考虑渗流作用的基坑抗突涌验算与降深设计

Uplifting Check and Groundwater Drawdown Design of Deep Excavations Considering Seepage

利用渗透变形理论研究了考虑渗流作用的基坑抗突涌验算方法—渗透力平衡法,从原理、表达式以及适用范围等方面,讨论了该方法与现有的经典压力平衡法之间的关系,指出用经典压力平衡法计算安全系数偏于安全,而用渗透力平衡法较为经济。且相对于承压水层而言,上覆土层应视为弱透水层,不能忽视渗流的作用。考虑渗流作用的渗透力平衡法计算安全系数更为经济合理。另外,参考《碾压式土石坝设计规范》(SL274-2001)中对边坡稳定系数中关于简化毕肖普法与瑞典法的取值原则,建议用渗透力平衡法计算的最小安全系数宜大于1.1,但应小于新规范中的下限值1.5。同时,基于对抗突涌验算方法的分析,研究了考虑渗流作用的基坑降水降深的计算方法,并与原有方法进行对比,在其他条件相同时,考虑渗流作用求得的水位降深要小。

The seepage balance method, which is used in checking the uplift force in deep excavations, is studied based on the mechanism of seepage deformations. In this paper, this method is also compared with the classical force balance method in terms of theoretical derivation, variables and range of applicability. It is concluded that the classical force balance method oftenleads to a conservative solution whereas the seepage balance method results in an economical solution. It is also noted that, in the Roller Compacted Earth Dam Design Specifications （SL274-2001）, the factor of safety from the resultant seepage balance method should be greater than 1.1 and should be less than the 1.5, which is the lower bound suggested in the new specifications. The suggested factor of safety values are obtained similar to the derivation of safety factors using the Simplified Bishop Method and the Swedish Method in slope stability analyses. This paper also compares the results from the seepage balance method and from other methods when estimating the groundwater drawdown in deep excavations. It is suggested that the seep- age balance method results in a smaller groundwater drawdown.