热应力作用下的岩石破裂过程分析

热应力引起的岩石破裂称为岩石的热破裂，它是热和力之间相互耦合作用的结果。岩石热破裂研究的工程意义重大。根据岩体介质变形及其热力学的理论基础，充分考虑岩石的非均匀性和热固耦合作用，在原有的岩石破裂过程分析系统的基础上，建立了具有热固耦合作用的岩石热破裂分析模型。数值模型再现岩石的热破裂过程，并反映岩石热破裂的规律。运用数值模型，对含有单个内嵌颗粒的岩石试件在温度变化过程中的热开裂进行了数值模拟。研究结果表明：在温度升高过程中，如果内嵌颗粒的热膨胀系数大于基质的热膨胀系数，在基质内产生径向裂纹；如果内嵌颗粒的热膨胀系数小于基质热膨胀系数，便在基质内产生环向裂纹。数值模拟结果与试验结果有较好的一致性。RFPA^2D-thermal模型为从细观力学角度上分析岩石的热破裂过程和机制提供了一种新的方法。     

随机非均质热弹性力学模型与岩石热破裂门槛值的数值试验研究

考虑岩石细观组构的不同，建立了随机非均匀介质的热弹性力学模型，给出了一般意义下的有限元分析方法。进而，仅考虑热膨胀系数为随机变量，在平面应力模型下，进行了岩石热破裂的数值试验，以花岗岩为样本，对均匀分布、正态分布、韦泊分布3种随机分布下热膨胀系数变化引起的岩石破裂门槛值的变化做了详细研究。结果表明，热膨胀系数的概率分布形式对花岗石热破裂规律及门槛值温度有重要影响。     

升温和降温对无约束花岗岩热破裂的影响

温度变化会引起岩石内部矿物颗粒膨胀(收缩)不均匀,发生热破裂。温度变化有温度升高和降低两种作用方式,本文通过无约束花岗岩在升温和降温两种温度作用方式下的热破裂声发射实验研究,得到如下结论:(1)花岗岩升温过程中热破裂主要表现为中高温弹塑性破裂;降温过程中热破裂主要表现为中低温脆性破裂;(2)升、降温过程岩石的热破裂机理不同,升温过程主要为压缩热应力集中形成的压剪破裂,降温过程主要为局部拉应力集中造成的拉剪破坏;(3)根据声发射特征参数统计分析,同等温度范围内,岩石降温过程的热破裂声发射事件频度和强度均高于升温过程,约为2倍,降温过程的热破裂比升温过程剧烈。     

北山花岗岩细观非均质性对单轴压缩力学特性影响的FDEM数值研究

为了研究细观非均质性对北山花岗岩中微裂纹萌生、扩展和贯通等破裂过程的影响,基于有限元/离散元耦合方法(FDEM)和数字图像处理技术(DIP),结合矿物晶体模型(GBM),分别构建3类北山花岗岩细观结构表征模型：聚类均布模型、Voronoi颗粒模型和聚类镶嵌模型。基于3类模型开展了单轴压缩试验研究,探究细观非均质性对北山花岗岩力学特性、声发射(AE)特征以及颗粒尺度裂纹扩展规律的影响。研究结果表明：3类模型均能捕获从微破裂损伤至宏观破裂的演化过程,即首先以晶间张拉裂纹为主,随后产生穿晶断裂,转变为以晶内裂纹为主,张拉破坏占主导地位;细观结构表征方式对模拟岩石的特征应力(启裂应力和损伤应力)控制效应非常显著;Voronoi颗粒模型和聚类镶嵌模型的AE特征与室内试验更为吻合;硬矿物含量的增大,会导致单轴抗压强度、特征应力和弹性模量增大,而泊松比反之;颗粒尺寸的增大,会导致单轴抗压强度和损伤应力明显减小;特征应力与刚度非均质性因子呈负相关。     

高放废料地质处置中多场耦合作用下的岩石 破裂问题

 综述岩石力学中热–水–力耦合模型的研究进展,认为在热–水–力耦合作用下的岩石(岩体)破裂过程演化将直接影响高放射性废料地质处置库周围围岩的热力学特性、渗流特性和力学稳定性,进而影响高放射性核素在围岩中的迁移规律。通过建立一种描述热–水–力耦合条件下岩石破裂演化过程的细观力学模型,来揭示热–水–力耦合条件下宏观岩体结构破坏行为。计算分析结果表明,这种模型对于高放废料地质处置的可靠性分析具有重要的科学价值及现实意义。     

随机介质固热耦合数学模型与岩石热破裂数值实验

对高放射性核废料的深层处置、高温岩体地热资源开发等深部开采工程问题中,由于岩石材料的非均匀性、非连续性、以及几何结构的复杂性,迫切需要研究工程围岩在高温下的物理力学性质和力学行为的长期演变规律,因此,本文从岩石介质的非均匀性特征入手,在引入岩石非均匀性细观统计描述和物理学愈渗理论的基础上,主要研究内容如下:(1)考虑岩石颗粒的物理力学性质的随机非均匀性,从理论上建立了三维随机非均质热弹塑性力学模型和随机介质固热耦合数学模型,并推导随机介质模型的有限元数值解法。这些方法奠定了岩石热破裂研究的基础。(2)对岩石随机介质的热弹性力学模型的平面轴对称问题和球对称问题分别进行解析分析,提出了将岩石物理力学参数作为随机变量在解析分析中的处理方法,并给出在随机指数分布和韦泊分布下的解析解;对随机介质固热耦合数学模型的平面轴对称问题也求出了解析解,包括位移、变形和热应力的精确解。(3)在二维随机非均质热弹塑性力学模型和4种随机分布(均匀分布、指数分布、正态分布和Weibull分布)下,在高温条件下,对热膨胀系数变化引起的岩石破裂门槛值温度的变化做了详细研究,揭示了岩石热破裂规律及门槛值温度随分布参数的变化规律,得出结论:岩石热破裂门槛值温度随分布参数的增加而升     

不同冷却模式下花岗岩强度对比与热破坏能力表征试验研究

不同冷却模式下热对花岗岩的破坏能力不同,其细观破裂程度和宏观力学特性表现也不同。在20℃空气中自然冷却和20℃恒温水中热冲击急剧冷却2种模式下花岗岩单轴抗压强度和表面降温规律的对比试验研究的基础上,引入"热冲击因子",建立不同冷却介质环境下热传递数值模拟方法,从传热角度探究不同冷却介质对花岗岩强度劣化机制,找到能够清晰描述热对岩石破坏能力的物理量,从而对热的破坏能力做进一步的定量划分。研究结果表明:(1)2种冷却模式下,因热冲击急剧冷却模式的换热系数远大于自然冷却的换热系数,热冲击因子数值变大,动态热应力相应也随之变大,试件内部破裂严重,裂隙密度增多,力学强度劣化更严重;(2)20℃恒温水中热冲击冷却模式下,花岗岩的抗压强度仅为20℃空气中自然冷却模式下的抗压强度的85%~90%;(3)不同冷却模式下热传递过程中,花岗岩试件内部形成的温度梯度、热冲击因子、热应力的演化过程和规律一致,其最大值总是出现在靠近试件表面的位置;(4)热冲击因子能较好地表征热破坏能力,花岗岩的单轴抗压强度与最大热冲击因子具有很好的相关性;(5)根据热冲击因子的演化规律,可以确定花岗岩试件内部破裂最严重的具体时间,热冲击因子可以实现对热破坏能力的定量表征。     

非均质细胞元随机分布对高温岩石介质中裂纹扩展影响的数值试验研究

在平面应变模型下,以花岗岩为样本,采用随机介质固热耦合数学模型及有限元方法进行了高温岩石介质中裂纹扩展影响的数值试验研究。在指数分布、韦泊分布2种随机分布和温度的作用下,研究了材料非均质性对岩石介质中裂纹扩展的影响,并对岩石热破裂做了详细研究,揭示了概率分布形式、分布参数.时间与花岗岩样本的热破裂过程的变化规律。     

三类岩石热损伤力学特性的试验研究与细观力学分析

 运用偏光显微技术,比较不同温度处理后砂岩、花岗岩和大理岩微观结构的不同变化特征。分析对比常温～800 ℃高温处理后三类岩石纵波波速、孔隙率、弹性模量、峰值应力及应变的变化规律,并讨论其与微观结构变化的内在联系。结合岩石热损伤后初始损伤程度增大、微裂纹刚度弱化及张开度增大等特征,采用细观损伤力学模型研究热损伤岩石应力–应变曲线显著的非线性特征。研究结果表明：(1) 热处理砂岩细观结构的变化主要表现为胶结物变化及矿物相变,矿物内无明显热裂纹发育;热处理花岗岩内热裂纹发育明显,800 ℃处理后最大裂纹宽度可达100 ?m,较400 ℃时增加约1个数量级;大理岩热裂纹以晶界裂纹为主,600 ℃处理后最大裂纹宽度达20 ?m,约为400 ℃时的2倍。(2) 花岗岩和大理岩的弹性模量随热处理温度的增大持续降低,但砂岩的弹性模量在500 ℃热处理温度阈值之后才显著下降。(3) 三类热损伤岩石的宏观物理力学性质与其形成条件、矿物组分、微裂纹发育密切相关。(4) 基于均匀化理论的细观损伤力学模型的计算值与试验值吻合良好,热损伤岩石应力–应变曲线初始压密阶段显著延长的力学行为与微裂纹密度和刚度直接相关。     

热–水–力耦合作用下结晶岩渗透特性演化模型

在热力学框架下,采用细观力学方法,建立热–水–力(THM)耦合条件下低渗饱水结晶岩的各向异性损伤模型,考虑非等温条件下微裂纹水压力作用、法向刚度恢复以及滑动剪胀等细观力学机制对岩石宏观力学性能的影响。在此基础上,采用均匀化方法,建立各向异性损伤诱发的岩石有效渗透特性演化模型,指出损伤岩石有效渗透特性下限估计模型的局限性,进而给出可反映损伤演化过程中微裂纹连通性等细观结构特征的岩石有效渗透特性上限估计模型。采用三轴压缩过程中花岗岩的渗透率变化、高温热处理后花岗岩的单轴压缩性能、TSX巷道开挖产生的围岩损伤与渗透率变化等室内外试验成果对模型进行验证。     

A novel true triaxial test system for microwave-induced fracturing of hard rocks

This study introduces a test system for microwave-induced fracturing of hard rocks under true triaxial stress. The test system comprises a true triaxial stress loading system, an open-ended microwaveinduced fracturing system, a data acquisition system, an acoustic emission(AE) monitoring system, and an auxiliary specimen loading system. Microwave-induced surface and borehole fracturing tests under true triaxial stress were fulfilled for the first time, which overcomes the problem of microwave leakage in the coupling loading of true triaxial stress and microwave. By developing the dynamic monitoring system, the thermal response and fracture evolution were obtained during microwave irradiation. The monitoring system includes the infrared thermometry technique for monitoring rock surface temperature, the distributed optic fiber sensing technique for monitoring temperature in borehole in rock, the AE technique and two-dimensional digital speckle correlation technique for monitoring the evolution of thermal damage and the rock fracturing process. To validate the advantages of the test system and investigate the characteristics of microwave-induced fracturing of hard rocks, the study demonstrates the experimental methods and results for microwave-induced surface and borehole fracturing under true triaxial stress. The results show that thermal cracking presented intermittent characteristics(calm eactiveecalm) during microwave-induced surface and borehole fracturing of basalt. In addition, true triaxial stress can inhibit the development and distribution of thermal cracks during microwave-induced surface fracturing. When microwave-induced borehole fracturing occurs, it promotes the distribution of thermal cracks in rock, but inhibits the width of cracks. The results also prove the reliability of the test system.     

热力耦合作用下花岗岩流变模型的本构关系研究

 热力耦合作用下岩石的微观结构的变化是引起宏观力学变化的主要原因,从热力耦合作用下花岗岩的流变机制研究出发,建立热力耦合作用下花岗岩的流变模型,从而推导流变本构方程是一种可行的方法。通过热力耦合作用下花岗岩的流变机制研究可知：(1) 花岗岩是一种由多种成分构成的具有多晶复合介质特点的脆性坚硬岩石,具有很大的非均质性,内部微观结构可分为晶粒、晶粒边界、晶间胶结物及晶间孔隙,这样的组分和结构将决定花岗岩在热力耦合作用下的流变特性。(2) 热力耦合作用下花岗岩流变现象主要是热力耦合作用下岩体内晶间胶结物及晶粒内部产生的位错及微破裂过程,即温度产生的热破裂和应力产生损伤破裂的复合破裂过程,微观结构上的变化使得标志着热力耦合作用下宏观力学特性的力学参数成为温度的函数。因此,将岩石现象流变学与物理流变学结合起来,提出热力耦合作用下岩石热黏弹塑性流变元件力学元件,在广义西原模型的基础上建立热力耦合作用下花岗岩流变模型,推导出可描述150 MPa及600 ℃以内花岗岩的流变本构方程,用试验结果验证了其适用性和合理性。热力耦合作用下花岗岩流变模型的本构方程的建立为高温岩体地热开发钻井施工及其稳定性研究提供了依据。     

甘肃北山地区深部花岗岩的热开裂试验研究

 通过岛津SEM全数字液压高温疲劳试验系统,实时观察不同温度下北山花岗岩的热开裂过程,获得北山花岗岩的热开裂临界温度为68 ℃～88 ℃。在较低温度时,北山花岗岩热开裂以沿颗粒热开裂为主;在较高温度时,热开裂以穿颗粒热开裂及沿颗粒穿颗粒混合热开裂为主。热开裂不仅受到矿物颗粒的热膨胀性质不匹配及热膨胀各向异性的影响,还受到矿物颗粒的物理、力学、热学性质及矿物颗粒形状结构的影响。而花岗岩内流体包裹体也可能是影响北山花岗岩热开裂的一种重要因素,这是种新的影响机制。在微细观层次对热开裂模式进行分类,并由热开裂的分形模型定量解释沿颗粒和穿颗粒热开裂等发生的难易程度。当温度升高超过250 ℃时,北山花岗岩有可能存在热熔效应,这导致热开裂裂纹数有减少趋势,并且温度与其对应的热裂纹数量的统计关系符合Gauss曲线关系。     

Influence of stress-induced and thermal cracking on physical properties and microstructure of La Peyratte granite

New data are presented on the influence of thermal cracking and stress-induced cracking on several physical properties (porosity, acoustic velocity, attenuation, electrical conductivity, permeability) of a fine-grained granite from La Peyratte, France. Two sets of samples were studied: the `TC' set was made of samples in which thermal cracking was induced, the `MC' set included samples in which cracks were generated at increasing stress levels in mechanical tests. Good correlations were found between the evolution of the physical properties and the amount of damage induced. For the mechanical cracking process, we show that acoustic emissions recording was the key point in order to control in real time the evolution of the cracking processes. The strong anisotropy in the acoustic velocity data found only in the MC samples is clearly due to the anisotropy of the crack distribution, as shown by microstructure analyses and 3D reconstructions of crack networks from confocal scanning laser microscopy images. A model for the propagation of elastic waves in cracked solids was used in order to infer the crack density and the mean crack aspect ratio for the granite samples. Our results show that the aspect ratio of artificially induced cracks is significantly smaller than that of cracks in `natural' rocks. Network modelling for fluid flow in porous media was done using data from mercury injection tests and available information on the crack network geometry as input data. Although the numerical model gives the correct order of magnitude for the permeability, it could not account for relative permeability evolution with induced damage, presumably because of oversimplified assumptions in the model. All in all, our study confirms the strong control of the rock microstructure on physical properties. The data set presented in this paper might be very useful for studies on safety assessment for potential nuclear waste storage in geological environment.     

Effect of rock mechanical properties on electromagnetic radiation mechanism of rock fracturing

The influence of rock mechanical properties on the electromagnetic radiation(EMR) mechanism of rock fracturing is an important research topic in solid mechanics and earthquake prediction.In this study,an EMR model of rock fracturing considering the fracture factor,elastic modulus,Poisson's ratio,radiation distance and crack length is derived based on the Hertz oscillator array assumption.An experimental system,including an electromagnetic shielding module,an EMR signal induction and transmission module,a signal recording module and a loading module,is developed to understand the EMR characteristics of four different rocks.The validity of the EMR theoretical model is verified and the relationships between the rock cracking morphology and the EMR waveform,amplitude and frequency are revealed.It is found that rock mechanical properties have obvious influences on the EMR waveform,amplitude and frequency during rock fracturing.This study provides a better understanding on the EMR mechanism of rock fracturing and can help to improve the accuracy of rock disaster prediction based on EMR.     

Assessment of excavation damaged zone using a micromechanics model

It is well known that acoustic emission (AE) and microseismic (MS) events are indicators of rock fracturing or damage as the rock is brought to failure at high stress. By capturing the microseismic events, underground excavation induced rock mass degradation or damage can be located. The use of microseismic method has been shown as a valuable tool in a number of nuclear waste repository research programs to monitor the extent of the excavation damaged zone (EDZ), but most of the works are limited to a qualitative assessment.This paper presents a study on the quantification of the degree of damage, in terms of crack density calculated from the crack length, and the extent, in terms of crack density distribution, from microseismic event monitoring data. The approach builds on the finding that a realistic crack size corresponding to a microseismic event can be established by applying a tensile cracking model instead of the traditional shear model, commonly used in earthquake data analysis. It can be shown that brittle rock failure is the result of tensile crack initiation, propagation, accumulation, and interaction. Tensile stress can be generated in a confined rock with heterogeneous material properties. When a crack is formed by tensile cracking in this fashion, its orientation tends to become parallel to the direction of maximum compressive stress. A method is developed to take microseismic event monitoring data as input to determine the damage state and the extent of the EDZ by crack distribution. Based on the crack orientation and crack density information, the rock is modeled by a micro-mechanics based constitutive model which considers the anisotropic material properties. Numerical examples are presented using field monitoring data from a tunnel in granite to demonstrate how microseismicity can be quantitatively linked to dynamic rock mass properties.     

化学腐蚀下裂隙岩石的损伤效应及断裂准则研究

对不同化学溶液腐蚀的岩石试件试验结果的分析表明,化学溶液腐蚀作用下,矿物颗粒间联结受到扰动,同时颗粒受到溶蚀等作用,使岩石强度显著下降,岩石结构产生损伤。因此,化学溶液对岩石材料的腐蚀影响可以归结为岩石颗粒骨架部分性质的劣化和空隙的增大两部分。对于裂隙岩体来说,化学溶液的腐蚀则主要体现在断裂应力的减小和裂隙的增大。从这两个主要影响因素出发,引入应力放大系数,建立了化学腐蚀下裂纹体的断裂准则。给出了考虑化学溶液作用的裂隙岩石断裂准则的研究思路。     

花岗岩板渐进破坏过程的微观研究

研究了花岗岩板在单轴压缩应力状态下的微观破坏过程。试验主要采用了液压加载台、光学显微镜、同步录象系统以及二次复型技术等。研究发现，花岗岩原开裂是局部发生的，并首先开始于石英颗粒的边界，而这些边界多数位于近轴向。轴向裂纹的发生和发展最终导致样品的劈裂破坏。不同的矿物颗粒表现各自特有的、与其微观结构密切相关的破坏行为。石英在花岗岩的破坏过程中起着极其重要的作用。表面裂纹的分形维数随破坏的发展而持续增加直到样品突然失稳。