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1.
实验和野外观测表明颗粒破碎显著影响高孔隙岩石的变形特征.为建立高孔隙岩石变形的数值模型,我们以弹性理论为基础并根据问题的特征进行合理简化,给出了一种颗粒破碎机制,并根据此颗粒破碎条件改进传统的离散单元模型.利用改进的离散单元模型,研究了不同压力条件下高孔隙岩石变形的宏观和微观特征.数值模拟结果表明考虑颗粒破碎的模型能重现高孔隙岩石在不同围压下变形的应力-应变关系、声发射特征、应变局部化和剪切增强压缩等特征.我们还发现,与野外观测结果一致,在高孔隙岩石脆性阶段剪切带内部及附近伴有显著的颗粒破碎. 相似文献
2.
Failure Mode and Spatial Distribution of Damage in Rothbach Sandstone in the Brittle-ductile Transition 总被引：4，自引：0，他引：4
— To elucidate the spatial complexity of damage and evolution of localized failure in the transitional regime from brittle faulting to cataclastic ductile flow in a porous sandstone, we performed a series of triaxial compression experiments on Rothbach sandstone (20% porosity). Quantitative microstructural analysis and X-ray computed tomography (CT) imaging were conducted on deformed samples. Localized failure was observed in samples at effective pressures ranging from 5 MPa to 130 MPa. In the brittle faulting regime, dilating shear bands were observed. The CT images and stereological measurements reveal the geometric complexity and spatial heterogeneity of damage in the failed samples. In the transitional regime (at effective pressures between 45 MPa and 130 MPa), compacting shear bands at high angles and compaction bands perpendicular to the maximum compression direction were observed. The laboratory results suggest that these complex localized features can be pervasive in sandstone formations, not just limited to the very porous aeolian sandstone in which they were first documented. The microstructural observations are in qualitative agreement with theoretical predictions of bifurcation analyses, except for the occurrence of compaction bands in the sample deformed at effective pressure of 130 MPa. The bifurcation analysis with the constitutive model used in this paper is nonadequate to predict compaction band formation, may be due to the neglect of bedding anisotropy of the rock and multiple yield mechanisms in the constitutive model. 相似文献
3.
Compaction and Failure in High Porosity Carbonates: Mechanical Data and Microstructural Observations
P. Baud S. Vinciguerra C. David A. Cavallo E. Walker T. Reuschlé 《Pure and Applied Geophysics》2009,166(5-7):869-898
We investigated systematically the micromechanics of compaction in two carbonates of porosity above 30%, Majella grainstone and Saint Maximin limestone. The composition, grain size and pore surface area of these rocks were determined. Hydrostatic compression experiments were performed under dry and wet conditions beyond the onset of grain crushing. A significant water weakening effect was observed in both rocks. A set of conventional triaxial experiments was also performed on both rocks under dry conditions at confining pressures ranging from 3 to 31 MPa. Microstructural observations were carried out on the deformed samples. The mechanical behavior of these high porosity carbonates is dominated by shear-enhanced compaction associated in most cases with strain hardening. Stress-induced cracking and grain crushing are the dominant micromechanisms of deformation in both rocks. In Majella grainstone, compactive shear bands appeared at low confinement, in qualitative agreement with the deformation bands observed in the field. At higher confining pressures, compaction localization was inhibited and homogeneous cataclastic flow developed. In Saint Maximin limestone, compaction localization was observed at all confining pressures. An increasing number of compactive shear bands at various orientations appeared with increasing strain. These new data suggest that compaction localization is important in the mechanical compaction of high porosity carbonates. 相似文献
4.
岩石的变形机制是研究岩石圈变形和局部构造活动的重要基础,岩石的微观结构是研究其变形机制的关键。微观层析成像（微观CT）技术可以无损地获取样品内部高精度三维数字化图像,为观测岩石内部结构提供了技术保证。新近发展起来的动态CT技术,使得观测岩石变形过程成为可能。本文利用一组莱塔石灰岩受差应力变形的三维动态CT图像数据,通过图像切割、图像分割等处理步骤,以团簇为基本表征单位,表征不同形状、大小孔隙的动态变化过程,分析对比全部孔隙、大团簇、小团簇和裂隙型小团簇的动态图像。结果表明:随着岩石的压缩变形,其大孔隙在不断地缩小;在变形的初始阶段,靠近施压活塞的样品上部出现了密集的新生小孔隙;当岩石所受差应力到达73 MPa时,其下半部出现了明显的剪切带,具体表现为大量的新生裂隙生成并且新生裂隙集中带与轴向成约45°交角。此前的研究观测到该样品中下部若干压缩带形成的过程;本文通过基于团簇的可视化技术,观测到了高孔隙度岩石变形过程中压缩带和剪切带共同形成的过程。同时,新生的沿剪切带分布的微小裂隙并没有显示与剪切带相同的方向,而是具有各方向均匀分布的特征。该特征可能与岩石内部复杂的局部孔隙结构有关,是值得进一步探讨的问题。 相似文献
5.
Jerzy Sobotka 《Acta Geophysica》2010,58(1):163-172
The results of laboratory experimental studies of the DC-induced acoustic emission (AE) in saturated sand models of sedimentary
rock are presented. It is shown that direct current acting on a geological medium generates acoustic vibrations in it. The
experimental methodology is based on recording acoustic pulses generated by the rock model (sample) when the electric field
is applied. The amplitude-frequency parameters of the AE signals depend on petrophysical properties of the solid phase, on
the salinity of porous medium, and the electric field (current intensity and voltage). The above research is the first step
towards the full identification of the characteristics of the AE signals generated by rocks in a DC electric field. 相似文献
6.
Yu Huaizhong Yin Xiangchu Liang Naigang Xia Mengfen Li Min Xu Zhaoyong Peng Keyin Victor Kukshenko Wu Zhishen Qi Li Surguei Elizarov 《中国地震研究》2003,17(3):227-235
Implementing acoustic emission experiments with large rock samples, LURR (Load/Unload Response Ratio) theory was studied. The loading conditions in the experiments were designed to simulate the complicated loading process of underground rocks. The damages emerging inside the rock samples were recorded by the acoustic emission technique during the loading process. The experimental results were consistent with prediction by LURR theory. Integrating the changing processes of LURR value Y and the location process of acoustic emission events showed agreement between the variation of LURR value Y and the damage evolution inside the rocks. Furthermore, the high value of Y emerged before the complete breakdown of materials. Therefore, the damage evolution of rock specimen can be quantitatively analyzed with LURR theory, thus the failure of the rock materials and the earthquake occurrence may be predicted. The experimental results gave a further verification of LURR theory. 相似文献
7.
The influence of thermal and cyclic stressing on the strength of rocks from Mount St. Helens, Washington 总被引：1，自引：0，他引：1
Jackie Evan Kendrick Rosanna Smith Peter Sammonds Philip G. Meredith Matthew Dainty John S. Pallister 《Bulletin of Volcanology》2013,75(7):1-12
Stratovolcanoes and lava domes are particularly susceptible to sector collapse resulting from wholesale rock failure as a consequence of decreasing rock strength. Here, we provide insights into the influence of thermal and cyclic stressing on the strength and mechanical properties of volcanic rocks. Specifically, this laboratory study examines the properties of samples from Mount St. Helens; chosen because its strength and stability have played a key role in its history, influencing the character of the infamous 1980 eruption. We find that thermal stressing exerts different effects on the strengths of different volcanic units; increasing the heterogeneity of rocks in situ. Increasing the uniaxial compressive stress generates cracking, the timing and magnitude of which was monitored via acoustic emission (AE) output during our experiments. AEs accelerated in the approach to failure, sometimes following the pattern predicted by the failure forecast method (Kilburn 2003). Crack damage during the experiments was tracked using the evolving static Young’s modulus and Poisson’s ratio, which represent the quasi-static deformation in volcanic edifices more accurately than dynamic elastic moduli which are usually implemented in volcanic models. Cyclic loading of these rocks resulted in a lower failure strength, confirming that volcanic rocks may be weakened by repeated inflation and deflation of the volcanic edifice. Additionally, volcanic rocks in this study undergo significant elastic hysteresis; in some instances, a material may fail at a stress lower than the peak stress which has previously been endured. Thus, a volcanic dome repeatedly inflated and deflated may progressively weaken, possibly inducing failure without necessarily exceeding earlier conditions. 相似文献
8.
— It is well known that there is no “universal” permeability-porosity relationship valid in all porous media. However, the evolution of permeability and porosity in rocks can be constrained provided that the processes changing the pore space are known. In this paper, we review observations of the relationship between permeability and porosity during rock evolution and interpret them in terms of creation/destruction of effectively and non-effectively conducting pore space. We focus on laboratory processes, namely, plastic compaction of aggregates, elastic-brittle deformation of granular rocks, dilatant and thermal microcracking of dense rocks, chemically driven processes, as a way to approach naturally occurring geological processes. In particular, the chemically driven processes and their corresponding evolution permeability-porosity relationships are discussed in relation to sedimentary rocks diagenesis. 相似文献
9.
10.
Experimental Studies of Shear Deformation of Mantle Materials: Towards Structural Geology of the Mantle 总被引：1，自引：0，他引：1
S. Karato S. Zhang M. E. Zimmerman M. J. Daines D. L. Kohlstedt 《Pure and Applied Geophysics》1998,151(2-4):589-603
—A brief outline is given on experimental studies carried out in the Minnesota Mineral and Rock Physics Laboratory of microstructural evolution and rheology of mantle mineral aggregates or their analogues, using a simple shear deformation geometry. A simple shear deformation geometry allows us to unambiguously identify controlling factors of microstructural evolution and to obtain large strains at high pressures and temperatures, and thus provides a unique opportunity to investigate the "structural geology of the mantle." We have developed a simple shear deformation technique for use at high pressures and temperatures (pressure up to 16 GPa and temperature up to 2000 K) in both gas-medium and solid-medium apparati. This technique has been applied to the following mineral systems (i) olivine aggregates, (ii) olivine basaltic melt, (iii) CaTiO3 perovskite aggregates. The results have provided important data with which to understand the dynamics of the earth’s mantle, including the geometry of mantle convection, mechanisms of melt distribution and migration beneath mid-ocean ridges, and the mechanisms of shear localization. Limitations of laboratory studies and future directions are also discussed. 相似文献
11.
Since the similarity in size distribution of earthquakes and acoustic emissions (AE) was found in the 1960s, many laboratory studies have been motivated by the need to provide tools for the prediction of mining failures and natural earthquakes. This paper aims, on the one hand, to draw an outline of laboratory AE studies in the last 50 years, which have addressed seismological problems. Topics include the power laws in which the similarity between AEs and earthquakes is involved and progress that has been made in AE technology and laboratory AE study. On the other hand, this study will highlight some key issues intensively discussed, especially in the last three decades, such as aspects related to the pre-failure damage evolution, fault nucleation and growth in brittle rocks and discuss factors governing these processes. 相似文献
12.
This study present the result of conventional triaxial tests conducted on samples of Rothbach sandstone cored parallel, oblique (at 45 degrees) and perpendicular to the bedding at effective pressures ranging from 5 to 250 MPa. Mechanical and microstructural data were used to determine the role of the bedding on mechanical strength and failure mode. We find that samples cored at 45 degrees to the bedding yield at intermediate level of differential stress between the ones for parallel and perpendicular samples at all effective pressures. Strain localization at high confining pressure (i.e., in the compactive domain) is observed in samples perpendicular and oblique to the bedding but not in samples cored parallel to the bedding. However, porosity reduction is comparable whether compactive shear bands, compaction bands or homogeneous cataclastic flow develop. Microstructural data suggest that (1) mechanical anisotropy is controlled by a preferred intergranular contact alignment parallel to the bedding and that (2) localization of compaction is controlled by bedding laminations and grain scale heterogeneity, which both prevent the development of well localized compaction features. 相似文献
13.
为了深入理解断层带摩擦滑动速度依赖性转换及其机制,利用双轴摩擦实验对干燥及含水条件下岩盐断层带摩擦的速度依赖性进行了实验研究,并观测了摩擦滑动过程中的声发射,分析了断层带的微观结构.实验结果表明,干燥岩盐断层带在0.1~100 μm/s的速度范围内表现为速度弱化,增大σ2会使断层带向速度强化转变;含水条件下岩盐断层带在1~100 μm/s的速度范围内表现为速度弱化,而在0.1~0.01 μm/s的速度范围内表现为速度强化,速度依赖性转换出现在0.1~1 μm/s,其中断层表现为振荡或应力释放时间较长的黏滑事件;岩盐断层带在干燥条件下表现出很强的声发射活动,每个黏滑均对应一丛声发射事件,而在含水条件下一次黏滑只对应一个声发射事件.显微观察表明,局部化的脆性破裂是速度弱化域的主要变形机制,分布式的碎裂流动是干燥岩盐断层带在速度强化域的变形机制,颗粒边界迁移以及压溶作用的塑性变形是含水条件下岩盐断层带在速度强化域的主要变形机制,而脆性破裂和塑性变形共同控制着速度依赖性转换域断层带的变形.水的存在促进岩盐发生塑性变形,进而导致断层带从速度弱化向速度强化转换.上述结果有助于理解断层带上地震活动的特征和慢地震的机制. 相似文献
14.
15.
We present a formulation for mechanical modeling of the interaction between fracture and fluid flow. Our model combines the
classic Biot poroelastic theory and a damage rheology model. The model provides an internally consistent framework for simulating
coupled evolution of fractures and fluid flow together with gradual transition from brittle fracture to cataclastic flow in
high-porosity rocks. The theoretical analysis, based on thermodynamic principles, leads to a system of coupled kinetic equations
for the evolution of damage and porosity. A significant advantage of the model is the ability to reproduce the entire yield
curve, including positive and negative slopes, in high-porosity rocks by a unified formulation. A transition from positive
to negative values in the yield curve, referred to as a yield cap, is determined by the competition between the two thermodynamic
forces associated with damage and porosity evolution. Numerical simulations of triaxial compression tests reproduce the gradual
transition from localized brittle failure to distributed cataclastic flow with increasing pressure in high-porosity rocks
and fit well experimentally measured yield stress for Berea sandstone samples. We modified a widely used permeability porosity
relation by accounting for the effect of damage intensity on the connectivity. The new damage-permeability relation, together
with the coupled kinetics of damage and porosity evolution, reproduces a wide range of realistic features of rock behavior.
We constrain the model variables by comparisons of the theoretical predictions with laboratory results reporting porosity
and permeability variation in rock samples during isotropic and anisotropic loading. The new damage-porosity-permeability
relation enables simulation of coupled evolution of fractures and fluid flow and provides a possible explanation for permeability
measurements in high-porosity rocks, referred to as the “apparent permeability paradox.”
The text was submitted by the authors in English. 相似文献
16.
Time delays associated with processes leading to a failure or stress relaxation in materials and earthquakes are studied in
terms of continuum damage mechanics. Damage mechanics is a quasi-empirical approach that describes inelastic irreversible
phenomena in the deformation of solids. When a rock sample is loaded, there is generally a time delay before the rock fails.
This period is characterized by the occurrence and coalescence of microcracks which radiate acoustic signals of broad amplitudes.
These acoustic emission events have been shown to exhibit power-law scaling as they increase in intensity prior to a rupture.
In case of seismogenic processes in the Earth's brittle crust, all earthquakes are followed by an aftershock sequence. A universal
feature of aftershocks is that their rate decays in time according to the modified Omori's law, a power-law decay. In this
paper a model of continuum damage mechanics in which damage (microcracking) starts to develop when the applied stress exceeds
a prescribed yield stress (a material parameter) is introduced to explain both laboratory experiments and systematic temporal
variations in seismicity. 相似文献
17.
Sergei Stanchits Jerome Fortin Yves Gueguen Georg Dresen 《Pure and Applied Geophysics》2009,166(5-7):843-868
We investigated initiation and propagation of compaction bands (CB) in six wet and four dry Bentheim sandstone samples deformed in axial compression tests with strain rates ranging from 3.2 × 10?8 s?1 to 3.2 × 10?4 s?1. Circumferential notches with 0.8-mm width and 5-mm depth served to initiate CB at mid-sample length. Wet samples were saturated with distilled water and deformed at 195 MPa confining pressure and 10 MPa pore pressure. Dry samples were deformed at 185 MPa confining pressure. Twelve P-wave sensors, eight S-wave sensors and two pairs of orthogonally oriented strain-gages were glued to the sample surface to monitor acoustic emission (AE), velocities and local strain during the loading process. Nucleation of compaction bands is indicated by AE clusters close to the notch tips. With progressive loading, AE activity increased and AE hypocenters indicated propagation of a single CB normal to the sample axis. CB propagation from the sample periphery towards the centre was monitored. Microstructural analysis of deformed samples shows excellent agreement between location of AE clusters and CBs. In both dry and wet samples the lateral propagation of CBs was about 100 times faster than axial shortening rates. At the slowest displacement rate, AE activity during band propagation was reduced and CB nucleation in wet samples occurred at 20% lower stresses. This may indicate an increasing contribution of stress corrosion processes to the formation of the compaction bands. In dry and wet samples inelastic compaction energy per area ranged between 16 and 80 kJ m?2. This is in good agreement with previous estimates from laboratory and field studies. 相似文献
18.
Henryk Marcak 《Journal of Applied Geophysics》1994,31(1-4)
The essential conditions for effective and ecologically safe exploitation of underground waste storage are maintenance, prevention, and monitoring of tightness of rock masses covering and surrounding the reservoir rock complex. This monitoring can be realized by a especially designed acoustic measurement system.The reservoir rock complexes - without leakage - are supposed to be in physical equilibrium; without changes of rock dynamic properties the acoustic emission vanishes. In contrast, as is shown, the results of the field tests carried out in coal mines proved that there was a correlation between the stresses and the acoustic emission ratio. The laboratory experiments also showed correlation between changes of permeability of coal samples and acoustic emission.the explanation of the observed results is based on the development of inelastic deformation of a rock skeleton. The plastic strains in the porous rock appear after overcoming the yield point. The yield point value can be extended by increase of shear stresses, effective stresses and interstitial pressure.In particular, there are three kinds of dynamic phases which may appear preceding the failure of leak tightness:
- 1. (1) breaking of the rock masses due to stress (Griffith criterion of stability may be expressed in terms of the acoustic emission parameters),
- 2. (2) the dilatant corrosion of pressure plasticity resulting from chemical, physical and thermal activities, and
- 3. (3) the destructive increase of pressure in rock pores.
19.
Laboratory and field data indicate that rocks subjected to sufficiently high loads clearly deviate from linear behavior. Non-linear
stress–strain relations can be approximated by including third and higher-order terms of the strain tensor in the elastic
energy expression (e.g., the Murnaghan model). Such classical non-linear models are successful for calculating deformation
of soft materials, for example graphite, but cannot explain with the same elastic moduli small and large non-linear deformation
of stiff rocks, such as granite. The values of the third (higher-order) Murnaghan moduli estimated from acoustic experiments
are one to two orders of magnitude above the values estimated from stress–strain relations in quasi-static rock-mechanics
experiments. The Murnaghan model also fails to reproduce an abrupt change in the elastic moduli upon stress reversal from
compression to tension, observed in laboratory experiments with rocks, concrete, and composite brittle material samples, and
it predicts macroscopic failure at stress levels lower than observations associated with granite. An alternative energy function
based on second-order dependency on the strain tensor, as in the Hookean framework, but with an additional non-analytical
term, can account for the abrupt change in the effective elastic moduli upon stress reversal, and extended pre-yielding deformation
regime with one set of elastic moduli. We show that the non-analytical second-order model is a generalization of other non-classical
non-linear models, for example “bi-linear”, “clapping non-linearity”, and “unilateral damage” models. These models were designed
to explain the abrupt changes of elastic moduli and non-linearity of stiff rocks under small strains. The present model produces
dilation under shear loading and other non-linear deformation features of the stiff rocks mentioned above, and extends the
results to account for gradual closure of an arbitrary distribution of initial cracks. The results provide a quantitative
framework that can be used to model simultaneously, with a small number of coefficients, multiple observed aspects of non-linear
deformation of stiff rocks. These include, in addition to the features mentioned above, stress-induced anisotropy and non-linear
effects in resonance experiments with damaged materials. 相似文献
20.
通过对岩石样品进行变形及破坏试验，研究断裂形成过程中的声发射记录（ＡＥ），以找到能解释地震前兆现象的方法．另外，对试验过程中获得的大量数据及资料进行了数理统计处理． 相似文献