【作者】 李英；

【导师】 晏鄂川；

【作者基本信息】 中国地质大学 ， 地质工程， 2010， 硕士

【摘要】 随着城市建设的高速发展,高层建筑、地铁与地下建筑的建设日益加快,由此引发的环境岩土工程问题也越来越显著。其中,降水引发周边地表变形与沉降是最受关注的问题。武汉位于长江中游,大部分为第四纪松散堆积层覆盖,侵蚀区、沉积区和过渡区并存。受水流长期分选作用,沉积物颗粒由浅部至深部由细到粗,河漫滩相呈典型相变规律,地层渗透性由浅部至深部逐渐增大。二元结构地层主要分布在汉口、汉阳、武昌、青山的沿江地带,即长江和汉水两岸的Ⅰ级阶地上。目前对于在该地区如何进行深基坑降水,并得出该地区降水引起地表变形沉降规律的研究很少,也不系统。本论文首先广泛收集前人研究成果并加以归类总结,再分析武汉二元结构地层工程地质与水文地质特性,结合监测资料与可考虑三维非稳定流于非完整井降水的三维有限差分数值水文分析软件Processing Modflow,得出武汉市二元结构地层基坑降水产生地表变形沉降规律。具体研究内容如下：(1)结合武汉市地层岩相与水文地质特征,将武汉二元结构地层可分为三层：①覆盖层,由填土、河漫滩相粘性土和淤泥、淤泥质土构成,地下水赋存状态主要为潜水,上部的杂填土中有上层滞水。该层厚度变化较大,土体含水率高,孔隙率高,渗透性小。②过渡层,岩性为粉质粘土与粉土、粉砂互层,为承压水的上段；该层厚度变化较大,土体含水率高,孔隙率高,以压缩变形,渗透性小。③砂性土承压水含水层,以粉砂、粉细砂和细砂为主,底部中粗砂、卵砾石层,渗透系数高,不易压缩变形,以下为基岩隔水层,该层可作为建筑物持力层。在此基础上建立武汉二元结构地层基坑场地岩土工程模型。(2)对二元结构地层中的过渡层作重点研究对象,根据其表现出弱透水性承压水工程性质,在基坑降水工程中采取合理的方式疏导该层的地下水。(3)根据实测监测数据与理论分析,基坑工程周边地表变形沉降是由基坑降水土体固结引起的地表沉降与支护结构位移引发的地表变形两部分构成,为了更全面地评价基坑周边地表变形现象,首先,对支护结构位移引起的地表变形进行简单的分析。灰色理论广泛应用于深基坑位移预测,对基坑工程设计与施工具有重要意义。预测中灰色模型的建立是以等时距原始数据作为前提条件,而实际工程的位移监测数据多是非等时距,因此,难以建立合理的预测模型。论文采取引入单位时间差系数方法将不等间隔序列调整为等间隔序列,分析其差值后将序列还原,从而可以建立非等间隔时序灰色模型；同时将数据矩阵的第一列元素由原两个连续元素增加为三个连续元素平均值的相反数构成。以武汉音乐学院钢琴房深基坑工程为算例,验证了上述改进模型的正确性,其预测结果与监测结果更为接近。结果表明,非等间隔时序灰色模型在深基坑支护结构位移预测中更符合工程条件,精度更高,为深基坑支护信息化施工提供了更好的理论依据。(4)基坑周边地表变形的另一方面在于土体的固结沉降,论文在经典的固结沉降理论基础上,根据武汉二元结构地层基坑降水的特征,建立地下水三维渗流与地表变形沉降的耦合模型。(5)在理论研究的基础上,结合Processing Modflow软件,模拟实际工程情况,计算出基坑降水引发地表沉降量,并与实测值进行对比,得出基坑降水水位与沉降分布规律。在基坑降水过程中,水头在开始的前20天变化显著,20天之后基本达到稳定,维持新的平衡状态。基坑降水引起的地表沉降在降水开始的前20天变化较快,在20～30天阶段,变化速率减慢,30天后基本趋于稳定,沉降滞后于水头下降。由此,将整个降水引起的地表变形分为三个阶段：沉降阶段、滞后阶段与稳定阶段。本论文研究特色与创新点在于：(1)在武汉市深基坑工程实例基础上提出了二元结构地层基坑岩土工程模型,对基坑支护与降水计算具有指导意义。(2)研究表明,具有二元结构的基坑工程地表变形沉降主要由两个部分构成：支护结构水平位移产生的沉降以及因降水导致的过渡层固结沉降。以武汉市国税局地下停车车库基坑为例,研究了地表变形沉降随降水过程的变化规律；基坑工程地表变形可以分为三个阶段：沉降阶段、滞后阶段与稳定阶段。更多还原

【Abstract】 With the rapid development of urban, it was speeding up the construction of the multilayer buildings, subway and underground construction. And the impact on the environmental geotechnical engineering problems is also growing, which caused the most concern on subsidence and deformation by foundation pit dewatering.Wuhan is located in the Yangtze River. And most stratum are covered by Quaternary unconsolidated layers. Erosion, sedimentary zone and transition zone coexist in the landform. Because the role of water a long time sorting, the sedimentary particles changes from fine to coarse from top to bottom. As the complexity formation of the binary structural stratum of Wuhan, how to dewatering in the area of deep foundation, and draw law of land subsidence caused by foundation pit dewatering in the binary structural stratum in Wuhan, is very difficult. And there is very little research in these areas, nor the systemly.In this thesis, the previous studies are collected to be classified. Ground subsidence rules caused by foundation pit dewatering are obtained based on analyzing engineering geology and hydrogeology of binary structural stratum of Wuhan,combination of monitoring data and numerical hydrological analysis software Processing Modflow which consider three-dimensional transient flow in non-complete three-dimensional finite difference of precipitation well. Specific study are as follows:(1) Base on the study of stratigraphic lightfaces and hydrogeological characteristics of the dual structure of Wuhan, stratum can be divided into three layers:①Cover layer, which is consisting of the fill, clay, silt floodplain, and silty soil. Phreatic is in this layer. The thickness of layer changes rapidly. And it is with high Moisture Content and porosity, while the permeability small.②Transition layer. It is made silty clay and silt, interbedded silt. And it is the upper section of the confined water; The thickness of layer changes rapidly. And it is with high Moisture Content and porosity, while the permeability small.③Sandy soil confined water aquifer, to silt, fine sand and fine sand-based, bottom-sand, gravel layer, high permeability, not easy to deformation. The following bedrock is confining layer, the layer can be used as support layer of the building. (2) Study on the transition layer of the binary structure of the transition layer, according to their performance in a weak engineering geological properties of confined water permeability. A reasonable way is dealed with the level of groundwater.(3) A number of prediction problem of inadequacy information is successfully solved by using Grey System Theory. The Grey Model GM (1,1) is based on the equal interval original data. So it is difficult to predict when the data is unequal interval. For the shortcoming, the Grey Model is improved. The difference which is formed when unequal interval is transformed to interval is adjusted by unit time difference coefficient. The difference part and the initial part are accumulated respectively. Then the interval model is established.So the unequal interval Grey Model GM (1,1) is obtained after reverting the equal interval sequence. The deformation prediction of the deep foundation pit is made with the monitoring data of the various stages of a project. Through comparison and analysis on the predicted and actual data, it shows that unequal interval Grey Model GM (1,1) is more closed to the reality.(4) Study on classical theory of settlement and characteristic of foundation pit dewatering of Wuhan the dual structure, three-dimensional seepage of groundwater and surface subsidence coupled model are established.(5) Combined with theory and Processing Modflow software to simulate the actual project, subsidence caused foundation pit dewatering are calculate and compared with the measured values. The settlement of foundation pit water level distribution is obtained. In the process of foundation pit, water head in the beginning 20 days change significant. And new balance is got after 20 days. Subsidence caused Foundation pit dewatering changes fast in the beginning 20 days, change slowly 20 to 30 days. Settlement lags behind water head down. As a result, the settlement is divided into three stages:the settlement stage, the lag phase and the stable stage.The advantage of this paper are as following:(1) Geotechnical model of foundation pit on the binary structural stratum in Wuhan is obtained from the examples of deep excavation. And it’s useful for the foundation pit support and foundation pit dewatering design.(2) Ground subsidence of foundation pit on the binary structural stratum in Wuhan includes two sides:the settlement of foundation pit support and the settlement caused by consolidation settlement. Taking parking garage foundation pit of Wuhan Internal Revenue Service underground as an example, the settlement is divided into three stages:the settlement stage, the lag phase and the stable stage.更多还原