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针对饱和软土地基中大间距摩擦型桩筏基础抗震问题,采用离心振动台开展了桩筏基础地震响应的试验研究。为模拟实际软土场地浅部超固结黏土和深部正常固结黏土的地层特征,试验在高岭土土样表面预铺砂层,然后在50g离心加速度下进行固结。上部结构简化为质点和杆构件,基础形式包括桩头刚接和桩头自由2种类型的大间距桩筏基础模型。试验分析了模型的加速度和位移、土层内部孔隙水压力以及桩身应变等响应。试验结果表明:在软土场地自振频率范围内,结构–基础–地基三者相互作用十分明显,基础与结构加速度放大系数高于其它频率范围;桩头刚接与桩头自由的基础在地震时均产生了较周围地表土体更大的竖向沉降,但震后较长时间内基础与地表沉降速率基本一致;地震结束时,桩头刚接的上部结构侧向位移与基础倾斜值均较桩头自由时减少一半以上,但上部结构加速度放大作用更加明显;桩筏基础承载能力因土体软化行为有所降低,震后部分上部荷载由群桩转移到筏板,但桩筏荷载分担比例总体变化不大。试验揭示了软土震陷时桩基的变形控制机理,为软土地基减沉桩基础的抗震设计提供参考。
Aimed at aseismic problems of large-span friction piled raft foundation in saturated soft soil foundation, the seismic response of piled raft foundation is studied by centrifugal shaker. In order to simulate the stratigraphic characteristics of shallow consolidated clay and deep consolidated clay in the actual soft soil site, pre-sand layer on the surface of kaolin soil samples was tested and then consolidated under 50g centrifugal acceleration. The superstructure is simplified as the mass point and the rod member. The basic form includes two types of large-pitch piled raft foundation models: the first joint and the second one. The experiment analyzes the acceleration and displacement of the model, the pore water pressure in the soil layer and the response of pile strain. The experimental results show that the interaction between structure-foundation-foundation is obvious and the acceleration amplification factor of foundation and structure is higher than other frequency ranges in the natural frequency range of soft soil; The vertical subsidence occurred more than that of the surrounding surface soil. However, the foundation and surface subsidence rates were basically the same in a long time after the earthquake. At the end of the earthquake, both the lateral displacement of the superstructure immediately after the pile head and the basic inclination Which is more than half of that when the pile head is free, but the acceleration of the superstructure is more obvious. The carrying capacity of the piled raft foundation is reduced due to the softening behavior of the soil, and the upper part of the post-earthquake load is transferred from the pile group to the raft. The overall proportion of little change. The experiment reveals the deformation control mechanism of pile foundation when the soft soil collapses and provides reference for the anti-seismic design of the foundation of the piles with reduced pile foundation.