【作者】 王常晶；

【导师】 陈云敏；

【作者基本信息】 浙江大学 ， 岩土工程， 2006， 博士

【摘要】 我国东南沿海地区是经济最发达的区域,也是深厚饱和软粘土地基广泛分布的区域。“九五”期间该区域内建成了许多重要的交通基础设施,在有力地支持经济建设快速发展的同时,也出现了突出的技术问题:交通设施的长期运行引起了可观的地基附加沉降。这个问题的解决可以为现有交通设施的安全运行和今后重大交通基础设施建设提供重要的技术支撑,具有重大的理论和现实意义。列车引起地基动应力的分析,以及在这种动应力作用下饱和软粘土动力特性的研究恰恰是预测地基长期附加沉降的基础。 本文在国内外对列车振动和循环荷载作用下土体动力特性的研究基础上,在理论分析和室内试验两方面进行了如下研究工作: (1) 推导了弹性半空间-Timoshenko梁在移动荷载作用下的位移和地基表面反力解答,研究了荷载的临界速度,并比较了弹性半空间-Timoshenko梁和弹性半空间-Euler-Bernoulli梁,发现对实际工程Euler-Bernoulli梁可以满足计算精度,从而为采用弹性半空间-Euler-Bernoulli梁分析列车振动提供了理论基础。 (2) 对列车振动进行现场测试,分析了列车振动的特征,利用实测数据对本文建立的理论模型的合理性进行了验证。 (3) 采用移动荷载作用下弹性地基-Euler-Bernoulli梁模型,对列车移动荷载引起的地基内部动应力进行分析。研究了应力的空间分布特征,时间变化特征,应力路径变化和主应力轴旋转。发现列车移动荷载引起的动应力是一种低幅非对称循环应力,以一定的偏移应力为基准循环变化。主应力轴发生连续旋转,土单元应力状态周期地由单剪模式变化到三轴剪切模式再回到单剪模式。 (4) 分析了列车车速、路堤刚度、地基剪切模量对应力的影响。发现列车车速更多还原

【Abstract】 The South-East China is the most developed in China most area of which is covered with deep soft clay. Many important traffic fundamental projects have been built during the 9th five year plan. They have done a lot for the economic fast development. At the same time some technological problems occurred: considerable settlement developed during the long term operation of these projects. To solve this problem is a significant technological support for the safe operation of these projects in use and the building of future projects and is greatly meaningful. It does be the foundation of predicting long term settlement of ground induced by traffic load to study the complex stress in ground induced by train and dynamic properties of soft clay under this kind of stress.On the base of the important advances in the field of train-induced vibration and cyclic properties of soil under cyclic loading, some subjects as following were investigated on theoretical analysis and cyclic triaxial tests:(1) The solutions of displacement and contact force of Timoshenko beam lying on an elastic half-space under a moving load were obtained. The critical velocities of moving load were studied and the displacement of Timoshenko beam on an elastic half-space and Euler-Bernoulli beam on an elastic half-space was compared. And it is found that Euler-Bernoulli beam is precise enough for most practical projects. As proves the rationality of using Euler-Bernoulli beam on an elastic half-space to analyze train-induced vibration.(2) Some in-situ measurements were carried out to analyze characteristics oftrain-induced vibration. And based on these data the rationality of the presented theoretical model was proved.(3) A theoretical model of Euler-Bernoulli beam on an elastic half space under moving loads was presented in order to calculate stress in ground induced by train. The spatial distribution, time histories, stress path and principal stress axes rotation were studied. It is found train-induced stress is characteristics of low amplitude, low frequency, non-symmetric cyclic loading, which fluctuates from a deviated stress. The principal stress axes rotate continuously and stress state of soil element changes from simple shear to triaxial shear and back to simple shear repeatedly.(4) The influence of train speed, embankment stiffness and soil shear modulus on stress was analyzed. It is found that the static solution is precise enough to calculate stress when train speed is low. But stress amplitude increases greatly when train speed is high. Stress decreases with the embankment stiffness increasing but varies little when the embankment stiffness increases to some extent. The variation of stress with soil shear modulus is complex, which is related to train speed and the location of soil element.(5) Cyclic triaxial tests were carried out using the lOHz GDS bi-directional triaxial system and the characters of low amplitude, low frequency, long acting time, deviated stress and bi-direction of train-induced stress were simulated. The law of the deformation, pore pressure and cyclic strength of Xiaoshan nature soft clay was studied. It is shown that the deviated stress promotes the development of strain and pore pressure, lowers the cyclic strength curve but has small effect on the minimum limited cyclic strength. Due to the anisotropy and localization of soil, dynamic confining pressure can also induce plastic deformation accumulation and residual pore pressure development. And the velocity of plastic deformation accumulation and residual pore pressure development is higher than that under dynamic deviator stress of the same amplitude.The bigger the dynamic stress amplitude is, the bigger the difference is. (6) At last the principle of train-induced long-term settlement is analyzed. It is found that softening of soil, plastic deformation accumulation, and soil structure destruction within the critical boundary induced by train are the reason of long-term settlement.The presented study has important theoretical value for soil dynamic mechanics and will provide important technological support for the construction of future key traffic fundamental projects.更多还原