【摘要】 基于已进行的可液化地基-桩-高层结构振动台试验,利用参数识别技术对试验记录的土体加速度和孔隙水压力进行分析,研究场地液化机制及土的动力特性。由振动台试验的土体加速度记录,通过剪切梁模型,求出土体的动剪切应力-剪切应变曲线,研究土体的动剪切模量及阻尼特性随动剪切应变的变化关系,并进一步研究土体剪切波速、有效应力路径及桩和土的剪切应变等情况。结果表明:在较强地震激励下,动剪切应力和动剪切应变滞回圈更饱满,表现出更强的滞回特性;土的刚度随着深度的增加而增大;孔压比存在明显的上升,孔隙水压力增长对土的剪切波速有影响,土的刚度随着孔隙水压力的上升而降低;利用参数识别技术得到的土的刚度与土动力性质试验得到的结果比较一致,而阻尼要高于土动力性质试验的结果;群桩内外土体的剪切应变形状相似,外侧土体的剪切应变比内侧土体的剪切应变大。该土性参数识别技术对于研究液化场地及液化场地中结构的抗震设计具有一定的参考价值。更多还原

【Abstract】 Based on the shaking table tests on liquefiable soil-high-rise buildings interaction system,the site liquefaction mechanism and dynamic characteristics of liquefiable soil during earthquake excitation were analyzed by using parameter identification technique to study the acceleration and water pore pressure records.The time-history curves of cyclic shear stress and shear strain in the soils were evaluated from the acceleration records in the soil by one-dimensional shear beam model.These time-history curves were used to estimate variation in dynamic shear modulus of soil and material damping characteristics with shear strain amplitude.Shear wave velocity,effective stress path and shear strain of pile and soil were discussed further.The analysis result shows that:Under the stronger earthquake excitation,the soil stiffness increases with the increasing depth;the stress-strain loops are rounded and show larger hysteretic damping characteristics for large earthquake excitation;the ratio of pore water pressure to vertical effective consolidation pressure goes up obviously;the increasing pore water pressure has influence on shear wave of soil;soil stiffness and shear strength both decrease with the increase in pore water pressure.Soil stiffness calculated from measured accelerations is consistent with that obtained through independent laboratory tests;but the material damping calculated from measured accelerations is much larger than that measured in laboratory tests,which is smaller than the equivalent damping associated with hysteretic damping.The shear strains in the soils inside and outside the pile group were found to be compatible.However,the amplitude of the shear strain outside the pile group is larger than that inside the pile group.The parameter identification technique of soil properties is useful for studying liquefaction field and practical seismic design of structure in liquefaction field.更多还原