RESEARCH ON LAWS OF STRATA DEFORMATION INDUCED BY EXCAVATION OF KARST TUNNEL BENEATH HIGHWAY

The stability of overlying land embankment was often influenced when a tunnel underpass the existing highway, which induced deformation of strata and highway. Based on the Dafang tunnel of Chengdu-Guiyang railway beneath expressway, the geological model of tunnel beneath highway was built based on the characteristics of the local layers. At the same time, according to the importance of the surface structure, the danger level was divided into the field monitoring area. According to the special geological conditions of karst, the damage mechanism of the road under karst tunnel was revealed. The corresponding construction key technology was given in combination with practical engineering cases. Finally, Settlement deformation characteristics of surface subsidence, road surface subsidence and subgrade layered settlement were analyzed. Research results show that subsidence curve has the characteristics of inverse parabola,the settlement value of the upward projection area of the tunnel boundary was larger, the deformation away from the boundary of the tunnel was smaller. At the same time, the subsidence curve characteristics of tunnel underpass the highway was divided into three stages:the initial stage of small deformation, medium-term accelerated deformation stage and late deformation stable stage. On the whole, settlement deformation was within the allowable range, demonstration of tunnel support parameters was reasonable. The research results can provide similar reference for the construction of the project below in the future.