【作者】 胡卫；

【导师】 金峰；

【作者基本信息】 清华大学 ， 水利工程， 2010， 博士

【摘要】 本文在张冲的三维模态变形体离散元方法(3-D Mode Distinct Element Method,3MDEM)工作的基础上,将块体的本构关系从线弹性扩展到弹塑性,并用于模拟拱坝的破损溃决过程,研究拱坝的破坏机理。由于3MDEM在大规模计算上的局限性,基于3MDEM对拱坝破坏机理的研究,利用非线性有限元提出高拱坝的安全评价方法,并基于工程类比法对小湾拱坝进行全面的安全评价。主要研究内容包括:1.阐述了3MDEM的基本原理和计算流程,在张冲工作的基础上,将块体的本构关系从线弹性扩展到弹塑性,包括Mises和Drucker-Prager模型,并提出了一种基于塑性应变的接触断裂准则,基于3MDEM平台,初步实现了对结构弹性-弹塑性-断裂-破坏的全过程模拟。通过若干数值算例验证弹塑性本构的正确性,表明该方法可用于模拟拱坝的破损溃决的全过程。2.考虑坝体材料的弹塑性性质,采用3MDEM对梅花拱坝进行了分析,通过裂缝的扩展过程研究了拱坝的破坏机理,并重现梅花的溃决过程。结果表明,周边缝的破坏导致坝体上抬,拱坝的破坏从梁开始,梁受到削弱后,荷载向拱转移,最终拱的破坏导致全坝的溃决。随后为研究一般拱坝的破坏机理,假定梅花拱坝的周边缝完好,进行超载分析,定性得到拱坝的破坏规律,经历三个阶段:梁破坏阶段、拱破坏阶段以及拱坝整体失稳阶段。3.在3MDEM对拱坝的破坏机理研究的基础上,基于非线性有限元和工程类比,针对坝踵开裂和极限承载力,提出一组安全系数:帷幕安全系数k1,荷载分配突变安全系数k2以及极限安全系数k3。选取类比工程K?lnbrein和二滩拱坝,基于工程类比对小湾进行了安全评价。4.将小湾数值计算的结果与周维垣教授地质力学模型试验的结果进行对比分析,随后对小湾工程的加固措施进行研究,并分析了施工期坝体产生的温度裂缝对拱坝整体安全的影响,最后在混凝土材料中引入软化性质,用于小湾拱坝的安全评价,使得小湾的安全评价更为完整。更多还原

【Abstract】 On the basis of 3-D Mode Distinct Element Method (3MDEM) by Zhang Chong, the linear elastic constitutive relationship of blocks is extended to elasto-plastic. 3MDEM with elasto-plastic is used to simulate the failure process of Meihua arch dam and failure mechanism is studied. Because of the limitations on mass computation of 3MDEM, a procedure of comparative study for safety evaluation of high arch dams is carried out by the nonlinear finite element method (FEM) based on the failure mechanism. Xiaowan arch dam is studied with the comparative projects. The main contents are summarized as follows:1. The groundwork and computational procedure of 3MDEM are introduced at first. 3MDEM is a distinct element method under the assumption of a small strain, finite displacement, and finite rotation for blocks. The deformation of blocks is expressed by a combination of deformation modes in 3MDEM. Then the elasto-plastic constitutive relationship of blocks is investigated through continuum to discontinuum simulation, including Mises and Drucker-Prager model. Due to the shortcomings of the common criterion for contact fracture, a new criterion based on plastic strain is introduced. A failure process from elastic, elasto-plastic to fracture can be simulated on the 3MDEM platform. This is verified by several numerical examples comparing with FEM.2. 3MDEM with elasto-plastic properties is used in failure simulation of Meihua arch dam. The failure mechanism is studied through the crack expanding process. It turns out that the instability of upward sliding of dam is the cause of the failure. Arch dam is a high-order statically indeterminate structure with bearing capacity of arch and cantilever structure. 3 stages are usually involved in the failure process of arch dam:The cantilever failure stage: the failure first occurs at cantilever structure; the arch failure stage: when cantilever structure is weakened, a great many load moves to arch structure especially the middle-up arch, then the middle-up arch damages rapidly; the whole arch dam failure stage: when applied load is continued, most of the dam is damaged, which leads to dam burst at last.3. Based on the failure mechanism studied by 3MDEM, a procedure of comparative study for safety evaluation of high arch dams is carried out by FEM. A set of safety factors for dam heel crack and ultimate bearing capacity is suggested: safety factor for curtain k1, structural mutation safety factor k2, and ultimate safety factor k3. The safety evaluation of Xiaowan arch dam is studied based on engineering analogical method, chosing K?lnbrein and Ertan as comparative projects.4. Firstly the numerical results of Xiaowan are compared with geomechamical model test results. Secondly, the strengthen measurement of Xiaowan project is studied, and the the thermal cracks of dambody is simulated to discuss the influence for dam security. Finally, softening behaviors of concrete material are involved approximatively to give a full-scale safety evaluation of Xiaowan arch dam.更多还原