高富水复合砂层盾构隧道渗透破坏原因分析

Analysis of Seepage Failure in Water-Rich Composite Sand Layer Caused by Shield Tunneling

特殊的地层条件及水力条件是事故发生的关键因素。本文通过砂土流失模型试验,发现单一砂层、复合砂层的渗流破坏特征存在显著不同。单一砂层和“上粗下细”复合砂层的侵蚀空洞呈漏斗形,而“上细下粗”复合砂层的侵蚀空洞呈碗形。当渗流出口处于粗细交界面时,上细下粗的复合砂层,使大部分的水头损失消耗在上部的细砂层中。相同条件下,“上细下粗”复合砂层中的渗流破坏最为强烈。广东某地铁区间突发涌水涌砂导致地面坍塌。事发地为珠三角河网地带,盾构机处于由下层中粗砂和上粉细砂组合而成的复合砂层中,同时邻近河涌强供水,两种结合极易发生涌水涌砂,引发周围地层砂水快速流失,造成上覆土层的大面积塌陷。试验结果与现场现象相吻合,揭示了高富水复合砂层中容易导致事故的地层和水力方面原因及上述多种因素组合致灾的机理。在类似工程勘察设计阶段,需重视复合砂层的识别,并做好盾构的“密封”措施,防止渗流出口的出现。

In 2018,a sudden influx of water and sand in a section of Foshan Metro Line 2 caused the ground to collapse.Special formation conditions and hydraulic conditions are the key factors for the accident.Through a sand loss model test,it is found that the seepage erosion of single sand layer and composite sand layer is significantly different.The erosion cavity of single sand layer is funnel-shaped,and that of composite sand layer is bowl shaped.Under the same conditions,the seepage failure in the composite sand layer is stronger than that in the single sand layer.The incident occurred in the river network of the Pearl River Delta.The shield machine is in a composite sand layer composed of the lower medium coarse sand and the upper silty fine sand.At the same time,it is adjacent to the strong water supply of the river.The combination of the two is prone to water and sand gushing,causing rapid loss of sand water in the surrounding strata and large-area collapse.The field phenomena are consistent with the test results,revealing the formation and hydraulic reasons that are easy to cause accidents in the high water-rich composite sand layer.In the survey and design stage of similar projects,it is necessary to pay attention to the identification of composite sand layer,and take“sealing”measures for shield to prevent seepage outlet.