Study On The Rule Of Foundation Pit Dewatering And Land Subsidence In Xi’an Metro Construction

In recent years, more and more problems about loess foundation pit are aroused due to the increasing urban constructions in Loess Area. In this paper, combined with the foundation pit project of the main structure in Da Yanta Station of Xi’an Metro Line 3, the numerical simulation is used in the study of loess foundation pit dewatering by applying transient seepage theory. The main contents are as follows:(1) The increase of water content in loess layer can reduce the strength of loess and subsequently reduce the overall stability of loess foundation pit, and the safety of foundation pit is reduced obviously. To ensure the safety, it is needed to take measures to lower the underwater level during the excavation of foundation pit.(2) The dewatering process and its effect on ground subsidence of the foundation pit project of the main structure in Da Yanta Station of Xi’an Metro Line 3 is simulated dynamically by using transient seepage theory. The results show that: the greatest change takes place in the nodes head outside of the foundation pit near the bottom of waterproof curtain. The variation range is greater at the previous week, and then becoming smooth. Water head varies linearly roughly with time, and the regularity is close to the water level observation data on site. Based on the Biot consolidation theory,the subsidence caused by actual engineering dewatering is calculated. The difference between sedimentation value and monitoring value is small. 20 days after the dewatering, the calculation of 5m from the foundation pit is 2.36 cm, and the actual monitoring value is 2.69 cm.(3) The functional mechanism of waterproof curtain and the impact of distance between tube well and waterproof curtain on dewatering effect are studied by using transient seepage theory in this paper. The results indicate that: the groundwater outside of the pit flows into the tube well from its bottom bypassing the waterproof curtain, thus extending the seepage path. Setting waterproof curtain can significantly reduce the head loss outside of the pit, and then effectively reduce the consolidation settlement. 20 days after the dewatering, the larger the distance is, the smaller water head loss outside of the pit is, and the more favorable for the reduction of consolidation settlement.