Abstract: Cone penetration test (CPT) is an in-situ test method to obtain common geotechnical parameters accurately, but CPT data cannot be directly converted into macro constitutive model parameters (i.e., a type of fine geotechnical parameters). The principal reason is that there is insufficient research on the macro and micro penetration mechanism. Based on the Mohr-Coulomb failure criterion of cylindrical (cone) cavity expansion theory, a macro and micro coupling numerical calculation method for the CPT process is established. Firstly, based on the cavity expansion theory, the limit pressure in expansion is solved, and the relationship between the cone resistance, sleeve friction and the limit expansion stress are derived. Secondly, taking the ②1 silty clay of the shallow bearing layer as the research object in Shanghai, through the same scale triaxial compression tests, the conversion formula of the geotechnical parameters in the macro finite element with micro discrete element coupling calculation is established, the formula is calibrated by ②1 silty and ⑤1-1 gray clay. Finally, taking the ②1 silty clay as the research object, the error of the theoretical solution, numerical solution and measurements of cone resistance, sleeve friction and limit pressure in expansion of cylindrical cavity are analyzed from a macro perspective. Soil particle deformation and contact force chain are analyzed from the micro perspective. The errors of the limit pressure of expansion, cone resistance and sleeve friction calculated using the theoretical method are 1.30%, 0.45% and 0.77%, respectively. The errors of the limit pressure in expansion, cone resistance, sleeve friction and pore water pressure calculated by the macro and micro coupling method are 9.68%, 2.99%, 9.19% and 8.42%, respectively. The results of the macro and micro coupling numerical calculation are not only close to the results of the cylindrical (cone) cavity expansion theory, but also considering the effect of pore water pressure. Above research provides a macro and micro coupling numerical method for simulating the CPT mechanism and obtaining the parameters of the specific constitutive model.

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