基于Mindlin解的搅拌桩施工挤土效应预测分析——上海某近地铁区间隧道工程案例分析

Squeezing Effect Prediction and Analysis of Tri-Axial Cement-Mixing Pile (TCMP) Based on Mindlin Equation—A Case Study of a Project near the Subway Tunnel in Shanghai

摘要: 水泥土搅拌桩是地基处理的常用方法。在大直径钻孔灌注桩成孔施工时，为了防止坍孔，以确保邻近地层稳定，经常采用三轴水泥土搅拌桩对钻孔桩周围地层进行加固处理。但三轴水泥土搅拌桩沉桩施工因为其高压注浆和快速钻进原因，会对邻近土层产生挤压作用，这种挤压作用将导致邻近土体的位移。为此，需要根据邻近地铁区间隧道的运营维护要求，适当控制搅拌桩的注浆压力和沉桩速度，将搅拌桩的挤土不利影响降至最低程度。本文基于Mindlin理论，采用理论解析的方法，就三轴水泥土搅拌桩施工对邻近土体及邻近隧道的影响进行了公式推导和计算分析，并将计算结果和试验监测结果进行了对比。本案例表明，采用理论解析方法来预测搅拌桩的挤土效应具有快速方便的特点，在搅拌桩施工参数选择决策中，不失为一种有益的方法。

Abstract: Tri-axial cement-mixing pile (TCMP) is a very common option for soil improvement. During pile driving of bored pile with large diameter, TCMP is often adopted in order to avoid caving of bored hole, and accordingly to ensure the safety of the neighbouring subway tunnel. But unfortunately, TCMP can also lead to rather large movement of surrounding soil due to the high grouting pressure and rapid boring speed when TCMP driving, which is called pile-driving’s squeezing effect. To meet the requirement of the displacement of subway tunnel, it is necessary to control the grouting pressure and boring speed of TCMP in order to reduce the adverse effect to the minimum. Based on Mindlin Equation, this paper has derived the analytical formula of the displacement induced to TCMP driving and carried out relevant calculation, and finally, this paper has compared this calculation with the site measurement. This paper has shown that this analytical method, being fast and convenient, is a recommendable one in predicting the squeezing effect of TCMP driving, and is very helpful in selecting appropriate grouting pressure and boring speed of TCMP.