潜水层基坑降水引起地表沉降试验与理论研究

Experimental and theoretical study on the surface subsidence by dewatering of foundation pit in phreatic aquifer

为研究基坑内外含水层未完全隔离条件下基坑内不完整井降水引起坑外地表沉降变化机制,以深圳地铁综合枢纽基坑工程为研究实例,选取深圳典型潜水地层,采用模型试验方法,结合理论分析,揭示潜水地层不完整井降水有效影响深度和坑外土层孔隙水压变化规律,分别提出不完整井降水有效影响深度、坑外水位变化曲线和绕渗区划分计算公式。基于提出的理论公式,研究提出基坑外地表沉降简化计算方法,理论计算地表沉降曲线变化趋势与试验结果基本吻合,但理论结果偏于保守,因此进一步利用绕渗区渗流作用原理对简化方法进行修正,有效提高了理论计算精度,分析对比现场监测数据,结果表明该方法具有较高的工程实用价值。上述研究成果可为类似潜水地层基坑工程降水设计、施工提供参考。

The ground surface subsidence outside the foundation pit caused by the incomplete well dewatering in the foundation pit under the condition that the aquifer inside and outside the foundation pit is not separated completely is studied in the foundation pit in Shenzhen Metro hub by means of the model tests and theoretical analysis. The effective depth due to incomplete well dewatering in the phreatic water stratum and the variation of the soil pore water pressure outside the foundation pit are revealed. The calculation formulas for the effective depth due to the incomplete well dewatering,the varying curve of water level outside the foundation pit and the percolation zone partition are put forward respectively. A simplified calculation method for the surface subsidence outside the foundation pit is proposed. The theoretically calculated trend of the surface subsidence curve is basically consistent with the measured results. However,the theoretical results tend to be conservative. Therefore,the simplified method is revised further by using the seepage principle of a by-pass seepage zone,which improves effectively the precision of theoretical calculation. Finally,the comparison between the in-situ monitoring data and theoretical calculated results shows that the proposed method is applicable in practical engineering.