Research On The Initial Stress Around The Tunnel Of Daxiangling In YaLu Freeway

The stress in primary rock is one of the basis factors which decidesurrounding stability and support pattern of tunnel engineering. Based on the collecting and analyzing predecessor's studying fruits ,the paper takes the tunnels projection of daxiangling for example, studies and summarizes the cause and influencing factors of the initial geostress. Try to proceeding the research of daxiangling tunnel's initial geostress from these parts, which are measure methods, analysis of the measured results,methods of regression and simulation calculation. supply exact initial condition for the excavation of tunnels.Geological environment of tunnel area is evaluated by geological survey at on-the-spot site,then studied the cause and influencing factors of the initial stress. In-situ stress is measured by hydraulic fracturing method at 4 drill holes of tunnel site. Measuring results and analysis of regional present stress field shows: Present area stress field plays a leading role in the NNW direction extrusion, and intersect at big angle with the tunnel's direction,which is disadvantageous to the tunnels' stability; The present principal stress increases along with the deep increasing; Horizontal stress and structural stress is dominant in the present area stress field of tunnel site;The principle stress direction of tunnel area is basically conform to the direction of earthquake focus mechanism solution.Based on the field investigation of in-situ stress in daxiangling tunnel, in-situ stress around the tunnel was regressed by 3D numerical simulations when the influence of gravitiational field and tectonic field are considered. The regression coefficients are obstained from step-by-step regression analysis. The results show that the regressed initial geostress are fit well to the field measurements and can be used for support design and stability analysis of the tunnel.Numerical modeling by the distinct element method demonstrate much information about stress variation caused by the existence of fractures. It is found from modeling that the variation stresses in the vicinity of fractures depends on the mechanical and strength properties of both fractures and rock masses as well as boundary conditions.