摘要
基坑采用悬挂式帷幕减压降水时,因隔水帷幕局部存在缺陷,而导致坑内承压含水层水头抬升所诱发的基坑底侧突涌事件常有发生。为研究这种现象,以某地铁线风井基坑为范例,建立了三维非稳定流的地下水数值模型,重点考虑了渗透系数的各向异性,对隔水帷幕无缺陷,28~33m、33~38m、38~43m深度的缺陷,加大流量抽取等7种情况,进行了模拟和比较分析。研究结果表明,悬挂式帷幕降水帷幕无缺陷时,帷幕内外的水头差在含水层顶最大,并沿帷幕向下递减;在帷幕缺陷形成的渗流通道附近,渗流场的等势线非常密集,补给的地下水抬升了坑内水头,并加剧了坑外的水头下降;经缺陷处的渗流通道流入坑内的地下水,渗流速度矢量以水平向为主;帷幕缺陷位于渗透系数较大的含水层时,相应补给量也较大;加大流量抽取,可以减小水头抬升的平面范围,但缺陷附近过大的流速也会诱发地层流土;缺陷位置与帷幕底竖向距离越远,坑内水头的抬升率越大,缺陷位置与帷幕底竖向距离越近,抬升率越小。研究成果对分析承压水底侧突涌的致灾机制、预测预警以及基坑动态风险评估等有一定的参考意义。
When unclosed waterproof curtain is used for pit dewatering,some defects may exist in the curtain.Bursting issues caused by water-head rise in the pit have been recorded multiple times. In the subway airshaft discussed in this article,at the end of the excavation process,large inflow occurred at west side of the pit. A threedimensional numerical model with anisotropic permeability into consideration of unsteady flow of underground water is built to simulate and analyze seepage field under seven working conditions. They are no defect on the waterproof curtain,defect at 28 - 33 m deep with/without increased water drawing volume,defect at 33 - 38 m deep with/without increased water drawing volume,defect at 38 - 43 m deep with/without increased water drawing volume. The research shows that when the waterproof curtain has no defect,the waterproof curtain inside and outside water-headdifference is largest at top of aquifer and the difference decreases with depth. Contours are dense near the seepage path near the defect. The water inflow raises water-head in the pit and lower water-head outside the pit. Seepage vectors of the water coming into the pit through the defect are mainly horizontal. When the defect is at the aquifer of high permeability,the corresponding water inflow is large. Increasing water drawing volume decreases impact area of the water-head rise,but excessive drawing can incur soil-piping flow. The larger the vertical distance between the defect and bottom of the curtain,the larger the rising potential is,and vice versa. The results provide guidance to incident mechanism analysis,predication and dynamic risk assessment of soil burst at down-side place of foundation pit.
出处
《工程地质学报》
CSCD
北大核心
2017年第3期699-705,共7页
Journal of Engineering Geology
基金
上海市科学技术委员会项目(13231201004
14DZ1207802
16DZ1201301)资助
关键词
悬挂式帷幕
隔水帷幕缺陷
减压降水
底侧突涌
渗流场
Unclosed waterproof curtain
Leakage of waterproof curtain
Dewatering in confined aquifers
Soil burst at down-side place of foundation pit
Seepage field
