Abstract: To investigate the mechanism of soil plug during jacked pipe pile in clay, coupled Eulerian- Lagrangian(CEL) approach is used to simulate the large deformation penetration process. On the basis of verifying the influence of mesh density on the accuracy of numerical calculation, the evolution and mechanism of soil plug is presented with soil velocity fields inside and outside pipe pile, stress field, height of soil plug and incremental filling ratio. The influence of friction coefficient, the soft or hard soil interlayer on the formation of soil plug is discussed. The numerical simulation results are verified by centrifuge experiments and theoretical calculations. The computational results show that the evolution of soil plug is mainly divided into three stages including the upwelling stage, the transition stage and the downward sliding stage during the penetration of pipe pile. As the pile jacking, the continuous concave plastic arch forms at the axis under the pile tip, where the vertical stress reaches 7-8 times the undrained shear strength indicates the initial formation of soil plug. With the increase of friction coefficient between pile and soil and so as the pile diameter, the plugging effect enhances. The soft or hard soil interlayer can significantly affect the plugging effect. Pipe pile is prone to a fully plugged mode when the hard soil is over the soft soil, while the hard soil is prone to squeeze into pile when the soft soil is over the hard soil.

Key words: soil plugging effect, pipe pile, clay, CEL, incremental filling ratio