有明黏土中搅拌桩施工时的孔隙水压力

Excess pore pressure around deep mixing column in soft Ariake clay

深层搅拌桩施工时,固化剂的注入与叶片的搅拌作用不可避免地会扰动周围土体,改变桩周土体中的应力状态,产生超静孔隙水压力。在高灵敏性的日本有明黏土中搅拌桩施工时对周围土体中的孔隙水压力进行了现场监测。监测结果表明周围土体中产生了很高的超静孔隙水压力,其量值较土体的初始上覆压力还要大,使土体中的有效应力为零,处于张拉状态,但是该超静孔隙水压力在初始阶段消散得非常快。为分析施工引起的超静孔隙水压力,将搅拌桩施工时和周围土体的相互作用采用受剪的孔穴扩张过程来模拟,提出一种简单的方法来计算搅拌桩施工时周围土体中的超静孔隙水压力,同时考虑了固化剂注入时的膨胀压力与旋转叶片在搅拌时所产生的剪切力的作用。超静孔隙水压力由土的不排水抗剪强度、剪切力、注浆压力和孔隙压力系数所确定。所提出的计算方法得到实测数据的验证。

Deep mixed （DM） column is installed in field through mixing the injected chemical binder with in-situ soft soil using rotating blades. The injection of chemical binder and rotating mixing disturb the surrounding clay, change the stress state, and cause excess pore water pressure in the surrounding ground. The excess pore water pressure was measured during installation of DM columns in sensitive Ariake clay, Japan. Field measured results showed that significant excess pore water pressure was generated in the surrounding clay and its value was greater than its effective overburden stress to make the surrounding clay under tension state. However, at the initial stage （5 minutes）, the excess pore water pressure dissipated very fast. The interaction mechanism between deep mixing column and the surrounding clay during installation can be simulated by using sheafing-expanding process of cylindrical cavity. An approach is presented for the calculation of excess pore water pressure around DM column. The proposed method considers the effect of sheafing force caused by the rotation of blades during mixing. In the proposed approach, the excess pore water pressure is determined in terms of undrained strength of clay, sheafing force, injection pressure and pore water pressure parameter. The proposed method is verified by the laboratory test and field measured data.