【作者】 杨海清；

【导师】 周小平； 张永兴；

【作者基本信息】 重庆大学 ， 土木工程， 2010， 博士

【摘要】 损伤局部化现象是岩体破坏的开始,表现为岩体在经历一定的均匀变形后,突然进入局部化变形的阶段,它是岩体破坏的前兆。损伤局部化产生的主要原因是裂隙扩展到一定长度后裂隙的扩展状态发生分叉,一部分裂隙继续扩展,另一部分裂隙停止扩展。因此,研究裂隙岩体损伤局部化的起始条件和失稳模式,对于分析地下工程围岩稳定性具有重要的工程应用价值。本文依托国家自然科学基金项目(Nos.50778184,51078371)、教育部新世纪优秀人才支持计划(NCET-07- 0911)和重庆市杰出青年基金项目(No. CSTC, 2009BA4046),围绕岩体中裂隙扩展和连接等核心问题,对裂隙岩体动态损伤局部化的实验观察、损伤局部化临界条件及损伤演化数值模拟方法三个主要方面进行了研究。本文的主要研究内容如下:①采用多种试验手段和数据处理方法,测试了岩石断裂力学参数,分析了岩石动态损伤演化规律。首先,采用三点弯曲试验测试了岩石断裂韧度,分析了不同加载速率下岩石断裂韧度的变化规律。然后,基于单轴压缩应力应变关系,利用岩样体积应变与裂纹体积应变的关系得到了岩石启裂点,揭示了单轴压缩条件下岩石损伤演化规律。其次,采用图像增强与分割技术,分析了灰岩三轴压缩条件下损伤演化规律,从图像定量分析的角度探讨了CT扫描图像与损伤演化的关系。最后,采用霍普金森压杆研究了黄龙灰岩在应变率为15.2～124.3 s-1之间的动态应力应变关系,获得了黄龙灰岩动态损伤局部化的临界条件以及破坏特征。②利用伪力法考虑多裂隙之间的相互作用,获得了含周期型分布裂隙的岩体损伤局部化临界条件。通过对多裂隙扩展状态的分叉分析,不仅得到了裂隙岩体损伤局部化裂纹弯折扩展临界长度及临界应力,而且确定了裂隙岩体损伤局部化的位置。此外,本文还探讨了岩体的动态应力应变关系,通过参数敏感性分析获得了裂隙长度、列间距、行间距、裂隙表面摩擦系数、岩石断裂韧度、围压、裂隙扩展速率和原生裂隙倾角等参数对岩石损伤局部化起始条件及损伤局部化模式的关系。③基于扩展有限元法,建立了裂隙岩体多尺度损伤演化数值模型。裂隙岩体多尺度损伤演化数值模型可以有效的模拟不同尺度裂隙的相互作用、扩展和连接,而且还考虑了岩体动态卸荷的影响。本文建立的裂隙岩体多尺度动态损伤演化数值模型计算网格不需要与内边界(如裂隙和洞室)保持协调,而且采用结点位移投影法和边界位移加载法实现了不同尺度网格的平滑过渡,降低了网格划分的困难节约了大量的存储空间。利用裂隙岩体多尺度损伤演化数值模型分析了加载速率对岩石损伤局部化的影响,验证了多尺度网格之间误差可以满足工程要求。④基于Matlab平台编制了裂隙岩体多尺度动态损伤演化数值模型应用程序(MCWRM),该程序能够模拟不同尺度裂隙加载和卸荷、拉伸和压缩等不同工况下的损伤演化行为。详细说明了裂隙岩体多尺度损伤演化数值模型的程序的调用关系及计算流程,解决了多裂隙扩展过程连接处理和多尺度网格过渡等难题,最后通过算例验证了本文数值模型的可靠性。算例分析表明,MCWRM程序模拟结果与室内模型实验结果和理论计算结果吻合较好。⑤将裂隙岩体多尺度损伤演化数值模型分析程序(MCWRM)应用于模拟锦屏二级水电站引水隧洞围岩卸荷损伤演化过程,计算结果与弱单元法及室内模型试验结果吻合,表明本文建立的裂隙岩体多尺度损伤演化数值模型适用于分析裂隙岩体动态损伤演化过程。更多还原

【Abstract】 The phenomena of Damage localization, which characterized as the rock mass suddenly enter into the deformation localization stage after a period of uniform deformation, is the beginning of rock failure. Damage localization is also the precursor of rock failure. Damage localization mainly yielded by the bifurcation of crack growth pattern, which means some cracks go on propagating while others remian still. So, it is significant for the stability analysis of surrounding rock mass of underground projects to study the onset condition and bifurcation pattern of damage localization in crack weakened rock mass. Supporting by the National Natural Science Foundation of China (Nos.50778184, 51078371), the Program of New-Century Talents by the Ministry of Education (NCET-07-0911) and Natural Science Foundation Project of CQ CSTC (No. CSTC, 2009BA4046), this paper mainly focuses on the growth and coalescence of cracks in the rock mass. Three main aspects, which are experimental observations, onset condition for damage localization and numerical method for simulating the evolution of damage in crack weakened rock mass, are studied in this paper. The main work is summarized as follows:①Adopting multiple kinds of testing means and data processing methods, the fracture mechanic parameters are obtained and the rule of dynamic damage evolution of rock is analysed too. Firstly, the fracture toughness of limestone is tested by using three point bending experiments, the rate dependence of fracture toughness is also analysed. Secondly, based on the stress-strain relationship of rock sample under uniaxial compression condition, the initial point of crack growth is determined by using the relationship between the volume strains induced by rock matrix material and cracks respectively. Meanwhile, the rule of damage evolution of rock under uniaxial compression is revealed. Thirdly, utilizing the image enhancement and segmentation technology, the rule of damage evolution of limestone under triaxial compression condition is discussed. Moreover, quantitative analysis of CT image, the relationship between CT image and damage evolution is discussed. Last but not least, uniaxial impact-compressive loading tests of different strain rate (15.2~124.3 s-1) were produced in the split Hopkinson pressure bar (SHPB) on Huanglong limestone specimens, the dynamic stress-strain curves are obtained. The onset condition of damage localization and the failure characteristic are determined too. ②Taking into account of the interaction of multiple cracks by pseudo traction method, the onset condition for rock mass that contain periodic distribution cracks is obtained. By analyzing the bifurcation of crack growth pattern, not only the critical length and critical stress for damage localization of crack weakened rock mass are obtained, but also the location of damage localization is determined. In addition, the dynamic stress-strain relationship is discussed in this paper. Parameters sensitivity analysis is carried out, the effects of the length of crack, friction coefficient, fracture toughness, confining stress, velocity of crack growth, inclination and spacing between lines and rows on the onset condition for damage localization and bifurcation pattern of rock are discussed.③On the basis of eXtended Finite Element Method, a multiscale numerical model for simulating the process of damage evolution in crack weakened rock mass is proposed. This model can be used to simulate the interaction, growth and coalescence of multiple cracks, and the effects of unloading is also taken into account. The coordination between the internal boundary (such as cracks and holes) and mesh is not needed in this multiscale model. By combining the displacement projecting method and displacement loading method, the connection between different sizes of mesh behave smoothly. This multiscale model indeed surmounts difficulties in meshing and it really save the storage space. Moreover, the multiscale model is applied to analyse the dependence of damage localization on the loading rate. It is shown from examples that the error of this multiscale model can be accepted in engineering application.④Based on the platform of Matlab, a program for simulating the multiscale dynamic damage evolution in crack weakened rock mass is compiled (MCWRM). This program is suit for simulating multiscale damage evolution behaviors of rock mass under different loading state, such as unloading, tensile and compression. The calling relation of subroutines and calculation procedure of this multiscale model are detailly explained in this thesis. Fortunately, the difficulties of dealing with the crack coalescence and connection between different sizes of mesh have been overcomed. Some examples are carried out to test and verify the MCWRM program. The numerical simulation results that obtained by MCWRM show good agreement with experimental and theoretical results.⑤Finally, the MCWRM program is applied to simulate the damage evolution process when the tunnels is excavating in JinpinⅡHydropower Station. Comparison between the results obtained by MCWRM, weak element method and experimental results of similar specimens are executed in this paper. It shows that the results are realistic and the MCWRM fit for simulating damage evolution behaviors in crack weakened rock mass.更多还原