承压水降水引起深基坑变形研究

发布时间：2019-07-03 09:39

【摘要】：随着城市地下空间的开发利用和城市轨道交通工程建设的快速发展,深基坑开挖越来越深,承压水治理在基坑工程中的地位逐渐上升。本文采用解析计算方法建立了基坑边坡滑动时安全系数的解析算式,利用地质雷达探测了地铁车站基坑的地质情况,明确了地下水的分布,结合地质勘察报告和现场实测数据利用智能位移反分析确定了承压含水层地质参数的取值,最后利用FLAC3D模拟分析了不同渗流特征下承压水降水引起的深基坑变形特点。本文主要得到以下结论:(1)采用解析计算方法,建立了基坑边坡平面滑动和圆弧滑动时安全系数的解析算式,计算得出了所研究基坑竖直边坡围护结构的最小深度应为25.38m。(2)采用地质雷达对所研究地铁车站施工场地的地质情况进行了探测。发现所测区域存在土体疏松或脱空现象,且从地下2m处有开始出现地下水的迹象。根据现场监测数据对地表沉降、地下连续墙侧移、基坑坑底隆起进行了处理分析,总结了基坑变形规律。(3)采用正交试验法分析了承压含水层不同参数对基坑外围土体沉降的敏感性,确定了承压含水层需要反演的4个参数:弹性模量E、泊松比?、渗透系数K、孔隙率n。采用均匀试验法构建反演分析的学习样本和测试样本,利用MATLAB神经网络工具箱对试验样本进行学习和测试得出符合误差要求的训练函数,结合实测数据通过反演得出承压含水层的参数取值。进行正演试验,结果表明:数值计算值与相应的现场实测值最大相对误差为7.89%,吻合度较高,能够满足工程精度的需要。(4)根据基坑底板抗突涌计算公式,得出车站基坑在开挖施工前必须降低承压水水头9m。承压水降水导致基坑外围土体出现“抛物线”状沉降变形,在距离基坑2倍开挖深度时沉降值达到最大。沉降变化趋势与降水漏斗形式相似,证明在最大沉降处外侧土体的沉降是由于降水引起的。承压水降压引起的沉降变形主要发生在承压含水层上覆土体中,其沉降变形呈现“上小下大”特点,土体的最大位移发生在承压含水层与上覆土体分界处。(5)根据围护结构的不同将基坑承压水降水时渗流特征分为三类。在第一类渗流特征下,承压水降水引起的土体沉降相对最小。第二类渗流特征下土体沉降变形最大,比同等围护方案下坑内降水方案导致的最大沉降变形大141%。在第三类渗流特征下,随着地下连续墙插入承压含水层深度的增加,基坑周围地表沉降减小。深基坑地下连续墙的侧移和坑底隆起主要由支护结构刚度和开挖土体深度决定,承压水降水导致的影响相对较小。地下连续墙侧移最大值发生在基坑坑底附近,基坑底部的隆起呈现中心大两边小的特点。
[Abstract]:With the development and utilization of urban underground space and the rapid development of urban rail transit engineering, the excavation of deep foundation pit is getting deeper and deeper, and the position of confined water treatment in foundation pit engineering is gradually rising. In this paper, the analytical formula of safety factor of foundation pit slope sliding is established by means of analytical calculation method, the geological condition of foundation pit of subway station is detected by geological radar, the distribution of groundwater is clarified, and the value of geological parameters of confined aquifer is determined by intelligent displacement back analysis combined with geological survey report and field measured data. Finally, FLAC3D simulation is used to analyze the deformation characteristics of deep foundation pit caused by pressure water drop under different seepage characteristics. The main conclusions of this paper are as follows: (1) by using the analytical calculation method, the analytical formulas of the safety factor of the plane sliding and circular arc sliding of the foundation pit slope are established, and it is calculated that the minimum depth of the vertical slope envelope structure of the studied foundation pit should be 25.38. (2) the geological conditions of the construction site of the studied subway station are detected by using geological radar. It is found that the soil is loose or empty in the measured area, and there are signs of groundwater beginning from 2m underground. According to the field monitoring data, the surface settlement, the lateral displacement of underground continuous wall and the uplift at the bottom of foundation pit are treated and analyzed, and the deformation law of foundation pit is summarized. (3) the sensitivity of different parameters of confined aquifer to the settlement of soil around foundation pit is analyzed by orthogonal test method, and four parameters that need to be inversed in confined aquifer are determined: elastic modulus E, Poisson's ratio? permeability coefficient K, porosity n. The uniform test method is used to construct the learning samples and test samples of inversion analysis, and the MATLAB neural network toolbox is used to study and test the test samples to obtain the training function that meets the error requirements. Combined with the measured data, the parameters of the confined aquifer are obtained by inversion. The results show that the maximum relative error between the numerical calculation value and the corresponding field measured value is 7.89%, and the coincidence degree is high, which can meet the needs of engineering accuracy. (4) according to the anti-surge calculation formula of foundation pit floor, it is concluded that the confined water head must be reduced by 9 m before excavation. The "parabola" settlement deformation of the soil around the foundation pit is caused by the pressure water dewatering, and the settlement value reaches the maximum when it is twice the excavation depth of the foundation pit. The change trend of settlement is similar to that of precipitation funnel, which proves that the settlement of lateral soil at the maximum settlement is caused by precipitation. The settlement deformation caused by confined water pressure reduction mainly occurs in the overlying soil of confined aquifer, and its settlement deformation is "small and small". The maximum displacement of soil occurs at the boundary between confined aquifer and overlying soil. (5) according to the difference of enclosure structure, the seepage characteristics of foundation pit under pressure water dewatering are divided into three categories. Under the first kind of seepage characteristics, the settlement of soil caused by confined water drop is relatively small. The settlement deformation of soil under the characteristics of the second kind of seepage is the largest, which is 141% larger than that caused by the precipitation scheme in the pit under the same enclosure scheme. Under the third kind of seepage characteristics, the surface settlement around the foundation pit decreases with the increase of the depth of the confined aquifer inserted into the underground continuous wall. The lateral movement of the underground continuous wall and the uplift of the bottom of the pit are mainly determined by the stiffness of the supporting structure and the depth of the excavated soil, but the influence caused by the pressure water precipitation is relatively small. The maximum lateral displacement of the underground continuous wall occurs near the bottom of the foundation pit, and the uplift at the bottom of the foundation pit shows the characteristics of the large and small sides of the center.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU753

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