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

为确立超大断面、长距离隧道的设计理念，进行了隧道衬砌模型试验和三维活门试验。然后，讨论了隧道衬砌的弯矩和土压力，以及隧道开挖的机理。以隧道衬砌模型试验中的砂土地基开挖为例，在重力和离心机两种条件下进行了考虑不同超载和不同形状的隧道衬砌模型试验。根据试验结果，讨论了影响隧道机理的几个因素，即作用在隧道衬砌上的土压力和弯矩、作用在隧道周围地面上的土压力和地表沉降量。并利用太沙基土压力理论对作用在隧道衬砌上的土压力进行了理论探讨。…结果表明：1)隧道断面形状平整时，作用在隧道衬砌上的弯矩越大；2)在相同的断面形状下，弯矩的大小和分布随超载的增加而变化不明显；3)在围岩系数K_0为0.5~1.0的范围内，重力和离心力作用下的土压力与Terzaghi理论结果具有较好的相关性。另一方面，进行了不同超载作用下的三维活门试验，以阐明隧道的受力和变形特性。在各种超载作用下，进行了考虑隧道交叉口的三维活门试验。三维地板门试验结果表明：1)随着地板门的下降，下部地板门上的土压力显著增大；2)当地板门下降时，即假定隧道开挖时，由于地板门上方的地面已经松动，下部地板门上会出现显著的下沉；3)在各种超载作用下，交叉角较小的情况下，分支地板门下降时，作用在主洞上的土压力会很大。较少

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