【作者】 柳伟；

【导师】 蔡袁强； 徐长节；

【作者基本信息】 浙江大学 ， 岩土工程， 2007， 硕士

【摘要】 地震是一种严重的自然灾害，特别是软土场地，因为对地震动的放大作用显著，造成的危害更大。而在我国沿海地区及部分内陆城市广泛分布着深厚软粘土层，因此，研究这些软土层的地震反应具有十分重要的意义。但是，动荷载作用下，土体的行为十分复杂。因而，在地震反应分析中，如何确定实用的土体应力—应变关系又成为问题的核心。本文首先在前人研究的基础上，针对实际工程中软粘土存在的各向异性，采用英国GDS公司研制生产的高精度动静三轴试验设备进行应力控制的循环三轴试验，研究分析了初始静偏应力、循环应力比、加荷周数、频率及超固结比对循环荷载作用下杭州地区饱和软粘土的应变和孔压的影响。其次，本文根据试验结果，提出了杭州地区饱和软粘土在循环荷载作用下的应变软化模型和应变累积模型，并确定了参数。然后将其引入Iwan模型中，结合Masing准则对软粘土的动应力—应变关系进行描述。通过计算结果和试验数据的对比分析表明，此模型能正确反映土体的循环特性。最后，本文基于一维非线性波传播的原理，采用修正的Iwan模型模拟每一层土的动应力—应变特性，并结合显式有限差分法数值求解，自编计算程序对地震的速度(加速度)时程以及反应谱进行对比分析，得出了一些有益的结论。更多还原

【Abstract】 Earthquake is a kind of catastrophe. Specially, it will induce more heavy disaster in clay site because of amplification of seismic ground motion. However, there are coverd by deep and thick soft soil layers in coastal areas and inland cities in China. So, seismic site response analyses is a very important problem. But, soil behavior is complex under dynamic loading. Thus, ’How to determine stress-strain relationship’ becomes the key of the problem.Firstly, based on previous researches and anisotropic clay in actual engineering, a series of undrained cyclic stress controlled triaxial tests were performed on typical Hangzhou soft clay by GDS dynamic triaxial system. The effects of initial static deviator stress, cyclic stress ratio, loading cycles, loading frequency and overconsolidation ratio on strain and pore-pressure were investigated.Secondly according to experimental data, this paper proposed a cyclic degradation model and a empirical equation of plastic strain, and determined the parameters in the models. And then, the empirical models were incorporated into Iwan’s series-parallel model to account for cyclic degradation and cumulative plastic strain during cyclic loading individually. Subsequently, the dynamic stress-strain relationship of saturated soft clay is described with modified Masing’s rules. As compared with experimental data and other models, the present model is proved to be reasonable and effective.Finally, in the present paper, the dynamic behavior of soil layers was described by modified Iwan’s series-parallel model. And then, based on principles of one-dimensional nonlinear propagation, a program is worked out to analyze velocity(accelerogram) time history and spectra of seismic motion by an explicit technique. As compared with input data and other solutions, some useful conclusions were gotten.更多还原