ISSN 1000-3665 CN 11-2202/P

    基坑施工抽水诱发土体渗透破坏的临界抽水量预测

    Predicting the critical drainage induced by soil seepage failure during pumping in foundation pit construction

    • 摘要: 在地下水位埋深较浅的基坑施工过程中,常因抽水强度控制不当导致土体渗透破坏引起工程事故,造成人员伤亡及财产损失。目前,已有研究主要针对抽水诱发土体渗透破坏的土层条件、沉降变形预测、施工抽水措施等方面,较少涉及抽水诱发土体渗透破坏的临界抽水量。然而,临界抽水量是基坑施工抽水安全的关键参数,当前无有效的方法计算测试该参数。基于《水电工程钻孔抽水试验规程》(NB/T 35103—2017)推荐的抽水试验渗透系数计算公式,结合达西定理及等价无穷小公式,推导得出潜水非完整孔、潜水完整孔、承压水非完整孔和承压水完整孔四种工况条件下土体渗透破坏的临界抽水量表达式,并引入修正系数对推导的表达式进行修正。结果表明:(1)四种工况下,诱发土体渗透破坏的临界抽水量表达式是关于临界渗透速度的一次函数,说明通过测算场地土体渗透破坏的临界渗透速度可求出临界抽水量;(2)以呼和浩特某基坑为例,场地内最大可能发生抽水渗透破坏的地层为圆砾层,通过室内试验得出破坏临界渗透速度为7.1×10−4 m/s,为了确保场地圆砾层不受抽水破坏,设计的潜水完整抽水井SJ1临界抽水量为174.45 m3/d,实际抽水量控制在150 m3/d内未出现渗透破坏现象,说明提出的方法具有可应用性。因此,相比于基坑施工中临界抽水量预测的现有定性经验方法,文章提出的定量计算方法更具有实践应用价值。

       

      Abstract: In the construction of foundation pits with shallow groundwater levels, improper control of pumping strength often leads to soil penetration failure, resulting in engineering accidents, casualties, and property losses. Currently, existing research mainly focuses on soil conditions, settlement deformation prediction, construction pumping measures, etc., and rarely involves the critical pumping quantity. However, the critical pumping quantity is a key parameter for pumping safety in foundation pit construction and there is no effective method to calculate or test this parameter. Based on Darcy’s law and the equivalent infinitesimal formula, and the formula for calculating the permeability coefficient of pumping tests recommended by the specification for borehole pumping test of hydropower projects (NB/T 35103—2017), this study deduced the expressions of critical pumping quantity of the seepage failure under four conditions, including submersible incomplete hole, submersible integral hole, confined water incomplete hole and confined water integral hole. To ensure that the calculated result is more effective, the calculated expression was modified by introducing correction coefficient. The results indicate that the relationship between the critical drawdown volume for inducing soil permeability failure in the four cases and the critical permeability velocity is linear, suggesting that measuring the critical permeability velocity of the soil at the site can determine the critical drawdown volume. In a case study of basement excavation in Hohhot, it is found that the cobble layer has the highest potential for water permeability failure. Laboratory measurements revealed a critical permeability velocity for its failure of 7.1×10−4m/s. To prevent damage to this layer during pumping, an artesian well SJ1 with a designed critical drawdown volume of 174.45 m3/d was used, and actual pumping volumes were controlled within 150 m3/d without observing any permeability failures, demonstrating applicability of the proposed method. Therefore, compared to existing qualitative experience-based methods for predicting critical drawdown volumes in basement excavation, the quantitative calculation method holds greater practical application value.

       

    /

    返回文章
    返回