Research On The Construction And Support Method Of Thin-Layered Fracture Hard Rocks

As our country has made a huge investment in transportation, the infrastructure construction of transportation in the western area of China enters a fast-developing period. In the southwest of China, the geology condition is complicated, the surrounding rock has many cracks and joints, the rock physics mechanical properties are inferior. For tunneling construction, the geology condition is not well enough. It is a considerable challenge for both design and construction during the process of building a large-scale tunnel in these areas.This thesis focused on the Longdongbao Airport tunnel in Guiyang, Guizhou province, taken distinct method as the theoretical basis and 3DEC as the main study tool. In this thesis, the construction method and support pattern of tunnel in thin-layered fracture hard rock were analyzed. The conclusions were proved by both numerical simulation and monitoring data and can be used as reference for other similar projects. The main conclusions are listed below:(1) A circle tunnel model was built to calculate the influence of different structural plane parameters on tunnel stability. The main fracture model of thin-layered fracture hard rock is shear slip damage along the structural plane. The calculation results shows that the parameters of the structural plane such as joint space, cohesion, dip angle has an influence on the tunnel stability and find the worst value of these parameters that make the surrounding rock and tunnel easy to damage. When there is lack of design parameters, these values can be taken as reference.(2) Based on the Longdongbao Airport tunnel, a large section tunnel model was built in 3DEC. The calculation results showed that the partial excavation method could reduce the deformation and stress under the construction of a large-scale tunnel or tunnel group in thin-layered fracture hard rock. However, the decrease of shear slip damage is not obvious. Rock bolt could improve the overall strength of surrounding rock and reduce the deformation of shear slip, for the cohesion and friction angle are changed. Compared the numerical computed results and monitoring data, the optimized construction method could meet the demands.(3) The distinct method is not as widespread as the finite element method or finite difference method and has some limits. As a result, it is useful to find an equivalent method. The ubiquitous-joint model in FLAC3D is a feasible way to replace the distinct method of 3DEC. A comparison computation was made both by 3 DEC and FLAC3D. The results showed that the tendency of surface settlement is different while the maximum value is almost the same. The surface settlement calculated by 3DEC performed a character of discontinuity.