Land Subsidence Prediction Simulation Of A Section In Jinwei Railway

With the steady development of China's economy,people's requirements for convenient transportation are getting higher increasingly.High-speed rail has become the first choice for long-distance travel with its advantages of fast,efficient,safe and environmental protection.The Jinwei high-speed railway is a part of the coastal channel of the "eight vertical and eight horizontal" high-speed railway network planned in the 14th Five-Year Plan.As part of the Jinwei high-speed railway,the section(the south of Dongying to Shouguang)starts from Liulu Township,Shouguang City to Dingzhuang Town,Guangrao,which total length is about 60 kilometers,passing through the land subsidence area in the northeast of Shandong,and its construction and operation may be affected by the land subsidence.By investigating the development history and current status of land subsidence in the area where the proposed railway is located,it is found that the main cause of land subsidence in this area is excessive exploitation of groundwater.In order to ensure the smooth and efficient operation of the railway after its completion,it is very necessary to study the development trend of land subsidence along the project.This paper is based on the theory of groundwater dynamics and soil mechanics,with the project background from the Dongying South to Shouguang section of the proposed Tianjin-Weifang Railway,to carry out land subsidence prediction and risk assessment along the railway.The main contents are as follows:(1)Based on InSAR monitoring technology,the development history and current situation of land subsidence in the study area are summarized and analyzed.According to the data of InSAR monitoring from 2016 to 2018,most lines in the area pass through the 10?20mm/a subsidence area,and only the DK337+150?DK338+100 section pass through the 20?30mm/a subsidence area.According to the monitoring data from 2019 to 2020,the land subsidence rate in DK316+900?DK324+500m area is relatively high,ranging from 20mm/a to 30mm/a,while the subsidence rate of other lines is less than 20mm/a.Combined with the geological conditions of the study area and the general situation of groundwater exploitation,the causes of regional land subsidence are analyzed,and it is determined that the over-exploitation of groundwater is the main inducing factor,and the subsidence mechanism is expounded by using the principle of effective stress.(2)Based on the geological drilling and geological profile data of the study area where the proposed railway is located,a three-dimensional geological visualization entity model is established,which realizes the multi-angle display of the stratigraphic structure of the study area,and generalizes and integrates the strata of the study area.Physical geography and hydrogeological conditions have constructed a numerical model of coupling three-dimensional groundwater flow and one-dimensional soil deformation.After the groundwater seepage model and the ground subsidence model were separately identified and tested,a numerical model meeting the accuracy requirements was used to carry out a numerical simulation study on the ground subsidence along the railway.The simulation results show that under the plan of maintaining the current groundwater extraction volume,the peak surface subsidence along the line is located between DK321 and DK323,the maximum subsidence rate is 16mm/a,the slope peak value is 0.0531‰,and it is located near DK315;The land subsidence and groundwater level along the line rebounded under the banned mining plan of both sides of the line 200 meters,but the settlement rate of some mileage sections still could not meet the design target of ?10mm/a.Based on this prediction result,the mining ban range was extended in the DK295-DK309 and DK315-DK325 sections.The simulation results show that the settlement rate and slope value along the railway under this scheme have reached the design goals.(3)Based on the prediction results,using FAHP and comprehensive evaluation methods,selecting the severity of land subsidence,the slope of land subsidence and the depth of groundwater table as evaluation factors,the 4km area along the two sides of the line is divided into??? four sections from low to high according to the risk level,which accounting for 39.66%,31.31%,17.30%and 11.73%respectively.According to the results of zoning,no mileage section of the proposed railway crosses the IV level danger zone,most of which are located in Zone ?,with little risk;DK285?DK295;DK315?DK323;DK327?DK329 sections pass through Zone ?,and the cumulative value of ground subsidence in this area is in between 70mm?130mm;DK302?DK309 are located in Zone ? due to the large change in the slope of settlement.