Study On The Construction Methods Of Large Deformation Tunnel With Carbonaceous Shale

With the consummation of layout in high-speed rail network, tunnel accounts for a higher proportion of new line. Greater demands are being placed on construction technology and method of tunnels, which through the extremely complicated geological conditions of large deformation in soft rock. This paper takes Xingyuan tunnel of Mu-Sui line as an engineering example, combines with comprehensive analysis methods of the field research and test, theoretical analysis and calculation, and the numerical simulation to study the construction method of large deformation tunnel in carbonaceous shale. The main research contents and results are as follows:1. According to the field investigation and analysis of the results of the construction site monitoring measurement, this paper summarized that the surrounding rock of the carbonaceous shale of Xingyuan tunnel has characteristics of large deformation amount, fast deformation rate, high pressure of surrounding rock and long deformation duration. The deformation of surrounding rock shows strong rheological behavior.2. Field stress and strain monitoring results combining with the engineering hydrogeological data showed that the factors affecting the deformation of surrounding rock and the mechanism of large deformation are discussed from four aspects: the characteristics of rock mass, groundwater factors, weak intercalation and construction methods. The weak, broken and low strength of the surrounding rock of the carbonaceous shale is the intrinsic factor of the large deformation. Its thin layered structure makes the surrounding rock deformation, which determines the type of large deformation. The environmental factors such as groundwater aggravated the development of large deformation. Construction disturbance affects the probability and degree of deformation of surrounding rock. At the same time, the deformation mechanism of carbonaceous shale is determined by plastic rheology of soft rock under high surrounding rock pressure, bending deformation of layered rock and softening effect of weak intercalation.3. Through Xingyuan tunnel test sectionⅥclass surrounding rock under different conditions of plastic ring distribution of theoretical calculation, it is concluded that the area of the arch waist and the arch foot is affected by the plastic zone more easily and the plastic circle range increased with the increasing of buried deepness. According to the shearing slide failure theory, the bearing capacity of double-deck initial support structure of tunnel test section is calculated and analyzed. And the stability of double deck support structure is verified. According to the formula of wall displacement, the relations of deformation and time of surrounding rock in different buried deep conditions is roughly calculated. And the rheological characteristics of the surrounding rock of the test section are further revealed. According to the result of deformation analysis in combination with the actual situation and field monitoring data, the large deformation classification of the test section of the Xingyuan tunnel were carried out; It is obtained that the tunnel test section belongs to the gradeⅡlarge deformation.4. Through the finite element numerical simulation software of 3D construction process, the construction methods of the control effect of the deformation of surrounding rock and supporting structure are simulated and optimized. At the same time, according to the characteristics of the tunnel test section, the different deformation control measures are put forward. From the excavation methods, excavation footage, step length, pre-reinforcing length and range in front of working face, and the interval timing of double initial supporting, this paper gets conclusions through layer by layer optimization that three-steps-seven-footwork tunneling method with 0.5m excavation footage, 5m step length, 6m and 180-degree of pre-reinforcement and double initial supporting interval with 1 excavation steps are suitable for the optimum construction method of Xingyuan tunnel in carbonaceous shale.