CFD SIMULATION ON THE PENETRATION OF FFP INTO UNIFORM CLAY

The cone penetration test (CPT) has been widely used to measure the soil undrained shear strength. On the basis of CPT, the free fall penetrometer (FFP) is developed to improve the test efficiency, which penetrates into soil by its kinetic energy gained from free fall in the water/air column and potential energy. However, the soil-FFP interaction is rather complex, which refers to the shear strain rate effect and drag force. Therefore, it is necessary to analyze the forces acting on the FFP accurately to improve its practicability and the accuracy of soil strength measurement. The FFP penetration procedure in uniform soils was simulated in the present study by using the commercial software ANSYS CFX 17.0, which is based on the computational fluid dynamics (CFD) approach. The dynamic mesh approach was applied to simulate the moving boundary. The thin layer element method was proposed to simulate the FFP-soil interaction. In the CFD simulation, the soil was modeled as non-Newtonian fluid and the shear strain rate effect was considered. Different FFP velocities, soil strengths and densities, interface frictional coefficients and shear strain rate parameters were considered to investigate their effects on the bearing and sleeve resistances of FFP. The fitted formulas of the cone bearing capacity factor, the strain rate parameters and drag coefficients for the cone and sleeve were established based on the present numerical results. In addition, the process to estimate the undrained shear strength of clayed soils was put forward, which may be beneficial for analyzing the recorded data from FFP.