可液化土层分布对土-地铁地下结构地震响应影响的振动台试验研究

Shaking Table Test on Influence of Liquefiable Soil Distribution on Seismic Response of Soil and Subway Underground Structures

针对目前地铁区间隧道建设中常见的单层双跨断面形式结构,开展饱和地基土自由场、结构整体位于可液化土层、结构底部存在可液化土层、结构位于非液化土层共4种工况下的振动台试验;通过分析地基土的宏观表现、位移响应、动土压力响应以及结构位移响应,研究可液化土层分布对土-地下结构地震响应的影响。结果表明:受输入地震动正负波幅值不对称和地基土不均匀震陷影响,地基土表层的喷砂、开裂、冒水现象表现出不均匀性,结构上浮会加剧液化现象的不均匀性;土体液化造成结构上浮和地基土沉降,使二者产生相对位移,当相对位移较大时土体易出现较大贯通裂缝,使得超静孔压消散,液化现象得以缓解;地基土水平向位移在结构底部存在可液化土层工况时最大,在结构整体位于可液化土层工况时次之,在结构位于非液化场地工况时最小;可液化土作用在结构上的动土压力大于非液化土,导致结构整体位于可液化土层时上浮较大,仅底部存在可液化土层时会加大结构侧墙顶底动土压力差。

In view of the common single-layer and double-span cross-section structures in the construction of subway tunnel at present,shaking table tests are carried out under four working conditions:the free field of saturated foundation soil,whole structure in liquefiable soil layer,liquefiable soil layer at the bottom of structure and structure in non-liquefied soil layer.Through analyzing the macro performance,displacement response,dynamic earth pressure response and structural displacement response of foundation soil,the influence of liquefiable soil layer distribution on the seismic response of soil-underground structure is studied.The results show that under the influence of the asymmetry of positive and negative wave amplitudes of input ground motion and uneven seismic subsidence of foundation soil,the phenomena of sandblasting,cracking and water gushing of surface foundation soil show inhomogeneity,and the floating of structure will aggravate the inhomogeneity of liquefaction phenomenon.Soil liquefaction causes structural floating and foundation soil settlement,resulting in relative displacement.When the relative displacement is large,the soil is prone to large through cracks,which dissipates the excess pore pressure and alleviates the liquefaction phenomenon.The horizontal displacement of foundation soil is the largest when there is a liquefiable soil layer at the bottom of the structure,followed by when the whole structure is in the liquefiable soil layer and the minimum when the structure is in the nonliquefied site.The dynamic earth pressure of liquefiable soil on the structure is greater than that of non-liquefied soil,which leads to a larger floating of the structure when the whole structure is located in the liquefiable soil layer.When there is only the liquefiable soil layer at the bottom,the dynamic earth pressure difference between the top and bottom of the side wall of the structure will be increased.