单轴压缩砂岩细观裂纹动态演化特征试验研究

岩石细观裂纹的动态演化特征作为岩石破坏的重要信息,其研究对于分析岩爆的孕育过程及预测岩石动力灾害发生有着重要意义。采用应力分析和声发射参数方法,研究了砂岩在单轴压缩条件下的细观裂纹的强度动态演化特征。试验结果表明,应力与砂岩细观裂纹扩展诱发声发射（AE）事件的强度特征有较好的阶段性变化规律,将峰前裂纹动态演化划分为三个阶段。进一步分析裂纹的类型特征,提出三阶段四维演化过程分析方法。细观裂纹多为张拉型,随着时间的增加,细观裂纹向剪切型裂纹转变,裂纹数量迅速增加,裂纹强度逐渐增大。提出将第三阶段AE事件出现的高强度、高RA、低AF特征作为砂岩破裂失稳的定性预警条件。通过矩张量反演对比分析了的细观裂纹数量和类型的动态演化。     

Crack evolution of soft–hard composite layered rock-like specimens with two fissures under uniaxial compression

Acoustic emission and digital image correlation were used to study the spatiotemporal evolution characteristics of crack extension of soft and hard composite laminated rock masses (SHCLRM) containing double fissures under uniaxial compression. The effects of different rock combination methods and prefabricated fissures with different orientations on mechanical properties and crack coalescence patterns were analyzed. The characteristics of the acoustic emission source location distribution, and frequency changes of the crack evolution process were also investigated. The test results show that the damage mode of SHCLRM is related to the combination mode of rock layers and the orientation of fractures. Hard layers predominantly produce tensile cracks; soft layers produce shear cracks. The first crack always sprouts at the tip or middle of prefabricated fractures in hard layers. The acoustic emission signal of SHCLRM with double fractures has clear stage characteristics, and the state of crack development can be inferred from this signal to provide early warning for rock fracture instability. This study can provide a reference for the assessment of the fracture development status between adjacent roadways in SHCLRM in underground mines, as well as in roadway layout and support.     

Experimental investigation on fracturing process of marble under biaxial compression

In this study, servo-controlled biaxial compression tests were conducted on marble specimens to investigate their failure characteristics and fracturing process. The complete stress–strain curves were obtained, and the three-dimensional (3D) features of the failure surfaces were acquired by 3D laser scanning. Acoustic emission (AE) monitoring and moment tensor (MT) analysis were used in combination to better understand the fracturing mechanism of marble under biaxial compression. It was noted that a type of 3D stepwise cracking behaviour occurred on the fracturing surfaces of the examined specimens. The stress dropped multiple times, and a repeated fracturing mode corresponding to the repeated stress drops in the post-peak regime was observed. Three substages, i.e. stress stabilisation, stress decrease and stress increase, were identified for a single fracturing mode. Then quantitative and statistical analyses of the fracturing process at each substage were discussed. Based on the testing results, it was found that at the stress stabilisation substage, the proportion of mixed-mode fractures increased. At the stress decrease substage, the proportion of mixed-mode fractures decreased, and the tensile or shear fractures increased. At the stress increase substage, the proportion of mixed-mode or tensile fractures decreased, and the shear fractures increased. Finally, a conceptual model for the stepwise crack formation was proposed.     

Experimental investigation of the mechanical behaviors and energy evolution characteristics of red sandstone specimens with holes under uniaxial compression

Bulletin of Engineering Geology and the Environment - To explore the mechanical behaviors and energy evolution characteristics of rock materials with hole defects, eight types of red sandstone...     

含双圆形孔洞砂岩单轴压缩力学特性试验研究

孔洞作为岩石内部微缺陷的基本形式之一,其破裂演化机制是岩石力学领域研究的重要课题。对预制双圆形孔洞的板状砂岩试样进行室内单轴压缩试验,研究孔心距2b和倾角?对砂岩强度、变形特征及破裂演化过程等的影响规律。试验结果表明:随孔心距2b的增大,试样的峰值强度和弹性模量均表现为先增大后又减小的特征,孔心距2b分别为22 mm和27 mm时峰值强度和弹性模量达到最大值;随倾角?的增大,峰值强度和弹性模量整体表现为先减小后增大的趋势,倾角?等于60°时峰值强度和弹性模量达到最小值。双圆形孔洞的初始破坏均表现为孔洞内壁塌落破坏,而孔心距2b和倾角?对起裂应力水平、孔洞搭接方式及破裂演化过程均具有重要的影响。     

单轴加载条件下花岗岩声发射及波传播特性研究

 采用声波、声发射一体化装置,研究单轴压缩下花岗岩波速与声发射演化规律,通过宏细观方法确定各应力门槛值,研究裂纹扩展不同阶段声发射演化及波传播规律。结果表明：细观裂纹的演化与宏观变形直接对应,由于微裂纹主要沿轴向扩展,导致轴向刚度对裂纹起裂及贯通的敏感度弱于非线性增长的侧向变形,瞬时泊松比曲线斜率变化点与应力门槛值对应,声发射测试确定的起裂应力比宏观应变法偏小,但反映了微裂纹的初始萌生;采用实测波速变化分析声发射震源的时空及幅值演化分布,较好地描绘了裂纹的扩展过程,由于不同阶段声发射信号的幅值及能量存在差异,导致声发射特征参数演化规律差异较大(尤其在损伤应力之后),AE能量在破坏前呈突发性增长,可作为灾害性破坏的前兆;加载初始阶段,由于微裂隙的闭合,波速及波幅均随应力逐渐增大,但增加速率逐渐下降,侧向波速在闭合应力附近基本达到峰值,此后一定阶段基本保持不变,但其他方向波速则继续增大,随着波传播方向与径向夹角的增大,波速增加幅度及波速下降点对应的应力(损伤应力前、后)逐渐增大,峰值应力附近对应波速下降幅度减小;波速受损伤演化的影响要滞后于声发射事件。     

高温后砂岩单轴压缩加载速率效应的试验研究

温度是影响岩石材料物理力学性质的重要因素,为考察温度对砂岩加载速率效应的影响规律,对25℃～800℃之间6种温度水平后的砂岩试样分别进行不同加载速率下的单轴压缩试验。试验结果表明：① 高温后砂岩的物理性质出现一定的劣化,由25℃升高至800℃,密度和纵波波速分别减小了5.89%和73.72%;② 随着温度的升高,砂岩峰值强度和弹性模量逐渐减小,峰值应变逐渐增大,而峰值强度随温度的变化过程受加载速率的影响较大;③ 高温后砂岩的峰值强度和峰值应变具有明显的加载速率效应,且服从正线性关系,相关性参数A表征了材料受加载速率影响的显著程度,随着温度的升高参数A呈现先减小后又增大的趋势;④随着温度和加载速率的增大,砂岩破坏形态由拉剪混合破坏逐步转化为单一斜剪破坏,破坏程度愈渐剧烈,分形维数也逐渐增大。     

岩石单轴压缩下损伤表征及演化规律对比研究

采用声波、声发射一体化装置同步测试单轴压缩下花岗岩应力应变、超声波及声发射(AE)特征演化规律,分析岩石特征应力对应的宏–细观表征,通过裂纹体积应变、声发射及声波特征等共同量化岩石损伤演化过程。结果表明:裂纹体积应变和波速对应的损伤起始应力吻合较好,AE事件、幅值分布、b值对应的应力特征值基本一致,但AE事件表征的损伤累积开始早于宏观变形和声波;初始加载阶段波速及各项异性系数K均逐渐增加,之后变化趋缓,起裂应力后侧向波速开始减小,而K逐渐增大;峰值应力前裂纹的快速聚结引起AE信号幅值大幅增加,伴随的是b值的快速下降和AE累积能量的陡增;基于起裂应力后损伤才开始累积的假定,量化并对比了裂纹体应变、AE事件等多参量表征的损伤演化规律,发现花岗岩损伤累积绝大部分发生在损伤应力之后。裂纹体应变表征的损伤具有明确物理意义,但裂纹体应变计算中泊松比选取存在一定主观性,裂纹体应变、AE能量、模量等参数表征的损伤在接近峰值应力前均出现大幅增加,与b值的快速下降对应。综合对比分析,AE能量表征的损伤具有更好的可靠性,反映了岩石损伤破裂的本质特征。     

Mechanical behaviours of sandstone containing intersecting fissures under uniaxial compression

Predicting rock cracking is important for assessing the stability of underground engineering. The effects of the intersecting angle α and the distribution orientation angle β of intersecting fissures on the uniaxial compressive strength and the failure characteristics of sandstone containing intersecting fissures are investigated through laboratory experiments and two-dimensional particle flow code (PFC2D). The relationship between the mechanical properties of sandstone and the intersecting angle α and the distribution orientation angle β is analysed. Crack initiation forms and the final failure modes are then categorised and determined via empirical methods. In addition, the cracking processes of intersecting fissures with different α and β values are discussed. The results show that variations in the peak stress, peak strain, average modulus, and crack initiation stress of sandstone containing intersecting fissures show a “moth” shape in the space of the α-β-mechanical parameters. Two crack initiation forms are identified: inner tip cracking (usually accompanied by one outer tip cracking) and only outer tips cracking. Two failure modes are observed: (1) the main fracture planes are created at the inner tip and one outer tip, and (2) the main fracture planes are formed at the two outer tips. Two main crack evolution processes of sandstone containing intersecting fissures under uniaxial compression are found. Approaches for quickly determining the crack initiation form and the failure mode are proposed. The combination of the determination equations for the crack initiation form and the failure mode can be used to predict the crack evolution. The approach for determining the crack evolution processes is hence proposed with acceptable precision.     

单轴压缩下填充含缺陷砂岩力学性能试验研究

通过单轴压缩试验,对含孔洞砂岩岩样及充填含孔洞砂岩岩样进行了研究,并从裂纹扩展角度,阐释了填充含缺陷砂岩力学性能的变化规律,得出了一些有意义的结论,为同类问题的研究提供了依据。     

基于EMD的粉砂岩单轴压缩破裂损伤分析

通过RMT-150C岩石力学测试系统与SAEU2S型声发射仪器,对粉砂岩进行了单轴压缩声发射试验。运用荷载—时间—振铃累计计数关系对岩样损伤阶段进行划分,利用经验模态分解法(EMD)对不同损伤阶段的典型信号源进行了分解,并结合EMD能量熵分析声发射信号能量分布,进而对岩体损伤阶段进行描述。结果表明,粉砂岩单轴压缩破裂可分为起始损伤期、损伤发展期、损伤加剧期、试件屈服期及试件断裂层剥离期五个阶段,其EMD能量熵主要能量所占优势频率分布情况呈现先往高频发展、再往低频发展的趋势。利用EMD能量熵能有效分辨岩样损伤过程中的声发射源信号特征,为评估岩体损伤变化奠定了基础。     

砂岩裂纹起裂损伤强度及脆性参数演化试验研究

岩石起裂强度σci及损伤强度σcd作为岩石重要的强度特征值,其研究对于分析岩石的渐进破坏过程及预测隧洞脆性破坏有着重要意义。首先采用应变分析及声发射监测方法,研究了两组硬质砂岩试样在单轴及三轴压缩过程中的裂纹演化特征。试验结果表明,试样的侧向膨胀变形及声发射计数值可以较好地反映其内部的裂纹演化情况,二者随着裂纹的萌生积累都表现出一致的阶段性变化规律。同时通过进一步分析应变及声发射曲线中的阶段性变化拐点,确定了砂岩试样的起裂强度及损伤强度值。其中青砂岩平均起裂强度约为其峰值强度的0.42倍,红砂岩平均起裂强度则约为其峰值强度的0.48倍。最后通过对比不同围压下的试验结果,发现两组砂岩试样起裂阶段内摩擦角均小于其峰值阶段,初始φ0约为终值的1/2。由此定义了可反映岩石脆性程度的起裂摩擦水平φ_0/φ,并建立考虑摩擦作用的线性起裂准则。     

单轴压缩下非贯通节理岩体损伤破坏能量演化机制研究

能量的积聚与释放伴随发生在节理岩体受荷变形全过程。为探寻加载过程中节理岩体能量演化规律,基于单轴压缩试验及岩石能量原理,研究非贯通节理岩体变形破坏过程中总能量U、弹性应变能U~e及耗散能U~d的转化特征,揭示节理岩体损伤破坏能量演化机制,建立了基于弹性能耗比变化率(dK/dε)的非贯通节理岩体裂缝扩展及强度失效准则。研究表明:节理存在对岩体中能量的存储具有明显的削弱作用,峰值点总能量与弹性应变能随节理数量的增加逐渐减小;节理岩体的弹性应变能U~e及耗散能U~d变化曲线存在"阶梯状"突减或突增,双节理岩样弹性应变能和耗散能突增或突减的数值明显小于单节理岩样;峰前与峰后阶段弹性能耗比变化率发生连续突变(dK/dε正负交替变换)与突变(dK/dε保持为正无穷)作为节理岩体裂缝扩展及强度失效判据。     

Deformation and failure characteristics of sandstone under uniaxial compression using distributed fiber optic strain sensing

This paper investigates the deformation and fracture propagation of sandstone specimen under uniaxial compression using the distributed fiber optic strain sensing (DFOSS) technology. It shows that the DFOSS-based circumferential strains are in agreement with the data monitored with the traditional strain gage. The DFOSS successfully scans the full-field view of axial and circumferential strains on the specimen surface. The spatiotemporal strain measurement based on DFOSS manifests crack closure and elastoplastic deformation, detects initialization of microcrack nucleation, and identifies strain localization within the specimen. The DFOSS well observes the effects of rock heterogeneity on rock deformation. The advantage of DFOSS-based strain acquisition includes the high spatiotemporal resolution of signals and the ability of full-surface strain scanning. The introduction to the DFOSS technology yields a better understanding of the rock damage process under uniaxial compression.     

Fatigue properties of intact sandstone samples subjected to dynamic uniaxial cyclical loading

In this paper, the fatigue behaviour of intact sandstone samples obtained from a rockburst prone coal mine and studied under dynamic uniaxial cyclic loading in the laboratory is presented. Tests were conducted on dry and saturated samples with loading frequencies ranging from 0.1, 1 and 10 Hz and amplitudes of 0.05, 0.1 and 0.15 mm. From the laboratory investigations, it was found that the loading frequency, as well as the amplitude, was of great significance and influenced the rock behaviour in dynamic cyclic loading conditions. The dynamic fatigue strength and the dynamic axial stiffness of the rock reduced with loading frequencies and amplitude. The dynamic modulus was found to increase with the loading frequency but decrease with the amplitude. In the case of the saturated samples, it was found that the dynamic fatigue strength reduced by approximately 30 per cent, while the dynamic Young's modulus reduced by about 20 per cent. From the presented study, the dynamic energy was found to be independent of the testing conditions while other rock properties were found to be dependent on these. Finally, it was concluded that rock would more readily succumb at low frequencies and amplitude than at high frequencies and amplitude for a given energy availability.     

标准钢筋混凝土三点弯曲梁双K断裂特性试验研究

为研究缝高比对钢筋混凝土起裂韧度、失稳韧度等断裂参数的影响,以及钢筋在混凝土裂缝扩张过程中对裂缝的限制作用,设计制作了4组初始缝高比分别为0.2、0.3、0.4、0.5的标准钢筋混凝土三点弯曲梁,对其进行了断裂性能试验研究。根据试验现象分析了裂缝扩展过程,在此基础上建立了断裂韧度计算模型,给出了考虑钢筋限裂作用后的有效裂缝长度计算式。研究结果表明：在引入适应于钢筋混凝土的断裂韧度后,其裂缝扩展过程也可以用双K断裂准则来描述;当试件的初始缝高比大于或等于0.4时,钢筋混凝土三点弯曲梁的起裂断裂韧度和失稳断裂韧度与初始缝高比无关;声发射参量可以准确地确定试件的起裂荷载值,而且与传统的应变片法相比,声发射信号能更好地反映试件内部真实的起裂状态。     

单轴加载下热处理混凝土声电信号特征

为研究火灾发生后混凝土力学性能变化及结构失稳的前兆特征,对混凝土试样进行20、100、200、300、400 ℃的热处理,并进行单轴压缩实验,监测试样受载破坏过程的声电响应信号,识别结构失稳的前兆特征。结果表明：高温热处理后,混凝土试样的外观颜色、内部结构及力学性质均发生了变化,且目标温度越高,试样外观的色变越显著,裂隙发育越丰富,峰值应力越低,而峰值应变越高;随着目标温度的增高,声发射信号和表面电位信号更加活跃,且两种信号的响应与裂纹的扩展密切相关,能够反映试样内部结构损伤演化的过程;对声发射及电位的时序信号进行变异性系数统计,结果表明声发射的变异性系数在试样受载过程中相对稳定,并在试样失稳前具有快速增大至峰值的异常响应,可作为判断试样结构稳定性的前兆。相比声发射信号,电位信号的变异性特征在试样受载初期处于较高值,随后下降,并在试样失稳前快速增大至峰值。     

单轴压缩下大理岩细观裂纹扩展试验研究

利用带有加载装置的扫描电镜（SEM）实时动态观测系统和数字图像处理技术,对大理岩试件在受单轴压缩时所产生的微裂纹的萌生、扩展过程进行了定量分析,得到微裂纹扩展的规律,对岩石力学研究有一定的理论意义。