An Advance Geological Forecast And Risk Assessment In New Wulong Tunnel Underground River

Affected by the geological conditions,the new Wulong tunnel needs to pass through many underground rivers when it is built,which easily leads to geological disasters such as water inrush,mud inrush and collapse,etc.Timely prediction and risk assessment of the dark river reach of the tunnel is crucial to the safety construction and operation of the entire tunnel.This paper takes the ZDK179+886~+986 section of the 2~#underground river of new Wulong Tunnel as the research object,analyzes the hydrogeology and engineering geological conditions,introduces the distribution law,lithology and structure of the underground river in the tunnel area.Three advanced geologic forecasting methods such as comprehensive TSP method,geological radar method and infrared detection method are used to forecast the dark section of the tunnel area 2~#underground river.More accurate geological information was obtained;the risk assessment model of the 2~#dark river reaches was established using fuzzy analytic hierarchy process,and risk probability evaluation was performed.The main results obtained through research are as follows:(1)The three kinds of advanced forecasting methods were used to detect the 2~#underground river section of the tunnel area.The analysis results showed that the rock mass of the surrounding rock at the mileage ZDK179+886~+910 is relatively hard,and the karst is weakly developed.The surrounding rock grade is grade IV to V.The rock contains a small amount of water,which is drip-like or linear flow.In the segment ZDK179+925~+951,the karst develops strongly,forming a channel for groundwater.The interior of the surrounding rock contains water and flows linearly to strand-shaped.The joints within the section are developed,and the spacing is assumed to be between 0.5-0.2centimeterand about 7 groups.The karst development in other mile sections is poor,the possibility of internal water content is low,the lithology is good,and the joints and fissures are weakly developed.(2)Refer to the index of the probability of tunnel construction risk occurrence and assign values to each index as a basis for risk assessment.Five first-rate risk factors such as geological structure,karst water,2~#underground river,tunnel structure,risk of excavation and support,and 19 corresponding secondary risk factors were selected,and a new Wulong tunnel construction risk assessment system was established.The qualitative and quantitative calculation methods for weight values of various factors have been modified and improved,and a single analysis and comprehensive fuzzy analysis have been carried out on all risk factors.The results show that the risk probability level of comprehensive indicators of the 2~#underground river section of new Wulong tunnel is 4,which is higher risk.(3)The work of advanced forecasting and risk assessment was summarized and provided effective theoretical support for the rational construction of 2~#underground river section of new Wulong tunnel.The excavation of the tunnel site verified the reliability of the geological information obtained from this advance forecasting work.