【作者】 张宏博；

【导师】 黄茂松；

【作者基本信息】 同济大学 ， 岩土工程， 2006， 博士

【摘要】 当前，随着交通的日益繁忙，路基的长期沉降问题已经引起人们的广泛关注，如何控制和减少路基沉降已经成为道路工程界和岩土工程界共同关注的热点问题。由于长期以来道路工程土力学和传统的岩土工程土力学作为两个不同学科而各自发展，导致现行道路设计还主要依靠经验方法。同时，尽管以弹塑性理论为核心的本构理论在道路工程中也有涉及，但由于多数模型采用传统的小步长积分方式，造成计算时间过长，难以在实际工程中应用。总之，迄今为止，还未发现有合适的本构模型能够同时考虑计算的简便性和无粘性材料复杂的变形特征。文献表明，近年来，基于安定性理论而提出的弹塑性本构模型由于只需考虑循环加载过程中的最大塑性变形，可采用较大的积分步长，具有良好的应用前景。因此，为了能够填补目前道路长期沉降计算方法上的空白，本文在系统研究砂土变形特性的基础上，基于安定性理论提出了双硬化弹塑性本构模型，可以合理有效地计算无粘性材料在大数目循环加载时的累积塑性变形，从而为下一步探索控制和减少路基长期沉降的有效途径提供了可靠的理论依据和数值分析手段。因此，本课题具有重大的理论意义和工程实用价值。 本课题取得了如下创新性的研究成果： 1．在试验室内运用GDS土体多功能三轴试验机，对上海粉细砂进行了一系列的常规三轴压缩试验，针对其在不同试验条件下的变形规律进行了系统分析。试验表明，无论排水还是不排水试验条件，砂土都表现出两类显著的变形特征，一是应力-剪胀性特征，二是剪切应变硬化／软化特征，这两类特征均与试样的初始密实度及有效围压密切相关。同时，对比等向与非等向固结时的三轴剪切试验结果，可知后者的峰值强度及剪胀性特征均高于前者，表明初始应力各向异性对砂土应力-应变关系有较为显著的影响。 2．利用上述仪器，对上海粉细砂进行了大数目循环次数(5000次)的非等向固结三轴压缩试验，得出其在不同初始密实度、不同围压和不同动应力时的变形规律，发现初始密实度及围压相同时，动应力比越大，累积变形越大；而在同样的应力水平下，密实度越高，累积变形越小；另外，围压对累积变形也有一定的影响。同时，有两点需要注意：一是累积变形主要发生在加载初期，更多还原

【Abstract】 With the rapid development of traffic engineering, the long term settlement of subsoil induced by repeated loading has received much attention recently. Controlling and reducing settlement have been a common interest to the pavement engineers and the geotechnical engineers. Pavement soil mechanics and traditional soil mechanics have developed as two separate disciplines. As a result, current pavement design methods are mainly based on empirical equations with rough results. Although there are some constitutive models based on fundamental elasto-plasticity theory, most of them can not be used in a large number of repeated loading, e.g. 10~6, which is because that the numerical implementation of such a model through a classical step-by-step procedure proves unrealistic beyond a few load cycles. Therefore, a constitutive model based on shakedown theory that only accounts for the maximum plastic deformation for each load cycle is needed. To settle the puzzle problem, the author firstly summarizes deformation mechanisms in this dissertation, and then formulates an elasto-plastic model within the framework of shakedown theory. Computation results show that the model can consider both computational efficiency and complex deformation features of cohesionless soil. In brief, the research production is of importance both for theoretical analysis and practical engineering.The main achievements of this thesis are as follows:1. In order to investigate the deformation characteristics of sand under static loading, a series of traditional triaxial compression tests of Shanghai silt sand are performed in the laboratory on GDS triaxial apparatus. Test results show that subjected to shear, a sand will exhibit either dilative or contractive behavior under both drained condition and undrained condition. Whether a sand dilates or contracts depends on the initial state of the sand, that characterized by both the density of the sand and the effective mean normal stress applied. The larger the density, the lower the effective mean normal stress, the more dilative response is. And the strain hardening or softening laws has the similar features. What’s more, the initial stress anisotropy has significant influence on the strength and dilatancy of sand.2. Secondly, to obtain the cumulative deformation pattern, a series of cyclic triaxial compression tests are performed on the same apparatus. The test results show that the cumulative plastic strain will be larger with the smaller density, the lower effective mean normal stress and the higher dynamic stress level. At the same time, it should be noted that most of cumulative deformation happens mainly at initial stage and approaches to stable deformation gradually. What’s more, the mechanical process can be characterized as cyclic densification with volumetric compaction.更多还原