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1.
Z. H. Chen L. G. Tham M. R. Yeung Y. Tsui P. K. K. Lee 《Rock Mechanics and Rock Engineering》2002,35(4):255-270
Summary
A study on the peak strength of brittle rock materials having random strength distributions was carried out using the re-normalization
group theory approach. A major advantage of the approach is that it is scale invariant, and therefore, one can relate the
micro-fractures with macro-fractures of rocks at the critical state. The stress transfer from the broken sub-sections to the
unbroken sub-sections is defined by a conditional probability. The critical probability P
* and the relation between the peak strength and the mean strength of the elements have been obtained theoretically. On the
other hand, the whole process of rock brittle fracture has also been simulated numerically from micro-fracture to macro-fracture
by using the Rock Failure Process Analysis (RFPA) code. The peak strengths obtained by the numerical model agree fairly well
with those obtained by the re-normalisation group theory. Due to the stress transfer from the broken subsections to the unbroken
subsections, the peak strength is considerably less than the mean strength of the elements.
Received October 24, 2000; accepted February 26, 2002 Published online September 2, 2002 相似文献
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Results of an experimental programme on heterogeneous rock-like specimens of dental plaster confirm the pronounced role of
tensile microcracks on brittle failure. Microbuckling of very small rock-columns formed amid closely located tensile cracks
was observed as the key incident connecting stable phenomenon of tensile cracking to unstable phenomenon of shearing and subsequent
macroscopic failure. Using the classical beam and buckling theories and considering geometry of the problem a new failure
criterion is proposed. As a novel attempt, this new failure criterion relates the compressive strength of rock to three basic
microstructural properties, i.e. degree of crystal interlocking, average Young modulus and average tensile strength of rock
forming minerals. 相似文献
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根据目前岩石声发射确定Kaiser点存在的问题采用小波包分析研究方法,在单轴加载岩石声发射试验的基础上,首先提出了基于小波包变换的Kaiser点信号的信噪分离方法,其次确定了Kaiser点信号的频率范围,最后利用小波包分析对岩石声发射信号的能量分布特征进行研究,得到了砂岩Kaiser点信号的特征频带。结果表明,小波包分析是处理岩石声发射Kaiser点信号的一种有效的方法,进而为AE法测量地应力确定Kaiser点奠定了一定的试验基础。 相似文献
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A biaxial testing program has been performed to study the process of brittle failure in crystalline rocks. Dental plaster
has been selected as a model material, and mixing with different ratios of distilled water, different types of common minerals
of crystalline rocks have been simulated in the form of brick-like small elements. These elements have been interlocked together
according to four systematic patterns and final specimens with 180 × 180 × 76 mm dimensions have been obtained. Details of
different types of cracks observed during loading process, effects of mechanical, geometrical and confining pressure on the
cracking intensity, the influence of different types of heterogeneity on the macroscopic properties of a system of interlocked
elements, and the sequence of events during the failure process are presented in this paper. Based on these observations,
a revised mechanism for brittle failure is proposed. 相似文献
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Yao Yao 《Rock Mechanics and Rock Engineering》2012,45(3):375-387
Hydraulic fracturing technology is being widely used within the oil and gas industry for both waste injection and unconventional
gas production wells. It is essential to predict the behavior of hydraulic fractures accurately based on understanding the
fundamental mechanism(s). The prevailing approach for hydraulic fracture modeling continues to rely on computational methods
based on Linear Elastic Fracture Mechanics (LEFM). Generally, these methods give reasonable predictions for hard rock hydraulic
fracture processes, but still have inherent limitations, especially when fluid injection is performed in soft rock/sand or
other non-conventional formations. These methods typically give very conservative predictions on fracture geometry and inaccurate
estimation of required fracture pressure. One of the reasons the LEFM-based methods fail to give accurate predictions for
these materials is that the fracture process zone ahead of the crack tip and softening effect should not be neglected in ductile
rock fracture analysis. A 3D pore pressure cohesive zone model has been developed and applied to predict hydraulic fracturing
under fluid injection. The cohesive zone method is a numerical tool developed to model crack initiation and growth in quasi-brittle
materials considering the material softening effect. The pore pressure cohesive zone model has been applied to investigate
the hydraulic fracture with different rock properties. The hydraulic fracture predictions of a three-layer water injection
case have been compared using the pore pressure cohesive zone model with revised parameters, LEFM-based pseudo 3D model, a
Perkins-Kern–Nordgren (PKN) model, and an analytical solution. Based on the size of the fracture process zone and its effect
on crack extension in ductile rock, the fundamental mechanical difference of LEFM and cohesive fracture mechanics-based methods
is discussed. An effective fracture toughness method has been proposed to consider the fracture process zone effect on the
ductile rock fracture. 相似文献
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岩体受压破坏是由于岩体内裂纹扩展及新的宏观裂纹产生不断积累的结果,大规模岩体受压破坏前会发生局部岩体的先前断裂破坏。裂纹起裂、快速扩展和止裂会产生声发射现象,局部岩体断裂破坏会产生强烈的声发射现象,通过对岩体声发射的监测分析可以预报受压岩体破坏的时间。因此,通过对地壳岩体声发射的监测分析,可以进行地震的短期和临震预报。通过对岩体受压应力分布规律的分析,得出通过监测地壳浅部地应力和地形变预报地震是没有实际意义的结论。 相似文献
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为研究脆性岩石变形机制与渗透率- 应变的关系,根据脆性岩石应力- 应变和渗透率- 应变关系曲线分析指出:脆性
岩石经压密、弹性变形和非稳定破裂后,内部微裂隙出现丛集式发展,且不断合并、贯通,导致微观结构发生明显变化,
使渗透率在临界破坏点处急剧增大;当岩石宏观破坏后,内部结构面上的岩桥或凸起体部分被剪断或磨平,使得岩石强度
随变形突然下降,此时渗透率到达峰值。结合重整化群理论分析表明,脆性岩石在应力- 应变曲线拐点处应变和渗透率峰
值点处应变对应、临界破坏点处应变和渗透率急剧增大点处应变对应。通过试验研究和实例统计分析,验证了结论的合理性。 相似文献
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This paper presents a new analytical criterion for brittle failure of rocks and heavily over-consolidated soils. Griffith’s model of a randomly oriented defect under a biaxial stress state is used to keep the criterion simple. The Griffith’s criterion is improved because the maximum tensile strength is not evaluated at the boundary of the defect but at a certain distance from the boundary, known as half of the critical distance. This fracture criterion is known as the point method, and is part of the theory of critical distances, which is utilised in fracture mechanics. The proposed failure criterion has two parameters: the inherent tensile strength, σ 0, and the ratio of the half-length of the initial crack/flaw to the critical distance, a/L. These parameters are difficult to measure but they may be correlated with the uniaxial compressive and tensile strengths, σ c and σ t. The proposed criterion is able to reproduce the common range of strength ratios for rocks and heavily overconsolidated soils (σ c/σ t = 3–50) and the influence of several microstructural rock properties, such as texture and porosity. Good agreement with laboratory tests reported in the literature is found for tensile and low-confining stresses. 相似文献
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S. Y. Wang S. W. Sloan S. G. Fityus D. V. Griffiths C. A. Tang 《Rock Mechanics and Rock Engineering》2013,46(5):1165-1182
Rock is a heterogeneous geological material. When rock is subjected to internal hydraulic pressure and external mechanical loading, the fluid flow properties will be altered by closing, opening, or other interaction of pre-existing weaknesses or by induced new fractures. Meanwhile, the pore pressure can influence the fracture behavior on both a local and global scale. A finite element model that can consider the coupled effects of seepage, damage and stress field in heterogeneous rock is described. First, two series of numerical tests in relatively homogeneous and heterogeneous rocks were performed to investigate the influence of pore pressure magnitude and gradient on initiation and propagation of tensile fractures. Second, to examine the initiation of hydraulic fractures and their subsequent propagation, a series of numerical simulations of the behavior of two injection holes inside a saturated rock mass are carried out. The rock is subjected to different initial in situ stress ratios and to an internal injection (pore) pressure at the two injection holes. Numerically, simulated results indicate that tensile fracture is strongly influenced by both pore pressure magnitude and pore pressure gradient. In addition, the heterogeneity of rock, the initial in situ stress ratio (K), the distance between two injection holes, and the difference of the pore pressure in the two injection holes all play important roles in the initiation and propagation of hydraulic fractures. At relatively close spacing and when the two principal stresses are of similar magnitude, the proximity of adjacent injection holes can cause fracturing to occur in a direction perpendicular to the maximum principal stress. 相似文献
16.
Experimental Calibration of ISRM Suggested Fracture Toughness Measurement Techniques in Selected Brittle Rocks 总被引:1,自引:4,他引:1
Summary A wide variety of specimen types and methods are employed in fracture toughness measurement of rocks, which result in scattered
values for the same rock type. In order to provide some consistency to the values, the International Society for Rock Mechanics
(ISRM) recommended three suggested methods using core based specimens, the Chevron Bend (CB) test, the Short Rod (SR) test
and the Cracked Chevron Notch Brazilian Disc (CCNBD) test. This standardization helped obtain more consistent values but still
a variation of 20–30% was observed in the values of fracture toughness obtained with the CB and SR methods. The values obtained
with the CCNBD method were found to be consistently lower (30–50%) than those of the other two methods (CB and SR). Many reasons
have been offered to explain this deviation. These include size of the specimen, anisotropy of rock, a dimensionless parameter
in the fracture toughness calculation equation for the CCNBD test, etc. A comprehensive test program was initiated to identify
the cause of these discrepancies between the CB and CCNBD methods. Three brittle rock types were selected for the study and
more than 200 tests were conducted to measure the values of fracture toughness.
A rigorous statistical analysis was carried out to determine the confidence level and find the significance of the test results.
It was found that the CB and CCNBD methods were very comparable provided the correct equation for fracture toughness calculation
was used for the CCNBD method and the size of the specimens was selected carefully. The error in the ISRM 1995 formula of
fracture toughness for the CCNBD method could be the major factor responsible for the consistently lower values obtained with
the method. 相似文献
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Victor Abioye Akinbinu 《Geotechnical and Geological Engineering》2016,34(3):877-887
Tests to determine the complete stress–strain curve of rocks indicate whether the rocks can be classified a Class I or Class II. Class II rocks exhibits the potential for self-sustained failure in the post-peak region. The purpose of the research described in this paper was to investigate whether or not this self-sustained failure characteristic is related to the fragmentation of the rock. The aim of the research was, therefore, to determine possible relationships between fragmentation and various properties of several rocks types, including the influence of the Class II characteristic. Fragmentation of rock depends on its self-sustaining failure behaviour and the energy available in the post-peak region to shatter the rock. The correlation of static and dynamic rock properties with size of fragments resulting from compression tests demonstrate clear relationships of Class II rocks, but the same cannot be said for Class I rocks. Analyses of test results show that fragmentation increases with an increase in rock strength, and is explosive for Class II rocks. Probability density distributions were constructed to show the overall comparison of fragment sizes produced during failure of Class II and Class rocks. The calculated probability of passing at X50 and X10 sieve sizes show that Class II rocks as a group are more finely fragmented. It can therefore be concluded that, when breaking rocks under the same steady loading conditions, Class II rocks will show greater fragmentation than Class I rocks. 相似文献
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准确确定Kaiser点是研究声发射测量地应力的关键.通过对模拟岩心的水泥块进行单轴受压破坏过程的声发射试验,得到了试件在试验过程中的应力-应变曲线、应力、声发射强度、声发射累积数与时间的关系图.分别对试样用突变点法、最大曲率法、双切线法、重加载法(抹录不尽现象、两次加载相减法)、多方面综合判定法以及声发射强度信号的统计分析法进行了分析.从不同的方面认识了试样的Kaiser点的特性,总结并分析了确定Kaiser点的方法以及各自的适应性,并进行了优选.研究表明,试验确定了试样的物理特性,各种方法都能从不同角度和机理上解释Kaiser点现象,综合判定法能相对更加全面、准确地确定Kaiser点. 相似文献
20.
Onset of Hydraulic Fracture Initiation Monitored by Acoustic Emission and Volumetric Deformation Measurements 总被引:1,自引:1,他引:1
Sergey Stanchits Aniket Surdi Patrick Gathogo Eric Edelman Roberto Suarez-Rivera 《Rock Mechanics and Rock Engineering》2014,47(5):1521-1532
In this paper, the results of laboratory studies of fracture initiation, early propagation and breakdown are reported. Three experiments were conducted on a low permeability sandstone block, loaded in a polyaxial test frame, to representative effective in situ stress conditions. The blocks were instrumented with acoustic emission (AE) and volumetric deformation sensors. In two experiments, fluids of different viscosity were injected into the wellbore, fluid injection was interrupted soon after the breakdown pressure had been reached. This allowed us to investigate hydraulic fracture initiation. In the third test, fracture initiation criteria were applied to stop hydraulic fracture propagation significantly earlier, prior to breakdown, and as it propagated a short distance from the wellbore. The analysis of AE results shows an increase in AE activity and a change in the AE spatial correlation, during the fracture initiation. This early stage of fracturing correlates strongly with the onset of rock volumetric deformation, and is confirmed by the analysis of ultrasonic transmission monitoring. The rock microstructure, after the test, was investigated by analysis of scanning electron microscope images. These indicated the development of leak-off zone near the wellbore and a dry hydraulic fracture at the farther distance from the wellbore. 相似文献