Deformation Process Of Rock Research Articles

Experimental study on damage evolution of rock under uniform and concentrated loading conditions using digital image correlation

ABSTRACTDamage evolution and crack propagation in sandstone specimens have been observed by digital image correlation method. To investigate deformation and failure process of rock under different loading conditions, uniaxial compression and indentation tests were performed. Through the experiment, displacement and strain fields are simultaneously obtained that can visually display the distribution, mode and evolution of deformation and cracking in rock. Experimental results show that the damage distributes diffusely in rock at early loading stage, and the measured apparent strain increasingly concentrates with loading because of the nucleation of crack; propagation of the crack leads to the eventual failure of the specimen. Damage factor is calculated on the basis of deviation of apparent strain, and localization factor is presented to describe the level of deformation localization. The combined use of two factors can well represent the damage evolution of rock under compression.

Comparison Between Stress and Strain Quantities of the Failure–Deformation Process of Fennoscandian Hard Rocks Using Geological Information

The aim of this paper was to compare the stress and strain quantities that are related to the failure-deformation process of hard rock. The data used here was obtained from laboratory uniaxial comp ...

Dynamics of inelastic deformation of porous rocks and formation of localized compaction zones studied by numerical modeling

The paper presents a numerical analysis of the inelastic deformation process in porous rocks during different stages of its development and under non-equiaxial loading. Although numerous experimental studies have already investigated many aspects of plasticity in porous rocks, numerical modeling gives valuable insight into the dynamics of the process, since experimental methods cannot extract detailed information about the specimen structure during the test and have strong limitations on the number of tests. The numerical simulations have reproduced all different modes of deformation observed in experimental studies: dilatant and compactive shear, compaction without shear, uniform deformation, and deformation with localization. However, the main emphasis is on analysis of the compaction mode of plastic deformation and compaction localization, which is characteristic for many porous rocks and can be observed in other porous materials as well. The study is largely inspired by applications in petroleum industry, i.e. surface subsidence and reservoir compaction caused by extraction of hydrocarbons and decrease of reservoir pressure. Special attention is given to the conditions, evolution, and characteristic patterns of compaction localization, which is often manifested in the form of compaction bands. Results of the study include stress–strain curves, spatial configurations and characteristics of localized zones, analysis of bifurcation of stress paths inside and outside localized zones and analysis of the influence of porous rocks properties on compaction behavior. Among other results are examples of the interplay between compaction and shear modes of deformation. To model the evolution of plastic deformation in porous rocks, a new constitutive model is formulated and implemented, with the emphasis on selection of adequate functions defining evolution of yield surface with deformation. The set of control parameters of the model is kept as short as possible; the parameters are carefully selected to have simple and intuitive physical interpretation whenever possible. Results demonstrate that evolution of the yield surface with deformation has major influence on the resulting characteristics of deformation patterns, which is not sufficiently acknowledged in the literature.

Experimental Study on Time Series Characteristics of Rock Acoustic Emission in Complete Stress-Strain Process under Uniaxial Compression

Analysis of rock acoustic emission characteristics in complete stress-strain process under uniaxial compression shows that the evolution process of rock deformation and damage can be divided into five stages—compaction, linear elastic deformation, accelerate inelastic deformation, damage and development, plastic flow. Acoustic emission characteristics of rock can well reflect its compressive deformation and damage evolution process. Acoustic emission time series of typical plastic coal is comparatively dispersed and presents group shock type. The acoustic emission frequency events and their energy of coal are bigger around the damage point, but the maximum amplitude and the secondary maximum amplitude have not much difference. The acoustic emission events and their energy of very uniform and dense fragile limestone are mainly concentrated in a very short period of time before its damage and the acoustic emission time series manifests as isolated shock type. For sandstone whose homogeneous degree lies between typical plastic coal and very uniform and dense fragile limestone, its acoustic emission time series manifest as main shock type.

Drilling, Sampling, and Monitoring the Alpine Fault: Deep Fault Drilling Project—Alpine Fault, New Zealand; Franz Josef, New Zealand, 22–28 March 2009

Several fundamental geological and geophysical phenomena are associated with the midcrust. These include the transitions from brittle to ductile behavior and from unstable to stable frictional sliding; earthquake nucleation; maximum crustal stresses; and mineralization associated with permeable fractures. However, knowledge of deformation, seismogenesis, and mineralization in the midcrust is based largely on remote geophysical observations of active faults and direct geological observations of fossil faults.The Alpine Fault is a major dextral‐reverse fault that is thought to fail in large earthquakes (Mw ≈ 7.9) every 200–400 years and to have last ruptured in 1717 C.E. Ongoing uplift has rapidly exhumed a crustal section from 20‐to 30‐kilometer depths, yielding a young (<∼1‐million‐year‐old), well‐preserved sample of structures currently active at depth. The Deep Fault Drilling Project (DFDP) proposes to drill, sample, and monitor the Alpine Fault to better understand processes of rock deformation, seismogenesis, and mineralization.

Numerical simulation of rock fracturing under uniaxial compression using virtual internal bond model

A multi-scale virtual internal bond (VIB) model for the isotropic materials has been recently proposed to describe the material deformation and fracturing. During the simulation process of material fracturing using VIB, the fracture criterion is directly built into the constitutive formulation of the material using the cohesive force law. Enlightened by the similarity of the damage constitutive model of rock under uniaxial compression and the cohesive force law of VIB, a VIB density function of rock under uniaxial compression is suggested. The elastic modulus tensor is formulated on the basis of the density function. Thus the complete deformation process of rock under the uniaxial compression is simulated.

Folding with thermal–mechanical feedback: Discussion

A recent paper in this Journal by Bruce Hobbs, Klaus Regenauer-Lieb and Alison Ord [Hobbs, B., Regenauer-Lieb, K., Ord, A., 2008. Folding with thermal–mechanical feedback. Journal of Structural Geology 30, 1572–1592] presents an alternative theory to the traditional Biot-Ramberg theory for folding of viscous rocks that involves non-equilibrium thermodynamics and thermal–mechanical feedback. The authors convey a strong message throughout their paper that the folds produced by this theoretical and numerical modelling are geologically realistic and provide a better explanation for many natural folds than the traditional theory. They promise the same approach for boudinage, and present this folding paper as part of a “unified framework for rock deformation processes”. Readers of the Journal of Structural Geology might be led to conclude that this paper provides a good alternative model for folding of rocks. Our discussion will disagree, on four counts.

Modeling the Effects of Heterogeneity and Anisotropy on the Excavation Damaged/Disturbed Zone (EDZ)

When modeling the mechanical behavior of underground excavations, it is necessary to include the influence of the rock mass characteristics on the Excavation Damaged/Disturbed Zone (EDZ). In this paper, the Realistic Failure Process Analysis code, RFPA, is used to model the extent of the EDZ. The inhomogeneous characteristics of rock at the mesoscopic level are included by assuming that the material properties of the constituent elements conform to a Weibull distribution; the anisotropy is incorporated as a transversely isotropic medium; the non-elastic characteristic is simulated via an elastic damage-based constitutive law. A finite element program is adopted as the basic stress analysis tool. In this study, a notable feature is that no a priori assumptions need to be made about where and how fracture and failure will occur – cracking can take place spontaneously and can exhibit a variety of mechanisms when certain local stress conditions are met. The deformation and failure process of anisotropic rock around excavations of different geometries is analyzed, and compared to experimental tests, showing similar fracture patterns. Additionally, the effect of confining stress and of different material layers is modeled and discussed. It is found that the model clearly illustrates that fracturing, both initiation and propagation, occurs as a combination of the stress concentrations and weakness planes introduced via the transverse anisotropy – which could represent either foliations or ubiquitous joint sets.

Shock Metamorphism of Bosumtwi Impact Crater Rocks, Shock Attenuation, and Uplift Formation

Shock wave attenuation rate and formation of central uplifts are not precisely constrained for moderately sized complex impact structures. The distribution of shock metamorphism in drilled basement rocks from the 10.5-kilometer-diameter Bosumtwi crater, and results of numerical modeling of inelastic rock deformation and modification processes during uplift, constrained with petrographic data, allowed reconstruction of the pre-impact position of the drilled rocks and revealed a shock attenuation by approximately 5 gigapascals in the uppermost 200 meters of the central uplift. The proportion of shocked quartz grains and the average number of planar deformation feature sets per grain provide a sensitive indication of minor changes in shock pressure. The results further imply that for moderately sized craters the rise of the central uplift is dominated by brittle failure.

Folding with thermal–mechanical feedback

Folding of viscous layered rocks is traditionally viewed as an instability arising from viscosity differences between layers. This approach derives from Biot, and for purely viscous materials predicts the growth of single wavelength systems; the dominant wavelength is sensitive to layer thickness, the viscosity ratio between the layers, the amount of shortening and the boundary conditions. This paper presents one alternative theory of folding to that of Biot and addresses the deformation of elastic-viscous materials where the viscosity ratio between layers is small and Biot theory predicts folds will not form. Such ratios are consistent with situations in the mid to lower crust as indicated by experimental data. Folding results from the coupling between temperature dependent viscosity and heat generated by deformation; the result is weakening in the hinges of embryonic folds and subsequent buckling. This process is distinct from the Biot buckling process. The structures that develop resemble natural structures in that folds develop at a range of length scales, hinges undergo strong thickening, and axial plane crenulations form. This approach is grounded in non-equilibrium thermodynamics; the coupling of deformation to fluid flow and chemical reactions is explored as part of a unified framework for rock deformation processes.

A comparative study of natural and experimental nano-sized grinding grain textures in rocks

In three shallow-level fault systems in eastern China, nano-sized (30–100 nm) grinding grain textures are found in the thin-shelled rheological layer representing frictional-viscous high strain field. The surface layer near slipping plane is composed of stacks of grinding grains with high sphericity and uniform nano-sized diameter, while the underlying layer appears as a mixture of irregular ones with diverse diameters. Rock deformation experiments indicate that the grinding grain texture is a common phenomenon in shearing fractures, suggesting a potential transition from sliding friction to rolling one during the rock deformation process. This transition is crucial for many tribological processes in geological fields.

Three-Dimensional Elastoplastic Deformation Analysis Coupled With Oil Flow for Perforation Tunnels of an Oilwell

Instability of completed sand reservoirs reduces oil production rate and degrades production equipments. A major cause of such instability is plastic deformation of perforation tunnel, resulting in sand production. Influence of direction of maximum principal stress on perforation tunnel has not been investigated either experimentally or theoretically. Elastoplastic consolidation analysis is the foundation of sand production prediction of an oilwell. Three dimensional elastoplastic consolidation analyses were made numerically for the deformation of perforation tunnel of an oilwell coupled with oil flow within sand reservoir with ABAQUS-6.5 finite element software. The drilling processes of borehole and perforation tunnel were simulated in combination of rock deformation process which was regarded as a coupled multiphase problem. Mohr-Coulomb yielding criterion was adopted in the calculation. The designs with 4-perforation density and with 8-perforation density were numerically analyzed and compared. Influence of the direction of principal horizontal effective geostress on the instability of perforation tunnel and that of perforation density were investigated. Numerical results indicate that 1) there is rather large plastic zone occurs when the axis of perforation tunnel is alone the direction of the maximum principal horizontal direction. If the axis of perforation tunnel is alone the direction of the minimum principal horizontal direction, there will be no plastic zone under the same loading conditions. 2) When the density of perforation tunnel is reduced from 8-shots per foot to 4 shots per foot, the plastic zone around the perforation tunnels will be much smaller.

Displacement, stress and seismicity in roadway roofs during mining-induced failure

Roof stability in gateroads is a long-standing issue in many of the underground mines in Australia that use longwall extraction methods, due primarily to a significant increase of vertical stresses ahead of the longwall face. Although numerous studies have been done in the past, the process of roof rock deformation and breakage prior to and during a roof failure in an actual mining environment is still being debated. This paper describes a new integrated roof monitoring system and the results from applying this system in an Australian underground coal mine. The system integrates displacement, stress and seismic monitoring. It has been applied to two roadways in an Australian underground coal mine during two field experiments. The key roof behaviour identified by the integrated monitoring package during the two field monitoring experiments is reported and discussed in this paper. The experiments were conducted in the “tailgate” roadways that are adjacent to the caved zone, or “goaf”, of the previously mined panels. It was found in the experiments that, prior to roof falls, roof displacement accelerates whereas the horizontal stresses reduce. Seismic activity intensifies before major roof displacement or stress changes are evident, and subsides in the later stage of roof failure when large roof displacement is visible. The seismic resonance frequencies decrease during roof failure development. The field monitoring studies have also identified a number of quantitative and site-specific roof fall precursors potentially useful for roof fall prediction and prevention.

Study on Complete Stress-Strain Experiment and Destruction Characteristics of Rock under Lower Confining Pressure

A complete stress-strain experiment curve, gained through exerting low confining pressure on brittle rock, reflects the deformation and destruction process of rock under different confining pressure, and reveals that after the destruction of rock, not only slip deformation but also re-destruction process will take place, which would possibly lead to further reduction of the mechanical properties of the rock mass. Through the analysis of the relation between complex failure modes, load carrying capacity after rock destruction and the volumetric strain, the paper gives us a further explanation of the complex destructive process of rock. The basis for the rock’s load-carrying capacity after destruction is an effective restraint stress, which shows that effective supporting in underground engineering is the key factor for providing the cracked surrounding rock with load-carrying capacity and guaranteeing the stability of the structure.

Rock deformation processes in the Karakoram fault zone, Eastern Karakoram, Ladakh, NW India

The Karakoram fault shows a full range of fault rocks from ductile (deformation by intracrystalline plasticity) mylonites to low temperature brittle fault rocks along the trace of the fault in the Eastern Karakoram, Ladakh, NW India. The Karakoram fault is a prominent feature on satellite images and has estimated long-term average slip rates between 3 and 11 mm/year, based on U-Pb geochronology of mapped offset markers, notably mid-Miocene leucogranites. Mylonitic marbles, superimposed by cataclastic deformation and clay-bearing fault gouges and late fracturing were found on a presently active strand of the fault, and testify to progressive deformation from plastic through brittle deformation during unroofing and cooling. From microstructural analysis we confirmed the right-lateral strike slip character of the fault, estimated peak differential stresses of ca. 200 MPa at the transition from plastic to brittle deformation, and found microstructural features to be consistent with inferences from the extrapolation of deformation behaviour from experimental rock deformation studies. Implied long-term averaged slip rates from microstructural constraints were found to be broadly consistent with estimates from geochronologic and geodetic studies.

PASSCHIER C. W. & TROUW R. A. J. 2006. Microtectonics, 2nd ed. xvi + 366 pp. + CD-ROM. Berlin, Heidelberg, New York: Springer-Verlag. Price Euros 59.95 (+ VAT at local rate), SFr 106.00, £46.00, US $79.95 (hard covers). ISBN 3 540 64003 7

Microtectonics is a book that I have come to value highly since its publication in 1996. I like the excellent photographs of deformed rocks under the microscope, with their precise descriptive captions. I like the lucid qualitative descriptions of deformation processes in rocks, complemented by simple effective line drawings. Perhaps, subconsciously, I like the poetic vocabulary of microtectonics – snowball garnets and unswept cores, …

On drilling directions for optimizing horizontal well stability using a dual-porosity poroelastic approach

Horizontal wells are often drilled in pay zones, where formations frequently contain dominant natural fractures. For characterizing such reservoirs the dual-porosity poroelastic model appears to be relevant to assess stresses as well as flow fields. Traditionally, various combinations of elastic, elastoplastic and poroelastic models are employed to predict wellbore stability and calculate mud weight windows. However, the majority of such models are either limited to the case of vertical wells, or unsuitable for applications to naturally fractured porous formations. A novel wellbore model, based on the dual-porosity poroelastic theory, has been developed, which can effectively simulate the coupled processes of fluid flow and rock deformation in fractured porous formations. The numerical implementation of the theoretical model leads to a pseudo-three-dimensional generalized plane strain finite element model specialized in analyzing borehole stability problems. The numerical model not only performs the effective stress and fluid pressure analyses, but also conducts the mud weight calculation and optimizes the drilling direction. The model has been further applied to analyze the stability of horizontal wells with open-hole completion, drilled parallel or perpendicular to the maximum horizontal stress direction. Results show that horizontal borehole stability depends strongly on the in-situ stress state and borehole orientation: the horizontal wells drilled in the maximum stress direction in a strike slip faulting stress regime are usually more stable during both drilling and production.

Crack-seal patterns: records of uncorrelated stress release variations in crustal rocks

Abstract Statistical properties of crack-seal veins are investigated with a view to assessing stress release fluctuations in crustal rocks. Crack-seal patterns correspond to sets of successive parallel fractures that are assumed to have propagated by a subcritical crack mechanism in the presence of a reactive fluid. They represent a time-sequence record of an aseismic and anelastic process of rock deformation. The statistical characteristics of several crack-seal patterns containing several hundreds of successive cracks have been studied. Samples were collected in three different areas, gold-bearing quartz veins from Abitibi in Canada, serpentine veins from the San Andreas system in California and calcite veins from the Apennine Mountains in Italy. Digitized pictures acquired from thin sections allow accurate measurement of crack-seal growth increments. All the samples show the same statistical behaviour regardless of their geological origin. The crack-seal statistical properties are described by an exponential distribution with a characteristic length scale and do not show any spatial correlation. They differ from other fracture patterns, such as earthquake data, which exhibit power-law correlations (Gutenberg-Richter relationship). Crack-seal series represent a natural fossil record of stress release variations (less than 50 bars) in the crust that show a characteristic length scale, associated with the resistance of rock to effective tension, and no correlation in time.

Shear localisation and strain distribution during tectonic faulting—new insights from granular-flow experiments and high-resolution optical image correlation techniques

Brittle faults reflect a complex strain history that emerges from contrasting modes of distributed and localised deformation, and their interaction on various spatial and temporal scales. To better understand this process, we monitor the displacement field in scaled tectonic model experiments using high-resolution optical image correlation techniques (particle imaging velocimetry, PIV). 2D and 3D surface displacement data of extensional and contractional sandbox experiments show that the mode, pattern, and temporal variation of strain accumulation are strongly dependent on the non-linear strain-dependent frictional strength of granular model materials similar to natural deformation processes in brittle rocks. Strain hardening and softening control the shear zone formation. The pattern of localised deformation is established much earlier than is visible from visual inspection of the experiment. Evolution of distributed strain in the surrounding material of the shear zones and discontinuous shear re-localisation control later stages irrespective of the kinematic boundary conditions. High-resolution optical strain monitoring quantifies the spatial and temporal patterns of strain accumulation in our model experiments with unprecedented detail. Together with detailed characterisation of the deformation behaviour of the model materials, our experiments will help to re-evaluate important scaling issues, and allow accurate comparison of analogue experiments with numerical simulations.

Theoretical, Numerical and Experimental Study of Deformation and Failure Process of Rock

In this paper, theoretical constitutive model, numerical tool, viz., RFPA code and servo-type testing machine, viz., RMT-150B rock testing systems were briefly described, respectively. Then, based on theoretical analysis, numerical simulation and experimental tests for rock specimens in uniaxial compression, the relations and differences between theoretical, numerical and experimental results, especially the complete stress-strain curves, were contrastively analyzed and investigated. The reason for these relations and differences among results was also proposed in this paper.