承压水地层基坑抗突涌稳定性的计算方法

Calculation method of stability against inrush of excavation overlying a confined aquifer

现行规范计算基坑抗突涌稳定性采用压力平衡法,该方法未考虑上方土体强度和基坑尺寸的影响,对接近临界承压水压力情况的评价偏于保守。针对上述问题,首先根据强度折减原理定义安全系数,采用有效应力分析并考虑基坑被动区的存在,改进了已有的考虑土体四周抗剪强度抗突涌计算方法,并基于弹性板理论提出了新的基坑抗突涌计算方法;随后在平面应变条件下利用强度折减有限元计算结果进行了讨论,并进一步分析了基坑长宽比的影响;最后对工程实例进行了计算分析。分析表明,改进后和新提出的方法相较于现有方法能更好地说明基坑抗突涌稳定性随承压水压力的变化情况,在保证工程安全的前提下提高经济性。

The pressure balance method is adopted in calculating the stability against the inrush of excavation in the current criterion.The effects of soil strength and excavation size are not considered in this method.Therefore,the method gives a conservative evaluation of the situation approaching the critical artesian pressure.Aiming at these problems,firstly,the safety factor is defined according to the principle of shear strength reduction in this paper.The existing method considering soil shear strength along slip surfaces is improved by adopting effective stress analysis and considering the passive zone of excavation.Then,a new calculation method for inrush resistance is proposed based on the elastic plate theory.Subsequently,the results of the finite-element method with reduced shear strength are compared with those of above calculation methods under the plane strain condition.And the effects of the excavation length-width ratio for the improved and proposed methods are further analyzed.Finally,the analysis of an engineering practice is carried out.The analysis shows that compared with the existing methods,the improved and proposed methods in this paper can better reveal the trends of excavation stability against inrush with the change of the artesian pressure and improve the economy on the premise of ensuring the safety of engineering practice.