Study On Influence Of Karst On Line Selection In Pengshui Section Of Yuqian High-Speed Railway

Karst phenomenon has always been a serious engineering geological problem in southwestern China.For the proposed high-speed rail Pengshui section,the entire line is located in Chongqing in the southwest.There are very many tunnels running through it.Among them,carbonate rock formations such as the Cambrian,Ordovician,Permian and Triassic are exposed.Because more than 70% of the routes pass through the carbonate rock area,and a large number of underground rivers and springs are exposed in the area,they are not only large in flow but also in large quantities.The underground river pipeline is very likely to appear on the railway.During the construction process,a series of unfavorable geological disasters include the occurrence of unfavorable geological phenomena such as tunnel water inrush caused by karst,surface subsidence,and mud.This is a huge and potential safety hazard during the railway construction process.The Pengshui area is located in the central part of the high-speed railway,with Wulong in the west and Lijiang in the east,while the Wujiang and Wujiang tributaries traverse between them,forming an arch-shaped hydrological boundary.At the same time,because the stratum of the Pengshui section can more typically reflect the Custer landform in the southwestern region and highlight the karst problem,this paper analyzes the Pengshui section of the Yuqian Railway from the perspective of karst problems.In the early part of this paper,we collected and reviewed the relevant literature materials in Pengshui area and developed a field investigation plan.Field investigations,measurements and sampling of the dark rivers,caves,wellheads,rivers and springs in the Pengshui section were carried out.In the later stage,the indoor data collection and summary,including the complex conditions of the Pengshui section including its stratigraphic group,geomorphological features,geological structural characteristics of the fold fault,replenishment of surface water and groundwater,runoff,and excretion process,have a detailed understanding of the area.The flow,location,function,and influence of wells,springs,rivers,dark rivers,and caves are analyzed.After analysis,the Pengshui section was hydrogeologically divided,the karst hydrogeological conditions of the line were analyzed,and the line karst hydrology was partitioned.Finally,through mathematical and numerical analysis methods: atmospheric rainfall infiltration method,underground runoff modulus method,Modflow numerical simulation method for mathematical analysis.Through the first two mathematical analysis methods,the predicted water inflow of the tunnels in each of the Pengshui sections was calculated.By using the Modflow simulation method,using the data of each hydrological point obtained in the field,and referring to the relevant literature,the head value and water inflow of the five railways going through the Pengshui area were calculated.Finally,through the above two mathematical analysis methods and numerical simulation methods,the lengths,head pressure values and water inflow values of the various tunnels of the proposed railway in Pengshui section are used as reference for comparison to determine the optimal traversing scheme.Railway line selection provides reference.