Foundation Pit Dewatering And Ground Subsidence In Binary Structural Stratum Of Wuhan

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:â‘ Cover 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.â‘¡Transition 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.â‘¢Sandy 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.