粉土与粉质黏土互层中静压桩桩土界面径向土压力研究

Study on radial soil pressure at interface of jacked pile between silty soil and silty clay

为研究静压管桩贯入过程中桩土界面总径向土压力的变化规律,选取山东东营某工地进行现场足尺试验,得到贯入过程中桩侧总径向土压力随贯入深度的变化规律;然后,结合土的极限平衡理论,考虑贯入过程中粉土中孔隙水的消散和桩土界面循环剪切引起的桩土界面土压力的退化,建立沿深度方向桩土界面总径向土压力的极限平衡理论修正公式,探讨贯入过程中桩土界面总径向土压力的分布特征。研究结果表明:桩土界面总径向土压力与土层性质密切相关;在同一贯入深度不同桩身位置处(H/D)桩土界面总径向土压力存在退化现象,并且粉土中的退化幅度比粉质黏土中的退化幅度大,退化幅度最大相差14.22%;在饱和粉土中采用极限平衡理论计算桩土界面总径向土压力时,应考虑孔隙水的消散特性,超孔压消散系数为0.7~0.8;不同土层桩土界面总径向土压力退化幅度与H/D有关,两者呈幂函数关系,粉土和粉质黏土中剪切退化系数分别为0.19和0.12;采用极限平衡理论计算沉桩过程中不同桩身位置处(H/D)桩土界面总径向土压力时,需考虑桩长效应即剪切退化效应;所提出的考虑孔隙水消散和剪切退化修正的极限平衡理论公式,理论计算结果与实测结果吻合较好。

In order to study the variation law of total radial earth pressure at pile-soil interface during the jacking penetration of jacked pile, a full-scale in-situ test was conducted in Dongying, Shandong Province. The variation of the total radial earth pressure on the pile side with the penetration depth during the jacking penetration was obtained. Combined with the limit equilibrium theory of soil and considering the dissipation of pore water in silty soil and the degradation of soil pressure at the pile-soil interface caused by cyclic shear at the pile-soil interface during penetration, a theoretical correction formula for the limit equilibrium of total radial soil pressure on the pilesoil interface along the depth direction was established. The distribution characteristics of total radial earth pressure at pile-soil interface during penetration were discussed. The results show that the total radial earth pressure on the pile-soil interface is closely related to the soil properties. At the same penetration depth, the radial earth pressure on the pile-soil interface is degraded with the pile-soil interface(H/D), the degree of degradation in the silt is greater than the extent of degradation in silty clay, and the maximum extent of degradation is 14.22%.When using the limit equilibrium theory to calculate the total radial earth pressure on the pile-soil interface in saturated silt, the dissipation characteristics of pore water should be considered, and the excess pore pressure dissipation coefficient is 0.7-0.8. The total radial soil pressure degradation amplitude of pile-soil interface in different soil layers is related to H/D, which can be expressed as a power function. The shear degradation coefficient in silt and silty clay are 0.19 and 0.12, respectively. When the limit equilibrium theory is used to calculate the total radial earth pressure at the pile-soil interface at different pile body position(H/D) during jacking, the pile length effect, which is shear degradation effect, needs to be considered. The theoretical calculation results of the proposed limit equilibrium theory formula considering pore water dissipation and shear degradation correction, are in good agreement with the measured values.