Study On Safe Thickness For Rock Between Tunnel And Karst Cave In Karst Region

ABSTRACT:Yi-Wan railway tunnels are constructed in extremely complex karst regions, therefore a large number of disasters such as rock collapse and water bursting have occurred during constructing. To avoid disasters, while take the construction costs and difficulties into account, determining a reasonable distance between tunnel and karst cave is of great important. This paper researches the methods of determining the distance between tunnel and karst caves, which mainly contains as follows:(1) Several relatively important factors are chosen after summarizing extensive literature and analyzing basic theories of rock mechanics. The influence of width of caves, ratio of highness to width of caves and lateral pressure coefficient of rock mass is qualitatively analyzed through numerical analysis using FLAC3D respectively.(2) Safe distance between tunnels and hidden dry caves around is researched. This paper mainly researches on three situations of the karst caves:caves lying above tunnel, under tunnel and on side of tunnel. With FLAC3D software, through the Orthogonal design method, the importance and influence law of five factors, which contains surrounding rock levels, lateral pressure coefficient of rock mass, width of caves, ratio of highness to width of caves and tunnel depth, are discussed detailedly. Then three forecasting models of the safe distance between tunnel and hidden dry karst caves around are given through the multiple regression method.(3) Safe distance between the drainage holes (tunnels) and karst caves with high water pressure in front is also researched. Method for researching is the same as above, while the influence factors contains seven items:surrounding rock levels, strength of joints, direction of joints, lateral pressure coefficient of rock mass, diameter of karst caves, depth of caves and water pressure. Two forecasting models of the safe distance between drainage holes (tunnels) and karst caves with high water pressure in front are obtained.(4) Influence of water pressure is analyzed by UDEC software when considering permeability of water.(5) By applying the forecasting models to the real projects of Yi-Wan railway tunnels, the reliability of the results is proven, which can provide some guidance to choose the safe distance between tunnel and caves in similar projects.