【作者】 刘敏；

【导师】 雷华阳；

【作者基本信息】 天津大学 ， 结构工程， 2017， 硕士

【摘要】 在大规模基础建设投资的推动下,新一轮的交通基础设施建设如高速铁路和地铁等带来了诸多的岩土工程问题。尤其是在沿海软黏土地区,由于软黏土具有高含水率、高压缩性和低渗透性等不良工程特性,在长期复杂动载作用下,会发生较大的变形和长期沉降,给列车的安全运行造成威胁。因此,系统开展动荷载作用下软黏土地基的动力响应和长期沉降的研究工作,具有重要的理论意义和实用价值。本文针对软黏土地基,系统开展了单一频率和变频率条件下的循环三轴试验,研究从累计轴向应变、应变软化和应力-应变关系三方面分析了其变形特性;采用ABAQUS进行数值建模,分析了振动频率、振动次数和循环应力比对软黏土变形特性的影响;在考虑频率组合和荷载间歇作用的基础上,采用动-静耦合加载方式,分析软黏土的动力响应和长期沉降特点,给出振动次数和循环应力比对其最终沉降量的影响。研究结果显示,变频率下滞回曲线向应变轴的倾斜明显。软黏土的变形大于其较高频率单一作用下的变形,小于其较低频率单一作用下的变形。变频率下,振动次数对土体的变形影响明显,不同变频率方式对土体变形的影响较小。考虑频率组合的间歇式动载下,软黏土的变形呈现阶梯形的发展趋势。孔压增量随振动周期的增加呈递减的趋势。循环应力比为0.3时,孔隙水压力在刚开始加载时瞬间增大,在间歇式加载阶段达到峰值,之后产生消散。循环应力比对软黏土长期沉降的影响明显,周期内振动次数的影响很小。循环应力比为0.1和0.15时,软黏土长期沉降呈稳定型发展趋势,拟合经验公式,能较好的反映长期沉降的变化趋势和变化量值。更多还原

【Abstract】 Driven by large scale of infrastructure investment,a new round of rail transport facilities construction such as high-speed rails and subways has brought a series of geotechnical engineering problems.The soft clay has properties of high water content,high compressibility and low permeability.Under the long-term complex dynamic loading,soft clay produces great deformations and long-term settlement,which results in a threat to the safe operation of trains especially in the soft-clay coastal areas.It is of great theoretical and practical value to study systematically the dynamic response and long-term settlement of soft clay subjected to cyclic loading.In this work,a series of cyclic triaxial tests are carried out systematically on the soft clay under the effect of single frequencies and variable frequencies.The deformation of the soft clay is analyzed through cumulative axial strain,strain softening and stress-strain relationship.The factors of vibration frequency,vibration times and cyclic stress ratio on the deformation of soft clay are analyzed under the condition of variable frequency through the numerical simulation of ABAQUS.The characteristics of dynamic response and long-term settlement of soft clay are analyzed and the influences of vibration frequency and cyclic stress ratio on the ultimate settlement of soft clay are discussed.The results show that the hysteresis curves have a list to the strain axis obviously.The deformation of soft clay is greater than that under the effect of the single higher frequency and smaller than that under the effect of the single lower frequency.The number of vibration times has an obvious influence on the deformation of soft clay under the effect of variable frequencies.The effect of different ways of variable frequencies on the deformation is small.The deformation of soft clay increases in a ladder type under the effect of intermittent cyclic loading,considering frequency combination.The pore water pressure increment decreases with the increasing of vibration periods.When the number of vibration times is within a certain range,the relation between the long-term settlement and vibration frequency is nearly linear.When the cyclic stress ratio is 0.3,the pore water pressure increases instantaneously at the beginning of cyclic loading,reaches its peak value at the intermittent loading stage and dissipates afterwards.The effect of cyclic stress ratio on the long-term settlement of soft clay is obvious.However,the number of vibration times in a loading period has little impact on that.The long-term settlement of soft clay presents a stable trend.The empirical formula is given,which can reflect the developmental trend and values of the long-term settlement.更多还原