软土动力特性及其地震动效应研究

发布时间：2018-05-13 07:06

本文选题：软土动力特性 + 离心模型试验　；参考：《中国地震局工程力学研究所》2016年博士论文

【摘要】：软土在动力作用下的非线性特征和地震动放大效应是地震工程界一直以来关注和研究的热点问题之一,由于当前已获取的强震动观测资料几乎没有软土覆盖的场地条件资料,使得软土场地地震反应分析结果无法用实际的强震记录进行检验,因此软土地区的抗震设计存在潜在的风险。针对近年来软土动力特征以及自由场地震反应分析存在的若干科学问题以及不确定性,本文通过理论分析、数值模拟和试验研究相结合的手段,围绕动荷载作用下软土的动力特性及动强度特征、软土在地震作用下的非线性特征和表现行为、软土自由场的动态离心模型试验分析、离心模拟与数值模拟比较及其验证等四方面开展了理论分析和试验研究。目标是试图揭示软土的动力学参数特征及在地震作用下的表现行为,评价软土场地的抗震性能和动力灾变过程,合理地估计软土场地地震动效应问题,弥补由于强震动观测资料的缺失导致理论计算无法验证的这一现状,推动软土场地地震动效应这一领域的研究,为我国软土地区工程抗震设防提供参考依据。在充分吸收总结前人已有成果的基础上,本文以天津地区滨海相软土为研究对象,围绕上述科学问题,开展的主要工作及研究创新如下:1.开展了软土宏观动力特征及微观结构的室内试验研究,分析了软土的动力学特性、动强度特征以及微观孔隙的定量化结果。针对典型软土开展了常规物理力学性质试验、应变控制和应力控制条件下的循环动三轴试验、微观电子显微镜扫描试验等描述宏观动力特征和微观结构性的室内试验。研究在循环荷载作用下固结时间、有效围压、固结比等因素对软土动力特性参数,提出一套最优化的拟合精度较高的试验数据拟合方法,给出了天津软土的G/Gmax-γ和λ-γ经验曲线;依据动强度试验结果分析了软土在不同动应力幅值作用下累积塑性应变、双幅应变与循环振次的关系;利用电镜扫描技术开展软土单元体试样的微观结构分析,定量地描述软土的微观结构特征。2.开展典型软土和硬土自由场的大型土工离心机振动台试验,通过模拟强震台站,获取完整的加速度记录,围绕关键地震动参数进行数据分析,给出设定地震动的场地效应。设计并构造了软土和硬土两个均质成层场地的离心模型,开展离心机振动台试验,并以此来人工模拟强震动观测台站,将天然地震波和人工地震波作为基底输入,通过调整输入峰值加速度来模拟不同强度的地震波,利用在模型箱中部和边界布设加速度和位移传感器,获取软土场地不同深度、不同层位监测点的加速度峰值、时程、反应谱、侧向位移和沉降等量测结果,达到了利用离心模型试验模拟强震台站并获取完整记录的试验目标和效果。通过比对两个离心模型试验结果,研究表明相比于硬土而言,软土具有强滤波和非线性特性,地震动从底部至地表能量和幅值有一定的损失和衰减,峰值加速度总体上呈现先增大后缩小的趋势。试验结果可与理论计算进行对比分析,进而达到离心模型试验与数值模拟互为验证的目的。3.编制可嵌入多种非线性滞回本构模型的一维时域非线性地震反应分析程序,通过将离心模型还原至原型场地,开展了软土自由场非线性地震反应分析。利用现有较为成熟的三种土体非线性动本构模型(Davidenkov骨架曲线模型、“阻尼比退化系数”模型、“动态骨架曲线”模型),结合多次透射边界条件和时域逐步递推格式,编制可嵌入三种本构模型的一维时域非线性地震反应分析程序包,形成以不同本构模型方案为基础的数值模拟计算程序。依据离心模型,还原建立均质成层的软土场地和硬土场地原型,通过动三轴试验给出与离心模型试验土一致的动力学参数,并以此建立软土和硬土自由场的动力计算模型,开展多种算法的地震反应数值模拟,计算给出典型自由场地表及地下层位的峰值加速度、时程、反应谱以及地震动放大系数等。4.对动态离心模型试验与多种数值模拟结果进行了互为比较和相互验证,通过模拟强震台站的离心模型试验来验证选取动本构模型的合理性以及数值模拟方法的可行性。在上述研究成果的基础上,将动态离心模型试验与多种数值模拟结果进行认真对比及差异分析,重点考察地表及地下层位的峰值加速度、反应谱以及地震动放大系数的量测结果,比选和分析各土体时域非线性本构模型的实效性,遴选出较适合软土非线性特征的动本构模型,进而达到与数值模拟互为验证的目的,为今后开展软土场地地震反应分析提供新的思路和技术支撑。本文的学术贡献和应用价值:为软土动力学研究提供了新的路径,对软土的动态离心模型试验提供了经验,给出的天津滨海软土的动力学参数对该地区工程抗震具有重要的应用价值。
[Abstract]:The nonlinear characteristics of soft soil under dynamic action and the amplification effect of ground motion are one of the hot issues that have been concerned and studied by the earthquake engineering circle. Because there is almost no ground condition data of soft soil covered by the strong seismic observation data obtained at present, the results of the seismic response analysis of the soft soil site can not be recorded by the actual strong earthquake. The seismic design of soft soil area has a potential risk. Aiming at some scientific problems and uncertainties existing in the dynamic characteristics of soft soil and the analysis of the seismic response of free field in recent years, the dynamic characteristics and dynamic characteristics of soft soil under dynamic load are discussed by means of theoretical analysis, numerical simulation and experimental research. The characteristics of strength, nonlinear characteristics and behavior of soft soil under earthquake action, dynamic centrifugal model test and analysis of soft soil free field, comparison between centrifugal simulation and numerical simulation and its verification are carried out in four aspects. The aim is to reveal the characteristics of dynamic parameters of soft soil and its performance under earthquake action. In order to evaluate the seismic performance and dynamic catastrophe process of soft soil site, to estimate the ground motion effect in soft soil site, to make up for the present situation that the theoretical calculation can not be verified due to the lack of observation data of strong vibration, and to promote the research in the field of ground vibration effect in soft soil site, to provide reference for the seismic fortification of the soft soil area in China. On the basis of fully absorbing the previous achievements of the predecessors, this paper takes the coastal soft soil in Tianjin as the research object. The main work and research innovation around the above scientific problems are as follows: 1. the indoor experimental research on the dynamic characteristics and microstructure of the soft soil was carried out, and the dynamic characteristics and dynamic strength of the soft soil were analyzed. Characteristics and the quantitative results of microscopic pores. In the typical soft soil, the conventional physical and mechanical properties test, cyclic three axis test under strain control and stress control, micro electron microscope scanning test, and other indoor experiments describing macroscopic dynamic characteristics and microstructure are carried out, and the consolidation time under cyclic loading is studied. A set of optimal fitting methods of experimental data fitting is proposed for soft soil dynamic characteristic parameters, such as effective confining pressure and consolidation ratio, and the G/Gmax- gamma and lambda gamma experience curve of Tianjin soft soil is given. According to the dynamic strength test results, the cumulative plastic strain, double amplitude strain and cycle under the action of different dynamic stress amplitude are analyzed. The analysis of the microstructure of the soft soil unit samples by the scanning electron microscope and the quantitative description of the microstructure characteristics of the soft soil.2. to carry out the large geotechnical centrifuge shaking table test of the typical soft soil and the hard soil free field. Through the simulation of the strong seismic station, the complete acceleration records are obtained, and the key ground vibration parameters are carried out. A centrifuge model of two homogeneous layer sites of soft soil and hard soil is designed and constructed. The centrifuge shaking table test is carried out to simulate the strong vibration observation station. Natural seismic waves and artificial seismic waves are used as base inputs and the input peak acceleration is adjusted to simulate the input peak acceleration. The acceleration and displacement sensors are set up in the middle and boundary of the model box to obtain the acceleration peak, time history, response spectrum, lateral displacement and settlement of the monitoring points of different layers, and the test of simulating strong earthquake stations and obtaining a complete record by centrifugal model test is achieved. By comparing the results of two centrifuge models, it is shown that the soft soil has strong filtering and nonlinear characteristics compared with the hard soil, and the ground motion has a certain loss and attenuation from the bottom to the surface, and the peak acceleration tends to increase first and then reduce. The experimental results can be carried out with the theoretical calculation. Comparative analysis, and then to achieve the purpose of mutual validation between centrifugal model test and numerical simulation.3., a one-dimensional nonlinear seismic response analysis program which can be embedded in a variety of nonlinear hysteretic constitutive models is developed. By reducing the centrifuge model to the prototype site, the non linear seismic response analysis of soft soil free field is carried out. Three kinds of soil nonlinear dynamic constitutive models (Davidenkov skeleton curve model, damping ratio degradation coefficient "model," dynamic skeleton curve "model), combined with multiple transmission boundary conditions and time domain recursive scheme, a one-dimensional time-domain nonlinear seismic response analysis program which can be embedded into three constitutive models is developed to form different constitutive models. The model based numerical simulation program is based on the centrifuge model. Based on the centrifugal model, the soft soil site and the prototype of the hard soil site are reduced. The dynamic parameters consistent with the centrifuge model test soil are given by the dynamic three axis test, and the dynamic calculation model of the free field and the free field of the soft soil and the hard soil is established, and the seismic responses of various algorithms are carried out. The numerical simulation is used to calculate the peak acceleration, time history, response spectrum and seismic amplification factor of the surface and underground layers of the typical free field. The dynamic centrifugal model test and a variety of numerical simulation results are compared and verified each other. The dynamic model test is used to verify the selection of the dynamic constitutive model by simulating the centrifugal model test of the strong earthquake station. On the basis of the above research results, the dynamic centrifugal model test and a variety of numerical simulation results are carefully contrasted and different, and the peak acceleration, the response spectrum and the large coefficient of seismic dynamic discharge are investigated, which are compared to the selection and analysis of soil mass. The effectiveness of the domain nonlinear constitutive model is to select the dynamic constitutive model suitable for the nonlinear characteristics of the soft soil, and then to achieve the purpose of mutual validation with the numerical simulation, and provide new ideas and technical support for the seismic response analysis of soft soil sites in the future. The academic contribution and Application value of this paper provide a new method for the research of soft soil dynamics. The path has provided experience for the dynamic centrifugal model test of soft soil. The dynamic parameters of Tianjin coastal soft soil are of great value to the earthquake resistance in this area.

【学位授予单位】：中国地震局工程力学研究所
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TU435;P315.9

【参考文献】