摘要
海洋环境荷载复杂多变,海上构筑物基础周围土体作为主要承载体受地震作用的影响非常大。我国已建及拟建的沿海区域存在着大量饱和砂土层,相比于沙漠戈壁等干旱区域,基础周围土体的动力特性有极大不同。已有研究主要考虑单一地震作用下自由场土体力学性状演化,少有关注地震序列及地震历史对基础周围土体动力特性的影响。基于ZJU-400超重力振动台,开展了干砂地基和饱和砂地基离心模型试验,从离心模型尺度对比了两种地基中桩周土体在地震作用下的动力响应。研究发现,饱和地基的自振频率受地震历史的影响较明显,而干砂地基受其影响并不显著。桩-土强烈的相互作用会加速桩周土体超孔压发展。受地震历史效应的影响,土体剪胀特性逐渐加强;桩周超孔压的累积发展逐渐放缓,而消散速度却有所加快。在饱和地基中,桩周土体放大系数随着地震序列呈现明显的震荡增加现象,而在干砂地基中这种现象并不显著。采用反演方法发现,在整个施振过程中饱和砂地基桩周土体模量逐渐减小且不受剪应变关联的现象,揭示了其受超孔压的影响程度要大于剪应变的规律。
The load of marine environment is complex and unpredictable. The soil around the foundation of offshore structure is the main bearing body, which is greatly affected by the earthquake. There are a large number of sand layers in the coastal areas which have been built or are planned to be built in China. Compared with the desert Gobi area, the dynamic characteristics of the soil around the piles are significantly different. The existing studies mainly consider the evolution of soil mechanical properties under a single earthquake, and little attention is paid to the influence of earthquake sequence and earthquake history on the dynamic characteristics of soil around the foundation. With the use of the ZJU-400 centrifuge shaking table, this paper carried out a centrifuge modeling test in dry sand and saturated sand grounds, and compared the dynamic response of soil around the pile in two grounds under the earthquake. It is found that the natural frequency of saturated foundation is obviously affected by the historical effect of earthquake, while that of the dry sand ground is not. The strong pile-soil interaction can accelerate the development of excess pore pressure around the pile. Due to the historical effect of earthquake, the dilatancy characteristics of soil are gradually strengthened, the accumulation and development process of excess pore pressure around the pile is gradually slowed down, and the dissipation process becomes faster. Saturated sand ground has the characteristics of low frequency amplification and high frequency weakening. The historical effect of earthquake has no significant effect on the amplification factor of soil in dry sand ground, but for saturated ground,the amplification coefficient of soil shows an obvious increase. In the saturated sand ground, the shear modulus of soil around the pile is more affected by the excess pore pressure than the shear strain. During the shaking, the modulus gradually decreases without the phenomenon of gradual recovery in the dry sand ground.
作者
吴小锋
汪玉冰
朱斌
WU Xiao-feng;WANG Yu-bing;ZHU Bin(Key Laboratory of Soft Soils and Geoenvironmental Engineering of Ministry of Education,Zhejiang University,Hangzhou,Zhejiang 310058,China;Institute of Geotechnical Engineering,Zhejiang University,Hangzhou,Zhejiang 310058,China;Center for Hypergravity Experimental and Interdisciplinary Research,Zhejiang University,Hangzhou,Zhejiang 310058,China)
出处
《岩土力学》
EI
CAS
CSCD
北大核心
2020年第10期3385-3394,共10页
Rock and Soil Mechanics
基金
国家自然科学基金青年科学基金(No.51808490)
国家自然科学基金重点项目(No.41630638)
中央高校基本科研业务费专项资金(No.2018FZA4016)。
关键词
地震序列
地震历史效应
桩周土体
超重力振动台
earthquake sequence
earthquake history effect
soil around pile
centrifuge shaking table
