Risk Assessment Of Water Inrush From Karst Tunnels In Panbei Area

The karst development has nurtured complex engineering hydrogeological conditions and fragile ecological geological environment,which has brought severe challenges to the construction of China’s mountain tunnels and the sustainable development of karst ecological environment.The karst development has nurtured complex engineering hydrogeological conditions and fragile ecological geological environment,which has brought severe challenges to the construction of China’s mountain tunnels and the sustainable development of karst ecological environment.Affected by the difference in lithology of the strata,the soluble rock strata in the non-soluble rock strata will form independent karst systems.Since the early Paleogene,the karst system in the Panxi area has been deepened by the horizontal rivers,the depth of groundwater circulation has increased,and the karst has developed strongly.This has deteriorated the hydrogeological conditions of the construction of the tunnel,which brought the construction of the tunnel unable difficulty and induced a variety of karst ecological problems.Through the above research,the main conclusions are obtained:(1)The Panxi area is located in the southern part of the western Sichuan Plateau and the northern part of the eastern plateau.The terrain is high in the north and low in the south and the stratification of the topography is relatively clear.The first to third level planes are distributed from north to south and the river creeks in the area are dendritic.all of which belong to the Jinsha River water system,and the Yalong River runs from north to south in the eastern part of the region,serving as the main drainage datum;(2)Based on the vertical superposition of soluble and non-soluble rocks and the mineral characteristics of soluble rocks,the soluble rock strata are divided into inter-carbonate karst layer,pure limestone karst layer,and impure ash.According to the difference of lithological characteristics and groundwater circulation pattern,karst water mainly moves by pipeline flow or fissure flow;based on GIS platform,the elevation coefficient of variation,surface roughness and karst negative topography of the study area are extracted.The results show that tectonic movement and karst erosion are the main factors leading to elevation variation.The karst negative topography is mainly distributed in the elevation sections of 2850~3050m,2450~2650m and 1850~2250m.These elevations represent the main karst development period of the study area.It reflects the deep and inherited nature of karst development in the region;(3)Based on the karst hydrogeological characteristics and karst development laws in the study area,the controlling factors of the risk of karst water inrush in Panbei area are analyzed.Then follow the selection principle of evaluation index,extract the evaluation index of the risk of water inrush from karst tunnel in Panbei area and analyze the evaluation index by single attribute.Use the modified linear interpolation formula to assign weights and then analyze the comprehensive attribute and construct the climbing.Risk assessment system for water inrush from karst tunnels in the northern region;(4)Select the typical karst section of K162+800~K163+932 in Gesala Tunnel as the research object,and select the lithology,bad geology,negative terrain area ratio,rock formation,groundwater level and tunnel floor distance as indicators,the data After normalization,the single-index attribute measurement analysis is carried out,and the weight of the improved linear interpolation formula is used.The comprehensive attribute measurement interval and the comprehensive attribute measurement value are obtained by combining the evaluation index classification criteria.Finally,the risk of water inrush disaster in the tunnel research section is judged according to the confidence criterion.Grade;comparing the evaluation results with the THK method,the evaluation model is basically reliable.