Catastrophic Mechanism And Risk Assessment On Water Inrush Of Karst Tunnel Working Face

With the continuous advancement of the"One Belt,One Road"initiative and the implementation of the strategy for a powerful country in transportation,the transportation network has extended to the western mountainous areas and karst areas that are all over the mountains and mountains.As an important part of the traffic road network,tunnel projects often encounter various karst geological disasters during the construction of karst areas due to complex engineering geology and hydrogeology,development of karst disaster-causing structures,and active groundwater.The water inrush is one of the most common and extremely destructive geological disaster,which will cause huge economic losses,seriously endanger the safety of construction workers,and cause bad social impacts.The complex mechanism of water inrush disasters and the lack of effective water inrush risk assessment and disaster state identification methods are the fundamental reasons why water inrush disasters in karst tunnel are difficult to prevent.Based on those,this paper comprehensively adopted the methods of literature research,theoretical analysis,laboratory test and model test for the water inrush disaster of karst tunnel face,systematically carried out research on the disaster mechanism and risk assessment of water inrush of karst tunnel face,as well as the methods for identifying disaster states.The main research findings were as follows:(1)The scale of water inrush disasters and the characteristics of water-resistant rock mass in 60 typical karst tunnels were statistically analyzed.It was found that the water inrush disasters mainly occurred in deep and long karst tunnels,and the amount of water inrush was mainly concentrated in 100～10000 m~3/h.Six types of water-resistant rock mass structures were proposed,which were complete structure,layered fractured structure,massive fractured structure,intermittent structure,soil-rock mixed structure and dense scattered structure.On the basis of revising and perfecting the karst development reduction coefficient,combined with the concept of engineering rock mass classification,the homogenization idea and determination method of mechanical parameters of water-resistant rock mass of karst tunnel were put forward,which provided a clear disaster-bearing body for the subsequent research on the stability of karst tunnel face and the law of water inrush disasters.(2)Based on the upper bound theorem of limit analysis and Hoek-Brown failure criterion,the criterion for instability of water-resistant rock mass ahead of karst tunnel face considering the effect of permeability was proposed,and a calculation method for safe thickness of water-resistant rock mass ahead of karst tunnel face was established.The influence law of outburst-prevention rock mass strength,karst water pressure,tunnel section size and Hoek-Brown strength parameters on the safety thickness of outburst-prevention rock mass on the face of karst tunnel was proved;Based on the energy principle,the safety factor of the anti-water inrush stability of the karst tunnel face was defined,and the dynamic evolution law of the stability of water-resistant rock mass ahead of karst tunnel face was revealed when the tunnel was continuously excavated close to the former high-pressure water-rich cavities.(3)The parameters of physical mechanics and permeability of(karst)limestone rock mass obtained by on-site in-situ tests and empirical reduction methods were systematically investigated and statistically analyzed.This is the first time to provide those parameters for the prototype of water-resistant rock mass ahead of karst tunnel face.Based on the fluid-solid coupling similarity theory,an orthogonal test of the optimal mix ratio of similar materials for the water inrush model test of the water-resistant rock mass on the face of the tunnel was carried out.The influence laws of sand-soil ratio,calcium-iron ratio,wax-silicon ratio,cement content and chlorinated paraffin content on the compressive(tensile)strength and permeability coefficient of similar materials were clarified,and the optimal mixing ratio was determined.(4)Developed a karst tunnel water inrush disaster physical model test system integrating the excavation disturbance effect and multi-information monitoring technology,which realized the reproduction of the water inrush process on the face of the karst tunnel under the conditions of excavation disturbance and high water pressure,and solved the problem of strong concealment of multivariate information evolution in the process of water inrush prevention of rock mass instability in karst tunnel face.The water inrush disaster model test of the water-resistant rock mass of the karst tunnel face was carried out,the evolution characteristics of instability and fracture of the water-resistant rock mass on the face of the karst tunnel and the formation process of the water inrush channel were deeply analyzed.And the evolution law and indicative sensitivity degree of multivariate catastrophic information such as stress,seepage pressure,displacement and acoustic emission during the process of water inrush were revealed.(5)Based on the water inrush criterion for the instability of water-resistant rock mass ahead of karst tunnel face considering the effect of permeability,a risk assessment index system for water inrush of karst tunnel face was constructed.This paper proposed a method for the classification of evaluation index levels and quantification of boundaries,and established the membership function of each evaluation index of the face water inrush risk.According to the principle of maximum membership degree,the implementation process of the four-level water inrush risk assessment level of the face was determined,and a new risk assessment method for water inrush of a karst tunnel face is formed.The application and verification of engineering cases showed that the risk assessment method was reasonable and feasible.(6)The mathematical model of the evolution of multivariate information of water inrush in the karst tunnel face outburst prevention rock mass was established by using the function fitting method,and based on the entropy weight method,the influence weight of the multivariate information on the water inrush disaster of tunnel face was determined.Combined with the extreme point,stagnation point,value range and other points of the multivariate information evolution function and the influence weight of each information,a fine identification method of the water inrush disaster state of the tunnel face was established,and the duration characteristics of different water inrush disaster states of the multivariate information were revealed.According to the water inrush disaster status of different face,a comprehensive management technology system is constructed.Taking the Micangshan super-long highway tunnel of Bashan Expressway as an example,the relevant research results of this paper are verified.This doctoral dissertation has 96 figures,55 tables and 177 references.