共查询到20条相似文献,搜索用时 46 毫秒
1.
2.
利用 Kolsky 扭转棒作为实验装置,笔者在常温常压条件下对干燥的和潮湿的大理岩试样进行了一系列的动态简单剪切的实验变形研究,以期了解在高应变率(373-1-1736-1)时岩石中孔隙水对于岩石抗剪强度的影响.结果表明,孔隙水的存在不但没有降低,反而稍微提高了岩石的抗剪强度.结合前人在静态条件下的实验研究资料,笔者认为水对岩石变形的作用机制随应变率的变化而改变.在低应变率(例如:10-9-1)时,水对岩石变形的影响分别表现为压溶作用、应力侵蚀作用和降低有效应力的效应.压溶作用和应力侵蚀作用导致岩石强度的降低;而有效应力的降低则导致岩石强度的相对提高. 相似文献
3.
4.
Crack widths and rock temperatures were monitored on an andestic bedrock cliff in the summit area of the Daisetsu Mountains, Hokkaido, northern Japan. Sequential data recorded the gradual widening of a crack to the point of critical crack extension, which resulted in catastrophic rock breakage. The data indicate that a combination of liquid water in?ltration into crack tip and subsequent freezing is the most signi?cant factor contributing to critical crack extension. The recorded sub‐critical crack movements involved a number of minor crack extensions and contractions, the timing of which correlates well with the magnitude of the reconstructed thermal stresses at the crack tip derived from thermal deformation of the plate‐shaped rock fragment. Larger crack extensions occurred when stress at the crack tip exceeded a threshold value, possibly re?ecting the control of rock fracture mechanics by which cracks are thought to propagate when the stress intensity factor at the crack tip exceeds the threshold values for stress corrosion cracking and the fracture toughness of the material. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
5.
Jan Kozák Jan Šílený Ludvík Waniek Reviewer V. Červený 《Studia Geophysica et Geodaetica》1981,25(4):332-342
Summary Tensile cracks induced by stress concentration around a fault plane in physical models under uniaxial load were analyzed. The results characterizing the decisive role of the fault plane inclination to the the stress direction are presented. Two stages of tensile crack life were determined, i.e. the first, seismoactive stage, accompanied by seismic energy release and the second aseismic one characterized by low velocity of crack propagation. Results obtained seem to be relevant to a better understanding of the character and regime of actual seismoactive faults. 相似文献
6.
岩石变形破裂过程中电荷感应信号的检测 总被引:9,自引:0,他引:9
设计了采用非接触方式、高放大倍数、高效率的电荷传感器,并给出了电荷传感器的设计原理和技术指标。利用研制的电荷传感器对岩石变形破裂过程中产生的电荷感应信号进行了检测试验。结果表明,岩石在变形破裂过程中会产生电荷感应信号,并能够被研制的电荷传感器检测到;电荷感应信号是瞬时脉冲的;随着加载应力水平的增加,电荷感应信号强度增强,在峰值应力前,电荷感应信号强度达到最大值;在破裂面接收到的电荷感应信号较强,主破裂面接收到的信号最强,因而电荷的产生和岩石的破裂有很大的关系。作为正在探索的检测岩石破坏过程的手段之一,电荷感应方法应是一种很具潜力的方法,值得深入研究。 相似文献
7.
Jiin‐Shuh Jean Chuan‐Cheng Liu Wei‐Teh Jiang Jinder Chow Ting‐To Yu Ching‐Weei Lin Shih‐Wei Huang 《地球表面变化过程与地形》2002,27(1):1-10
The 1999 Chi‐Chi earthquake significantly altered the landscape of central Taiwan. Surface deformation produced by the earthquake along the trace of the Chelungpu thrust can be classified into two styles: (1) uplift without significant surface rupture, and (2) uplift accompanied by surface rupture. Here we examine areas that exhibited the first style of deformation (e.g. Wufeng). Seismic stress at the time of the main shock may have been relieved by high pore‐fluid pressure in a 300‐m‐thick sand and gravel aquifer. Along the thrust fault, frictional heating of these sediments resulted in thermal expansion and an increase in pore‐fluid pressure. High pore‐fluid pressure damped seismic‐wave energy and enhanced intergranular slips of unconsolidated sandy and gravel sediments, which were possibly assisted by sulphuric acid corrosion, leading to a high sulphate content in the groundwater (c. 70 mg L?1). These changes permitted surface folding and terrace‐style uplifting to occur without significant rupture. In contrast, other areas in which the second style of deformation is dominant (e.g. Fengyuen‐Shihkang) have thin (0–10 m) sand and gravel deposits and lower concentrations of sulphate (c. 30 mg L?1) in groundwater. In these areas, sediments were heated but not sufficiently to produce significant thermal expansion and increase in pore‐fluid pressure; accumulation of stress in these locations led to rupture at the ground surface, with the formation of steep fault scarps. The areas exhibiting the first deformation style are characterized by the presence of high pore‐fluid pressure, frictional heat conduction, and possibly chemical corrosion related to sulphuric acid attack and formation of sulphate, in contrast to those involving significant uplift and surface rupture. The areal distribution of these two surface deformation styles suggests that the aforementioned fluid‐related subsurface processes may have altered the characteristics of sediments and caused diverse responses to the quake. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
8.
Shi-Rong Mei 《地震学报(英文版)》1996,9(1):1-12
In this paper, the stress concentration process and the time-space distribution of stress when earthquakes are in preparation
in one or more earthquake-generating bodies in a tectonic block have been analyzed and their relation with seismicity and
earthquake precursors have been studied. The results show that: 1 When the regional stress field has intensified to a certain
level, fracture begins in some block or blocks. The regional stress field will vary with time and the occurrence of strong
earthquakes in groups is the result of the evolution of this dynamic stress field. In this process, the existence and development
of more than one high stress concentration zone may give rise to a variety of pre-seismic anomaly-to-earthquake relations.
2 The process of stress variation in an earthquake-generating block generally appears as a nonlinear one. After the long-term
elastic deformation, there may be more than one time of inelastic deformation and fault-softening from the beginning of the
stage of inelastic deformation to just before the main fracture. Corresponding to such a nonlinearity, the stress and strain
fields in the earthquake-generating block will display a complex pattern of time-space evolution; and thus the earthquake
precursor fields controlled by stress and strain must display complexities in many aspects. 相似文献
9.
W. Müller 《Pure and Applied Geophysics》1986,124(4-5):693-709
Fracture phenomena in rocks are associated with mainly mode I crack growth, sometimes superposed by shear or torsion. The present paper contributes to a fracture mechanics analysis of mode I and mixed mode crack propagation, by presenting reliable fracture toughness data for some rocks which include the effect of induced crack propagation rate, and the influence of effective pressure, and by numerical calculations on fracture propagation in layered rock formations. Empirical relations between fracture toughness,K
Ic' and induced crack opening displacement rate, as well as effective pressure, are given. The observedK
Ic pressure relation supports a theoretical model which takes into account the existence of microcracks in the crack tip region. Finite element calculations of fracture propagation in layered rock formations demonstrate the important effect of mixed mode crack growth. The numerical approach is particularly applied to single crack growth in hydraulic fracturing and in three point bending tests on layered single edge crack specimens. 相似文献
10.
Brittle deformation of oceanic lithosphere due to thermal stress is explored with a numerical model, with an emphasis on the spacing of fracture zones. Brittle deformation is represented by localized plastic strain within a material having an elasto-visco-plastic rheology with strain softening. We show that crustal thickness, creep strength, and the rule governing plastic flow control the formation of cracks. The spacing of primary crack decreases with crustal thickness as long as it is smaller than a threshold value. Creep strength shifts the threshold such that crust with strong creep strength develops primary cracks regardless of crustal thicknesses, while only a thin crust can have primary cracks if its creep strength is low. For a thin crust, the spacing of primary cracks is inversely proportional to the creep strength, suggesting that creep strength might independently contribute to the degree of brittle deformation. Through finite versus zero dilatation in plastic strain, associated and non-associated flow rule results in nearly vertical and V-shaped cracks, respectively. Changes in the tectonic environment of a ridge system can be reflected in variation in crustal thickness, and thus related to brittle deformation. The fracture zone-free Reykjanes ridge is known to have a uniformly thick crust. The Australian-Antarctic Discordance has multiple fracture zones and thin crust. These syntheses are consistent with enhanced brittle deformation of oceanic lithosphere when the crust is thin and vice versa. 相似文献
11.
Apparent fracture toughness in Mode I of microcracking materials such as rocks under confining pressure is analyzed based
on a cohesive crack model. In rocks, the apparent fracture toughness for crack propagation varies with the confining pressure.
This study provides analytical solutions for the apparent fracture toughness using a cohesive crack model, which is a model
for the fracture process zone. The problem analyzed in this study is a fluid-driven fracture of a two-dimensional crack with
a cohesive zone under confining pressure. The size of the cohesive zone is assumed to be negligibly small in comparison to
the crack length. The analyses are performed for two types of cohesive stress distribution, namely the constant cohesive stress
(Dugdale model) and the linearly decreasing cohesive stress. Furthermore, the problem for a more general cohesive stress distribution
is analyzed based on the fracture energy concept. The analytical solutions are confirmed by comparing them with the results
of numerical computations performed using the body force method. The analytical solution suggests a substantial increase in
the apparent fracture toughness due to increased confining pressures, even if the size of the fracture process zone is small. 相似文献
12.
Shi-Rong Mei 《地震科学(英文版)》1996,9(1):1-12
In this paper, the stress concentration process and the time-space distribution of stress when earthquakes are in preparation in one or more earthquake-generating bodies in a tectonic block have been analyzed and their relation with seismicity and earthquake precursors have been studied. The results show that: 1 When the regional stress field has intensified to a certain level, fracture begins in some block or blocks. The regional stress field will vary with time and the occurrence of strong earthquakes in groups is the result of the evolution of this dynamic stress field. In this process, the existence and development of more than one high stress concentration zone may give rise to a variety of pre-seismic anomaly-to-earthquake relations. 2 The process of stress variation in an earthquake-generating block generally appears as a nonlinear one. After the long-term elastic deformation, there may be more than one time of inelastic deformation and fault-softening from the beginning of the stage of inelastic deformation to just before the main fracture. Corresponding to such a nonlinearity, the stress and strain fields in the earthquake-generating block will display a complex pattern of time-space evolution; and thus the earthquake precursor fields controlled by stress and strain must display complexities in many aspects. 相似文献
13.
The microstructural state and evolution of fault gouge has important implications for the mechanical behaviour, and hence
the seismic slip potential of faults. We use 3D discrete element (DEM) simulations to investigate the fragmentation processes
operating in fault gouge during shear. Our granular fault gouge models consist of aggregate grains, each composed of several
thousand spherical particles stuck together with breakable elastic bonds. The aggregate grains are confined between two blocks
of solid material and sheared under a given normal stress. During shear, the grains can fragment in a somewhat realistic way
leading to an evolution of grain size, grain shape and overall texture. The ‘breaking up’ of the fault gouge is driven by
two distinct comminution mechanisms: grain abrasion and grain splitting. The relative importance of the two mechanisms depends
on applied normal stress, boundary wall roughness and accumulated shear strain. If normal stress is sufficiently high, grain
splitting contributes significantly to comminution, particularly in the initial stages of the simulations. In contrast, grain
abrasion is the dominant mechanism operating in simulations carried out at lower normal stress and is also the main fragmentation
mechanism during the later stages of all simulations. Rough boundaries promote relatively more grain splitting whereas smooth
boundaries favor grain abrasion. Grain splitting (plus accompanying abrasion) appears to be an efficient mechanism for reducing
the mean grain size of the gouge debris and leads rapidly to a power law size distribution with an exponent that increases
with strain. Grain abrasion (acting alone) is an effective way to generate excess fine grains and leads to a bimodal distribution
of grain sizes. We suggest that these two distinct mechanisms would operate at different stages of a fault’s history. The
resulting distributions in grain size and grain shape may significantly affect frictional strength and stability. Our results
therefore have implications for the earthquake potential of seismically active faults with accumulations of gouge. They may
also be relevant to the susceptibility of rockslides since non-cohesive basal shear zones will evolve in a similar way and
potentially control the dynamics of the slide. 相似文献
14.
在临近大地震前,震源过程和前兆现象存在着一定的时间关系。本文从组合模式出发,利用断裂力学的应力一化学腐蚀理论来讨论临近大震前的震源过程和外因时震源过程的调制作用。在诸外因当中,为了研究宇宙线对地震的影响,本文具体分析了1965-1979年宇宙线μ介子强度变化的功率谱,首次得到了在所有周期分量中,准九天周期占有优势的结果。最后列举了宇宙线调制地震前兆的几个实例,并讨论了宇宙线对地壳中不稳定物质如过热液体暴沸的触发作用。 相似文献
15.
16.
Experimental study of the formation and propagation of three-dimensional (3D) faults is of great sig- nificance in the understanding of the propagation process developing from initial natural faults. In the study described in this paper, experimental investigations of 3D propagation processes of a type of surface fault are carried out under biaxial compression. The strain field near the surface fault is dy- namically measured and fully analyzed with a high-density Multi-Channel Digital Strain Gauge (MCDSG) and Digital Speckle Correlation Method (DSCM) based on the white-light image analysis. Simultane- ously the micro-fracture process involved in fault formation is observed by a 3D acoustic emission (AE) location system with a set of multi-channel whole-wave record equipment. The experimental results show that the 3D propagation process of surface fault differs greatly from that of the two-dimensional (2D) state and that a new more complicated type of 3D morphological characters and deformation mechanisms are produced. The 3D propagation process of surface faults may be divided into three stages: 1) the first stage of crack propagation initiated by wing cracks; 2) the conversion stage propa- gated by petal cracks; and 3) the second stage of crack propagation formed by shell-shaped fracture surface. The primary propagation patterns of the three stages are different. The corresponding defor- mation fields and micro-fracture distributions are likewise different. The fracture activities from petal cracks especially are of vital importance during surface fault propagation. This is also a key conversion state and marks an intrinsic difference between 2D-like and the 3D state in fault development. 相似文献
17.
Introduction ZHOU, et al (1994) collected and investigated periods of level deformation data from 1954 to 1992, and gained sequence of a picture per year (or several years) that vividly showed the varia-tion of the deformation field of Tangshan earthquake source area around the Tangshan diamond block which was 21.3. They indicated that the Tangshan earthquake source area showed de-formation gap and the hard solid characteristic of relative stabilization or relative closedown. In the investig… 相似文献
18.
Compaction of a Rock Fracture Moderated by Competing Roles of Stress Corrosion and Pressure Solution 总被引:1,自引:0,他引:1
Unusually rapid closure of stressed fractures, observed in the initial stages of loading and at low temperatures, is examined
using models for subcritical crack growth and pressure solution. The model for stress corrosion examines tensile stress concentrations
induced at the Hertzian contact of propping fracture asperities, and mediates fracture growth according to a kinetic rate
law. Conversely, pressure solution is described by the rate-limiting process of dissolution, resulting from the elevated stresses
realized at the propping asperity contact. Both models are capable of following the observed compaction of fractures in novaculite.
However, closure rates predicted for stress corrosion cracking are orders of magnitudes faster than those predicted for pressure
dissolution. For consistent kinetic parameters, predictions from stress corrosion better replicate experimental observations,
especially in the short-term and at low temperature when mechanical effects are anticipated to dominate. Rates and magnitudes
of both stress corrosion and pressure solution are dependent on stresses exerted over propping asperities. Rates of closure
due to stress corrosion cracking are shown to be always higher than for pressure solution, except where stress corrosion ceases
as contact areas grow, and local stresses drop below an activation threshold. A simple rate law is apparent for the progress
of fracture closure, defined in terms of a constant and an exponent applied to the test duration. For current experimental
observations, this rate law is shown to replicate early progress data, and shows promise to define the evolution of transport
properties of fractures over extended durations. 相似文献
19.
Double-torsion specimens of two granitic rocks were prepared in several directions with reference to microcracks fabric. Even for the same rock and at the same stress levels, the observed crack velocities in two granitic rocks were dependent on both the propagation direction and the opening direction. The maximum difference by several orders of magnitude was found for both rocks. The highest crack velocity was observed when the subcritical crack was parallel to most of the preexisting cracks. The maximum critical stress intensity factor was about twice as high as the minimum one in different directions. An analysis for a thin plate having anisotropic elasticity under torsional load showed that the observed difference in the crack velocity and the critical stress intensity factor was not an error due to conventional equations derived on the assumption of isotropic elasticity but the true material's property. As the preferred orientation of microcracks has been pointed out for many granitic rocks, we can conclude that the anisotropic nature of the fracture resistance of the two granitic rocks used in this study was not exceptional. A region of a transport-limited velocity was not found for rocks, even at the velocity of 10–2 m/s, that is almost equal to the theoretical limit of the stress corrosion cracking. 相似文献
20.
A numerical procedure for evaluation of the fracture process of gravity dams during strong earthquakes is presented. The BEM is used to discretize the dam reservoir system including the crack surfaces, and stress intensity factors at the crack tip are employed in a stage by stage procedure which simulates the crack extension. For each stage of constant crack length the mode superposition technique is applied; this is made possible by simulating the impact process of crack closing by a load pulse applied at the contact points which permits the structural stiffness to be assumed unchanged. To verify the proposed procedure, a cantilever beam model structure made of gypsum was tested on a shaking table. Good correlation with the numerical results was obtained, from which it is concluded that the procedure can be employed for evaluation of the crack propagation process in concrete structures subjected to dynamic loadings. 相似文献