Seepage Point Impact in Urban Rail Transit Station Foundation Pit Enclosure Structure on the Variation Law of Surrounding Groundwater Seepage Field

Abstract

Objective In terms of underground engineering construction accident causes, approximately 20% of foundation pit accidents are caused by water seepage through enclosure structures. Such seepage can lead to significant deformation or instability of foundation pit. To enhance the safety of foundation pit project construction, it is necessary to detect seepage points before foundation pit excavation and study the impact of these seepage points on the groundwater seepage field around the foundation pit enclosure structure. Method Taking the foundation pit of a station on Qingdao Metro Line 4 as the engineering background, a distributed optical fiber detection method is employed to identify seepage points in the enclosure structure prior to construction, locating the potential seepage points. The groundwater levels near these suspected seepage points are monitored. The SEEP/W software is utilized to simulate the effects of different sizes and quantities of seepage points on the groundwater seepage field around the enclosure structure. Groundwater level monitoring points are set up near the seepage points to obtain field data. Result & Conclusion During the dewatering process of foundation pit excavation, the difference in groundwater pressure inside and outside the pit gradually increases, causing the groundwater level inside the pit to decrease, thus forming a dewatering funnel around the waterproof curtain. When the groundwater is close to the waterproof curtain without seepage points, the groundwater level outside the pit decreases to about 20% of the excavation dewatering depth inside the pit. With a seepage point width of 10 mm, the groundwater level outside the pit decreases to about 30% of the excavation dewatering depth inside pit. The presence of seepage points in the waterproof curtain leads to groundwater entering the pit near these points, sharply increasing water flux, hydraulic conductivity, and water pressure at the seepage points, with these values rising as the size of the seepage points increases. The numerical simulation results of foundation pit groundwater seepage using SEEP/W software prove to be in good agreement with the field measurements, demonstrating that using SEEP/W for simulating groundwater seepage fields is reasonable and feasible.

Keywords

• urban rail transit
• station
• foundation pit enclosure structure
• seepage point
• groundwater seepage field