【作者】 肖燕；

【导师】 赵明华； 陈昌富；

【作者基本信息】 湖南大学 ， 岩土工程， 2004， 硕士

【摘要】 软土具有应力应变随时间的发展而不断变化的特殊工程特性——流变性，其内容包括蠕变、应力松弛、弹性后效和长期强度等，其中蠕变特性是工程实践中较为关注的热点问题之一。软土的蠕变特性将导致建于软土地区的桥台和桥墩等在建成若干年后都不同程度地发生水平位移，台后土体下沉，台前土体上拱，对交通的正常运营和桥梁的安全造成极大的危害。 本文在对已有岩土介质流变理论以及典型软土蠕变曲线进行深入分析和讨论的基础上，提出了改进的西原非线性蠕变模型，并推导出相应的本构方程。然后，根据室内蠕变试验原理，自行设计改造出室内直剪蠕变仪，并针对本文依托工程——广东江门某大桥的原状土进行了为期近3个月的室内直剪蠕变试验，获得了大量的试验数据，其次，在前述试验数据的基础上，本文利用具有自适应性、自组织性和并行性等优点的遗传算法反演得出改进西原模型本构方程中的各参数值，理论拟合曲线和试验实测结果吻合良好。本文根据“时步—粘性初应变”法，在Visual Fortran 6.5的平台上，开发出桩—土—桥台共同考虑的蠕变有限元程序，该程序可用来对具有分层结构的软基蠕变特性进行分析，同时还可预测不同时期的桥台软基受力和变形状态，为工程设计提供定性参考。最后，本文将上述各项成果应用于依托工程实践分析，得到了初始地应力场、加载瞬间应力场以及流变应力场的各方向应力、应变等值线图，并就是否考虑软土的蠕变效应对桩的水平位移及土压力进行了对比分析，且计算结果表明考虑软土的蠕变效应与实测结果更为吻合。更多还原

【Abstract】 The stress and strain developing with the time, which is called rheology, is the especial engineering characteristics of the soft clay. The rheological trait of the soft clay includes creep, stress relaxation, elastic aftereffect and long-term strength. Creep is one of the hottest issues in engineering practice. Because of the creep trait, many bridges those built in weak subgrade have encountered a lot of problems, such as the subsidence of the floor behind the abutment, the cambering of the floor before the abutment and the forward movement of the abutment itself, which have done great harm to the transportation and the security of the bridge.Firstly, through deeply study of the rheological theory and the typical rheological curve of the soft clay, an improved nonlinear elastic-viscous elastic-viscous plastic model is presented and the corresponding constitutional equation has been worked out too. Secondly, based on the principle of the indoor creep direct shear test, the direct shear apparatus is designed and fabricated. Thirdly, by using above apparatus an indoor direct shear test with the parent soil in Jiangmen City, Guangdong Province, has been finished and a great deal of experimental data are obtained. Then, according to the experimental data, the Genetic Algorithms method with the virtues of intelligence and parallelism is used to back analyze the parameters in the constitutional equation and the theoretic curves fit the actual ones very well. Moreover, on the "time step-viscous initial strain" theory, a FEM procedure, which can analyze the reological problems of the whole system of pile-abutment-ground has been worked out on the floor of Visual Fortran 6.5. This procedure can also be used for forecasting the qualities such as displacement or stress of the pile or the soil in different periods, which will give some qualitative reference to the engineering design. Finally, all above results are used in the supportive engineering practice, and the displacement vector diagrams, the stress and strain contour diagrams are obtained. At the same time, the contrastive analysis of the displacement of the piles and the soil pressure has been done as to whether consider the creep effect or not. The last results indicate that the curve considering the creep effect matching the actual curve much better.更多还原