截断墙法降低地下结构地震液化上浮

位于饱和可液化土中的地下结构在地震激励下会由于土层液化而上浮,从而对结构造成严重破坏,设置截断墙是减少这种破坏的有效措施,在国外已经得到成功应用.但是,截断墙减小地下结构地震液化上浮的工作机理尚不明了,其设计参数的影响亦亟待进一步研究.采用以动力两相体有限元法,分析了钢板桩截断墙在不同地震强度激励下降低地下结构地震液化浮的效果,探讨了其工作机理.分析结果表明截断墙对降低地下结构地震液化上浮有明显效果.同时,通过对地层中超静孔隙水压、土体变形、应力路径、应力-应变关系的分析发现,截断墙的主要作用在于抑制可液化土的变形和流动.虽然,在较弱地震激励下截断墙可以抑制超静孔隙水压的上升,但在较强地震作用下超静孔隙水压不减反增,通过分析解释了这种矛盾.同时还分析了钢板桩的水平位置、嵌入下卧非液化土层深度与地下结构搭接长度等设计参数对降低地下结构上浮影响,为钢板桩截断墙的设计提供科学依据.

Reducing uplift of underground structures using cutoff walls

The uplift of underground structures in liquefiable soil due to earthquake induced liquefaction may lead to severe damage. The use of cutoff wails is believed to be an effective approach in diminishing the uplift, but its mechanism is still not clear, and the design parameters of the cutoff wails also deserve investigation. Effective stress based dynamic finite element method was used in the efforts to clarify the mechanism as well as the influences of different design parameters of the cutoff wails. It was found that cutoff wails could reduce the liquefaction-induced uplift of underground structures to considerable amount. After looking into the excess pore pressure, soil deformation, stress path as well as stress-strain relationship, the effects of the cutoff walls were identified as reducing the deformation and flow of the liquefiable soil. Although the cutoff wails could decrease the excess pore pressure at small earthquake excitation; but during large earthquake, the excess pore pressure was larger for the cases with cutoff wails. The reasons were identified and explained. The important design parameters including the location, embedment length into the non-liquefied soil, and the lapping length with the underground structure, were investigated. In order to be effective, the cutoff wails must be located as closely as possible to the underground structure; they also need to be embedded in the non-liquefied soil with sufficient length; and their stiffness must be higher enough.