饱水环境下脆性岩石介质损伤与破坏的微结构机理

The damage and failure of rocks were usually induced by the evolutions of microcracks embedded in rock materials. Considering that the recent micromechanical damage models for rocks can't well describe the micromechanism of microcracks, based on the analysis of the evolutions of microcracks, this research will investigate the micromechanism of damage and failure for water saturated rocks, and develop the three-dimensional macro-micromechanical damage model for brittle rocks. The deformation, growth, frictional sliding, kinked growth and coalescence of microcracks will be researched, and the corresponding growth criterion and coalescence criterion will be formulated. The mechanism of crack nucleation and the relation between the instable growth of macroscopic crack and the failure of materials will be researched. This research will investigate the effect of pore water pressure on the evolutions of microcracks. The three-dimensional micromechnical damage model which can describe the deformation, growth, frictional sliding, kinked growth, coalescence of microcracks, and the nucleation and growth of macroscopic crack will be constituted, and the corresponding calculation analysis code will be developed. This project could support a theoretical analysis method for the safety design in rock construction, such as the excavation of mountain and slope protection.

岩石介质的损伤与破坏行为与材料内部微裂纹的演化行为息息相关，针对现有的岩石细观损伤模型未能充分体现微裂纹的演化特性，本研究拟基于对椭圆形微裂纹的演化行为的分析，研究饱水条件下脆性岩石材料的损伤与破坏机理，建立岩石材料的三维宏细观损伤模型。研究椭圆形微裂纹的变形、扩展、摩擦滑移、偏折扩展以及微裂纹汇合规律，建立椭圆形微裂纹的扩展准则和汇合准则，研究宏观裂纹的萌生机制以及宏观裂纹的扩展、失稳与材料破坏的联系；研究孔隙水压对椭圆形微裂纹的多种演化行为的影响。建立能反映椭圆形微裂纹的变形、扩展、摩擦滑移、偏折扩展、汇合以及宏观裂纹的萌生、扩展的岩石材料三维宏细观损伤模型，并开发相应的数值计算程序，为山体开挖、边坡维护等岩土工程中的岩体安全设计提供理论分析依据。

岩石损伤及破坏与微裂纹的演化行为密切相关。本项目基于岩石内部椭圆形微裂纹的变形及演化行为，研究了脆性岩石介质损伤及破坏的细观机理。开展了自然状态和饱水状态下砂岩的单轴压缩实验，开展了饱水状态下和水渗流条件下砂岩的三轴压缩实验，实验结果表明围压/孔隙水压能显著提高/降低砂岩的抗压强度和刚度。考虑孔隙压力对微裂纹张开和摩擦滑移的影响，建立了椭圆形微裂纹的扩展准则和汇合准则，发展了微裂纹偏折扩展的计算方法，建立了脆性岩石介质的三维细观损伤模型。围压能极大地降低微裂纹的驱动应力，从而显著提高岩石强度；而孔隙压力则减小微裂纹的驱动应力，降低岩石强度。将理论模型嵌入有限元程序，开展了有限元模拟。基于Mori-Tanaka方法建立了能考虑微裂纹相互作用的三维细观损伤模型。微裂纹张开时的微裂纹相互作用比闭合时更明显，当考虑微裂纹扩展时微裂纹作用的效果随着应力水平的提高而明显增强。提出了一种微裂纹间距参数，计算结果表明当间距参数大于3时无需考虑微裂纹相互作用，而小于2时则需要分析微裂纹相互作用对岩石变形的影响。