| During the excavation of tunnels in karst regions, various concealed karst caves will be encountered; the question as to what safe thickness of the rock between the karst cave and the tunnel should achieve to enable the karst cave to have no influence upon the safe construction of the tunnel is one of the urgent problems required to be settled during the design and construction in the regions with karst caves. This thesis, as based on the Yaozhai tunnel located in the Liuzhai-Hechi Highway, by conducting a numerical simulation analysis of the safe thickness of the rock between the karst cave and the tunnel, has disclosed the rules of various factors that influence the safe thickness of the rock, and has established the safety requirements satisfying the excavation and operation of the tunnel, and a prediction model for the safe thickness of the rock between the karst cave and the tunnel which meets the economic requirement of the tunnel construction, so as to provide theoretical basis and technical support the actual engineering.By using the large finite element software ANSYS to establish a two-dimension finite element model for the karst cave and tunnel, this thesis has made analysis of the main affecting factors influencing the safe thickness of the rock including the rock bull weight, karst cave span, ratio of the height and span of the karst cave and depth of the tunnel. The analysis shows that the relationship between these four affecting factors and the safe thickness of the rock is a kind of increasing function; the relationship between the angle of internal friction of rock, cohesion, poisson’s ratio and the safe thickness is a kind of decreasing function; among all the affecting factors, the depth of rock, karst cave span and angle of internal friction of rock top all the other affecting factors, next comes the cohesion, poisson’s ratio and bull weight of the rock, the ratio of height and span of the karst cave span has little influence; the elastic modulus of the rock has insignificant influence upon the plastic zone and no influence upon the safe thickness of the rock between the karst cave and the tunnel.Based on the numerical simulation, this thesis has made a multiple linear regression analysis of the affecting factors influencing the safe thickness of the rock between the karst cave and the tunnel through the linear regression analysis, which results in the predication model for the safe thickness of the rock between the karst cave and the tunnel respectively located in the top, in the side and in the bottom of the horse-shoe tunnel.Considering that there exist large amount of no-continuous discontinuities such as soft interlayer, joint crack, dike and fault fractured zone, this thesis has corrected the predication model for safe thickness of the rock between the karst cave and the tunnel by reducing the cohesive force and internal friction angle of rock with the strength reduction method. |
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