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Underground tunnels may run through ground consisting of both liquefiable and nonliquefiable soils under seismic loading. This difference in liquefaction susceptibility may lead to different developments of excess pore pressure and different decreases of soil stiffness and strength, resulting in complicated three-dimensional deformation and damage of tunnels, the knowledge of which is still not well understood at present. In this study, three dimensional (3D) Finite Element analyses were carried out to investigate the 3D seismic response of underground tunnels passing through both saturated dense and loose grounds. Twin subway tunnels at a diameter of 5 meter with grey cast-iron lining were considered in this study. It was found that underground tunnels passing through both dense and loose saturated ground exhibited two distinctive deformation modes: the uplift and the lateral deformations due to the difference in the soil liquefaction susceptibility. The tunnels were twisted due to these distinctive deformation modes and the maximum stress in the tunnels occurred at the boundary between dense and loose grounds. It was also found that when soil liquefaction was not extensive, the tunnels settled instead of uplifted. Different frequency characteristics of input motions resulted in significantly different responses of the ground-tunnel system, which was also related to soil thickness above bedrock. Synthesized motions from the same design response spectrum might still result in different stresses in the tunnels.
Underground tunnels may run through ground consisting of both liquefiable and nonliquefiable soils under seismic loading. This difference in liquefaction susceptibility may lead to different developments of excess pore pressure and different decreases of soil stiffness and strength, resulting in complicated three-dimensional deformation and damage of tunnels, the knowledge of which is still not well understood at present. In this study, three dimensional (3D) Finite Element analyses were carried out to investigate the 3D seismic response of underground tunnels passing through both saturated dense and loose grounds. Twin subway tunnels at a diameter of 5 meter with grey cast-iron lining were considered in this study. It was found that underground tunnels passing through both dense and loose saturated ground exhibited two distinctive deformation modes: the uplift and the lateral deformations due to the difference in the soil liquefaction susceptibility. The tunnels were twisted due to these distinctive deformation modes and the maximum stress in the tunnels occurred at the boundary between dense and loose grounds. It was also found that when soil liquefaction was not extensive, the tunnels settled instead of uplifted. Different frequency characteristics of input motions resulted in significantly different responses of the ground-tunnel system, which was also related to soil thickness above bedrock. Synthesized motions from the same design response spectrum might still result in different stresses in the tunnels.
Three-Dimensional Analysis of Underground Tunnels in Liquefiable Soil Subject to Earthquake Loading
Liu, H. (author)
GeoCongress 2012 ; 2012 ; Oakland, California, United States
GeoCongress 2012 ; 1819-1828
2012-03-29
Conference paper
Electronic Resource
English
Three-Dimensional Analysis of Underground Tunnels in Liquefiable Soil Subject to Earthquake Loading
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