Study On Land Subsidence Of Beijing-Zhangjiakou High Speed Railway

Beijing Plain,located in the northern part of the North China Plain,has become one of the major land subsidence disaster areas in China.The Beijing section of the newly built Beijing-Zhangjiakou Railway starts at Beijing North Railway Station and ends at Nankou,northwest of Changping District,with a total length of 54.5 km.It passes through the central and western parts of Beijing Plain Area.Its construction and operation may be affected by land subsidence.Therefore,it is of great significance to study the cause,mechanism,current situation and development trend of land subsidence along the railway for the safe development of railway engineering activities and safe operation of trains.Fengtai District Shahe town area along the Beijing Zhangjiakou Railway is one of the mainland subsidence centers in Beijing.Based on the analysis of the geological structure,soil consolidation characteristics and the correlation between the variation of groundwater level and the variation of soil compression,it is revealed that the unconsolidated soil layer is the material basis for the occurrence of land subsidence and the overexploitation of groundwater is the inducing factor for the occurrence of land subsidence.Based on the study of physical and geographic conditions,basic geological conditions and hydrogeological conditions in a certain area along the high-speed railway,a conceptual model of hydrogeology in the study area is established.The mathematical model of groundwater flow and the mathematical model of land subsidence are constructed according to the conceptual model of hydrogeology.The MODFLOW module and its SUB subroutine package of groundwater modeling software GMS are used to solve the model.The model is debugged on the basis of fitting the measured flow field and the measured formation compression,and the hydrogeological parameters are adjusted within a reasonable range.Finally,a more accurate fitting result is obtained,which meets the accuracy requirements of the model.In the case of maintaining the current production,the model is used to predict the variation of formation compression along the high-speed railway until 2023.According to the predicted results,the land subsidence along the line appears as a bowl-shaped funnel;the maximum subsidence value of the funnel center is 2.85 m near K32 mileage;thesubsidence center of Changping Shahe River moves,and the maximum cumulative subsidence value along the line moves southeastward.Based on the differential settlement along the line in 2023,the impact of high-speed rail is further analyzed.According to the analysis results,the maximum settlement gradient along the project is 0.62500‰,the gradient meets the requirements of engineering technical standards,and the settlement gradient does not affect the construction along the project;the curvature radius of the subsidence basin along the project is between 80000 ~ 1890625 m,which is far higher than the design requirements.According to the conclusion,the reasonable measures and suggestions for the prevention and control of land subsidence and the construction of high-speed railway line are put forward.