and the CPT measurements, but also the effect of pore pressure can be simulated. The proposed macro and micro coupling simulation provides insight into the CPT mechanism and the approach to estimating the macro-micro parameters of the specific constitutive models.

Key words: cone penetration test, cavity expansion theory, macro and micro mechanics, coupling analysis