Water Inrush Risk Assessment And Water Inrush Mechanism In Karst Tunnels With High Water Depth

With the rapid development of China’s western development strategy and the implementation of the great strategy of "one belt and one road",the focus of transportation and water conservancy and hydropower projects is obviously shifting to the extremely complex western mountainous areas and karst areas with topographic and geological conditions.Tens of thousands of traffic tunnels are under construction,and there will be a large number of high risk factors,such as "big buried depth,strong karst and high water pressure".Deep karst tunnel engineering.In the construction of deepburied mountain tunnels in high-pressure and water-rich karst areas,water inrush and mud inrush will occur in an instant of more than 10,000 tons,which will cause hundreds of meters of blockage of tunnels being excavated,and result in the tragic situation of machine damage and human injury.Therefore,in the construction of tunnels in highpressure and water-rich areas,the risk assessment of tunnel water inrush and the mechanism of tunnel water inrush have become an important technical problem to be solved urgently in the construction of karst tunnels.Based on the background of the super-long and deep-buried karst tunnel in North Tianshan Mountains of Xinjiang,this paper studies the risk assessment and mechanism of water inrush of the karst tunnel in North Tianshan Mountains of Xinjiang.The main research contents are as follows:(1)On the basis of consulting the research results of predecessors and experts,and consulting the opinions of relevant experts,the first and second water inrush evaluation indexes of North Tianshan Tunnel in Xinjiang are selected,and on the basis of previous studies,combined with the actual situation of North Tianshan Tunnel in Xinjiang,the ranking of water inrush grade of water inrush evaluation indexes and the importance of each evaluation index are ranked.This paper divides the evaluation indexes into scientific ones and reasonable ones.(2)Combination of subjective and objective weighting methods is used to calculate the comprehensive weights of evaluation indicators,which takes into account the experience of experts in subjective weights and the objective weights in actual situations.It also proves whether the combination of subjective and objective empowerment methods is reasonable.The subjective and objective weighting methods are combined by linear weighting method.(3)The combination weighting method and TOPSIS method are combined to form a risk assessment system for water inrush in Karst tunnels,and the system is applied to the extra-long and deep-buried tunnels in North Tianshan Mountains,Xinjiang.In order to verify the accuracy of this method,a comparative analysis is carried out by using the fuzzy mathematics theory,which is a mature method used in the evaluation of tunnel water inrush,to verify the accuracy of the combined weighting method-TOPSIS method.(4)Using combination weighting method-TOPSIS method to calculate the risk of water inrush in the typical section of North Tianshan Mountain in Xinjiang,the two typical sections with the greatest risk of water inrush are calculated.Because the long and deep buried section of the North Tianshan Tunnel in Xinjiang is located in the high geostress and water-rich area,according to the fluid-solid coupling theory,the water inrush mechanism of the two typical sections with high risk of water inrush is analyzed by using the numerical simulation software Comsol Multiphysics.(5)The numerical simulation software Comsol Multiphysics is used to calculate the water inflow of two typical sections with high risk of water inrush,and then determine the water inrush grade of typical sections,to verify the accuracy of the evaluation results of combined weighting method-TOPSIS method.