黏土中静压管桩土塞机制研究

针对黏土中管桩土塞形成机制，利用耦合欧拉拉格朗日（CEL）法模拟钢管桩的大变形沉贯过程。在验证网格密度参数对数值计算精度影响的基础上，结合管桩内外土体速度场、应力场、土塞高度和增量充填比的变化分析了土塞演变和土塞形成机制，讨论了摩擦系数以及软硬土夹层对土塞形成的影响，并与离心机试验和理论计算数据验证。结果表明，管桩贯入过程土塞的演变可分为上涌期、过渡期和下滑期3个阶段。随着桩的贯入，桩端下轴线处形成连续的下凹塑性拱，当此处竖向应力增量达到7～8倍不排水抗剪强度时土塞初步形成。同时土塞效应随着桩-土间摩擦系数增大，桩径减小（壁厚相同）而增强；软硬夹层对土塞效应影响显著，上硬下软的土层易形成完全土塞，而上软下硬的土层，硬土挤入管桩不会形成土塞。

Mechanism of soil plug for jacked pipe pile in clay

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.