Study On Main Engineering Geological Problems In Through The Ancient Landslide Chuanzhusi Tunnel

Landslides are extensively developed in southwest area of China. Many highways are built along the rivers and mountains in the mountain areas. And the construction of highway does inevitably suffer engineering geological problems like landslide. To avoid the dangers of landslide on highway construction, in practical projects, we often choose to build the tunnel or the bridge. But due to lack of awareness of the geological conditions in the early stage of survey and design, or the requirement of improving highway, the highways still pass through the landslide by tunnels. Chuanzhusi tunnel, located in mileage pile number K1+090~K1+590 of Chuanwen highway rebuilding project, passes through an ancient landslide. That tunnel excavation may induce the local disintegration or resurrection of ancient landslide, surrounding rock cracked and turn broken like karst, which would cause many engineering problems mainly like cracking, spalling, dropping out and tunnel caving.there is an important construction guiding significance for the follow-up tunnel builded through the ancient landslideThis paper is based on the engineering geological conditions of Chuanzhusi tunnel. According to the geological tracking survey and the geological during the tunnel construction period, the deformation and failure mechanism such as the ancient landslide local disintegration or resurrection, surrounding rock cracked and turn broken induced by tunnel excavation in the hole was reserched, and the stability of tunnel surrounding rock on tunnel excavation and support conditions was studied by numerical simulation method. At last, corresponding treating measures are advised.The key contents and conclusions are as follows:(1)The first time to point out the Chuanzhusi ancient landslide, which is accumulated inⅠgrade terraces of Minjiang river, about 15×106m3 and belongs to super large landslide, mainly makes up by not fully broken up limestone and gravel soils; the whole ancient landslide is in stable condition, and the construction of tunnel won't cause the landslide integrity resurrection.(2)Chuanzhusi tunnel is in poor geological condition. The surrounding rock is poorer, showing a clastic structure. The tunnel excavation will cause many engineering problems, such as inducing the ancient landslide local disintegration or resurrection, surrounding rock cracked, turn broken like karst, and the stability of surrounding rock in the hole.(3) If the ancient landslide locally disintegrates or resurrects in the hole of the tunnel, the volume will be 5×104m3. Through ANSYS simulated and analyzed, the Deformation and failure mode of the resurrection-landslide is pull pattern. Meanwhile, the resurrection sliding could be effectively suppressed by H-beam arch frame supporting structures. By Transfer coefficient method calculated and analysis of the displacement field measurement, the resurrection is still in unstable condition. In order to more effectively preventing the resurrection mass further sliding,anchor cable and frame beams was taken to regulate the landslide.(4)The deformation and failure mode of cracked surrounding rock mainly is tunnel caving, spalling and dropping out. Its deformation and failure concentrate on the tension and pull crack damage caused by tensile stress and compressive stress and unloading rebound. Simulated the surrounding rock stress, deformation, distribution and dynamic characteristics of plastic zones after the tunnel excavation by FLAC3D, the result shows that the self-stability of cracked rock is much lower after fractured, the surrounding rock deforms like elastic-plastic deformation and relaxation deformation, and even produces a certain degree of creep. H-beam arch frame supporting structure will exert positive role for the stability of surrounding rock.(5) The karst-cracked rock mass mostly focus on vaults position, its scale is small and only partly developes in sidewall and arched bottom position, its scale is large and exists great harm; karst-cracked was mainly effectsd by the litho logical characters of surrounding rock, the disturbance on rock caused by landslide sliding and blasting effect during the construction period. Numerical simulation-analysis of Residual karst-rock by FLAC3D shows that the stability of cracked rock mass becomes lower after excavation, and the surrounding rock deforms like including elastic-plastic deformation and relaxation deformation, and even produces a certain degree of creep. The stability conditions of Surrounding rock and the size of the karts are positively proportional relationship. Lastly, some control measures such as grouting, concrete walls closed and continuous beam are proposed.