Research On Correlation Between Groundwater Exploitation And Land Subsidence From DK119 To DK123 Along Beijing-Shanghai High-Speed Railway

Land subsidence is the environmental and geological phenomena that in the role of natural and human factors, the topsoil of crust is compressed, and the regional ground elevation reduces slowly. The past studies about the land subsidence pay more attention to an certain area (such as the North China Plain, ect.), less attention to the effect in the linear project.In China, Beijing-Shanghai High-speed Railway(BSHR), which is building, has to pass through more serious areas of land subsidenceis.So, the first and critical issue to control the safty of High-speed Railway operation is to solve the problem of regional land subsidence. All in all, it is significant in theory and practice to research the status, production reasons and development of the regional ground subsidence along the railway line.In view of the land subsidence situation along BSHR, the situation of groundwater exploitation and land subsidence is investigated and collected. The causes of land subsidence along BSHR are analyzed.Based on the investigation,combining with the result of DInSAR and precise ground leveling, taking the land subsidence area (resulted by deep-well pumping in a thermal plant) in Yangliuqing Town, Xiqing District of Tianjin City as example, through the analysis of geological structure and hydro-geological conditions of the pumping wells region, the 3D numerical model was established and the numerical simulation research on groundwater level changes caused by groundwater exploitation was carried on with Visual Modflow. Based on the research above, according to the correlation between land subsidence and groundwater level variation, the influences on land subsidence under different groundwater exploitation amount were calculated and the land subsidence amplitude and velocity under BSHR were predicted. The countermeasures can be put forward for the safety of high-speed railway according to the research.The correlation between land subsidence and groundwater level variation from DK119 to DK123 along BSHR is systematically research in the paper. The main achievements and the conclusions are as follows:1,The investigation and research of Land subsidence serious areas along BSHR can conclude that except the impact of soft soil and low bearing capacity, the main factor of land subsidence is the long-term over-exploitation of groundwater along BSHR.The areas where groundwater exploitation is the most intensive along BSHR also are the areas where the accumulative total volumes of land subsidence are the largest. Both in the space position are consistent.2,There is a land subsidence area from DK119 to DK123 along BSHR.It is resulted by deep-well pumping in a thermal plant.The stratums of the research area include Quaternary silty sand. sand, mild clay, silty clay and clay.There are 400～470 meters thick and mostly are medium compressibility stratum.The water-bearing systems of the area include phreatic water stratum and four artesian water-bearing stratums. The second and the third artesian water-bearing stratums that are the main horizons of groundwater exploitation in the area are widespread, thick stratum and well water abundance of aquifer.3,The numerical simulation research on groundwater level changes caused by groundwater exploitation was carried on with Visual Modflow.lt show that groundwater in the second and the third artesian water-bearing stratums is approximate horizontal movement and that the leakage recharge to the second artesian water-bearing stratum is from phreatic water stratum or the first aquitard and the second aquitard.It also show that the leakage recharge to the third artesian water-bearing stratum is from the third aquitard.lt concludes that the over-exploitation of groundwater in the second artesian water-bearing stratum observably affected surface and shallow groundwater level variation. 4,According to the results of numerical simulation of groundwater, and the relationship between the changes of groundwater level and the land subsidence in this area, the research gets the calculation of land subsidence.And the analysis by sedimentation shows that if the power plant maintains the status and never changes the conditions of groundwater exploitation, the rate of land subsidence along the railway line will reduced slowly over time.In general, the exploitation from the pumping well above-mentioned will not only form the larger parts of land subsidence in the high-speed railway lines but also result in the non-uniform settling obviously.5,Compared with the map of land subsidence according to the numerical simulation and the other map of land subsidence from the actual measurement, it points that they have the similar character of land subsidence distribution.However, some errors about the amount of land subsidence exist, the model can be used in the study of simulation and prediction about the groundwater exploitation and land subsidence by analysing the main cause of errors.6,Maintaining the existing quantity and condition of groundwater exploitation, the model predicts the changes of goundwater level and land subsidence in the research areas from 2010 to 2019.The study analyses the prediction of land subsidence in 2012,2015,and 2019.The power plant will seriously affect the normal operation of BSHR in 2019,because the prediction points that the maximum total amount of land subsidence is 376.69 mm,and the largest settlement rate of land subsidence in the base part of BSHR reach 33.86 mm/a in 2019.