| Because of the influence of the special geological structure, karst often has the features of high water pressure, rich water, karst caves and faults. Therefore, during tunnel construction in karst area, it is extremely easy to lead to such project calamities as sudden and extensive inflow of water, mud and sand if enough care is not paid. Furthermore, the large amount of water, sand and mud flowing into the tunnel changes the effective stress of the ground, as well as the seepage field and the supply-drainage relation of the ground water, which causes the reduction and exhaustion of the ground water resources within the influenced area., therefore, more and more people have paid attention to the mechanism and control of the water burst in karst tunnels.This dissertation summarized the fundamental rules of water gushing and mud gushing; The mechanism of water gushing is studied by basic knowledge of catastrophic theory and fracture mechanics; The surrounding rock stability of tunnel heading and the influence facor of internal forces of lining are studied by similarity model test; A three dimensional numerical analysis for the tunnel with high water pressure karst cave were located in the front of tunnel face and the top of tunnel; On basis of the analysis result of the water burst mode and water burst mechanism of karst caves tunnel, the prevention and control principles for water gushing and mud gushing are put forward. The main contents of this dissertation are as follows:(1) Description of the water burst and mud burst occurring in the 5 typical karst caves tunnels in our country, and summarized the fundamental rules of water gushing and mud gushing.(2) Tunnel surrounding rock water bursting unstability is a typical catastrophic process. A catastrophic theory was applied in tunnel water bursting for the firs time. The bottom of tunnel has a filled high water pressure karst cave, on the basis of dimension of karst cave, the roof of karst cave simplified as large deformation elliptic plate, rectangular plate and beam with fixed supports. Through the research on the instability of energy in the floor system of tunnel, a cusp catastrophic model applied to forecasting water bursting in the floor was put forward. The formulas of the critical stress, the strain and the released energy of the instable floor were developed. So, a new theory approach was offered for the forecast of water bursting in karst cave tunnel.(3) Mechanical mechanism about tunnel surrounding rock water bursting unstability is studied from two aspects. One,based on stress state in fracture surface and fracture mechanics, the fracture propagation is divided into tension-shear mixed cracking and compression-shear mixed cracking under high water pressure. Using fracture propagation engineering criterion, calculation formulae of critical internal water pressure of two kinds of failure model are obtained respectively; The stress intensity factor and the propagation orientation of the complex cracks in rocks under different external stress are studies with the theory of maximum surrounding primary stress, and the effect of chemical damage and water pressure. Effects of water pressure on the complex cracks in rocks are different under different external stresses. Two, because of tunnel excavation, safety distance between karst cave filled with high pressure water and tunnel is smaller and lead to surrounding rock water bursting unstability.(4) Taking geometric similarity ratio CL= 30 and bulk density similarity ratioCr=1 as basic similarity ratio, so as to achieve complete similarity of various controlled physical and mechanical parameters in the elastic range and strictly simulate the characteristics of surrounding rock, physical property, original earth stress field, stiffness of support structures and support time.The axial displacement characteristics of excavating face with high water pressure and the influence of change of water pressure, distance of tunnel and karst cave, surrounding rock classification to internal force of lining are obtained form those model experiments.(5) Two type tunnels, which high water pressure karst cave were located in the front of tunnel face and the top of tunnel, is taken as an example.The mechanical response of full face excavation and support is studied using the three-dimensional fast Lagrangian analysis of continua method. The numerical simulation reveals the distribution characteristics of displacement and stress and plastic zone and the mechanics characteristic of support structure for the high water pressure filled karst caves tunnel under the condition of dynamic step excavation and support.(6) This dissertation summarized the dewatering technique and succeed experiments in domestic and overseas construction of tunnel (openings), on this base, grouting method is recommended, At the section rich of water and high pressure adopted the method that grouting after dividing influent for decreasing preesure; to the water inflow ouccured suddenly, some emergent programs would be adopted, for example, fast flood protection, dividing influent for decreasing pressure, grouting, and so on.
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