| Summary: | 碩士 === 國立中央大學 === 土木工程研究所 === 93 === The stress relaxation due to the closure of tail voids on tunnels in soft soils may cause the ground deformations. The soil deformations induced by tunneling will cause the stress rotations and changes on the distribution of earth pressure. The distribution of earth pressure around tunnel is essential for the design of tunnel lining and the safety of nearby structure. The variation of earth pressure around tunnel when tunneling are considerably complex and need to be studied in detail.
A series of centrifuge model tests were performed to assess tunneling-induced ground deformations in sandy ground and the variations of the distribution of earth pressure. Two topics were investigated by modeling the ground loss with the way of volume control in this study. First of all, the evolution of collapse of tunnel was analyzed in the cases of various ground losses. Secondly, the influence of the earth pressure on the arching effect was investigated to realize the earth pressure distributions in various ground losses. Furthermore, the horizontal earth pressures above the side walls of tunnel were analyzed to comprehend the stability of tunnel.
According to the result in the research, for the tunnel with the cover-to-diameter ratio of 3, the soil settlement zone grows from the tunnel axis level toward the ground surface and the half-width of settlement zone is about 0.67D (D=diameter of tunnel) away from tunnel central line. The extent of major arching zone is 2.5D from the tunnel central line. Moreover, the plastic zone grows from the tunnel axis level toward the ground surface and the plastic zone and major arching zone do not extend further even after the tunnel collapse. The arching effect causes the effective horizontal earth pressure above the tunnel side walls to decrease on the condition that the depth z is larger than 2.5D and to increase for z being smaller than 2.5D.
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