Study On The Evolution Mechanism Of Water Inrush In Complex Karst Tunnels And Its Comprehensive Prevention And Control

The geological conditions in southwest China are complex,and karst geologic phenomena are often encountered during the construction of mountain tunnels,especially the water inrush phenomenon in karst gushing.The changeable karst geologic structure,abundant underground underground river system and abundant rainy season rainfall make it very difficult to predict and control the water inrush disaster in Karst tunnel,causing huge economic loss and even casualties in the construction process,which has become a major safety hazard in tunnel construction and operation.The karst geological environment is ofen complex and diverse,the occurrence location and time of water inrush in tunnel construction are uncertain,which makes the evaluation of engineering construction suitability prone to deviation.The accurate understanding of the evolution process of karst gushing water inrush,the calculation of the safety thickness of rock-burst water inrush,the quantitative analysis of disaster risk and the comprehensive disposal of karst cavities are being discussed,in order to be used as the basis for evaluating the suitability of tunnel engineering construction under karst geological environment.Therefore,This thesis is entitled "Study on the Evolution Mechanism of Water Inrush in Complex Karst Tunnels and its Comprehensive Prevention and Control——A Case Study of Xuda Railway",based on research projects——"The Key Technology Research of the Advanced Geological Forecast of the Long Tunnel of the New Local Railway Xuda Line" and "The Study on the Forming Mechanism,Environmental Impact and Engineering Measures of D9K55+221 in the Zhongba Tunnel of Xuda Railway".Taking the evolution process of water inrush in karst tunnel as the research object,considering the influence of karst geological environment on water inrush,the paper divides the evolution process of karst gushing water into four stages,analyzes the algorithm of safety thickness of flood-proof rock wall,analyses the risk assessment and comprehensive control measures of water inrush,and discusses the suitability of tunnel engineering construction in karst area.The major research work completed and the progress made in the research include:(1)Based on systematic science to understand karst geological environment,the influence of karst geological environment on engineering construction is analyzed,the suitability of tunnel construction under karst geological environment is discussed.From the karst geological environment system theory research,regional karst geology research,Karst hydrogeology research,Karst cavern(dissolving cavity)research and so on,the disaster-causing factors are analyzed,and the risk of water inrush in karst tunnel is classified by karst geological survey and advanced geologic forecast.The research shows that the theory of system science makes the research content of karst geological environment more complete,which provides the basis for analyzing the disaster-causing factors of water inrush geological disaster in karst tunnel,and promotes the comprehensive understanding of the suitability of karst tunnel construction.(2)Based on the evolution process of water inrush disaster in karst tunnel,to analyze the influence of karst geological environment on water inrush,and to discusse the key factors to prevent disaster.This paper divides the evolution process of gushing mud in karst tunnel into four stages,analyzes the evolution characteristics of each stage,and discusses the different evolution types.The formation stage of karst geologic phenomenon is influenced by landform,lithology boundary surface,fold,fault and so on,which determines the spatial position and type of gushing water;the expansion stage of karst drainage channel is influenced by regional rainfall,surface morphology,geologic structure and stratigraphic lithology,which determines the scale and harmfulness of gushing water occurrence;The rock wall safety thickness critical state formation stage is influenced by the excavation of rock wall,the increasing of water potential,the blasting vibration and so on,the stability of rock wall decreases,promotes the possibility of water inrush,even mud burst;the surge water release energy step down stage will be harmful to the tunnel,the following rainfall,underground river,surface waters and other sources supplement,will control whether the gushing water.The results show that there are many disaster-causing factors,the safety stability of rock wall is the key factor of water inrush,the influence of high-pressure hydraulic action and construction disturbance on the safety critical state of rock wall is the focus of research.(3)Based on the damage theory,the cumulative effect and algorithm of blasting vibration on rock wall are analyzed,the attenuation law of peak velocity of particle vibration is considered,and the range formula of blasting damage zone in surrounding rock is deduced.Based on fracture mechanics,the mechanism and algorithm of high-pressure hydraulic action on rock wall are analyzed,considering the influence of water pressure of dissolved cavity on seasonal recharge conditions,the critical formula of hydraulic splitting initiation is deduced.Considering blasting vibration load according to the most unfavorable conditions,and using Quasi-static method to analyze blasting vibration and high pressure hydraulic joint action,the critical formula of hydraulic splitting initiation is expressed as follows:Combined with construction disturbance and high pressure hydraulic interaction,the critical safety thickness of rock wall is divided into four parts,which are serious damage area of blasting vibration,karst fissure zone,hydraulic splitting expansion zone and potential danger zone.(4)The method of comprehensive evaluation of water inrush risk in karst tunnel is discussed,at the same time the disaster-causing factors and evaluation criteria are analyzed.Considering the factors affecting the water inrush in karst tunnel from three aspects,include environmental factors,state of matter and human behavior,to establishe the risk assessment system of water inrush disaster,and to grade the scoring standard of risk evaluation index by the expert consultation method and investigation in karst tunnel with case.The integrated evaluation model of tunnel inrush water is practical and provides a basis for controlling risk in stages.(5)The countermeasures of water inrush disaster in tunnel is discussed,and the passing method and protection of the solution cavity is analyzed.Based on the prevention and cure principle of water inrush,to analyze the prevention ideas and construction countermeasures under different karst conditions.Combined with case study,the comprehensive control measures of preventing water inrush under complex karst environment are analyzed,and the key points of controlling technology in the process of construction are analysed.from two aspects of grouting reinforcement and energy release to study on the prevention and treatment of water inrush from cavities(underground river)in tunnel.The countermeasures and construction technology of water inrush disaster are the important supplement basis of engineering suitability evaluation,reasonable prevention and control measures will provide guarantee for construction and operation safety.