【作者】 崔杰；

【导师】 凌贤长；

【作者基本信息】 哈尔滨工业大学 ， 土木工程， 2020， 硕士

【摘要】 震害资料表明,液化引发的侧向扩展是引起桩基受损的主要原因之一。地震荷载作用下液化侧向扩展场地桩-土动力相互作用的规律和机理十分复杂,目前尚未对此形成统一的认识。p-y曲线法作为一种较为简单有效的桩土相互作用分析方法,常用于桩基设计和分析。目前研究的动力p-y曲线主要针对的是液化水平场地的饱和砂土,液化微倾场地饱和砂土动力p-y曲线的研究尚不成熟。本文针对易发生液化侧向扩展的液化微倾场地,基于已验证的建模手段和离心机试验建立液化微倾场地群桩-土动力相互作用足尺模型。利用足尺模型分析液化微倾场地饱和砂土动力p-y曲线的基本特性及影响因素,提出基于场地倾斜角度和埋深的液化微倾场地饱和砂土p-y曲线公式,并基于此建立拟静力分析方法。本文的基本研究内容和结论如下:首先,基于已完成的典型离心机试验,以ABAQUS为前处理软件、Open Sees为计算平台、GID为后处理软件。利用四节点等参水土耦合单元模拟土体,其中本构模型为多屈服面弹塑性本构模型;利用梁柱单元模拟桩基;通过静力荷载和孔压考虑自由水体的作用;在桩土刚性连接的基础上增加零长度单元模拟桩土接触面特性,进而提出了液化微倾场地群桩-土动力相互作用二维有限元模型,通过离心机试验数据与计算数据的对比,检验有限元模型和建模手段的合理性。接着,基于已验证的建模手段和离心机试验,提出液化微倾场地群桩-土动力相互作用足尺模型,讨论液化微倾场地饱和砂土动力p-y曲线的基本特性,发现液化微倾场地饱和砂土动力p-y曲线与液化水平场地饱和砂土动力p-y曲线明显不同。当土体即将发生液化时,作用在桩上的土压力最大,此时可以看做桩基受力的临界状态。土体完全液化后,作用在桩基上的土压力与液化土体的流动速度关系密切,表现了液化土体的流体特性。桩基底部和桩帽的约束程度对桩身峰值弯矩分布形式影响较大。随后,研究场地倾斜角度、桩径、加载幅值以及群桩中基桩位置等影响因素对饱和砂土动力p-y曲线的影响。最后,通过计算p-y曲线与API规范推荐的饱和砂土p-y曲线和p乘因子法的对比,说明在液化微倾场地上使用API规范推荐的饱和砂土p-y曲线和p乘因子法具有一定的局限性。基于API规范推荐的饱和砂土p-y曲线,建立考虑场地倾斜角度和埋深的p-y曲线公式。将修正的p-y曲线融入到p-y弹簧中,建立非线性温克尔地基梁拟静力分析模型,将各个土层的峰值位移施加到p-y弹簧的固定端,提出拟静力分析方法。将拟静力计算结果与二维数值模型的计算结果对比,验证了拟静力分析方法的正确性。本文的研究成果对同类型液化微倾场地桩基地震反应分析有限元数值模型的建立具有重要借鉴意义,有助于加深对液化微倾场地群桩-土动力p-y曲线的理解。同时,提出的液化微倾场地群桩地震反应拟静力分析方法可以更好地服务工程实际。更多还原

【Abstract】 The investigation of earthquake damage shows a lot of pile foundations have been subjected to severe damages due to liquefaction-induced lateral spreading during past earthquakes.The dynamic response of soil-pile interaction in liquefaction-induced lateral spreading ground is very complicated under the action of seismic loads,of which there is no unified understanding at present.Therefore,properly understanding the behavior of pile foundation during lateral soil flow is of major concern to both academicians and practitioners.Dynamic p-y curve method is an effective way to evaluate dynamic pile-soil interaction,which defines the relation between lateral soil pressure and the relative displacement of soil and pile.This approach requires that an appropriate p-y relationship be adopted,considering soil conditions.Although,some recent studies were carried out to more fully understand the behavior of p-y curve in liquefied soil,their studies were mainly concerned with smaller soil deformation on the level ground.However,in reality,piles undergo large soil deformation in the case of liquefaction-induced lateral spreading.Therefore,in the present paper,2D numerical analysis was performed to study the pile response in a mild slope under lateral spreading considering pile-soil interaction.The 2D model was validated by using centrifuge test.Based on proven modeling methods and centrifuge tests,develop a 2D full-scale model.Next,using the 2D analysis,dynamic p-y curve were computed.The important conditions affecting p-y curves were analyzed.The modified p-y curves of liquefying sand in a mild slope under lateral spreading was created and the pseudo-static analysis based on Beam on nonlinear Winkler Foundation for analysis of dynamic pile-soil interaction in a mild slope under lateral spreading was suggested.The important research content and results are as follows:First of all,a 2D finite element model was established for centrifuge test in a mild slope under lateral spreading.ABAQUS was used as pre-processing software,Open Sees was used as the computing platform,and GID was used as post-processing software.The saturated sand and clay were simulated with a multi-yield-surface plasticity constitutive model,the pile was simulated using beam-column elements.Consider the effect of free water through static load and pore pressure.Zero-length elements were added to simulate the characteristics of soil-pile contact surface on the basis of rigid soil-pile connection.The results of the 2D finite element model analysis was in reasonable agreement with the centrifuge test data.Secondly,based on the verified modeling methods and centri fuge tests,a full-scale model of soil-pile dynamic interaction in a mild slope under lateral spreading was established,and the basic characteristics of the dynamic p-y curve of the liquefied sand in a mild slope were analyzed,which was different from the dynamic p-y curve of the liquefied sand on the level ground.When the soil was about to liquefy,the earth pressure acting on the pile was the largest,at this time it could be regarded as the critical state of the pile foundation.After the soil was completely liquefied,the soil pressure acting on the pile foundat ion was closely related to the flow velocity of the liquefied soil,which showed the fluid characteristics of the liquefied soil.The degree of restraint at the bottom of the pile foundation and the pile cap had a great influence on the peak bending moment distribution of the pile body.The effects of ground inclined angle,pile diameter,loading amplitude and pile position on the dynamic p-y curve were studied,and these factors were found to have significant effects on the dynamic p-y curve.Comparing the calculated p-y curve with the saturated sand p-y curve recommended by the API and p-multiplier factor method showed that the use of the saturated sand p-y curve recommended by the API and p-multiplier factor method on liquefied slightly inclined sites had certain limitations.Based on the basic characteristics of the dynamic p-y curve of the liquefied sand in a mild slope,a p-y curve based on the ground inclined angle and burial depth was established by modifying the p-y curve of saturated sand specified by the API.The modified p-y curve was integrated into the p-y spring,Beam on nonlinear Winkler Foundation model was established,and the maximum displacement of each soil layer was input to the fixed end of the spring,and a pseudo-static analysis method was proposed.The pseudo-static calculation results were compared with the calculation results of the 2D numerical model to verify the correctness of the pseudo-static analysis method.The research results of this paper are of great reference significance to the establishment of a finite element numerical model for seismic response analysis of pile foundations in liquefying mild inclined sloping ground,which is helpful to deepen the understanding of the soil-pile group dynamic p-y curve in liquefying mild inclined sloping ground.At the same time,the proposed pseudo-static analysis method for seismic response of group piles in liquefying mild inclined sloping ground can better serve engineering practice.更多还原