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The time-dependent failure of rock subjected to repeated loading can be explained in terms of the residual strength locus: catastrophic failure occurs when the accumulation of deformation is such that the residual strength locus is intercepted. In a preliminary experimental study of the fatigue characteristics of rock masses, highly idealized models of jointed rock were subjected to a series of cyclic uniaxial compression tests. The results of these experiments show that intact and failed models of jointed rock are extremely susceptible to cyclic fatigue failure, and that in these cases the residual strength locus interpretation of time-dependent failure is correct. 相似文献
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利用拉格朗日元法模拟了平面应变单轴压缩条件下具有初始随机材料缺陷的岩石试样的破坏过程、前兆和宏观力学响应.利用若干FISH函数于岩样内部规定初始缺陷并计算全部变形特征.比密实岩石弱的缺陷在破坏之后经历理想塑性行为.密实岩石在破坏之后先是经历线性应变软化行为,然后是理想塑性行为.随着缺陷数目的增加,剪切带间距缩小;岩样的强度下降.在应变软化阶段,最大不平衡力的明显的突增是由于被剪切带切割的试样块体发生了沿剪切带方向的运动.试样内部的缺陷数目越少,应变软化阶段最大不平衡力的峰值越高.无论从单元破坏角度,还是从侧向应变-轴向应变曲线、体积应变-轴向应变曲线、计算得到的泊松比-轴向应变曲线角度,都得到了相同的结论(即,缺陷越多,破坏前兆越明显).采用两条倾斜的扫描线对岩样最终的破坏形态进行了扫描,发现当扫描线间距等于半个至1个单元长度时,初始随机缺陷位置与岩样最终破坏形态具有很好的相关性. 相似文献
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孔隙压力对含随机缺陷岩石破坏过程及全部变形特征的影响 总被引:2,自引:0,他引:2
对于平面应变压缩条件下含有随机缺陷的岩样,利用FLAC研究了孔隙压力对岩样破坏过程、全部变形特征及前兆的影响。以前编写的若干FISH函数,被用于生成缺陷和计算轴向、侧向、体积应变及侧向应变与轴向应变比值的负值(计算得到的泊松比)。在峰值应力之后,密实岩石单元服从线性应变软化行为及随后的理想塑性行为,而材料缺陷呈现理想塑性行为。当孔隙压力较高时,应力-侧向应变曲线具有一平台;破坏的前兆更明显;变形后岩样的体积总是大于原始体积;在初始加栽阶段、均匀变形阶段及峰后变形阶段,由于明显的侧向膨胀,计算得到的泊松比远大于0.5。当孔隙压力较低时,在峰值应力之前,变形后岩样的体积小于原始体积,体积扩容出现于峰值应力之后,引起了负的体积应变。利用广义虎克定律,解释了平面应变弹性状态下数值结果的合理性。对岩样进行带状区域扫描后,确认随机缺陷的初始分布与岩样的最终破坏形态紧密相关。 相似文献
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通过对饱和砂岩和大理岩的循环荷载实验,分析了饱和岩石在循环荷载下的应力-应变滞后回线、瞬时杨氏模量、泊松比的“X”形变化曲线,以及杨氏模量随应变振幅的增加而减少等滞后现象,并分析了施加外力的应变振幅对衰减的影响,认为岩石在循环荷载作用下的衰减与应变振幅成正比,提出的衰减b值反映了岩石在循环荷载作用下衰减的程度. 岩石的衰减和滞后存在密切的关系,通过饱和岩石的宏观行为,探讨了饱和岩石在循环荷载下的滞后和衰减现象的微观机理,认为孔隙流体流动在岩石的滞后和衰减中起着重要作用,岩石内部的颗粒接触粘合和黏滑摩擦可能是孔隙岩石在循环荷载作用下产生滞后和衰减的原因. 相似文献
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缺陷的演化繁衍与Kaiser效应函数 总被引:19,自引:0,他引:19
本文运用岩石的损伤理论,通过对岩石材料微元强度的统计分布假设,得到声发射积累N随应变ε的变化规律,并对于循环加载情形,给出了Kaiser效应函数的通式。文中还证明,声发射积累N的变化与损伤参量D具有一致性,得到了用声发射积累N描述的岩石本构关系。理论结果与实验资料吻合很好。 相似文献
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The influence of microcrack density on the elastic and fracture mechanical properties of Stripa granite 总被引:1,自引:0,他引:1
Ove Alm Lise-Lotte Jaktlund Kuo Shaoquan 《Physics of the Earth and Planetary Interiors》1985,40(3):161-179
Microcracks can have a strong influence on the elastic and fracture mechanical properties of rocks if they are numerous, or if they are orientated in unfavourable directions in anisotropic rocks in particular. This paper presents results from a great number of mechanical tests on Stripa granite containing various amounts of microcracks. Variations in the microcrack density were obtained by shock-heating the rock at different temperatures in the range 100–600°C for 3 h.The results presented are obtained from sound velocity measurements, uniaxial compression tests, Brazilian tests and three-point bending tests. The density of microcracks in the heated rock is studied by means of optical microscopy, SEM and differential strain analysis (DSA).Some of the calculated parameters show a maximum value for specimens heat-treated at about 100°C. The tensile strength is, for instance, substantially higher for specimens shock-heated at 100°C than for non-heated ones. Another striking feature is the initial decrease of the diameter observed in specimens heat-treated at 600°C when loaded in uniaxial compression. Both optical microscopy and DSA experiments reveal a large increase in microcracking when the heat-treatment temperature exceeds 300°C. 相似文献
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基于能量耗散理论建立非均质岩石的动态损伤破坏元胞自动机,分析单轴压缩试验中岩石破坏截面的损伤状态,得到该情况下的岩石裂隙微观动态发展过程、损伤演化关系以及全程应力应变曲线。研究发现:①加载过程中,均质度较低的岩样裂纹的萌生和扩展较为分散,损伤速率低;均质度较高的岩样裂纹的萌生和扩展非常集中,表现为脆性破坏。②损伤演化曲线呈3阶段S形发展。③随着岩石均质度参数的增加,岩石的峰值强度和峰值应变都有所提高,峰后曲线越来越陡。④给出的衡量岩石脆性破坏强弱程度的指标参数,能够较好地描述岩石破坏形式随着均值度参数m变化的规律。 相似文献
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实验研究了原煤、型煤单轴压缩电磁辐射记忆效应特征、记忆内容及变化规律,探讨并分析了煤岩电磁辐射记忆效应机理.结果表明,煤岩变形破坏电磁辐射具有记忆先期最大应力、纵向应变、横向应变和体应变的能力,最直接的记忆内容是先期受到的应力、纵向应变和横向应变;当先期施加的应力水平大于70%~80%时,电磁辐射记忆能力迅速减弱,甚至根本失去记忆能力;煤岩损伤破坏过程的不可逆决定了电磁辐射过程的不可逆,电磁辐射过程的不可逆是煤岩变形破坏电磁辐射记忆效应的直接原因.煤岩电磁辐射记忆效应理论在地应力测试、巷道围岩不同应力区范围的确定及煤岩动力灾害预测等方面具有广阔的应用前景. 相似文献
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Electric resistance and emissions of hydrogen and radon isotopes of concrete (which is somewhat similar to fault-zone materials) under increasing uniaxial compression were continuously monitored to check whether they show any pre- and post-failure changes that may correspond to similar changes reported for earthquakes. The results show that all these parameters generally begin to increase when the applied stresses reach 20% to 90% of the corresponding failure stresses, probably due to the occurrence and growth of dilatant microcracks in the specimens. The prefailure changes have different patterns for different specimens, probably because of differences in spatial and temporal distributions of the microcracks. The resistance shows large co-failure increases, and the gas emissions show large post-failure increases. The post-failure increase of radon persists longer and stays at a higher level than that of hydrogen, suggesting a difference in the emission mechanisms for these two kinds of gases. The H2 increase may be mainly due to chemical reaction at the crack surfaces while they are fresh, whereas the Rn increases may be mainly the result of the increased emanation area of such surfaces. The results suggest that monitoring of resistivity and gas emissions may be useful for predicting earthquakes and failures of concrete structures. 相似文献
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用几种不同加载方式对岩石样品进行了单轴压力实验。以恒定应变率(约为10-5)对样品加载时,岩石的破裂过程大致可分成四个阶段:孔隙压缩阶段、弹性变形阶段、体积膨胀阶段和临震阶级。后二个阶段显著的特点是岩石开始表现出非弹性的体积应变并在主破裂前急剧增大,它与微破裂累积总数二者存在着同步的变化。在重复加载时,发现岩石的微破裂过程具有不可逆的性质,这种现象似乎可以用来说明同一地区短期内发生的两次地震的地震序列的不同,指出运用历史地震资料时应注意该地区应力变化的历史情况。 相似文献
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In order to investigate the dynamic mechanical properties of amphibolite and sericite-quartz schist under confi ning pressure, two rocks are subjected to impact loadings with different strain rates and confi ning pressures by using split Hopkinson pressure bar equipment with a confi ning pressure device. Based on the experimental results, the stress-strain curves are analyzed and the effects of confi ning pressure and strain rates on the dynamic compressive strength, peak strain and failure mode are summarized. The results show that:(1) The characteristics of two rocks in the ascent stage of the stressstrain curve are basically the same, but in the descent stage, the rocks gradually show plastic deformation characteristics as the confi ning pressure increases.(2) The dynamic compressive strength and peak strain of two rocks increase as the strain rate increases and the confi ning pressure effects are obvious.(3) Due to the effect of confi ning pressure, the normal stress on the damage surface of the rock increases correspondingly, the bearing capacity of the crack friction exceeds the material cohesion and the slippage of the fractured rock is controlled, which all lead to the compression and shear failure mode of rock. The theoretical analysis and experimental methods to study the dynamic failure mode and other related characteristics of rock are useful in developing standards for engineering practice. 相似文献
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在单轴压缩下,对经过高温焙烧的含水辉长岩进行了轴向和径向电阻率变化以及体积应变的同时连续测量.结果表明,在完全饱和前的非弹性压缩阶段,电阻率随压应力增高而降低;在完全饱和的弹性压缩阶段,电阻率升高;在非弹性的体积膨胀阶段,电阻率继续上升.从Archie 公式出发,通过近似分析,导出了电阻率变化和体积应变的关系式.实验结果和近似分析定性上相附.本文的主要结果是发现含水岩样在膨胀阶段电阻率的升高,初步认为这是由于热开裂的张开,降低了饱和度的结果. 相似文献
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—Uniaxial compression, triaxial compression and Brazialian tests were conducted on several kinds of rock, with particular attention directed to the principal tensile strain. In this paper we aim to clarify the effects of the experimental environment—such as confining pressure, loading rate, water content and anisotropy—on the critical tensile strain, i.e., the measured principal tensile strain at peak load.¶It was determined that the chain-type extensometer is a most suitable method for measuring the critical tensile strain in uniaxial compression tests. It is also shown that the paper-based strain gage, whose effective length is less than or equal to a tenth of the specimen’s diameter and glued on with a rubber-type adhesive, can be effectively used in the Brazilian tests.¶The effect of confining pressure P C on the critical tensile strain ? TC in the brittle failure region was between ?0.02 × 10?10 Pa?1 and 0.77 × 10?10 Pa?1. This pressure sensitivity is small compared to the critical tensile strain values of around ?0.5 × 10?2. The strain rate sensitivities ?? TC /?{log(d|?|/dt)} were observed in the same way as the strength constants in other failure criteria. They were found to be from ?0.10 × 10?3 to ?0.52 × 10?3 per order of magnitude in strain rate in the triaxial tests. The average magnitude of the critical tensile strain ? TC increased due to the presence of water by 4% to 20% for some rocks, and decreased by 22% for sandstone. It can at least be said that the critical tensile strain is less sensitive to water content than the uniaxial compressive strength under the experimental conditions reported here. An obvious anisotropy was observed in the P-wave velocity and in the uniaxial compressive strength of Pombetsu sandstone. It was not observed, however, in the critical tensile strain, although the data do show some variation.¶A "tensile strain criterion" was proposed, based on the above experimental results. This criterion signifies that stress begins to drop when the principal tensile strain reaches the critical tensile strain. The criterion is limited to use within the brittle failure region. The critical tensile strain contains an inelastic strain component as well as an elastic one. It is affected by the strain rate, however, it is relatively insensitive to the confining pressure, the presence of water and anisotropy. 相似文献