双向搅拌桩施工对桩周土体扰动分析

为探究双向搅拌桩施工时桩周超孔隙水压力和有效应力的分布和变化规律,依托江苏某高速公路软基处理工程,通过在不同位置布置传感器,测得单桩和群桩施工时桩周孔隙水压力和土压力的变化。结果表明:在施工过程中桩周土体孔隙水压力和土压力变化剧烈,靠近桩的位置产生了很高的超静孔隙水压力,孔压在桩周土的固结作用下消散规律表现为先快后慢;背离施工方向孔压累积值小于沿着施工方向的累积值,遮拦效应阻挡了约60%的超孔隙水压力,工程中可利用该现象减小施工对土体的扰动;单桩施工时桩周超孔压的分布与半径比的对数呈线性关系,分布规律与Vesic圆孔扩张理论解答的趋势相同,扰动影响范围约为20倍桩半径;施工过程中孔隙水压力小于土压力,桩体不会出现下沉和孔周土体液化等灾变,基于该原理可以通过改良设备和施工方法避免掉桩等灾变的发生。研究结果可为软土加固工程的施工安全提供参考。

Soil Disturbance around Piles by Bidirectional MixingColumns Construction

With the soft foundation treatment project of a highway in Jiangsu Province as engineering background, we explored the distribution and variation law of excess pore water pressure during the construction of bidirectional mixing columns, and analyzed the effective stress of the surrounding soil during hole expansion, and then determined whether hazards would occur during the soft foundation reinforcement process. We obtained the variation of pore water pressure and earth pressure during construction of group piles by arranging sensors at different locations and different depths. Results showed that during the construction process, the pore water pressure and earth pressure of soil around the pile changed drastically, and in particular, high excess pore water pressure was found in the adjacent of the pile position. Under the consolidation of surrounding soil, pore water pressure dissipated rapidly at first and then slowed down. The pore pressure accumulation away from the construction direction was smaller than that along the construction direction, hence impeding about 60% of the excess pore water pressure. In single pile construction, pore pressure had a significant linear relationship with the logarithm of radius ratio. Such distribution was identical to the solution of Vesic’s cavity expansion theory.The disturbance range was about 20 times of pile’s radius. In the meantime, we found that during the construction, pore water pressure was smaller than earth pressure, thus refraining from pile subsidence and soil liquefaction. On this basis, methods of modifying equipment or construction process can be adopted to avoid the subsidence of pile.