Abstract: In order to study the deformation law caused by dewatering and excavation of foundation pit in red sandstone stratum with high water level, taking the deep foundation pit project of Lanzhou Dongfanghong square subway station as the background, the horizontal displacement of piles and ground settlement around foundation pit during dewatering and excavation were monitored on site. The finite difference software Flac3D was used tosimulate the displacement of foundation pit during dewatering and excavation. The monitoring results show that the position of the maximum horizontal displacement of the pile gradually moves down with the increase of foundation pit excavation, and finally it is near the bottom of the foundation pit, about 1 to 2 m abovethe bottom of foundation pit. The maximum settlement value of the surface appears at a distance of 5 to 7 m from the side of the foundation pit, about 0.29 to 0.41 times of the depth of foundation pit. Soil and water loss between piles is the main cause of excessive ground subsidence. Comparing the simulated results with the measured ones, it is concluded that the variation trend of simulated and monitored surface subsidence is basically the same. The simulated value of the horizontal displacement of the pile is very close to the measured value when it is less than 12 m away from the ground. When it is more than 12 m away from the ground, the measured value is obviously larger than the simulated value.

Key words: deep foundation pit, red sandstone, monitoring, simulation, displacement