Model Test and Numerical Simulation of Penetration Process of Sleeve for Cast-in-Place Piles Driven by Vibratory Hammers

A model test was carried out to investigate the excess pore pressure, the radial extruding stresses, and the degree of soil plug of a vibratory driven sleeve for cast-in-place piles. A finite element model was also introduced by using the commercial code, ABAQUS. The results from the finite element analysis are in a strong agreement with the experimental observations. The results show that the excess pore pressure and radial extruding stresses increase to 1 kPa and 8 kPa, respectively; nevertheless, the extruding effect is mainly limited within a radial distance of about 6 times the sleeve diameter. The soil shear strength and granular cementation force decrease during vibratory sleeve driving, which is induced by cyclic shearing action in the shear interface. As a result, the inside sleeve of the soil plug is in an incompletely plugged mode. During vibratory sleeve driving, the soil plug in the sleeve end forms an annular soil arch, which gives rise to an obvious increase in internal friction resistance. The soil plug of this section withstands 80%of the internal friction resistance. When the penetration depth is the same, the height of the soil plug in a saturated sand foundation is 1.2 times the height of the soil plug in a dry sand foundation. The vibration frequency, sleeve diameter, and saturation have significant effects on the soil plugging effect.