Tunnel liner is conventionally designed according to the deterministic design methods. However, the loads transmitted from the surrounding ground to the liner are very uncertain. In other words, the tunnel liner is subjected to nonuniform loading conditions which may affect its performance. This is mainly due to the inherent randomness and spatial variability of ground properties. In addition, since borehole drillings are usually carried out before tunnel excavation, the measured borehole data should be considered and reflected in the tunnel liner design practice, especially when it comes to the reliability-based design using the conditional random field theory. This paper presents an investigation of the tunnel liner performance from the perspective of probabilistic analysis and reliability-based design, and a probabilistic procedure for evaluating the tunnel liner performance is fully described. The random behavior of ground properties is accounted for by the conditional random field theory, and the performance of tunnel liner is examined via finite-difference modeling in FLAC 3D. The evaluation procedure is performed within the Monte Carlo simulation framework. An illustrative hypothesized tunnel is introduced to demonstrate the application of the probabilistic evaluation procedure, and the effects of site characterization parameters and conditioning on the tunnel liner performance are also inspected in a series of parametric studies. Before reaching conclusions, the reliability-based design of a real tunnel is performed with respect to the liner strengths and thickness, given target reliability levels, which provides some insights into a more reasonable and economical design of tunnel liner.
Tearing cutters are generally applied to break rocks when shield tunnelling in the strata with large size boulders. To improve rock breaking efficiency, the processes of tearing cutter impacting rock model are simulated, and the effects of cutter mass, impact velocity and spacings on specific energy of rock breaking are studied. The results indicate that the impact energy rises significantly by increasing the cutter mass or impact velocity. With the increase of cutter mass or impact velocity, the specific energy decreases rapidly at first and then increases slowly. The rock breaking efficiency increases firstly and then decreases, and the specific energy has a minimum value. Under the same impact energy, the rock breaking effect by changing the cutter mass is better than changing impact velocity. When cutter spacing increases, the specific energy decreases gradually and then increases. Once the cutter spacing is optimized, the specific energy of rock breaking is the minimum and the rock breaking efficiency is the highest. The research results can provide reference for the cutter design and layout in the similar strata.
Cutter wear is one of the important factors affecting the safety and efficiency of shield or TBM tunnelling. Based on the inclined shaft tunnelling project with long distance, large slope and constant excavation in Bulianta coal mine, regression analysis is applied to investigate the relationship between cutter wear and tunnelling parameters such as cutterhead rotation velocity, cutterhead torque, advance velocity, total thrust and penetration, and thus the prediction model of cutter wear is established. The results indicate that cutter wear is significantly correlated with each tunnelling parameter, and that the regression model expressed by cutterhead torque, total thrust and penetration can account for 97.8 percent of the cutter wear issue induced by potential influencing factors. The model has good effect on the prediction and could provide certain guidance and reference for the cutter wear problem in similar geological condition.
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