Calculation and verification of ground settlement due to precipitation in a confined aquifer
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摘要: 北京地铁13号线天通苑站暗挖施工中,因地下水丰富且隧道底板位于承压含水层内,采用止水帷幕效果不佳、成本高昂,故改为开挖前对承压含水层进行预降水减压以控制地下水。为预测降水引发的地表沉降,基于三维地下水动力学理论,建立了一个区域划分数学模型,综合考虑了承压含水层降水压力分布曲线与隔水层顶板的空间位置,并将承压含水层上覆隔水顶板受力区域划分为无压区与承压区。依据能量守恒方程构建了单井降水的孔隙水压力分布公式,并引入Mindlin解计算地表沉降。经实测数据验证,最终沉降值与解析解所求值误差平均值为15%。研究表明,该模型可为短期内深层承压含水层降水引起的地表沉降提供理论依据。Abstract: In the underground excavation construction of Tiantongyuan Station of Beijing Metro Line 13, due to the rich groundwater and the tunnel floor located in the confined aquifer, the effect of the waterproof curtain is not good and the cost is high. Therefore, the confined aquifer is pre-dewatered and decompressed before excavation to control groundwater. In order to predict the surface subsidence caused by precipitation, this study established a mathematical model of regional division based on the three-dimensional groundwater dynamics theory, which comprehensively considered the distribution curve of precipitation pressure in confined aquifer and the spatial position of aquiclude roof. After dividing the stress area of confined aquifer into non-pressure area and pressure area, the pore water pressure distribution formula of single well precipitation was constructed according to the energy conservation equation, and the Mindlin solution was introduced to calculate the surface settlement. Verified by the measured data, the average error between the final settlement value and the analytical solution is 15%. The research shows that the model can provide a theoretical basis for surface subsidence caused by precipitation in deep confined aquifer.
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表 1 数值模拟土层参数
Table 1. Numerical simulation of soil parameters
土层 初始水头
H/m土层重度
$ {\gamma }_{\mathrm{s}} $/(kN·m−3)孔隙率
n黏聚力
c/kPa内摩擦角
φ/(°)土压缩模量
ES/MPa动弹性模量
Ed/MPa静弹性模量
E0/MPa渗透系数
k/(m·d−1)杂填土 8 20.4 0.22 0 25 60 50 80 1.86 粉质黏土 8 20.3 0.376 33 12.5 20 160 100 0.008 承压含水层
(细砂−中砂)13 20.5 0.3 0 23.1 120 660 150 1.55 粉质黏土 2 20.3 0.25 33 11.7 20 160 100 0.008 -
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