| Accompanying the enforcement of strategy to develop western regions, transport and other infrastructures of western China expand substantially and long tunnel in karst zone increases dramatically. Geological hazard of water inrush and mud outburst often occur in the process of karst tunnel construction, which often lead to equipment destroyed and construction period bungled, even serious casualty and economic loss. This article is a subject which studies the disater-induced waterinrush of against-inrush rock in construction. Generalized model of mountain tunnel-Karst system and mechanism of water inrush of karst tunnel are studied in a deep-going way, and Against-inrush thickness of rock pillar between tunnel and concealed karst cave with high-pressure and rich water, safe thickness of rock wall in front of tunnel face are eatablished by engineering cases investigation, laboratory experiment, theoretical analysis and numerical simulation, Meantime, prevention measures of water-inrush of karst tunnel are summarized, consequently, series of meaningful research achievements has been obtained:(1) The property of karst development and underground karst of mountain tunnel are summarized through analysis the most representative karst tunnel on Yiwan railway, meantime, based on the practical example of karst tunnel, the location relationship between tunnel and karst structure is classified and the major geological hazards of karst tunnel are discussed. Finally, the system of tunnel and karst is generalized into four mechanics models, which supply support for analyzing the mechanism of water and mud inrush or mid-stratum collapse by quantitative analysis;(2) Mechanical behaviors and strength properties of limestone from karst region are studied intensively through uniaxial compression test, triaxial compression test, brazilian test and mechanical behaviors under natural an saturated condition are different remarkably. Combined with rock mass structural features and surface characteristics of discontinuitity obtained from field investigation, the geological strength index(GSI), Hoek-brown strength parameters and deform modulous are determined;(3) According to engineering cases of water inrush and mud outburst of karst tunnel, water-inrush is divided into high-pressure fissure water-inrush, water-inrush of karst cave with rich water, water-inrush of underground river, karst channel or fault. From micro and macro view, mechanism of water-inrush is analyzed and studied, and, it is pointed that comprehensive failure waterbust under secondary stress distribution and karst water pressure is the main type of karst tunnel waterinrush, process of disater-induced waterinrush of against-inrush rock under geostress and high water pressure is testified by means of discrete element numerical simulation;(4) As far as concealed karst cave at circumference is concerned, different mechanical models are established according to concrete situation. on account of large scale, the destabilization mechanism mid-rock is analyzed and simplified into restrained beam. The theoretical formula for the against-inrush thickness are deduced according to the elastic theory, based on anti-bending and anti-shear criterion; aiming at small and medium sized concealed cave, the against-inrush thickness is calculated by the mechanical model solved by Schwarz alternating methods with Griffith strength theory, moreover, base on this method, the program is designed on Maple platform, subsequently, each influential factor of against-inrush thickness is discussed, especially, water pressure in karst cave. As for model of water inrush along the activation fault, water-inrush orientation of activated concealed fault by use of minimum tensile stress theory, analytical formula of against-inrush thickness is deduced based on crack propagation criterion;(5) The frequent occurrence of water and mud inrush caused by karst cave with high pressurized water ahead of tunnel face has been the critical problem to be researched and resolved in tunnel construction in kasrt area. From view of fracture mechanics, the mechanism of crack extension is analyzed under high karst water pressure, as a result, the outcomes show that hydraulic fracturing under natural pressure mostly belongs to compression-shear(type 11) failure mode. The hysteresis effect and diameter-expanding effect of water-inrush of tunnel face have been studied by use of fracture mechanics and hydromechanics. It is illustrated that the hysteresis effect of water-inrush is macro-view property of the skip of crack extension, meantime, the results also demonstrate that the final formation of water-inrush passage need experience some stages and its final size is controlled by karst water pressure and the quality rock mass of tunnel face and so on and so forth. On the basis of comprehensive analysis, the reason why water-inrush occurs in the vicinity of tunnel face is that the critical water pressure of hydraulic fracturing decreases induced by excavation and disturbance. Accordingly, based on the critical water pressure, the calculating formula of safe thickness of rock wall has been established: (6) Finally, in the light of research achievements about against-inrush thickness and waterburst mechanism, the basic principles and prevention measures of against-inrush are summed up combined with cases of hazards management of many karst tunnel and research conclusions by other scholar. A new technical method to prevent water inrush-energies-release and depressurization technology is emphatically discussed.
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