兰州红砂岩地层地铁站深基坑变形规律分析

Analysis of deformation law of Lanzhou metro station deep foundation pit with red sandstone stratum

为研究高水位红砂岩地层基坑降水开挖引起的变形规律,以兰州东方红广场地铁车站深基坑工程为背景,对基坑降水开挖过程中桩体水平位移以及坑周地表沉降进行现场监测.采用有限差分软件Flac3D对基坑降水开挖过程中的位移进行模拟计算.监测结果表明:随着基坑开挖深度的增加,桩体最大水平位移的位置逐渐下移,最终靠近基坑底部,大约在坑底以上1~2 m;地表最大沉降值出现在距离基坑边5~7 m处,大约0.29~0.41倍的基坑开挖深度;桩间水土流失是造成地表沉降过大的主要原因.模拟结果与实测结果对比分析得出:地表沉降模拟值与监测值变化趋势基本一致;桩体在距地面小于12 m部分其水平位移模拟值与实测值非常接近,大于12 m部分实测值明显大于模拟值.

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 to simulate 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 above the 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.