Study On The Pre-release Of Rock Deformation Using Construction Of Pilot Heading In Soft Rock Tunnel With High Crustal Stress

The problem of large deformation of the tunnel caused by high crustal stress and soft rock is apparent in the Lan-Yu Railway, which caused great difficulty to determine the tunnel supporting parameter and project construction. In this paper, on the basis of in-situ experiment of pilot heading release technical, using theoretical analysis and numerical simulation, the mechanism of large deformation of the rock and squeezed surrounding rock ,the release technical and effect of pilot heading, as well as controlling factors and prevention measures were studied. The main conclusions are as follows:(1) The research data about large deformation of soft rock tunnels with high crustal stress were widely collected in the paper. The development history and current situation of high crustal stress, soft rock, design theory, construction technology were described in the paper.(2) Based on the basic characteristics of large deformation of soft rock tunnels with high stress, the formation and development of large deformation was researched, the mechanism of large deformation of squeezed surrounding rock ,the release technical of pilot heading were analyzed .(3) Using in-situ test deformation monitoring data of pilot heading and main tunnel, the dynamic evolution of tunnel rock during the construction process, the difference of using different supposing materials, like grille steel,U29 steel which can be contracted and I20b steel frame to control deformation of rock were analyzed. Besides, making comparison of different method to test the loose situation of tunnel rock during construction ,these methods contain acoustic method, multi-point displacement meter method and ground penetrating radar method.(4) Two protect noun: release rate and shizai release rate were produced to quantify the effect of pilot heading method to reduce rock deformation of tunnel compared with excavating main hole method. Finite difference software flac^3d were used to simulate different size, location, and construction methods of pilot heading method, and compare it with the measured data, and good combination of reasonable parameters of releasing deformation were presented.(5) Large sample of monitoring data were collected and analyzed during the construction of Lan-Yu Railway maoyushan tunnel, muzhailing tunnel and dazhangou inclined shaft, the factors that affect the large deformation were studied, finally the project control measures of large deformation and supporting construction technology were proposed.