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Residual stress measurement and analysis of siliceous slate-containing quartz veins
Abstract
Engineering geological disasters such as rockburst have always been a critical factor affecting the safety of coal mine production. Thus, residual stress is considered a feasible method to explain these geomechanical phenomena. In this study, electron backscatter diffraction (EBSD) and optical microscopy were used to characterize the rock microcosm. A measuring area that met the requirements of X-ray diffraction (XRD) residual stress measurement was determined to account for the mechanism of rock residual stress. Then, the residual stress of a siliceous slate-containing quartz vein was measured and calculated using the sin2ϕ method equipped with an X-ray diffractometer. Analysis of microscopic test results showed homogeneous areas with small particles within the millimeter range, meeting the requirements of XRD stress measurement statistics. Quartz was determined as the calibration mineral for slate samples containing quartz veins. The diffraction patterns of the (324) crystal plane were obtained under different ϕ and φ. The deviation direction of the diffraction peaks was consistent, indicating that the sample tested had residual stress. In addition, the principal residual stress within the quartz vein measured by XRD was compressive, ranging from 10 to 33 MPa. The maximum principal stress was parallel to the vein trend, whereas the minimum principal stress was perpendicular to the vein trend. Furthermore, the content of the low-angle boundary and twin boundary in the quartz veins was relatively high, which enhances the resistance of the rock mass to deformation and promotes the easy formation of strain concentrations, thereby resulting in residual stress. The proposed method for measuring residual stress can serve as a reference for subsequent observation and related research on residual stress in different types of rocks.
... Various geological phenomena in the lithosphere and the associated physical and chemical processes are closely correlated with the action of in-situ stresses [1][2][3][4][5][6]. Understanding the state of crustal stress, especially the stress conditions at great depths, is a necessary foundation for solving the scientific issues associated with geodynamics, such as plate driving mechanism, earthquake mechanism, volcanism, and tectonism, and is also a prerequisite for designing and devising underground projects and guiding the development of subsurface energy resources [7][8][9][10][11][12][13][14][15]. The origin of in-situ stress is quite complicated and has not yet been fully understood so far. ...
... The membership function of σ H is defined as 13) where λ (y j ) represents the membership degree of σ H at the discrete point y j ; λ (x i ) stands for the membership degree of C ERP at the discrete point x i . When the inference factor is unmeasurable or the accuracy requirement is not high, the most possible prediction value can be determined according to the principle of maximum membership [48]. ...
Understanding the mechanical properties of the lithologies is crucial to accurately determine the horizontal stress magnitude. To investigate the correlation between the rock mass properties and maximum horizontal stress, the 3D stress tensors at 89 measuring points determined using an improved overcoring technique in nine mines in China were adopted, a newly defined characteristic parameter ERP was proposed as an indicator for evaluating the structural properties of rock masses, and a fuzzy relation matrix was established using the information distribution method. The results indicate that both the vertical stress and horizontal stress exhibit a good linear growth relationship with depth. There is no remarkable correlation between the elastic modulus and elastic modulus and depth, and the distribution of data points is scattered and messy. Moreover, there is no obvious relationship between the RQD and depth. The maximum horizontal stress σH is a function of rock properties, showing a certain linear relationship with the ERP at the same depth. In addition, the overall change trend of σH determined by the established fuzzy identification method increases with the increase of ERP, and the fuzzy identification method also demonstrates a relatively detailed local relationship between σH and ERP, and the predicted curve rises in a fluctuating way, which is in accord well with the measured stress data.
... Consequently, mining operations in these formations face significant challenges (Liu et al., 2020;Liu et al., 2021;Liu et al., 2022;Asif et al., 2022;Liu et al., 2022;Li et al., 2022;Liu et al., 2023). This difficulty necessitates indepth research on utilizing the geological characteristics of western China to implement targeted measures for preserving the weakroof rock layer and regulating the working face weighting (Xu et al., 2018;Wang et al., 2023a;Wang et al., 2023b;Wang et al., 2023c). This study investigated the physical, mechanical, and hydrophysical properties of weakly cemented strata, using a coal mining face in a mine located in western China as a case study. ...
Extremely thick and hard roofs are difficult to break in the mining of a working face, and the large area of the suspended roof easily induces a strong ground pressure or dynamic impact disasters. The roof control of a coal mining face in a mine in western China was taken as a case study. The mineral composition, microstructure, and hydrophysical properties of the hard roof overlying the coal seam were analyzed. The characteristics of the weak-cementation strata that are prone to mud and collapse when encountering water were targeted to investigate the hydraulic softening roof-cutting and pressure relief technology. It was found that the clay mineral composition in the roof plate accounts for 60.6%. After 24 h of natural immersion, the rock strength decreased by approximately 10.3%–49%, and further immersion caused disintegration. By arranging high and low double-row water injection softening drilling holes in the cutting hole and roadway of the working face, the strength of roof rock strata in the target area was reduced, and the initial weighting step distance and weighting strength of the working face were reduced. The hydraulic softening roof-cutting pressure relief technology effectively regulated the weighting step distance of the hard roof and the peak weighting of the working face.
... According to the calculation method of the acoustic emission b value, the corresponding Python code was compiled to obtain the variation characteristics of the acoustic emission b value during the whole process of the monzogranite cyclic loading and unloading (Erarslan 2016;Liu and Dai 2021;Martin and Chandler 1994;Yu et al. 2021;Zhang and Zhang 2017;Wang et al. 2023; Yang et al. ...
The volume evolution behavior of rock fissures and the characteristics of acoustic emission under cyclic loading are critical for rock stability analysis. To study the volume change behavior of monzogranite fissures and the characteristics of acoustic emission signals under cyclic loading, we selected samples of monzogranite at − 1600 m from a gold mine located in the Jiaodong Peninsula at a depth of − 1600 m and investigated the samples using triaxial cyclic loading—unloading tests and acoustic emission monitoring. As the volume change behavior of the monzogranite fissures and acoustic emission signals were monitored and recorded, the calculated fracture volume strain ratio coefficient and acoustic emission entropy value were proposed to describe the evolution process of fissures inside the rock. The research results showed that the volume strain ratio curve of the rock fractures exhibited a logarithmic variation characteristic during the cyclic loading and unloading, and the fracture volume strain ratio better reflected the relative scale of the internal fracture strain in the rock to the total volume strain. The acoustic emission entropy value reflected the crack evolution behavior during the loading and failure processes, which was a rapid decline in the initial stage of loading and a rapid upward trend in the failure stage. The observed “V”-shaped change in the acoustic emission entropy can be used as an early warning for rock failure. The research results can provide theoretical guidance for rock stability analysis.
... Liu et al. [21] evaluated the importance of confining stresses on the mechanical properties of rock materials with the help of fitting analysis of quantitative equations in similar simulation experiments. Wang et al. [22] measured and calculated the residual stresses in quartz veins of silica-bearing slate by the X-ray diffractometer method. ...
Locked-in stress refers to internal stress present within rock formations that can influence the failure process of rocks under specific conditions. A simplified mechanical model is applied, drawing on elasticity and the hypothesis of locked-in stress, to explore the influence of locked-in stress on the mechanical properties of loaded rocks. An analytical solution is obtained for the stress distribution in a failure model of rocks that include locked-in stress. The findings demonstrate that the geometry and orientation of stress inclusions within the rock influence the initiation and propagation of cracks under the combined influence of locked-in stress and high-stress conditions. Moreover, the presence of locked-in stress substantially reduces the rock’s capacity to withstand maximum stress, thereby increasing its susceptibility to reaching a state of failure. The increase in closure stress leads to a significant increase in the magnitude of the maximum stress drop and radial strain variation within the rock, resulting in reduced strength and a shortened life of the ageing failure of the rock. In addition, the influence of stress inclusions on energy dissipation is investigated, and a novel relationship is established between the roughness coefficient of the rock structure surface and the angle of the rock failure surface. This relationship serves to characterize the linear dynamic strength properties of rock materials containing locked-in stress. This investigation not only advances the comprehension of stress distribution patterns and the effects of locked-in stress on rock failure patterns but also facilitates a more precise portrayal of the nonlinear features of alterations in the rock stress-strain curve under the influence of confined stress. These findings provide a solid theoretical foundation for ensuring the safety of excavations in various deep engineering projects.
... There are many initial cracks of different scales inside the rock mass. These cracks not only alter the mechanical characteristics of the rock but also, under external forces, the propagation and connection of cracks lead to rock failure and ultimately result in engineering accidents [2][3][4]. The propagation and interconnection of cracks within the rock mass account for the majority of failure occurrences in rock and soil engineering, such as the landslide that occurred in Yanchihe Phosphorus Mine, Yichang City, Hubei Province, China, in 1980, and the water seepage accident during the construction of Foshan Subway Line 2 in 2018. ...
To investigate the impact of crack inclination angle on the tensile strength and characteristics of splitting failure in rock, split tests were conducted on fine-grained sandstone with pre-existing cracks under different crack inclination angle conditions. Acoustic emission and digital image techniques were continuously monitored during the tests. The evolution of absorbed energy during the loading and failure processes was calculated and discussed, aiming to elucidate the interconnections among the maximum absorbed energy, the pre-existing crack inclination angle, the tensile strength, and the acoustic emission energy of the rock, which can provide a reference for the design and construction of tunnels or mines in rock formations with pre-existing cracks. The experimental findings indicate the following: (1) The tensile strength and failure displacement decrease first and then increase with the increase in the pre-existing crack inclination angle, demonstrating an approximate “V”-shaped alteration. (2) The failure modes of specimens with pre-existing cracks can be classified into three types: tensile failure along the center of the disk, tensile failure along the tip of the pre-existing crack, and tensile–shear composite failure along the tip of the pre-existing crack. (3) The crack inclination angle exerts a substantial influence on the evolution curve of energy absorption. The maximum energy absorption of the specimens first increases and then decreases with the increase in the crack inclination angle. Moreover, a corresponding nonlinear relationship is observed between the maximum energy absorption and the tensile strength, as well as the AE energy.
To improve the accuracy of rock failure monitoring, this article addresses the optimization problem of denoising acoustic emission (AE) signals. Combining laboratory experiments on rock AE and theoretical research on signal denoising, a denoising method based on improved complete ensemble empirical mode decomposition with adaptive noise (ICEEMDAN) is proposed for rock fracture AE signals. The method utilizes the ICEEMDAN algorithm to decompose the original noisy signal into multiple intrinsic mode functions (IMFs) and employs cluster analysis to determine data thresholds based on their characteristics. Subsequently, using multiple criteria such as permutation entropy, correlation coefficient, and variance contribution rate, the IMFs are categorized into two groups. The low-correlation portion is partially removed based on the combination of indicators, while the high-correlation portion is denoised using wavelet thresholding (WT). Finally, a wavelet analysis is performed to reconstruct the signal, effectively achieving an optimized denoising of the original signal. Quantitative analysis of denoising effects on typical rock uniaxial compression fracture AE signals reveals that the optimized method has a positive impact on high-frequency noise reduction. The peak frequency range is unaffected before and after optimization, while the main amplitude reduction is concentrated in the high-frequency range. Compared to traditional wavelet denoising methods, the proposed method exhibits higher signal-to-noise ratio (SNR) improvement, as well as varying degrees of reduction in mean squared error (MSE) and total harmonic distortion (THD). The research presented in this paper introduces a novel approach to optimizing the application of rock acoustic emission signals.
This article reviews the current status on the dynamic behavior of highly stressed rocks under disturbances. Firstly, the experimental apparatus, methods, and theories related to the disturbance dynamics of deep, high-stress rock are reviewed, followed by the introduction of scholars’ research on deep rock deformation and failure from an energy perspective. Subsequently, with a backdrop of high-stress phenomena in deep hard rock, such as rock bursts and core disking, we delve into the current state of research on rock microstructure analysis and residual stresses from the perspective of studying the energy storage mechanisms in rocks. Thereafter, the current state of research on the mechanical response and the energy dissipation of highly stressed rock formations is briefly retrospected. Finally, the insufficient aspects in the current research on the disturbance and failure mechanisms in deep, highly stressed rock formations are summarized, and prospects for future research are provided. This work provides new avenues for the research on the mechanical response and damage-fracture mechanisms of rocks under high-stress conditions.
The rock contains many inclusions which produce high locked-in stress under the ground stress. In order to study the influence of locked-in stress on the mechanical properties of rocks, the rock-like materials and nitrile rubber particles are used to make a test block of the rock-like model which contains inclusions. The rubber particles will expand as the test block is heated, which creates locked-in stress in the inclusions. Uniaxial compression tests of similar model blocks with different locked-in stresses and different inclusion contents were performed by using a water bath and MTS-5T uniaxial compression testing machine. The results show that the peak strength and elastic modulus decreased with the increasement of locked-in stress and inclusion content. In the meantime, the relationship among the peak strength, the elastic modulus of the test piece, the locked-in stress and the inclusion content were obtained with the help of a mathematical fitting analysis of the quantitative formula. Furthermore, the expression and value curve of the joint impact factor are calculated. This paper evaluates the importance of the locked-in stress in the mechanical properties of the rock-like material and provide a guide for other researchers to further investigate the locked-in stress in rocks.
Al composites are of interest due to their appropriate ratio of strength to weight. In our research, an Al/Co3O4 nanocomposite was generated using a sintering technique. The powders of Al with various Co3O4 nanoparticle contents (0wt%, 0.5wt%, 1.0wt%, 1.5wt%, 2.0wt%, and 2.5wt%) were first blended using planetary milling for 30 min, and compressed in a cylindrical steel mold with a diameter of 1 cm and a height of 5 cm at a pressure of 80 MPa. The samples were evaluated with X-ray diffractometry (XRD), scanning electron microscopy (SEM), Vickers hardness, and a vibrating sample magnetometer (VSM). Although the crystallite size of the Al particles remained constant at 7–10 nm, the accumulation of nanoparticles in the Al particle interspace increased the structural tensile strain from 0.0045 to 0.0063, the hardness from HV 28 to HV 52 and the magnetic saturation from 0.044 to 0.404 emu/g with an increase in Co3O4 nanoparticle content from 0wt% to 2.5wt%.
Hydraulic fracture is widely performed to enhance oil and gas production in the development of unconventional reservoirs. This paper proposes a numerical model for the calculation of the unpropped fracture conductivity of shale. This numerical model consists of three basic models, namely, the numerical reconstruction model of fracture morphology, fracture deformation model under closed stress, and fluid flow model. The numerical model can be used to analyze the influencing factors of the unpropped fracture conductivity of shale quantitatively. The results demonstrate that the fracture misalignment of shale is a prerequisite for unpropped fractures with conductivity at high closed stress. Furthermore, the unpropped fracture conductivity of shale decreases exponentially with the increase in closed stress. Moreover, closed stress is the factor having the most significant influence on the unpropped fracture conductivity of shale, followed by roughness and fracture morphology. The negative effect of closed stress can be reduced by increasing the fracture morphology during the fracturing operation.
Coated Electrodes with small amounts of nickel were developed for welding ductile iron (DI) and conversion of the same into austempered ductile iron (ADI) after austempering. Among six electrodes, Trials 3 and 4 were selected for establishing crack-free weld deposits via preheating and post-weld heat treatment. Austenitization was performed at 900°C for 2 h and austempering at 300 or 350°C for three different holding times to observe the results of austempering with respect to the microstructure, hardness, and austempering kinetics of the samples. The microstructures of the weld deposits showed needle-like bainitic ferrite with small amounts of retained austenite when treated at 300°C and feathery bainitic ferrite with large amounts of retainedaustenite when treated at 350°C. The electrode labeled with Trial 3 revealed greater austenite contents than that labeled with Trial 4 when treated with a 2 h holding time regardless of the austempering temperature applied. The transformation rate of the bainitic ferrite of Trial 3 was relatively higher than that of Trial 4 and showed a lower rate constant, leading to a higher diffusion rate of carbon in austenite.
With the research development of the magnesium alloys, the deformation or stress corrosion induced by residual stress (RS) attracted extensive interests in industry and research efforts extensive. However, there are relatively few studies on the RS of magnesium alloys in the world. The generation cause of RS in magnesium alloys was analyzed at first. Several methods of determinate the RS, including destructive methods (drilling hole, crack compliance, layer exfoliation etc.) and non-destructive methods (X-ray Diffraction, Neutron Diffraction, Short Wavelength X-ray Diffraction) were summarized. The factors that influence the measuring accuracy of XRD method were emphasized. The research trends of RS in magnesium alloys were put forward.
A rockburst is defined as damage to an excavation in a sudden or violent manner, frequently occurring during the excavation of civil engineering tunnels and deep-level mining. Small-scale structural planes in the vicinity of tunnels have been found to play an important role in controlling certain rockbursts in the deeply buried tunnels of the Jinping-II Hydropower Station. In order to study the mechanisms of bursts related to the structural plane, four typical examples were selected to illustrate the temporal and spatial characteristics of the burst and the exposed plane. Three types of rockbursts were classified based on these examples and on a preliminary analysis of the various mechanisms—namely, fault-slip burst, shear rupture burst, and buckling burst. Model experiments using cement mortar revealed three failure mechanisms of the structural plane under shear stress: slip dislocation of the asperities, tensile failure of the footwall and hanging wall initiated from the root of the asperities, and impact fracture of the front end of the hanging wall and back end of the footwall. These mechanisms are used to explain the development processes of fault-slip and shear rupture bursts. Analysis of the source mechanisms of buckling bursts caused by structural planes is also provided, and three proposed source mechanisms are put forth to illustrate the factors that may have triggered the buckling bursts: self-adjustment and accumulation, disturbance from machine or blasting excavation, and energy input from remote seismic sources. Issues that must be addressed in the future are outlined and discussed in the final section. The research results contribute to a mechanistic understanding of and control method for structure-type rockbursts in deep hard-rock tunnels.
We report on measurements of residual stress up to 300 MPa with a microfocused synchrotron X-ray beam in quartz fragments in a cataclasite from the damage zone of the San Andreas fault, California (USA). Samples were extracted from the San Andreas Fault Observatory at Depth drill core at a depth of 2.7 km. Stresses were derived from lattice distortions observed on Laue diffraction images. These stresses are distributed nonhomogeneously at the micron scale and are much higher than bulk-rock strengths of fault gouge, suggesting different processes at the microscopic and macroscopic scales. Our results indicate that residual lattice strain in quartz is a potential paleopiezometer to estimate stress in deformed rocks.
Warm laser shock peening (WLSP) is a new surface modification technique combining laser shock peening (LSP) and dynamic strain aging (DSA). In order to investigate the surface modification of Ni-based single-crystal superalloy by WLSP and the mechanism of action, and to compare LSP, WLSP, and LSP experiments were conducted on DD6 (Chinese Brand) samples. After that, the samples were subjected to heat treatment and hot corrosion experiments, respectively. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and field emission transmission electron microscopy (FE-TEM) to obtain the deformation and strengthening mechanisms of WLSP and LSP on the material. In addition, the experimental results were analyzed to obtain the improvement mechanism of WLSP on the thermal stability of compressive residual stress and the hot corrosion resistance of the samples. To summarize the experimental results, we obtained that the near-surface dislocation distribution, dislocation density, thermal stability of compressive residual stress, and hot corrosion resistance of the material all tend to improve with increasing temperature for the WLSP-treated samples.
Climate changes that occur as a result of global warming caused by increasing amounts of greenhouse gases (GHGs) released into the atmosphere are an alarming issue. Controlling greenhouse gas emissions is critically important for the current and future status of mining activities. The mining industry is one of the significant contributors of greenhouse gases. In essence, anthropogenic greenhouse gases are emitted directly during the actual mining and indirectly released by the energy-intensive activities associated with mining equipment, ore transport, and the processing industry. Therefore, we reviewed both direct and indirect GHG emissions to analyze how mining contributes to climate change. In addition, we showed how climate change impacts mineral production. This assessment was performed using a GHG inventory model for the gases released from mines undergoing different product life cycles. We also elucidate the key issues and various research outcomes to demonstrate how the mining industry and policymakers can mitigate GHG emission from the mining sector. The review concludes with an overview of GHG release reduction and mitigation strategies.
If a crystal lattice is subjected to a stress, it becomes distorted and no longer represents the ideal crystal symmetry, and if the stress introduces defects such as dislocations, some of this distortion is preserved after the applied stress is removed. In this study, we investigate lattice distortion in quartz at the micron scale with synchrotron X-ray Laue diffraction. From Laue images the local deviatoric strain tensor is derived and corresponding stresses are calculated based on elastic properties. The method is applied to metasedimentary quartzites from the Bergell Alps that were deformed at conditions of greenschist facies metamorphism. The residual palaeostrain is represented in maps of the deviatoric strain tensor components and with deviatoric strain axis pole figures. Data suggest overall shortening perpendicular to the schistosity plane but with considerable asymmetry relative to foliation and lineation, probably attributed to simple shear. Crystallographic pole figures from Laue diffraction agree with neutron diffraction and EBSD measurements and display quartz c-axes girdle distributions with maxima also perpendicular to schistosity. The method shows promise to be used as a palaeo-piezometer to unravel the stress field during tectonic deformation.
We use microstructural, electron backscatter diffraction (EBSD), and crystal vorticity axis (CVA) analyses to evaluate the effects of quartz Dauphiné twinning on strain localization. We compare a granodiorite mylonite and a tonalite mylonite from the Grebe Shear Zone, a mid-crustal transpressional shear zone in Fiordland, New Zealand. EBSD analysis reveals identical quartz grain boundary migration dynamic recrystallization microstructures in both samples, with abundant Dauphiné twinning only in the granodiorite mylonite. Bulk CVA patterns further distinguish the untwinned and Dauphiné-twinned samples, indicating a transition from simple shear-to pure shear-dominated transpression, respectively. The quartz CVA pattern from the Dauphiné-twinned sample indicates that twinned and untwinned grains record a transition from simple shear-to pure shear-dominated deformation, respectively. Pole figures of the Dauphiné-twinned sample reveal high-temperature slip systems in the untwinned and Dauphiné-twinned grains. We conclude that Dauphiné twinning formed early in transpression, and rendered the twinned grains less deformable relative to the untwinned grains over time. The effectiveness of Dauphiné twinning in localizing strain is therefore strongly influenced by its timing relative to the evolving shear zone kinematic deformation geometry.
The evolution of the mechanical properties of rock as a function of thermal damage is relevant to various engineering applications, such as nuclear waste repositories, underground coal gasification, dry-fracture shale system and geothermal energy extraction. The thermal properties of heterogeneous rock control heat transmission with differential thermal expansion potentially resulting in significant changes in the mechanical and transport behavior of reservoir rocks. We define a novel dual-damage thermal-mechanical model accommodating the interaction of thermal conductivity, thermally-induced deformation, rock mechanical deformation and damage to define the evolution of the thermal and mechanical properties of rock during thermal treatment. Importantly, the dual-damage constitutive model is capable of using elastic modulus and strength to solve for asynchronous changes in peak strain and peak strength, respectively. The proposed model is validated against analytical solutions and laboratory data. The results indicate that thermally-induced damage increases rock porosity and permeability while simultaneously decreasing elastic modulus and strength. Thermal treatment causes a realignment in the rock microstructure and results in a change in the ultimate failure pattern. Thermally-induced damage causes irreversible increases in rock porosity and permeability even as temperature is restored. Furthermore, it is confirmed that thermally-induced damage in rock is dominated by the type of tensile damage during the thermal expansion. The proposed dual-damage constitutive model better explains the non-proportional relationship between peak strength and peak strain observed in many experiments.
In view of the large rock and coalburst fatalities which rise with the ever increasing number, extension and depth of mines and underground hydroelectric tunnels, the author has studied many case records. In this connection creep dilatant and brittle behaviour of rocks and coal have been studied. On the basis of these field and experimental results he suggests the creep dilatancy theory (1981, 1983) and the simplified brittle failure theory. These theories have been used for the analysis of the metastable burst prone regions and the areas of accoustic emissions for the Nan Pang Jiang Tian Sheng Qiao pressure tunnel and a provisional coal layer. With the simplified brittle failure theory the extension of vertical cleavage regions in coal can be estimated; further the influence of water infusion can be studied. On the basis of his theoretical concepts the author suggests some practical methods for the location, prevention and mitigation of rock and coal bursts.
Rockburst is a kind of geological disaster attributed to dynamic instability. Based on the phenomena of both rock core disking and side wall scaling in cross-cut drift, which were found in the engineering geological drilling and the site investigation in Qilinchang Mining Area, Huize Lead-Zinc Mine, the basic patterns of rockburst in this mine are summed up, and the mechanism of rockburst is analyzed according to the results obtained from investigation and experiments. The study results provide an important basis for a reasonable selection of deep mining methods and the rockburst control.
The residual stress in a quartz vein from a metamorphic province is evaluated by an X-ray diffraction technique. Diffraction analyses at multiple incident angles yield residual stress magnitudes for the specified directions on the plane parallel to the sample surface. Residual stress formation in the vein is found to be determined by the platy geometry with respect to the host rock. The results indicate a compressive residual stress of −15 to −20 MPa parallel to the long axis of the vein. The compressive stress magnitude parallel to the quartz vein is found to increase with sample temperature, indicating that the quartz vein has a greater thermal expansion coefficient than that of the host rock. A two-dimensional model explaining residual stress formation in the vein in response to tectonic exhumation is proposed, and the paleostress magnitude at the time of vein formation is estimated from the residual stress magnitude and fluid inclusion microthermometric data. The quartz vein is concluded to have formed under a horizontal compressive stress of 550–660 MPa in the direction parallel to the long axis of the vein.
SEM/EBSD-based orientation and misorientation analyses are described for a lower amphibolite facies simple shear zone (Torridon, NW Scotland). It is shown that as well as conventional crystal-slip processes (i.e. basal-a, prism-a, rhomb-a and negative second order rhomb-a slip), dauphine twinning also plays a role in both microstructural and petrofabric evolution. Twinning assists in the initial grain size comminution processes, including dynamic recrystallization, from originally coarse wall rock grains to a typical nivlonitic microstructure in the centre of the shear zone. Subsequently, twinning helps to accommodate high shear strains in the mylonite whilst maintaining a stable microstructure and constant single crystal' petrofabric. The role of dauphine twinning appears to be to allow efficient switching between relatively 'soft' and relatively 'hard' slip directions that possibly exploit a distinction between negative and positive crystal forms. Misorientation analysis emphasizes the relationships between crystal-slip systems and grain boundary network, including dauphine twin planes, and suggests that the mylonitic microstructure contains preferred orientations of both tilt and twist boundaries that help to explain shear zone microstructural evolution and stability.
Many rocks appear to contain systems of internally balanced forces in static or dynamic equilibrium, even though free from exterior loads. Removal of a sample from a rock in such a state of residual stress causes both sample and host to adjust to new states of equilibrium involving changes in size and shape, and in level of balanced forces and internal strain energy. If these adjustments are time dependent, small samples may relax faster than large ones, and magnitude of internal forces that can be balanced may depend upon size and shape of the body. The implications for interpretation of in situ stress measurements are serious. Tunnels driven into rocks with residual stress may initiate relaxation of internal restraints and mobilize residual stress that can do work on supports and adjacent rock not predicted by conventional rock-load analysis.
This study determined the relative magnitudes and orientations of the horizontal residual stresses in the vicinity of the 755 Brecci Pipe at Cananea, Sonora, Mexico. These stresses were determined from eleven surface and underground orientated rock samples by the stress-relief overcoring technique. An elastic stress analysis for cylindrical and spherical inclusions was examined and compared to the calculated residual stresses. A petrographic examination for preferred mineral orientation was performed on orientated thin sections made from each of the overcores.Indications are that more confidence can be placed in residual stress orientations than in magnitudes. The secondary maximum principal horizontal residual stress in the host rocks has an orientation of S83°E and is normal to the secondary maximum principal horizontal residual stress in the 755 Breccia Pipe which acts in a N6°E direction. Comparison with the elastic analyses suggests the existence of a significant current tectonic N-S stress field in the 755 Area such that the in situ maximum principal horizontal stress is N-S. At the time of breccia pipe intrusion, it is estimated the magnitude of this N-S maximum principal horizontal stress was approximately 1·4 times the magnitude of the associated minimum principal horizontal stress.Large dispersions are noted in the calculated magnitudes of residual stresses. In general, little confidence can be placed in individual residual stress magnitudes and relative magnitudes are more meaningful.This study indicates that the stress-relief overcoring technique is acceptable for determining residual stress orientations; however, less confidence can be placed in residual stress magnitudes.
This paper examines the development of microscopic residual stresses on quartz particles in porcelain tile using the XRD technique. The study was conducted with a typical porcelain tile composition consisting of sodium feldspar, kaolin, and quartz, using quartzes with different particle sizes. The methodology used, based on determining the volume strain of the quartz unit cell, allowed a residual stress value equivalent to the entire particle and not just to a given crystalline plane to be obtained. The linear thermal expansion measurements indicated that, for all test compositions, the quartz in the mixture contributes to a thermal expansion coefficient comparable to the expansion of its c-lattice parameter. When this information was taken into account in the theoretical estimation of microscopic residual stress, the results were verified to be consistent with the experimental measurements.
This book is intended to give the reader a firm foundation in the theory of residual stress measurement with x-rays, as well as a comprehensive understanding of the experimental concepts involved in carrying out such a measurement. It is the only book available that covers all the new techniques such as separation of macro and micro residual stresses, triaxial stress measurement, as well as the errors associated with such techniques. The book is written for engineers and scientists who utilize non-destructive stress analysis in the field as well as for students in a discipline that involves non-destructive stress analysis. The book covers all topics (elasticity/plasticity, x-rays, measurement techniques, etc.) that impact residual stress analysis with x-rays. Problems at the end of selected chapters can be used to test the knowledge of the reader on the material covered therein, as well as providing a working model of the analysis that can be easily applied to different situations.
Locked in Stresses, Creep and Dilatancy of Rocks, and Constitutive Equations
A micro rheological analysis is presented of the deformation characteristics of rocks based on the multi mineral and polycrystalline structure of igneous metamorphic and some sedimentary rocks; in addition the polygranular structure of sandstone-type rocks is also considered. Due account is taken with the history of rock formation and tectonics.
Torsional creep test results on Ichang sandstone are presented and analysed. A new method of testing is introduced whereby the sample is subjected to a step wise loading function and the deformation measured as a function of the time. In this manner the creep as a function of stress and time can be obtained very easily from tests on only one sample.
A hypothesis is presented on the origin and formation of “locked in” stresses the release of internal strain energy is studied at the hand of some typical test results. The practical importance of these stress pockets is discussed and it is stressed that creep and “locked in” stresses are fundamental factors in the behaviour of rocks which must be carefully studied in practice.
On the basis of experimental results and physical reasoning constitutive equations are set up, which are three dimensional generalisations of the experimental Griggs equation:γ =a +b logt +ct, whereby the material parameters are scalar functions of the stress invariants.
Neutron diffraction methods (both time-of-flight- and angle-dispersive diffraction) are applied to intracrystalline strain measurements on geological samples undergoing uniaxial increasing compressional load. The experiments were carried out on Cretaceous sandstones from the Elbezone (East Germany), consisting of >95% quartz which are bedded but without crystallographic preferred orientation of quartz. From the stress–strain relation the Young’s modulus for our quartz sample was determined to be (72.2±2.9) GPa using results of the neutron time-of-flight method. The influence of different kinds of bedding in sandstones (laminated and convolute bedding) could be determined. We observed differences of factor 2 (convolute bedding) and 3 (laminated bedding) for the elastic stiffness, determined with angle dispersive neutron diffraction (crystallographic strain) and with strain gauges (mechanical strain). The data indicate which geological conditions may influence the stress–strain behaviour of geological materials. The influence of bedding on the stress–strain behaviour of a laminated bedded sandstone was indicated by direct residual stress measurements using neutron time-of-flight diffraction. The measurements were carried out six days after unloading the sample. Residual strain was measured for three positions from the centre to the periphery and within two radial directions of the cylinder. We observed that residual strain changes from extension to compression in a different manner for two perpendicular directions of the bedding plane.
The purpose of this paper is to clarify the concept of residual stress in rock. Residual stress is stress near a point in a body subjected to zero external tractions and to zero temperature gradients, excluding body forces. Thus, residual stresses can develop in rock if there are local phase transformations, inelastic strains, or differences in thermal or elastic properties. In these cases, residual stresses can result from changes in temperature, applied stress or configuration of the body.Analysis of residual stresses at the scale of mineral grains within a polycrystalline aggregate such as rock is virtually intractable. One can, however, obtain important insights into residual stresses within bodies with widely spaced sources of residual stress, such as inclusions, and within bodies comprised of multilayers. The analyses indicate that patterns of residual stress in rock can be expected to be extremely complicated. For example, study of residual stresses in a body containing a circular inclusion indicates that: 1.(1) There is a single state of residual stress within an inclusion but the state within the surrounding medium is variable. Thus, values of residual stress within rocks reported in the literature generally are of minor value because the sizes and shapes of the sources and the positions of the measurements relative to the positions of sources of residual stresses in the bodies have not been determined.2.(2) Residual stresses within an inclusion can be tensile or compressive, even though the applied stresses were compressive, depending upon the source of residual stress.3.(3) The magnitudes and orientations of residual stresses in an isolated body of rock containing one or more inclusions depends upon the size and shape of the body. The same general conclusions are derived from an analysis of residual stresses in a simple multilayered body.4.(4) In addition, however, the anisotropy of a multilayered body tends to cause principal residual stresses to parallel the layers rather than to parallel the applied stresses that were responsible for inducing the residual stresses. Thus, without identifying the sources of residual stresses in a body, one cannot infer the directions of principal tectonic stresses that might have been responsible for the residual stresses.Comparison of the theoretical results with measurements of change of residual stress in blocks of granite, with maximum dimensions of 2.5 m in the field and 0.2 m in the lab oratory, suggests that sources of residual stress are inhomogeneous elements or elements of inelastic deformation within the blocks that are smaller than the blocks themselves, but larger than individual mineral grains. The sources of residual stress are unknown in these granites.
Residual elastic strains (stresses) consist of locked-in strains, reflecting crystal distortions related to past external loads, and those that constrain them, the locking strains. The forces or stresses giving rise to locked-in and locking strains exist in rocks with no external loads across their boundaries and satisfy internal equilibrium conditions i.e., their sum is zero. The strains are stored by cementation and physical and chemical interactions between anisotropic grains while under load. The measure of residual strain provided by strain relief or X-ray methods consists of some unknown combination of locking and locked-in strains that depends on the distribution, relative magnitudes, and degrees of relaxation (strain relief method) of these components and the special bias of the measuring technique. With the X-ray technique, the bias is toward detection of strains in the most voluminous rock elements satisfying the Bragg condition for diffraction. In sandstone, therefore, the residual strains in the grains are sampled preferentially to those in the cement.
We present the first regional study of joints in the Jurassic–Cretaceous Otago Schist, New Zealand. The purpose of this study was to explore the origin and mechanism of joint formation in metamorphic rocks, especially any possible association between brittle and previous ductile deformation. The Otago Schist is cut by numerous systematic joints, up to tens of metres long, at any one exposure. We measured the orientation of joints, schist foliation planes, and quartz rods/mineral lineations at 46 sites across the Otago Schist, and calculated the spherical angles between their means. In relatively high metamorphic grade schists (greenschist facies) typically one systematic joint set has developed sub-perpendicular to penetrative foliation and lineation, irrespective of foliation and lineation orientations. This relationship also holds in lower grade schists (pumpellyite–actinolite facies), but more than one joint set is occasionally present. The flanking unfoliated schist protoliths (prehnite–pumpellyite facies) contain no systematic joint sets. A Late Cretaceous age for schist joint formation is indicated on the basis of lack of joint continuation into Late Cretaceous conglomerates that unconformably overlie jointed schists, cooling history, consistent orthogonality of joints with foliation and lineation, and lack of relationship of systematic joints to late Cenozoic plate-boundary features. We propose a model for joint formation during Late Cretaceous exhumation of the schist, and suggest that the systematic joints formed due to release of residual elastic strain energy preserved in the schists from Early Cretaceous ductile deformation.
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