【作者】 张琰；

【导师】 李广信；

【作者基本信息】 清华大学 ， 土木工程， 2009， 博士

【摘要】 张拉裂缝是土石坝常见的隐患和引起土石坝破坏的主要原因之一,也是对坝体安全造成威胁和亟待解决的关键技术难题。因此,开展压实粘土在三轴拉伸条件下拉伸特性和破坏机理的研究对于土石坝工程的安全评价具有重要意义。本文在前人研究成果的基础上,研究探讨了压实粘土在三轴拉伸条件下应力应变特性和破坏机理,建立了压实粘土张拉裂缝的三维无单元数值模拟方法。本文的主要研究工作和创新成果有:1.研制了卧式三轴拉压试验仪。该仪器采用位移控制式加载方式,轴向刚度大,可以测定三轴条件下土体拉伸破坏全过程应力位移曲线,可进行三轴压缩、三轴拉伸和三轴压缩和拉伸组合试验。2.采用糯扎渡和双江口心墙土料进行了系列的三轴拉伸、三轴压缩和三轴压缩-拉伸组合试验,研究了压实粘土在三轴拉伸和压缩-拉伸组合条件下的应力应变关系特性和拉伸破坏特性。在此基础上,提出了压实粘土拉压统一的联合强度准则,并对邓肯张EB模型进行了扩展,扩展后的模型可统一描述压实粘土在压缩、反向加载和拉伸条件下的变形特性。3.推导了三维点插值无单元法的计算公式,提出了点插值无单元法与有限元法的耦合方法。与比奥固结理论相结合,开发了无单元与有限元耦合的三维有效应力应变分析计算程序系统。4.提出了基于无单元法的弥散裂缝模型。通过将裂缝弥散到无单元法结点影响域中,并考虑压实粘土张拉断裂过程中的各向异性,构建了基于无单元法的裂缝弥散理论的计算模式,推导了压实粘土三维脆性断裂和钝断裂带无单元法模型。5.将上述研究成果嵌入已有有限元计算程序系统,发展了土石坝应力变形和裂缝分析三维计算程序系统。对双江口高心墙堆石坝坝体横向张拉裂缝和心墙水力劈裂裂缝问题进行了三维计算分析,对该坝发生坝体横向裂缝和心墙水力劈裂的可能性进行了分析和评价。更多还原

【Abstract】 Tensile crack is a common hidden trouble and one of the main causes of destruction of earth-rockfill dams, so it is a threat to the safety of dams and a key issue desiderated to be solved. Therefore, studying the tensile property and failure mechanism of compacted clay under triaxial tension condition has great significance to the safety evaluation of earth-rockfill dams. In this thesis, based on the previous research works, the stress-strain behavior and failure mechanism of compacted clay under triaxial tension condition were investigated, then a three-dimensional meshless numerical simulation method of tensile crack of compacted clay was proposed. The main achievements obtained in the thesis are as follows:1. A horizontal triaxial tension-compression apparatus for soil was developed. This apparatus adopts strain-controlling loading mode, and can be used to obtain the procedural stress-displacement curve up to tensile failure of compacted clay under triaxial condition due to its large axial rigidity. This apparatus also can be used to carry out conventional triaxial test, triaxial tensile test and triaxial compression-tension combining test.2. A series of triaxial tensile tests, conventional triaxial tests, and triaxial compression-tension combining tests on core clay materials of Nuozhadu and Shuangjiangkou high earth-rockfill dams were performed. The stress-strain behavior and tensile failure properties of compacted clay under triaxial tension and compression-tension combining condition were investigated. Based on the test results, a tension-compression uniform joint strength criterion of compacted clay was proposed, and Duncan-Chang’s EB constitutive model was extended to describe the deformation properties of compacted clay under compression, reversed loading and tension conditions.3. The calculating formulas for three-dimensional point interpolation meshless method were derived comprehensively, then a coupling approach of radial point interpolation meshless method and finite element method was proposed. By combining Biot’s consolidation theory and the proposed coupling approach, a three-dimensional effective stress-strain computing program system was developed.4. The smeared crack model based on meshless method was proposed. By smearing crack into nodal influence domain of meshless method and considering the anisotropy of compacted clay during tensile fracture process, the computing mode of smeared crack theory based on meshless method was established, and the three-dimensional brittle fracture and blunt crack band meshless model were derived.5. By embedding the above research achievements in existing FEM computing program system, a three-dimensional computing program system was developed, which can be used to stress-deformation and tensile crack analysis of earth-rockfill dams. The transverse tensile crack and hydraulic fracturing crack problems in Shuangjiangkou high earth-rockfill dam were simulated and analyzed under three-dimensional condition, then the transverse tensile crack and hydraulic fracturing crack was analyzed and evaluated.更多还原