含缺陷砂岩单轴压缩裂纹类型及演化规律试验研究

Experimental study on the types and evolution of uniaxial compression cracks in defective sandstone

摘要

【目的】裂隙岩体在荷载作用下力学强度会发生劣化,易进一步引发岩石破裂,对岩体工程造成影响,分析含0°~90°缺陷砂岩单轴压缩下的声发射能量特征、主频变化及RA-AF值分布。【方法】基于声发射参数探究砂岩的破裂机制、裂纹类型及演化规律并结合扫描电镜探究断口细观形貌特征与宏观断裂之间的联系。【结果】缺陷的存在对砂岩的力学强度具有明显劣化作用,声发射能量的变化存在“波动期、平缓期、剧烈波动期、上升激增期”四个阶段,声发射参数AF主要分布在0~500 kHz之间, RA主要分布在0~2.0 ms·V^-1之间,砂岩破裂面断口分为拉裂断口、剪裂断口、拉剪复合型断口三种。【结论】(1)砂岩强度随着裂隙角度增加,整体上呈现增大的趋势;(2)裂纹演化过程可以分为:初始翼型张裂纹-复合类裂纹(0°~45°)→初始反翼型张裂纹-反翼型裂纹(60°~75°)→初始翼型张裂纹-二次翼型裂纹(90°);(3)主频信号中低频占71%~96%,高频占3%~23%,破坏过程主要产生大尺度裂纹;(4)张拉裂纹比例超过70%,剪切裂纹占比在20%附近波动,张拉破坏占主导地位;(5)砂岩破裂面断口以穿晶断裂(TG)为主的同时,伴随着沿晶断裂(IG),完整砂岩主要为穿晶张拉型断裂,含缺陷砂岩主要为穿晶拉剪复合型断裂,砂岩的宏观裂纹断裂形式与微观形貌特征存在对应关系。

Abstract

[Objective] The mechanical strength of the fractured rock body will be deteriorated under loading, which is easy to further trigger rock rupture and affect the rock engineering, and analyze the acoustic emission energy characteristics, the main frequency change and the RA-AF value distribution of the defective sandstone under uniaxial compression. [Methods] Based on the acoustic emission parameters, we investigate the fracture mechanism, crack type and evolution of sandstone, and combined with scanning electron microscopy, we investigate the connection between the fracture micro-morphological characteristics and the macro-fracture. [Results] The presence of defects has obvious deterioration effect on the mechanical strength of sandstone, the change of acoustic emission energy exists in four phases, namely, “fluctuation period, smooth period, violent fluctuation period,and upward surge period”, and the acoustic emission parameter AF mainly distributes in the range of 0~500 kHz, and RA mainly distributes in the range of 0~ 2. 0 ms·V^-1, and the fracture surface of sandstone is divided into three types: tensile fracture,shear fracture, and composite fracture of tension-shear type. The sandstone fracture is divided into three types: tensile fracture,shear fracture, and tensile-shear composite fracture. [Conclusion] (1) The strength of sandstone shows an overall increasing trend with the increase of fracture angle;(2) The crack evolution process can be divided into: initial wing tension crackcomposite type crack(0°~45°) → initial anti-wing tension crack-anti-wing crack(60°~75°) → initial wing tension cracksecondary wing crack(90°);(3) The main frequency signal accounts for 71%~96% of the low-frequency, and the highfrequency accounts for 3%~23%, and the damage process mainly produces large-scale cracks;(4) the proportion of tension cracks is more than 70%, the proportion of shear cracks fluctuates around 20%, and the tension damage is dominant;(5) the fracture of the rupture surface of the sandstone is dominated by transgranular fracture(TG) and accompanied by along-granular fracture( IG), and the intact sandstone is mainly transgranular tensile-type fracture, and defective sandstone is mainly transgranular tension-shear composite-type fracture The macroscopic crack fracture forms of sandstones and the microscopic morphologic features have a corresponding relationship.

关键词

单轴压缩 / 声发射 / 裂纹类型 / 演化规律 / 扫描电镜 / 影响因素 / 力学性能 / 砂岩

Key words

uniaxial compression / acoustic emission / fracture mechanism / crack evolution / scanning electron microscope / influencing factors / mechanicalproperties / sand stone

基金资助

国家自然科学基金项目(42007271)

贵州省科技支撑计划项目(黔科合支撑[2023]一般119)