The estimation of the design concept of large face and long distance tunnel through the three dimensional trapdoor experiments and the numerical analyses

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In order to establish the design concept of extra large face and long distance tunnels in which the needs are increasing, tunnel lining modeling tests and three dimensional trapdoor experiments have been performed. Then, the bending moments and the earth pressures acting on the tunnel lining, and the mechanism of tunnel excavation have been discussed.Assuming the excavation on sandy ground in the tunnel lining modeling tests, the experiments in consideration of various overburdens and shapes of tunneling face have been carried out on both gravity and centrifuge conditions. Based on the experimental results, we have discussed some effective factors of tunnel mechanism, namely, the earth pressures and the bending moments acting on the tunnel lining, the earth pressure acting on the ground around tunnel, and the ground surface settlement. Moreover, theoretical discussions of the earth pressures acting on the tunnel lining have been performed with the aid of Terzaghi earth pressure theory. … More In consequence, 1) with the shape of tunnel face being flatness, the larger the bending moments acting on the tunnel lining become large, 2) in the same shape of tunnel face, the change of both value and distribution of bending moments does not present clear with increasing the overburdens, and 3) earth pressures on both gravity and centrifuge conditions show the good correlation with Terzaghi theoretical results under the confining coefficient K_0 between 0.5 and 1.0.On the other hand, three dimensional trapdoor experiments have been carried out under various overburdens so as to clarify the mechanical behavior and the deformability with the excavating tunnel, And then, under various overburdens, three dimensional trapdoor experiments in consideration of the tunnel intersection have been carried out. In consequence from three dimensional trapdoor experiments, 1) the earth pressures on the lowered trapdoor remarkable increase with descending trapdoor, 2) in case of the descending trapdoor streak, that is the assuming the tunnel excavation, the remarkable settlement can be observed on the lowered trapdoor since the ground above the lowered trapdoor has already been loosened, and 3) in case of small intersection angle under various overburdens, large earth pressures acting on the main tunnel can be observed when the branch trapdoors go down. Less