| Summary: | 碩士 === 國立中央大學 === 土木工程研究所 === 90 === Tunnels are driven nearby or underpass buildings as closely as possible due to the difficulty of land use in rapid transit system construction projects in urban areas. The stress relaxation due to the close of tail voids for tunnels in soft soils may cause the ground deformations around the tunnel. The ground deformations (including lateral and vertical soil movements) will damage nearby buildings and building protection measures must be properly taken during constructions. The load transfer mechanisms of the piles embedded in the movable soils are considerably complex and need to study in detail.
A series of centrifuge model tests have been performed to assess tunnelling-induced ground deformations in sandy ground and their effects on adjacent pile foundations. Two topics have been investigated in this study. First of all, the free-field ground deformations induced by tunneling in sandy ground have been measured. Secondly, the load transfer mechanism (such as bending moment, axial force and pile head deformation) of the piles has been analyzed in the different conditions, including the cover-to-depth ratios, and the distance of the pile and the tunnel.
When the measured ground loss induced by tunneling in sandy ground is greater than 3.5%, a large quantity ground loss will be caused violently. The result displays that the time of collapse in sandy tunnels will arise in the twinkling of an eye. In addition, when the ground loss is less than 3.5%, the bending moment and axial force of the nearby pile foundations have been occurred rapidly.
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