Study On Safety Distance Prediction Between The Water Rich Karst Tunnel And The Concealed Karst Cave

In this paper, based on Gangwu tunnel in Guizhou section of Shanghai Kunming high-speed rail project, study on the karst development law of the tunnel site area, karst geologic body detection method, tunnel face safety distance of karst aquifer:(1)Combined with the geological conditions of the tunnel site, the characteristics of groundwater in the tunnel area and the law of karst development were studied. Groundwater in tunnel site areas in addition to accept seasonal precipitation vertical recharge, also accepted lateral recharge between adjacent water bearing structure, is located in the vertical vadose zone and seasonal variation between by seasonal changes affect larger, sinkholes, horizontal caves have development, local existence of large karst cave; Tunnel site and compressive tectonic reverse fault block well-cherry pit faults intersect, the fault is groundwater for conveying channel also, fault structure near the surface are often developed gouge or mylonite non soluble rock separated from the water formed across the hose, and lava boundary edge prone to water stress concentration and development confined aquifer, therefore, the development of the karst area is formed. The resistivity geophysical imaging detection and engineering revealed and validated, the tunnel site and the fracture intersecting fault zone near the footwall are karst disaster body strong development situation.(2) Study on the detection method of karst aquifer. Comprehensive utilization of a variety of electromagnetic wave, seismic wave method and infrared water exploration and various geophysical methods of unfavorable geological body in tunnel site areas especially the karst water bearing bodies in the detection, the typical pop images for interpretation and analysis, the analysis of the advantages and disadvantages of various geophysical methods and the principle of the length of the combination of comprehensive prediction.(3) The tunnel face and cave rock is simplified for the clamped clamped beam model, according to the construction of potential energy of rock mass based on catastrophe theory of potential function, and by Taylor expansion to the transformation as the standard form of potential function, according to the mutation singularity set control plane U-V determined critical damage boundary conditions, and derive the critical safe distance analysis from the formula. The following conclusions can be obtained:The factors affect the critical safety distance from the cave and in front of the face area is oblique:gravity, ground stress, elastic modulus, wall pressure difference on both sides and oblique angle and the diameter of the tunnel; the cave is located in front of the face area (less than the span of tunnel) the critical safety distance influence factors:gravity, stress, elastic modulus dyke, the pressure difference of both sides, the skew angle and the diameter of the tunnel; the cave is located in front of the face area (greater than the span of tunnel) factors affecting the critical safety distance:the tunnel diameter, the pressure difference of both sides and rock dyke rock Poisson ratio and elastic modulus of surrounding rocks; simplified beams fixed at both ends by stress, when the depth of the tunnel increases, the safe distance increases nonlinearly; the higher the level of surrounding rock, elastic modulus of rock mass is small, the critical safety distance is, the more prone to sudden water; the cave span is bigger, the greater the critical safe distance, dyke plastic area is larger, more prone to sudden water.(4) The finite element numerical simulation model is established, and the numerical simulation is carried out on the different spatial shape, space position and water pressure karst aquifer. Research results show that the water inrush in tunnel face maximum displacement tend to be concentrated in the geometric center of the tunnel surface and holes along the axis toward the negative direction; Karst development scale, dike thickness, karst water pressure were the main influencing factors of water inrush disasters. When the distance of the tunnel face cave close to lm and pressure exceeds 1MPa, water inrush disaster occurrence probability is extremely high; The face vault is easy to produce stress, face lower bottom parts easy to produce stress concentration.