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1
Karato, Shun-ichiro, and Teng-fong Wong. "Rock deformation: Ductile and brittle." Reviews of Geophysics 33 (1995): 451. http://dx.doi.org/10.1029/95rg00178.
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Culshaw, Nicholas, and Carla Dickson. "Cape St. Marys shear zone and the Halifax Group – Rockville Notch Group disconformity, southwestern Nova Scotia: structural development and tectonic significance." Canadian Journal of Earth Sciences 52, no. 10 (October 2015): 921–37. http://dx.doi.org/10.1139/cjes-2015-0007.
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The Cape St. Marys shear zone, situated in a corridor of Alleghanian reworking in the southwestern Meguma terrane, contains the deformed, discordant contact of Lower Ordovician slate of the Halifax Group with the Silurian White Rock Formation. Close to the contact, the Alleghanian cleavage (S2) is parallel to the contact in both units, with S0 in the White Rock Formation metavolcanic rocks and Halifax slate parallel to and discordant to the contact. The geometry of deformed Neoacadian minor folds, quartz fringes on sulphide grains, and micro-porphyroclasts demonstrate thrust-sense shear (White Rock Formation over Halifax slate). Pure shear and volume loss are inferred as components of the strain path from S2 microstructure and estimates of strain in the Halifax slate. Estimates of shear strain imply moderate displacements within the Cape St. Marys shear zone during deformation of the northwestern limb of the Cape St. Marys syncline. The discordant contact of the Halifax slate with the White Rock formation cannot be a thrust plane because younger rocks overlie older rocks. Thus the contact is what it appears to be: an angular unconformity embedded within a ductile shear zone. Brittle-ductile faults, quartz vein arrays, and centimetre-scale kink bands disturb S2 in the Halifax slate a few metres northwest of the contact. The geometry of the brittle-ductile structures and the orientation of stretching lineation in the ductile structures link the episodes kinematically. Quartz veins accompanying brittle-ductile deformation suggest that fluids derived during pressure solution development of S2 drove the change from ductile to brittle-ductile deformation in the Cape St. Marys shear zone during the latter stages of convergence. In a regional context, the moderate shear values of the Cape St. Marys shear zone are reasonable for the diminishing displacement expected near the termination of a northwest-propagating regional shear system. Whereas the transition from ductile to brittle-ductile deformation occurred late in the development of the Cape St. Marys shear zone, brittle-ductile structures were dominant closer to the northwest border of the zone of Alleghanian deformation. The fluids required for the transition may have been driven along a pressure gradient from more internal parts of the corridor, where pressure solution was more active.
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Nichol, Susan L., Oldrich Hungr, and S. G. Evans. "Large-scale brittle and ductile toppling of rock slopes." Canadian Geotechnical Journal 39, no. 4 (August 1, 2002): 773–88. http://dx.doi.org/10.1139/t02-027.
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Slow, ductile toppling of rock masses commonly creates large-scale mountain slope deformations. In some cases, rock toppling can initiate an extremely rapid catastrophic landslide. This theoretical and field-based study was aimed at distinguishing the two alternative modes of toppling. The idea that certain key parameters of the undeformed rock mass may influence failure behaviour in a quantifiable way was examined through a parametric study of a large rock slope using the universal distinct element code (UDEC). The slope was modelled using variations of rock mass strength, discontinuity orientation and persistence, and toe over-steepening. The results indicated two distinct types of failure behaviour: (i) ductile, self-stabilizing flexural toppling in weak rock with a single dominant joint set; and (ii) brittle, catastrophic block toppling in strong rock containing persistent, down-slope oriented or horizontal cross-joints, which act as surfaces of separation at the base of the toppling blocks. The two mechanisms exhibit very different patterns of prefailure stress. During flexural toppling, the major principal stress is oriented predominantly parallel with the slope surface. In the case of block toppling, it is vertical and a large part of the unstable volume is horizontally destressed. Boundaries between the two types of behaviour have been approximately mapped. Two field case studies were then examined in light of the results. The first case involves a block topple in strong granitic rocks that failed catastrophically and produced a high velocity rock avalanche; and the second case is a large flexural topple in metamorphic rocks, exhibiting slow deformations.Key words: rock toppling, landslide, distinct element model, parametric study, hazard assessment.
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Wenning, Quinn C., Claudio Madonna, Antoine de Haller, and Jean-Pierre Burg. "Permeability and seismic velocity anisotropy across a ductile–brittle fault zone in crystalline rock." Solid Earth 9, no. 3 (May 29, 2018): 683–98. http://dx.doi.org/10.5194/se-9-683-2018.
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Abstract. This study characterizes the elastic and fluid flow properties systematically across a ductile–brittle fault zone in crystalline rock at the Grimsel Test Site underground research laboratory. Anisotropic seismic velocities and permeability measured every 0.1 m in the 0.7 m across the transition zone from the host Grimsel granodiorite to the mylonitic core show that foliation-parallel P- and S-wave velocities systematically increase from the host rock towards the mylonitic core, while permeability is reduced nearest to the mylonitic core. The results suggest that although brittle deformation has persisted in the recent evolution, antecedent ductile fabric continues to control the matrix elastic and fluid flow properties outside the mylonitic core. The juxtaposition of the ductile strain zone next to the brittle zone, which is bounded inside the two mylonitic cores, causes a significant elastic, mechanical, and fluid flow heterogeneity, which has important implications for crustal deformation and fluid flow and for the exploitation and use of geothermal energy and geologic waste storage. The results illustrate how physical characteristics of faults in crystalline rocks change in fault zones during the ductile to brittle transitions.
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Ma, Svieda M., Dawn A. Kellett, Laurent Godin, and Michael J. Jercinovic. "Localisation of the brittle Bathurst fault on pre-existing fabrics: a case for structural inheritance in the northeastern Slave craton, western Nunavut, Canada." Canadian Journal of Earth Sciences 57, no. 6 (June 2020): 725–46. http://dx.doi.org/10.1139/cjes-2019-0100.
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The north–northwest-striking Bathurst fault in the northeastern Slave craton displaced the 1.9 Ga Kilohigok basin and the ca. 2.02–1.96 Ga Thelon tectonic zone, and projects beneath the 1.7 Ga Thelon basin where unconformity-associated uranium deposits are spatially associated with basement faults. Here we investigate the deformation–temperature–time history of the Bathurst fault rocks using structural and microstructural observations paired with U–(Th–)Pb and 40Ar/39Ar geochronology. Highly strained hornblende-bearing granitoid rocks, the predominant rock type on the northeastern side of the Bathurst fault in the study area, show ambiguous sense of shear suggesting flattening by coaxial deformation. Quartz and feldspar microstructures suggest ductile deformation occurred at ≥500 °C. Along the main fault trace, brittle features and hydrothermal alteration overprint the pervasive ductile flattening fabric. In situ U–Th–Pb dating of synkinematic monazite suggests ductile fabric formation at ca. 1933 ± 4 Ma and ca. 1895 ± 11 Ma, and zircon from a cross-cutting dyke constrains the brittle deformation to ≤1839 ± 14 Ma. 40Ar/39Ar dating of fabric-defining minerals yield cooling ages of ca. 1920–1900 Ma and ca. 1900–1850 Ma for hornblende and muscovite, respectively, and a maximum cooling age of ca. 1840 Ma for biotite. We suggest the ca. 1933–1895 Ma ductile flattening fabric developed during orthogonal collision and indentation of the Slave craton into the Thelon tectonic zone and Rae craton. Brittle deformation on the Bathurst fault was localised parallel to the ductile flattening fabric after ca. 1840 Ma and preceded Thelon basin deposition. Brittle deformation features in Bathurst fault rocks preserve evidence for fluid–rock interaction and enhanced basement permeability, suggesting the fault is a possible conduit structure for mineralising fluids.
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Xing, Yan, Feng Gao, Zhizhen Zhang, and Wenqi Zheng. "Energy Storage and Release of Class I and Class II Rocks." Energies 16, no. 14 (July 20, 2023): 5516. http://dx.doi.org/10.3390/en16145516.
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As underground excavations become deeper, violent rock failures associated with the sudden release of elastic energy become more prevalent, threatening the safety of workers and construction equipment. It is important to figure out the energy-related failure mechanisms of rocks. However, the energy evolution across the complete deformation of different types of rocks and the effect of high confinement on energy storage and release are not well understood in the literature. In this study, a series of cyclic triaxial compression tests were conducted for Class I and Class II rocks to investigate the confinement-dependent characteristics of energy evolution. The results showed that three types of energy evolution were identified as the rock behavior changed from brittle to ductile. The energy storage limit was linearly enhanced by confinement. The nonlinear increase in dissipated energy at peak stress with increasing confinement was suggested to indicate the start of the brittle–ductile transition. The post-peak fracturing process was characterized using the ratio of the local withdrawn elastic energy and fracture energy, and a novel energy-based index was proposed to quantify the failure intensity of the rock. This paper presents a complete investigation of the energy conversion characteristics of the rock, which may shed light on the failure mechanisms of violent rock failures in underground projects.
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Tartarotti, Guerini, Rotondo, Festa, Balestro, Bebout, Cannaò, Epstein, and Scambelluri. "Superposed Sedimentary and Tectonic Block-In-Matrix Fabrics in a Subducted Serpentinite Mélange (High-Pressure Zermatt Saas Ophiolite, Western Alps)." Geosciences 9, no. 8 (August 16, 2019): 358. http://dx.doi.org/10.3390/geosciences9080358.
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The primary stratigraphic fabric of a chaotic rock unit in the Zermatt Saas ophiolite of the Western Alps was reworked by a polyphase Alpine tectonic deformation. Multiscalar structural criteria demonstrate that this unit was deformed by two ductile subduction-related phases followed by brittle-ductile then brittle deformation. Deformation partitioning operated at various scales, leaving relatively unstrained rock domains preserving internal texture, organization, and composition. During subduction, ductile deformation involved stretching, boudinage, and simultaneous folding of the primary stratigraphic succession. This deformation is particularly well-documented in alternating layers showing contrasting deformation style, such as carbonate-rich rocks and turbiditic serpentinite metasandstones. During collision and exhumation, deformation enhanced the boudinaged horizons and blocks, giving rise to spherical to lozenge-shaped blocks embedded in a carbonate-rich matrix. Structural criteria allow the recognition of two main domains within the chaotic rock unit, one attributable to original broken formations reflecting turbiditic sedimentation, the other ascribable to an original sedimentary mélange. The envisaged geodynamic setting for the formation of the protoliths is the Jurassic Ligurian-Piedmont ocean basin floored by mostly serpentinized peridotites, intensely tectonized by extensional faults that triggered mass transport processes and turbiditic sedimentation.
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Lu, Aihong, Xiya Chang, Shanchao Hu, Yu Xia, and Ming Li. "Impact of Moisture Content on the Brittle-Ductile Transition and Microstructure of Sandstone under Dynamic Loading Conditions." Advances in Civil Engineering 2021 (May 4, 2021): 1–16. http://dx.doi.org/10.1155/2021/6690171.
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Rockburst frequently occurred in an unstable or violent manner, which posed great safety risk and economic loss in deep underground engineering. The water injection into rock stratum was one of the most effectively ways to reduce rockburst by weakening rock mechanics. However, the moisture content was an important index related to rock mechanical properties. Many previous studies focused on the relationship between the moisture contents and macromechanical properties of rock materials under static load and seldom explored the impact of moisture variation on the mechanical properties and brittle-ductile transition characteristics of rock materials under dynamic loads. In this paper, we studied the dynamic mechanical properties of sandstone with different moisture contents under the same strain rate by the Split Hopkinson Pressure Bar (SHPB) experimental system. The relationship between dynamic mechanical properties of sandstone and moisture content was studied, and a dynamic ductility coefficient was proposed, which could be determined by the ratio between the peak strain and the yield strain. Then, it was used to assess the critical moisture content of the brittle-ductile transition of the sandstone. Through scanning electron microscopy (SEM) examination, the microstructure of sandstones with different moisture contents was inspected at magnifications of 500, 2000, and 5000 times, respectively. We showed that as the moisture content increased, the dynamic peak strength and elastic modulus decreased at different degrees, whereas the dynamic peak strain and ductility coefficient exhibited a nonlinear increase, respectively. When the moisture content reached 2.23%, the variation ratio of the dynamic ductility coefficient commenced to increase obviously, indicating that the sandstone began to transit from brittle behavior to ductile behavior. When the sample magnification was 500 times, the microstructure of the sandstone samples with zero and 2.01% to 2.40% moisture content mainly displayed the step pattern and river pattern, respectively, showing that the damage mode was brittle fracture. When the moisture content ranged from 2.49% to 2.58%, the microstructure of the sample included a large number of dimple clusters with local snake patterns and belonged to ductile fracture. When the sample magnification was 2000 and 5000 times, the microstructure was mainly brittle fracture with a moisture content lower than 2.23%. The microstructure of the sample with moisture content of 2.23% exhibited brittle-ductile composite fracture form, whereas others exhibited obviously ductile fracture. These characteristics were fundamentally consistent with the results reflected by the dynamic ductility coefficient. Our findings could provide a theoretical basis for mitigating coal and rock bursts by injecting water methods in underground coal mines.
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Koc, Salih, and Arash Dahi Taleghani. "A Fast Method to Determine the Critical Depth of Cut for Various Rock Types." Energies 13, no. 17 (August 31, 2020): 4496. http://dx.doi.org/10.3390/en13174496.
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Knowing correct values of the rock mechanical properties is crucial for many engineering applications in subsurface. Rocks may show two failure modes during cutting: ductile and brittle. In the ductile mode, rock deforms plastically, and the debris is powdered ahead of the cutting face. On the other hand, chips are the major cutting characteristics for the brittle failure during rock cutting. The critical depth of cut represents the transition point between these two models, so knowing this value helps better predict the failure mechanism of rock. In this paper, a new method is introduced based on measuring the roughness of the groove for determining the transition point of failure modes for every rock sample after the scratch test. The graph depicting the average change in the surface roughness (Rt) versus the scratched surface roughness (ΔR) can be used to identify the rock failure mode and determine the transition point for the cutting process. The value of this slope increases until the depth of cut reaches the transition point, and then the slope reaches a constant value. The main purpose of this paper is to estimate the critical depth of cut of different rock specimens employing the new surface roughness model.
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Bai, Hao, Wei Du, Yundong Shou, Lichuan Chen, and Filippo Berto. "Experimental investigation of cracking behaviors of ductile and brittle rock-like materials." Frattura ed Integrità Strutturale 15, no. 56 (March 28, 2021): 16–45. http://dx.doi.org/10.3221/igf-esis.56.02.
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The cracking characteristics of ductile rocks were studied by similar materials with sand, barite, epoxide resin, polyamide, silicone rubber and alcohol, while the cracking characteristics of brittle rocks were investigated by similar material with sand, barite, rosin and alcohol. In this paper, to enhance the application range of the rock-like materials in the field of geotechnical engineering model tests, the values of the elastic modulus and the compressive strength of the artificial rock-like materials are changed in a wide range by adjusting the amount of cementitious materials (epoxide resin, polyamide, rosin, etc). The elastic modulus, compressive strength and cracking characteristics were obtained from the complete axial stress–strain curves of the specimens made of similar materials, which were cast using the different mixture ratios. These experimental data can provide quantitative investigation on mixture ratios of similar materials of rocks to model the geotechnical engineering. Furthermore, the effect of mixture ratios on mechanical properties and crack propagation pattern of specimens were also investigated by the specimens with pre-existing flaws under uniaxial compressive tests
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MALATESTA, C., L. FEDERICO, L. CRISPINI, and G. CAPPONI. "Fluid-controlled deformation in blueschist-facies conditions: plastic vs brittle behaviour in a brecciated mylonite (Voltri Massif, Western Alps, Italy)." Geological Magazine 155, no. 2 (January 25, 2017): 335–55. http://dx.doi.org/10.1017/s0016756816001163.
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AbstractA blueschist-facies mylonite crops out between two high-pressure tectono-metamorphic oceanic units of the Ligurian Western Alps (NW Italy). This mylonitic metabasite is made up of alternating layers with different grain size and proportions of blueschist-facies minerals.The mylonitic foliation formed at metamorphic conditions of T = 220–310 °C and P = 6.5–10 kbar. The mylonite shows various superposed structures: (i) intrafoliar and similar folds; (ii) chocolate-tablet foliation boudinage; (iii) veins; (iv) breccia.The occurrence of comparable mineral assemblages along the foliation, in boudin necks, in veins and in breccia cement suggests that the transition from ductile deformation (folds) to brittle deformation (veining and breccia), passing through a brittle–ductile regime (foliation boudinage), occurred gradually, without a substantial change in mineral assemblage and therefore in the overall P–T metamorphic conditions (blueschist-facies).A strong fluid–rock interaction was associated with all the deformative events affecting the rock: the mylonite shows an enrichment in incompatible elements (i.e. As and Sb), suggesting an input of fluids, released by adjacent high-pressure metasedimentary rocks, during ductile deformation. The following fracturing was probably enhanced by brittle instabilities arising from strain and pore-fluid pressure partitioning between adjacent domains, without further external fluid input.Fluids were therefore fixed inside the rock during mylonitization and later released into a dense fracture mesh that allowed them to migrate through the mylonitic horizon close to the plate interface.We finally propose that the fracture mesh might represent the field evidence of past episodic tremors or ‘slow earthquakes’ triggered by high pore-fluid pressure.
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Wong, Teng-fong, and Patrick Baud. "The brittle-ductile transition in porous rock: A review." Journal of Structural Geology 44 (November 2012): 25–53. http://dx.doi.org/10.1016/j.jsg.2012.07.010.
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Yu, Weijian, Genshui Wu, Baifu An, and Ping Wang. "Experimental Study on the Brittle-Ductile Response of a Heterogeneous Soft Coal Rock Mass under Multifactor Coupling." Geofluids 2019 (May 2, 2019): 1–15. http://dx.doi.org/10.1155/2019/5316149.
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After a gas drainage event causes different degrees of initial porosity in the coal seam, the heterogeneity of the coal mass becomes much more obvious. In this paper, soft coal testing samples with different degrees of heterogeneity were prepared first by a new special experimental research method using hydrogen peroxide in an alkaline medium to generate oxygen. Then, a series of mechanical tests on the soft coal mass samples were carried out under multiple factor coupling conditions of different heterogeneities and confining pressures. The results show that with a low strength, the ductility failure characteristic and a kind of rheology similar to that for soft rock flow were reflected for the soft coal; i.e., the stress-strain curve of the coal mass had no apparent peak strain and residual strength. An interesting phenomenon was found in the test process: there was an upwardly convex critical phase, called the brittle-ductile failure transition critical phase, for the heterogeneous soft coal mass between the initial elastic compression phase and the ductile failure transition phase in the stress-strain curve of the coal mass. An evolution of the brittle-ductile modulus coefficient of the soft coal was developed to analyze the effect of the internal factor (degree of heterogeneity) and external factors (confining pressure) on the transition state of the brittle-ductile failure of soft coal. Further analysis shows that the internal factor (heterogeneity) was also one of the essential factors causing the brittle-ductile transition of soft coal.
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Cooper, Frances J., John P. Platt, and Whitney M. Behr. "Rheological transitions in the middle crust: insights from Cordilleran metamorphic core complexes." Solid Earth 8, no. 1 (February 21, 2017): 199–215. http://dx.doi.org/10.5194/se-8-199-2017.
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Abstract. High-strain mylonitic rocks in Cordilleran metamorphic core complexes reflect ductile deformation in the middle crust, but in many examples it is unclear how these mylonites relate to the brittle detachments that overlie them. Field observations, microstructural analyses, and thermobarometric data from the footwalls of three metamorphic core complexes in the Basin and Range Province, USA (the Whipple Mountains, California; the northern Snake Range, Nevada; and Ruby Mountains–East Humboldt Range, Nevada), suggest the presence of two distinct rheological transitions in the middle crust: (1) the brittle–ductile transition (BDT), which depends on thermal gradient and tectonic regime, and marks the switch from discrete brittle faulting and cataclasis to continuous, but still localized, ductile shear, and (2) the localized–distributed transition, or LDT, a deeper, dominantly temperature-dependent transition, which marks the switch from localized ductile shear to distributed ductile flow. In this model, brittle normal faults in the upper crust persist as ductile shear zones below the BDT in the middle crust, and sole into the subhorizontal LDT at greater depths.In metamorphic core complexes, the presence of these two distinct rheological transitions results in the development of two zones of ductile deformation: a relatively narrow zone of high-stress mylonite that is spatially and genetically related to the brittle detachment, underlain by a broader zone of high-strain, relatively low-stress rock that formed in the middle crust below the LDT, and in some cases before the detachment was initiated. The two zones show distinct microstructural assemblages, reflecting different conditions of temperature and stress during deformation, and contain superposed sequences of microstructures reflecting progressive exhumation, cooling, and strain localization. The LDT is not always exhumed, or it may be obscured by later deformation, but in the Whipple Mountains, it can be directly observed where high-strain mylonites captured from the middle crust depart from the brittle detachment along a mylonitic front.
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Meyer, Gabriel G., Nicolas Brantut, Thomas M. Mitchell, and Philip G. Meredith. "Fault reactivation and strain partitioning across the brittle-ductile transition." Geology 47, no. 12 (October 16, 2019): 1127–30. http://dx.doi.org/10.1130/g46516.1.
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Abstract The so-called “brittle-ductile transition” is thought to be the strongest part of the lithosphere, and defines the lower limit of the seismogenic zone. It is characterized not only by a transition from localized to distributed (ductile) deformation, but also by a gradual change in microscale deformation mechanism, from microcracking to crystal plasticity. These two transitions can occur separately under different conditions. The threshold conditions bounding the transitions are expected to control how deformation is partitioned between localized fault slip and bulk ductile deformation. Here, we report results from triaxial deformation experiments on pre-faulted cores of Carrara marble over a range of confining pressures, and determine the relative partitioning of the total deformation between bulk strain and on-fault slip. We find that the transition initiates when fault strength (σf) exceeds the yield stress (σy) of the bulk rock, and terminates when it exceeds its ductile flow stress (σflow). In this domain, yield in the bulk rock occurs first, and fault slip is reactivated as a result of bulk strain hardening. The contribution of fault slip to the total deformation is proportional to the ratio (σf − σy)/(σflow − σy). We propose an updated crustal strength profile extending the localized-ductile transition toward shallower regions where the strength of the crust would be limited by fault friction, but significant proportions of tectonic deformation could be accommodated simultaneously by distributed ductile flow.
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Tellez, Javier, Matthew J. Pranter, Carl Sondergeld, Chandra Rai, Jing Fu, Heyleem Han, Son Dang, and Chris McLain. "Mechanical stratigraphy of Mississippian strata using machine learning and seismic-based reservoir characterization and modeling, Anadarko Basin, Oklahoma." Interpretation 9, no. 2 (April 27, 2021): SE53—SE71. http://dx.doi.org/10.1190/int-2020-0167.1.
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The Sooner Trend in the Anadarko (Basin) in Canadian and Kingfisher counties play primarily produces oil and gas from Mississippian strata. The interval consists of interbedded argillaceous mudstones and calcareous siltstones. Such a contrast in rock composition is linked directly to the mechanical stratigraphy of the strata. Brittle (calcareous siltstones) and ductile beds (argillaceous mudstones) are related to the sequence-stratigraphic framework at different scales. We have used seismic and well-log data to estimate and map the geomechanical properties’ distribution and interpret the mechanical stratigraphy of rocks within the Mississippian strata. First, we defined the parasequences that form the main reservoir zones of the Meramecian-Mississippian strata. Once we established the stratigraphic framework, we estimated and compared rock brittleness index (BI) using two independent laboratory-based measurements from the core. The first method, the mineralogical-derived BI, uses mineralogical composition inverted from Fourier-transform infrared spectroscopy analyses, whereas the second method, the mechanical-derived BI, involves measurements of compressional and shear velocities from core plugs. We use the data from core-plug velocity measurements along with well logs and an artificial neural network approach to establish relationships among the geomechanical properties, well logs, and acoustic impedance values. We then applied these relationships to generate 3D geomechanical models constrained to seismic volumes. The resulting grid distributions illustrate the stratigraphic variability of the properties at the parasequence scale. Overall, brittle strata decrease in thickness and abundance basinward as the frequency of interbedded brittle and ductile zones increases and gradually transitions into thin calcite-cemented siltstones and clay-rich mudstones. Analysis of the production performance of selected horizontal wells drilled within the Mississippian strata indicates that the proportion of brittle and ductile rocks along the well path drilled and the drilled area vertical stacking pattern play a significant role in hydrocarbon production for these Mississippian units.
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Miller, Lance D., Christopher C. Barton, Rick S. Fredericksen, and Jason R. Bressler. "Structural evolution of the Alaska Juneau lode gold deposit, southeastern Alaska." Canadian Journal of Earth Sciences 29, no. 5 (May 1, 1992): 865–78. http://dx.doi.org/10.1139/e92-074.
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The Alaska Juneau lode gold deposit is hosted by a series of polydeformed Permian to Late Triassic volcanic, pelitic, volcaniclastic, and mafic intrusive rocks. Rocks in the mine area have been sheared and metamorphosed to greenschist grade. Interpretation of rock fabrics indicates several generations of ductile and brittle deformation. Prior to mineralization, reverse shear occurred along northwest-striking and northeast-dipping ductile shear zones. Mineralization consists of Eocene auriferous quartz–carbonate veins, which cut the regional metamorphic fabrics. Mineralization was followed by reverse right-lateral shear along northwest-trending ductile–brittle shear zones. Two northwest-striking and steeply dipping vein sets host the bulk of the ore. Orientation of carbonate fibers within the quartz veins were used to determine the deformation regime that existed during mineralization. Plunge of the fibers indicate that down-to-the-northeast extension occurred synchronous with mineralization. Structural data support a model whereby the Alaska Juneau deposit formed after the peak of ductile deformation during a period of local extension. Localization of veins to areas of infolded phyllite and gabbro suggests that competency contrasts within host rocks enhanced vein emplacement. Veining may have been facilitated by a change from a contractional to a transpressive deformational regime which may have led to local extension and fluid migration to favorable deposition sites.
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Zhang, Guang, Jing Xi Chen, and Bin Hu. "The Brittle-Ductile Transition Character of Rocks and Its Effect on Rockbursts." Key Engineering Materials 261-263 (April 2004): 171–76. http://dx.doi.org/10.4028/www.scientific.net/kem.261-263.171.
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The brittle-ductile character is one of the important mechanical indexes of rocks and also one of the important affecting factors of rockburst. Both conventional and true triaxial tests have shown that the brittle-ductile character of rocks varies with the variation in rocks stress state and stress path, but these two kinds of tests have revealed totally different laws of brittle-ductile transition. This present paper analyses the results from two tests firstly and then summarizes the effect of rock’s brittle-ductile transition character on rockburst and finally points out the deficiency in present studies of rockburst.
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Zhou, Yaneng, and Jeen-Shang Lin. "Modeling the ductile–brittle failure mode transition in rock cutting." Engineering Fracture Mechanics 127 (September 2014): 135–47. http://dx.doi.org/10.1016/j.engfracmech.2014.05.020.
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Wang, Susheng, and Weiya Xu. "A coupled elastoplastic anisotropic damage model for rock materials." International Journal of Damage Mechanics 29, no. 8 (March 12, 2020): 1222–45. http://dx.doi.org/10.1177/1056789520904093.
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In this study, a rigorous constitutive model within the framework of thermodynamics is formulated to describe the coupling process between irreversible deformation and anisotropic damage of rock materials. The coupling effect is reflected based on the “two-surface” formulation. The plastic response is described by a yield function while the anisotropic damage is defined by a novel exponential damage criterion. In the proposed model, another feature lies in introducing parameters β and k in the proposed model to capture strain hardening/softening behaviors and brittle–ductile transition. The computational formulation scheme for the coupled model is deduced in detail by using return mapping algorithm. The validity of the coupled model is compared with the numerical simulation results and the experimental curves of the fine-grained sandstone, Beishan granite, and Jinping marble. The results indicate that the model can take into account the nonlinear mechanical behaviors of rock: coupling anisotropic damage and plasticity as well as brittle-ductile transition behaviors. Without loss of generality, the coupled model is versatile to describe the mechanical characteristics of rock materials.
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Alavi, Mehdi, and M. A. Mahdavi. "Stratigraphy and structures of the Nahavand region in western Iran, and their implications for the Zagros tectonics." Geological Magazine 131, no. 1 (January 1994): 43–47. http://dx.doi.org/10.1017/s0016756800010475.
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AbstractSeveral rock stratigraphic successions, metamorphosed and non-metamorphosed, are found to be similar and/or identical with each other across the so-called ‘Main Zagros Thrust’. Stratigraphic successions form thin allochthonous sheets carried from northeast to southwest by numerous low-angle thrust faults of either ductile to brittle-ductile type or brittle type. Similarities in lithic and faunal characteristics of the stratigraphic units and in the style of structural deformation across the ‘Main Zagros Thrust’ imply that either the suture between the Afro-Arabian and Iranian lithospheric plates is not located in the Nahavand region or, if it is, it must be buried under several thrust sheets.
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Trushkin, Oleg B., and Hamzja I. Akchurin. "Performance dynamics of pdc cutters used in breaking ductile brittle rock." Nexo Revista Científica 34, no. 04 (October 23, 2021): 1490–98. http://dx.doi.org/10.5377/nexo.v34i04.12694.
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The widespread application of cutting - chipping action bits with PDC cutters is held back due to the intense chipping and breakage of the latter. This article presents the results of bench-scale tests conducted to determine the values of three mutually perpendicular components of the load on sharp-edged and beveled rock-breaking cutters of 13.5 mm in diameter as well as the dynamic-response factors and mean square deviations (MSD) of these components. The forces change in time by leaps, which reflects the rock fracturing under the cutter. The MSD accepted as per-cycle amplitude is four times as low on average as the mean axial force; when a sharp-edged and a beveled cutter is used, the MSD is by 150 to 300 and by 300 to 500 % lower than the mean circumferential force.
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Sitharam, T. G., M. Ramulu, and V. B. Maji. "Static and Dynamic Elastic Modulus of Jointed Rock Mass." International Journal of Geotechnical Earthquake Engineering 1, no. 2 (July 2010): 89–112. http://dx.doi.org/10.4018/jgee.2010070107.
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In this paper the compressive strength/elastic modulus of the jointed rock mass was estimated as a function of intact rock strength/modulus and joint factor. The joint factor reflects the combined effect of joint frequency, joint inclination and joint strength. Therefore, having known the intact rock properties and the joint factor, jointed rock properties can be estimated. The test results indicated that the rock mass strength decreases with an increase in the joint frequency and a sharp transition was observed from brittle to ductile behaviour with an increase in the number of joints. It was also found that the rocks with planar anisotropy exhibit the highest strength in the direction perpendicular to the anisotropy and the lowest at an inclination of 30o-45o in jointed samples. The anisotropy of the specimen influences the dynamic elastic modulus more than the static elastic modulus. The results were also compared well with the published works of different authors for different type of rocks.
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Wang, Sheng, Wanchun Zhao, Xiaofei Fu, Ziming Zhang, Tingting Wang, and Jing Ge. "A universal method for quantitatively evaluating rock brittle-ductile transition behaviors." Journal of Petroleum Science and Engineering 195 (December 2020): 107774. http://dx.doi.org/10.1016/j.petrol.2020.107774.
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Liu, Weiji, Xiaohua Zhu, and Jun Jing. "The analysis of ductile-brittle failure mode transition in rock cutting." Journal of Petroleum Science and Engineering 163 (April 2018): 311–19. http://dx.doi.org/10.1016/j.petrol.2017.12.067.
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He, Xianqun, and Chaoshui Xu. "Discrete element modelling of rock cutting: from ductile to brittle transition." International Journal for Numerical and Analytical Methods in Geomechanics 39, no. 12 (March 5, 2015): 1331–51. http://dx.doi.org/10.1002/nag.2362.
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Chen, Hao-Zhe, Zhu-Shan Shao, Dong-Dong Jin, Zhe Zhang, and Dong-Bo Zhou. "A Numerical Investigation into the Effect of Homogeneity on the Time-Dependent Behavior of Brittle Rock." Materials 14, no. 22 (November 11, 2021): 6818. http://dx.doi.org/10.3390/ma14226818.
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To investigate the brittle creep failure process of rock material, the time-dependent properties of brittle rocks under the impact of homogeneity are analyzed by the numerical simulation method, RFPA-Creep (2D). Deformation is more palpable for more homogeneous rock material under the uniaxial creep loading condition. At a low stress level, diffusion creep may occur and transition to dislocation creep with increasing applied stress. The law for increasing creep strain with the homogeneity index under a constant confined condition is similar to the uniaxial case, and dislocation creep tends to happen with increasing confining pressure for the same homogeneity index. The dilatancy index reaches its maximum at a high stress level when rock approaches failure, and the evolution of the dilatancy index with the homogeneity index under the same confining pressure is similar to the uniaxial case and is more marked than that under the unconfined condition. Both uniaxial and triaxial creep failure originate from the ductile damage accumulation inside rock. The dominant shear-type failure is exhibited by uniaxial creep and the conventional compression case presents the splitting-based failure mode. Under confining pressure, the creep failure pattern is prone to shear, which is more notable for the rock with higher homogeneity.
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Cui, Kai, Bin Hu, and Jing Li. "A Statistic Damage Model of Rocks considering the Effect of Loading Rate." Advances in Civil Engineering 2022 (February 9, 2022): 1–9. http://dx.doi.org/10.1155/2022/9124208.
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This paper develops a new statistic damage model for rock to mainly study the effect of a loading rate on its mechanical behaviours. The proposed model adopts a new loading rate-dependent damage density function and is capable of describing the macroscopic damage accumulation process for rock samples subjected to external high-speed dynamic loadings. The proposed model can also account for the residual strength of rocks by introducing a modified equivalent strain principle, which considers the contribution of the friction force to the strength of rocks. The friction force is generated by the movements of the nearby microcracks. The predicted stress-strain curves by the proposed model agree with the measured data of salty rock under the conditions of various confining pressures and loading rates. It can be found that both the peak strength and the corresponding axial strain are increased at high-speed loading conditions. At the same time, a transition from ductile failure to brittle failure can be observed in rock samples.
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Shan, Pengfei, Wei Li, Xingping Lai, Shuai Zhang, Xingzhou Chen, and Xiaochen Wu. "Research on the Response Mechanism of Coal Rock Mass under Stress and Pressure." Materials 16, no. 8 (April 19, 2023): 3235. http://dx.doi.org/10.3390/ma16083235.
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In this paper, the strength and deformation failure characteristics of bearing coal rock mass are related to the confining pressure, and the SAS-2000 experimental system is used to carry out uniaxial and 3, 6, and 9 MPa triaxial tests on coal rock to assess the strength and deformation failure characteristics of coal rock under different confining pressure conditions. The results show that the stress–strain curve of coal rock undergoes four evolutionary stages after fracture: compaction, elasticity, plasticity, and rupture. With confining pressure, the peak strength of coal rock increases, and the elastic modulus increases nonlinearly. The coal sample changes more with confining pressure, and the elastic modulus is generally smaller than that of fine sandstone. The stage of evolution under confining pressure constitutes the failure process of coal rock, with the stress of different evolution stages causing various degrees of damage to coal rock. In the initial compaction stage, the unique pore structure of the coal sample makes the confining pressure effect more apparent; the confining pressure makes the bearing capacity of the coal rock plastic stage stronger, the residual strength of the coal sample has a linear relationship with the confining pressure, and the residual strength of the fine sandstone has a nonlinear relationship with the confining pressure. Changing the confining pressure state will cause the two kinds of coal rock samples to change from brittle failure to plastic failure. Different coal rocks under uniaxial compression experience more brittle failure, and the overall degree of crushing is higher. The coal sample in the triaxial state experiences predominantly ductile fracture. The whole is relatively complete after failure as a shear failure occurs. The fine sandstone specimen experiences brittle failure. The degree of failure is low, and the confining pressure’s effect on the coal sample is obvious.
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Stauffer, Mel R., and John F. Lewry. "Regional setting and kinematic features of the Needle Falls Shear Zone, Trans-Hudson Orogen." Canadian Journal of Earth Sciences 30, no. 7 (July 1, 1993): 1338–54. http://dx.doi.org/10.1139/e93-115.
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Needle Falls Shear Zone is the southern part of a major northeast-trending ductile shear system within the Paleoproterozoic Trans-Hudson Orogen in Saskatchewan. Throughout its exposed length of ~400 km, the shear zone separates reworked Archean continental crust and infolded Paleoproterozoic supracrustals of the Cree Lake Zone, to the northwest, from mainly juvenile Paleoproterozoic arc terrains and granitoid plutons of the Reindeer Zone, to the southeast. It also defines the northwest margin of the ca. 1855 Ma Wathaman Batholith, which forms the main protolith to shear zone mylonites. Although not precisely dated, available age constraints suggest that the shear zone formed between ca. 1855 and 1800 Ma, toward the end of peak thermotectonism in this part of the orogen.In the Needle Falls study area, shear zone mylonites exhibit varied, sequentially developed, ductile to brittle fabric features, including C–S fabrics, winged porphyroclasts (especially delta type), small-scale compressional and extensional microfaults ranging from thin ductile shear zones to late brittle faults, early isoclinal and sheath folds, later asymmetric folds related to compressional microfaults, and variably rotated and (or) folded quartz veins. All ductile shear-sense indicators suggest dextral displacement, as do most later ductile–brittle transition and brittle features. In conjunction with a gently north–northeast-plunging extension lineation, such data indicate oblique east-side-up dextral movement across the shear zone. However, preexisting structures in country rock protoliths rotate into the shear zone in a sense contrary to that predicted by ideal dextral simple shear, a feature thought to reflect significant flattening across the shear zone. Other ductile to brittle fabric elements in the mylonites are consistent with general noncoaxial strain, rather than ideal simple shear. Amount of displacement cannot be measured but indirect estimates suggest approximately 40 ± 20 km.The Needle Falls Shear Zone is too small and has developed too late in regional tectonic history to be considered a crustal suture. Rather, it is interpreted as either a late-tectonic oblique collisional structure or as the result of counterclockwise oroclinal rotation of the southern part of the orogen.
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Li, Haoran, Zhikai Dong, Zuolin Ouyang, Bo Liu, Wei Yuan, and Hongwu Yin. "Experimental Investigation on the Deformability, Ultrasonic Wave Propagation, and Acoustic Emission of Rock Salt Under Triaxial Compression." Applied Sciences 9, no. 4 (February 14, 2019): 635. http://dx.doi.org/10.3390/app9040635.
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Ultrasonic waves, which constitute an active testing method, and acoustic emissions (AE), which can be applied as passive testing technology, can reveal rock damage processes in different ways. However, few studies so far have simultaneously adopted both, owing to the limitations of the experimental apparatus. However, the simultaneous use of both methods can improve the experimental efficiency and help to understand the rock damage evolution more comprehensively. In this study, concurrent experiments of ultrasonic waves and AE activities were carried out on rock salt under uniaxial compression, and the deformation characteristics were measured. The fracture process was divided into four stages with individual characteristics: the elastic compression stage, brittle-ductile transition with crack initiation, brittle-ductile transition with damage initiation, and plastic deformation and strain hardening stage. The ultrasonic wave velocity, crack density, ultrasonic wave amplitude, and attenuation coefficient were obtained to evaluate the damage process. The ultrasonic wave amplitude and the attenuation coefficient were recommended as forecast indicators, owing to their sensitivity and operability of measurement. The confining pressure had an inhibitory effect on crack expansion and on the AE activity, and the damage ultimate stress was defined and determined according to the AE activity and energy release characteristics. Four critical strengths of the crack initiation threshold stress, dilatancy boundary stress, short-term strength, and damage ultimate stress of rock salt were determined and then discussed. These results are valuable in evaluating rock damage and guiding the operation of underground salt caverns.
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Rizqulloh, M. R., and A. Riyanto. "Distribution analysis of brittleness index, modulus young, modulus bulk, and Poisson’s ratio using the integration of refraction seismic method and MASW case study of Fasilkom UI’s new building." IOP Conference Series: Earth and Environmental Science 846, no. 1 (September 1, 2021): 012030. http://dx.doi.org/10.1088/1755-1315/846/1/012030.
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Abstract This research was conducted by validating the results of the SPT data collection that had been previously taken using geophysical methods in the engineering and environmental fields. This study can help to determine the subsurface lithology used to find the right building foundation. This research conducting to determine the distribution of the Brittleness value and the rock mechanic parameter values below the surface of the cross-section of the refractive seismic data processing in the field of the case study of Fasilkom UI’s new building in January 2020. Analysis of the distribution of Brittleness values and rock mechanics was carried out based on the calculation of Vp and Vs values obtained from processing the results of data acquisition and supporting data in the form of data (Soil Penetration Test) SPT. The 2D cross-section of rock mechanic parameters are Poisson’s Ratio has results ranging from -1 to 0.5, bulk modulus has resulted in the range 0 to 5.4, and modulus young has resulted in the range 0 to 9.5. The distribution of Brittleness values below the surface of the first and second layers is dominated by the brittle layer, the third layer is the distribution of the brittle and ductile layers, the fourth and fifth layers are dominated by ductile layers.
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Rizqulloh, M. R., and A. Riyanto. "Distribution analysis of brittleness index, modulus young, modulus bulk, and Poisson’s ratio using the integration of refraction seismic method and MASW case study of Fasilkom UI’s new building." IOP Conference Series: Earth and Environmental Science 846, no. 1 (September 1, 2021): 012030. http://dx.doi.org/10.1088/1755-1315/846/1/012030.
Full textAbstract:
Abstract This research was conducted by validating the results of the SPT data collection that had been previously taken using geophysical methods in the engineering and environmental fields. This study can help to determine the subsurface lithology used to find the right building foundation. This research conducting to determine the distribution of the Brittleness value and the rock mechanic parameter values below the surface of the cross-section of the refractive seismic data processing in the field of the case study of Fasilkom UI’s new building in January 2020. Analysis of the distribution of Brittleness values and rock mechanics was carried out based on the calculation of Vp and Vs values obtained from processing the results of data acquisition and supporting data in the form of data (Soil Penetration Test) SPT. The 2D cross-section of rock mechanic parameters are Poisson’s Ratio has results ranging from -1 to 0.5, bulk modulus has resulted in the range 0 to 5.4, and modulus young has resulted in the range 0 to 9.5. The distribution of Brittleness values below the surface of the first and second layers is dominated by the brittle layer, the third layer is the distribution of the brittle and ductile layers, the fourth and fifth layers are dominated by ductile layers.
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Lajtai, Emery Z., and E. J. Scott Duncan. "The mechanism of deformation and fracture in potash rock." Canadian Geotechnical Journal 25, no. 2 (May 1, 1988): 262–78. http://dx.doi.org/10.1139/t88-030.
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Specimens of potash rock from the Rocanville mine of the Potash Corporation of Saskatchewan were subjected to uniaxial compression tests and to time-dependent creep tests under static, uniaxial loading.During the first cycle of loading, the main sources of the measured strain are compaction and dilation at grain boundaries and consolidation of the clay phase. The crystals of halite and sylvite deform elastically at low stress and in a brittle manner at high stress. There is little, if any, evidence for constant-volume plastic deformation at any level of uniaxial stress.The stress–strain curve can be divided into three parts, each representing a different dominant deformational process: a low-stress quasi-elastic, an intermediate-stress ductile, and a high-stress brittle mechanism. The three parts are separated by the yield point (1–8 MPa) and the crack initiation point (10–13 MPa). The strength of the Rocanville potash specimens ranged between 15 and 18 MPa.The deformation of potash rock is strongly time dependent. There is evidence for the existence of all three stages of creep: transient, steady-state, and tertiary. There is very little interrelationship between the axial and lateral creep strains; the volumetric strain is negative at low stress and positive (dilatant) at high stress, but rarely, if ever, constant. Key words: creep, dilatant, ductile, elastic, fracture, microfracture, plastic, potash, salt.
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Ren, Mingyang, Xuyang Wu, Longyun Zhang, Junkui Pan, and Ningjing Li. "Study on Mechanical Properties and Nonlinear Strength Model of Deep Water-Sensitive Rock in Xianglu Mountain Tunnel." Geofluids 2022 (August 9, 2022): 1–23. http://dx.doi.org/10.1155/2022/8398602.
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The complex mechanical properties of deep water-sensitive rocks during construction bring great challenges to the construction and stability analysis of underground engineering in water-sensitive strata. Taking Xianglu Mountain Tunnel in the Central Yunnan Water Diversion Project as the engineering background, the mechanical properties of two types of water-sensitive rocks including limestone and silty mudstone were studied through laboratory tests, and a nonlinear strength model based on Hoek-Brown criterion was proposed. The results show that (1) the stress-strain curves of deep limestone and silty mudstone have significant strain softening characteristics and brittle-ductile transformation trend. Compared with limestone, silty mudstone has stronger ductility and lower critical confining pressure for brittle-ductile transformation; (2) the dilation effect of rock is affected by both confining pressure and plastic deformation. Under the same confining pressure and plastic deformation, the dilation characteristic of limestone is more evident than that of silty mudstone; (3) the Hoek-Brown criterion can describe the nonlinear strength characteristics of deep rock well. The evolution law of strength parameters m b and s with modified plastic shear strain conforms to the negative exponential function, while the relationship between strength parameter a and modified plastic shear strain satisfies cubic polynomial function; (4) the simulation results based on the nonlinear strength model are consistent with the test results, and the established strength model has high reliability. The research results can provide a basis for the stability analysis of the Xianglu Mountain Tunnel and the optimal design of the supporting structure and can also provide a reference for the study of the mechanical characteristics of the deep rocks in water-sensitive strata.
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Farouk, Ali Khaleel, and Ayad A. Al-haleem. "Integrating Petrophysical and Geomechanical Rock Properties for Determination of Fracability of the Iraqi Tight Oil Reservoir." Iraqi Geological Journal 55, no. 1F (June 30, 2022): 81–94. http://dx.doi.org/10.46717/igj.55.1f.7ms-2022-06-22.
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Tight oil reservoirs have been a concerned of the oil industry due to their substantial influence on oil production. Due to their poor permeability, numerous problems are encountered while producing from tight reservoirs. Petrophysical and geomechanical rock properties are essential for understanding and assessing the fracability of reservoirs, especially tight reservoirs, to enhance permeability. In this study, Saadi B reservoir in Halfaya Iraqi oil field is considered as the main tight reservoir. Petrophysical and geomechanical properties have been estimated using full-set well logs for a vertical well that penetrates Saadi reservoir and validated with support of diagnostic fracture injection test data employing standard equations and correlations. Subsequently, breakdown pressures are computed, and two fracturing models have been developed. The petrophysical analysis infers that the reservoir has poor properties, while the findings of the geomechanical properties indicate that the reservoir is brittle with ductile rock strata. These ductile strata underlay and overlay more brittle formations than the reservoir. The results from diagnostic fracture injection test DFIT are quite consistent with well logs results. The breakdown pressure reflects that this reservoir could easily be fractured by inserting pressure equal to 6250 psi. However, the fracturing model design parameters manipulates the fracture height confinement within Saadi Formation and its propagation to Hartha and/or Tanuma Formations. Therefore, the employment of petrophysical and geomechanical properties of the rocks assists in understanding the fracability of the formation and demonstrating the orientation and the fracture propagation direction.
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Muir, T. L. "Structural evolution of the Hemlo greenstone belt in the vicinity of the world-class Hemlo gold deposit." Canadian Journal of Earth Sciences 40, no. 3 (March 1, 2003): 395–430. http://dx.doi.org/10.1139/e03-004.
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A complex history of volcano-sedimentary deposition, polyphase strain, multiple intrusive events, and various stages of porphyroblastesis is indicated for the Hemlo gold deposit area within the Hemlo greenstone belt. Structural elements can be assigned to at least six stages of development (D1D6). D1 generated small-scale folds and low-angle faults (thrusts?) with no planar fabric, except within strain aureoles around the earliest intrusions. D2 was a progressive event resulting from northeast-directed compression, which generated regional, predominantly S-shaped folds (early D2); penetrative planar and linear fabrics, overturned stratigraphy, and formation of an inflection in the strike of the greenstone belt (mid-D2); and development of high-strain zones with dominant sinistral and local dextral shear sense (late D2). D3 was a distinctly separate progressive event resulting from northwest-directed transpression, which generated variably penetrative east- to northeast-striking foliation (S3), ductile dextral shear fabrics, and small-scale Z-shaped folds (early D3), followed by brittleductile to brittle development of cataclasite and pseudotachylite in layer-parallel zones (late D3). D4 resulted in contractional kinks and brittle fractures, locally in conjugate sets. D5 and D6 are represented by brittle to brittleductile faults, which overprint Paleoproterozoic and Mesoproterozoic dikes, respectively. Four granitoid magmatic events span the interval 27202677 Ma, with emplacement mainly during D2, between ca. 2690 and ca. 2684 Ma. A protracted period of regional medium-grade metamorphism likely spanned the D2D3 stages. The Hemlo gold deposit was emplaced during mid-D2 and was largely controlled by D2 structural elements and competency contrast between rock units.
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CHATTOPADHYAY, A., L. KHASDEO, R. E. HOLDSWORTH, and S. A. F. SMITH. "Fault reactivation and pseudotachylite generation in the semi-brittle and brittle regimes: examples from the Gavilgarh–Tan Shear Zone, central India." Geological Magazine 145, no. 6 (August 20, 2008): 766–77. http://dx.doi.org/10.1017/s0016756808005074.
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AbstractIn the sheared and foliated granitoids of the Proterozoic Gavilgarh–Tan Shear Zone (GTSZ) in central India, two types of pseudotachylite (Pt-M and Pt-C) are recognized. Pt-M layers are interbanded with mylonite and ultramylonite, show strong internal plastic deformation and buckle folding concurrent with the host rocks, and appear to have formed within the greenschist facies (300–400 °C) in the brittle–plastic transitional (semi-brittle) regime. Pt-C layers show sharp contacts with the host rock, exhibit abundant coeval cataclasis, preserve no evidence of subsequent plastic deformation, and formed at shallower depths, at temperature < 300 °C. Sulphide droplets and embayment of quartz grain margins in the pseudotachylite (Pt-C) matrix indicates a melt origin. Ductile shear sense criteria in the host mylonites are consistently sinistral, while those associated with the deformed pseudotachylite (Pt-M) layers are dextral. It appears therefore that the host mylonite/ultramylonite foliation experienced reactivated slip movement in the ‘semi-brittle’ zone when pseudotachylite was generated and subsequently ductilely deformed. The brittle pseudotachylite (Pt-C) layers were generated later at a shallower level, and at a lower temperature. They are spatially associated with a set of foliation-parallel brittle shears with sinistral-sense displacements. The multiple episodes of frictional melt generation within the Gavilgarh–Tan Shear Zone illustrate that it has a complex history of multiple reactivations. It therefore represents an important new area for the study of seismic behaviour of the upper crust along pre-existing structures and may facilitate a better geological understanding of the present seismic activity in the central Indian Shield.
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Paterson, Scott R., T. Kenneth Fowler, and Robert B. Miller. "Pluton emplacement in arcs: a crustal-scale exchange process." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 87, no. 1-2 (1996): 115–23. http://dx.doi.org/10.1017/s0263593300006532.
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ABSTRACT:Buddington (1959) pointed out that the construction of large crustal magma chambers involves complex internal processes as well as multiple country rock material transfer processes (MTPs), which reflect large horizontal, vertical and temporal gradients in physical conditions. Thus, we have attempted to determine the relative importance of different magmatic and country rock MTPs at various crustal depths, and whether country rock MTPs largely transport material vertically or horizontally, rather than seeking a single model of magma ascent and emplacement.Partially preserved roofs of nine plutons and in some cases roof–wall transitions with roof emplacement depths of 1·5–11 km were mapped. During emplacement, these roofs were not deformed in a ductile manner, detached or extended by faults, or significantly uplifted. Instead, sharp, irregular, discordant contacts are the rule with stoped blocks often preserved immediately below the roof, even at depths of 10 km. The upper portions of these magma chambers are varied, sometimes preserving the crests of more evolved magmas or local zones of volatile-rich phases and complex zones of dyking and magma mingling. Magmatic structures near roofs display a wide variety of patterns and generally formed after emplacement. Transitions from gently dipping roofs to steep walls are abrupt. At shallow crustal levels, steep wall contacts have sharp, discordant, stepped patterns with locally preserved stoped blocks indicating that the chamber grew sideways in part by stoping. Around deeper plutons, an abrupt transition (sometimes within hundreds of metres) occurs in the country rock from discordant, brittle roofs to moderately concordant, walls deformed in a ductile manner defining narrow structural aureoles. Brittle or ductile faults are not present at roof–wall joins.Near steep wall contacts at shallow to mid-crustal depths (5–15 km), vertical and horizontal deflections of pre-emplacement markers (e.g. bedding, faults, dykes), and ductile strains in narrow aureoles (0·1–0·3 body radii) give a complete range of bulk strain values that account for 0–100% of the needed space, but average around 30%, or less, particularly for larger batholiths. A lack of far-field deflection of these same markers rules out significant horizontal displacement outside the aureoles and requires that any near-field lateral shortening is accommodated by vertical flow. Lateral variations from ductile (inner aureole) to brittle (outer aureole) MTPs are typically observed. Compositional zoning is widespread within these magma bodies and is thought to represent separately evolved pulses that travelled up the same magma plumbing system. Magmatic foliations and lineations commonly cross-cut contacts between pulses and reflect the strain caused either by the late flow of melt or regional deformation.Country rocks near the few examined mid- to deep crustal walls (10–30 km) are extensively deformed, with both discordant and concordant contacts present; however, the distinction between regional and emplacement-related deformation is less clear than for shallower plutons. Internal sheeting is more common, although elliptical masses are present. Lateral compositional variations are as large as vertical variations at shallower depths and occur over shorter distances. Magmatic foliations and lineations often reflect regional deformation rather than emplacement processes.The lack of evidence for horizontal displacement outside the narrow, shallow to mid-crustal aureoles and the lack of lateral or upwards displacement of pluton roofs indicate that during emplacement most country rock is transported downwards in the region now occupied by the magma body and its aureole. The internal sheeting and zoning indicate that during the downwards flow of country rock, multiple pulses of magma travelled up the same magma system. If these relationships are widespread in arcs, magma emplacement is the driving mechanism for a huge crustal-scale exchange process.
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Perez Altamar, Roderick, and Kurt Marfurt. "Mineralogy-based brittleness prediction from surface seismic data: Application to the Barnett Shale." Interpretation 2, no. 4 (November 1, 2014): T255—T271. http://dx.doi.org/10.1190/int-2013-0161.1.
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Differentiating brittle and ductile rocks from surface seismic data is the key to efficient well location and completion. Brittleness average estimates based only on elastic parameters are easy to use but require empirical calibration. In contrast, brittleness index (BI) estimates are based on mineralogy laboratory measurements and, indeed, cannot be directly measured from surface seismic data. These two measures correlate reasonably well in the quartz-rich Barnett Shale, but they provide conflicting estimates of brittleness in the calcite-rich Viola, Forestburg, Upper Barnett, and Marble Falls limestone formations. Specifically, the BI accurately predicts limestone formations that form fracture barriers to be ductile, whereas the brittleness average does not. We used elemental capture spectroscopy and elastic logs measured in the same cored well to design a 2D [Formula: see text] to brittleness template. We computed [Formula: see text] and [Formula: see text] volumes through prestack seismic inversion and calibrate the results with the [Formula: see text] template from well logs. We then used microseismic event locations from six wells to calibrate our prediction, showing that most of the microseismic events occur in the brittle regions of the shale, avoiding more ductile shale layers and the ductile limestone fracture barriers. Our [Formula: see text] to brittleness template is empirical and incorporates basin- and perhaps even survey-specific correlations of mineralogy and elastic parameters through sedimentation, oxygenation, and diagenesis. We do not expect this specific template to be universally applicable in other mudstone rock basins; rather, we recommend interpreters generate similar site-specific templates from logs representative of their area, following the proposed workflow.
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Waqas, Umer, Hafiz Muhammad Awais Rashid, Muhammad Farooq Ahmed, Ali Murtaza Rasool, and Mohamed Ezzat Al-Atroush. "Damage Characteristics of Thermally Deteriorated Carbonate Rocks: A Review." Applied Sciences 12, no. 5 (March 7, 2022): 2752. http://dx.doi.org/10.3390/app12052752.
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This review paper summarizes the recent and past experimental findings to evaluate the damage characteristics of carbonate rocks subjected to thermal treatment (20–1500 °C). The outcomes of published studies show that the degree of thermal damage in the post-heated carbonate rocks is attributed to their rock fabric, microstructural patterns, mineral composition, texture, grain cementations, particle orientations, and grain contact surface area. The expressive variations in the engineering properties of these rocks subjected to the temperature (>500 °C) are the results of chemical processes (hydration, dehydration, deionization, melting, mineral phase transformation, etc.), intercrystalline and intergranular thermal cracking, the separation between cemented particles, removal of bonding agents, and internal defects. Thermally deteriorated carbonate rocks experience a significant reduction in their fracture toughness, static–dynamic strength, static–dynamic elastic moduli, wave velocities, and thermal transport properties, whereas their porous network properties appreciate with the temperature. The stress–strain curves illustrate that post-heated carbonate rocks show brittleness below a temperature of 400 °C, brittle–ductile transformation at a temperature range of 400 to 500 °C, and ductile behavior beyond this critical temperature. The aspects discussed in this review comprehensively describe the damage mechanism of thermally exploited carbonate rocks that can be used as a reference in rock mass classification, sub-surface investigation, and geotechnical site characterization.
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Sun, Lihui, Yaxin Long, Xing Li, Zhixin Jiang, Yu Fan, Zongze Wang, and Xiangang Han. "Effect of Loading Rate on the Mechanical Properties of Weakly Cemented Sandstone." Sustainability 15, no. 3 (February 2, 2023): 2750. http://dx.doi.org/10.3390/su15032750.
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Weakly cemented rocks are characterized by low strength, loose structure, and easy disintegration. High-intensity mining activities can damage and rupture such rock bodies and induce damage, such as flaking and roofing on roadways. To reveal the mining intensity influence on the weakly cemented rocks’ deformation and damage, a numerical particle flow model of weakly cemented sandstone was established based on particle flow theory. Uniaxial compression simulation tests were conducted at four loading rates of 0.01, 0.1, 0.5, and 1 mm/min to study the weakly cemented sandstone’s stress–strain relationship, damage rupture, acoustic emission, and energy evolution. The results show that, with an increased loading rate, the uniaxial compressive strength of weakly cemented sandstone increases exponentially, and the rupture mode transforms from brittle damage to ductile damage; the greater the loading rate, the greater the degree of damage and crushing range of the rock. Further, with an increased loading rate, the peak hysteresis of rock acoustic emission events decreases, and the number of events increases; the energy accumulated in the rock increases, thus intensifying the degree of rock damage. Therefore, the possibility of engineering disasters should be considered when conducting high-speed underground mining activities.
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Cieślik, Jerzy. "Stress Drop as a Result of Splitting, Brittle and Transitional Faulting of Rock Samples in Uniaxial and Triaxial Compression Tests." Studia Geotechnica et Mechanica 37, no. 1 (March 1, 2015): 17–23. http://dx.doi.org/10.1515/sgem-2015-0003.
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Abstract Rock samples can behave brittle, transitional or ductile depending on test pressure, rate of loading and temperature. Axial stiffness and its changes, relative and absolute dilatancy, yield, and fracture thresholds, residual strength are strongly pressure dependent. In this paper the stress drop as an effect of rock sample strength loss due to failure was analyzed. Uniaxial and triaxial experiments on three types of rock were performed to investigate the stress drop phenomenon. The paper first introduces short background on rock behavior and parameters defining a failure process under uniaxial and triaxial loading conditions. Stress drop data collected with experiments are analyzed and its pressure dependence phenomenon is described. Two methods for evaluation of stress drop value are presented.
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Belkabir, Abdelhay, Claude Hubert, and Larry Hoy. "Fluid-rock reactions and resulting change in rheological behavior of a composite granitoid: the Archean Mooshla stock, Canada." Canadian Journal of Earth Sciences 35, no. 2 (February 1, 1998): 131–46. http://dx.doi.org/10.1139/e97-091.
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The composite Mooshla stock displays clear evidence of variations in style and intensity of strain that are closely related to its internal lithological heterogeneity. Gabbro-diorite, quartz diorite, and tonalite rocks are weakly foliated and characterized by brittle and brittle-ductile small-scale shear zones, whereas leucotonalitic rocks are strongly foliated and transected by numerous wide and extensive ductile shear zones. Increasing degrees of penetrative deformation and marked changes of strain style in the pluton, from the more mafic rocks to the more felsic ones, are interpreted to reflect metamorphism-related rheological contrasts, rather than differences in the physical conditions of deformation. Metamorphism of the stock is characterized by an intensive hydration of the igneous rocks that has greatly enhanced their original heterogeneities. Petrographic, microstructural, and chemical studies show that the least deformed rocks are characterized by abundant albite-oligoclase (65-80%) with a matrix of minor quartz (5-10%) and actinolitic amphibole. The resistant plagioclase laths, although altered and replaced, form a stress-supporting framework that has protected the interstitial weak minerals, such as quartz, chlorite, and biotite, from deformation. However, the least deformed leucotonalites are characterized by low albite (35-45%) and high quartz contents (up to 65%). Extensive metamorphic hydration of these rocks produces quartz and phyllitic minerals that had enhanced significantly the ductility of the leucotonalites. Characterization of the chemical changes and the thermochemical conditions of the fluid, using microstructure and measurement of stable isotopes, indicates that fluid-rock interactions during metamorphism and syntectonic hydrothermal alteration have played an important role in creating the contrasting deformation of the composite granitoid.
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Marsellos, Α. Ε., D. A. Foster, K. Min, W. S. F. Kidd, J. Garver, and K. Kyriakopoulos. "An application of GIS analysis on structural data from metamorphic rocks in Santorini Island." Bulletin of the Geological Society of Greece 47, no. 3 (December 21, 2016): 1479. http://dx.doi.org/10.12681/bgsg.10986.
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The Santorini volcanic island is located in the northern Cretan Sea and is part of the ecent subduction-related volcanic arc. The opening of Cretan Sea is the result of extension associated with a series of ductile and brittle detachment faults developed since the Middle Miocene. A detachment between two exhumed metamorphic units is exposed at Athinios, on Santorini Island. Two exhumed metamorphic units are identified that show evidence of similar brittle deformation, but distinctive ductile and ductile-brittle structures. Different thermal histories indicate that a Miocene metamorphic unit is juxtaposed structurally below an Eocene metamorphic unit. In this paper, a prediction map of structural observations in Athinios is generated with statistical and GIS software, and shows a spatial distribution consistent with the exposure of two metamorphic units. K-Mean Cluster analysis using SPSS software on lineation azimuths of the metamorphic rock units shows two populations with center values of 347.2o ± 0.73o degrees (NNW to N) and 003.4o ± 0.83o degrees (N to NNE). NNW-lineation (arc-parallel extension) population belongs to the lower Miocene metamorphic unit and the NNE-lineation represents the Eocene metamorphic unit that was affected by arc-normal extension. A geostatistical map of ordinary Kriging type displays the possible exposed tectonic contacts. This methodology provides a structural prediction map that after field verification facilitates efficient structural and thermochronological sampling.
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Sone, Hiroki, and Mark D. Zoback. "Mechanical properties of shale-gas reservoir rocks — Part 2: Ductile creep, brittle strength, and their relation to the elastic modulus." GEOPHYSICS 78, no. 5 (September 1, 2013): D393—D402. http://dx.doi.org/10.1190/geo2013-0051.1.
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We studied the elastic moduli, ductile creep behavior, and brittle strength of shale-gas reservoir rocks from Barnett, Haynesville, Eagle Ford, and Fort St. John shale in a series of triaxial laboratory experiments. We found a strong correlation between the shale compositions, in particular, the volume of clay plus kerogen and intact rock strength, frictional strength, and viscoplastic creep. Viscoplastic creep strain was approximately linear with the applied differential stress. The reduction in sample volume during creep suggested that the creep was accommodated by slight pore compaction. In a manner similar to instantaneous strain, there was more viscoplastic creep in samples deformed perpendicular to the bedding than parallel to the bedding. The tendency to creep also correlated well with the static Young’s modulus. We explained this apparent correlation between creep behavior and elastic modulus by appealing to the stress partitioning that occurs between the soft components of the shales (clay and kerogen) and the stiff components (quartz, feldspar, pyrite, and carbonates). Through a simple 1D analysis, we found that a unique relation between the creep compliance and elastic modulus, independent of composition and orientation, can be established by considering the individual creep behavior of the soft and stiff components that arises from the stress partitioning within the rock. This appears to provide a mechanical explanation for why long-term ductile deformational properties can appear to correlate with short-term elastic properties in shale-gas reservoir rocks.
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Ugbor, Charles Chibueze, Peter Ogobi Odong, and Aniefiok Sylvester Akpan. "Application of pre-stack seismic waveform inversion and empirical relationships for the estimation of geomechanical properties in Ruby field, central swamp depobelt, Onshore Niger Delta, Nigeria." Journal of Petroleum Exploration and Production Technology 11, no. 6 (June 2021): 2389–406. http://dx.doi.org/10.1007/s13202-021-01219-w.
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AbstractPre-stack seismic inversion, well log analysis approach and empirical relations were adopted in this study to better estimate geomechanical properties of Ruby field with minimum error. The use of conventional well log empirical method alone to evaluate geomechanical properties in oil/gas fields sometimes becomes problematic. Geomechanical properties were divided into: elastic moduli [Young’s modulus, shear modulus, bulk modulus and Poisson ratio (PR)] and rock mechanical strength properties (closure stress ratio (CSR), brittleness (BRI) and compressibility). Four geomechanical earth models (CSR, BRI, Young’s modulus and PR) were generated from the inversion analysis to understand the distribution of rock strength properties across the field. The results deciphered high Young’s, shear and bulk modulus in the reservoir zone compared to the cap/seal rocks and a decrease in PR. This implies that, the cap/seal are more ductile and less compressible than the reservoir rocks, indicating that the reservoirs are highly brittle. CSR result reveals high in cap/seal indicating that the cap/seal rock are harder to fracture and has a greater chance to withstand higher compressive stress before failing as opposed to reservoir rocks. The inverted earth model shows that, Young’s modulus and brittleness increase toward the northeastern part of the field, while CSR and PR increase toward the southwestern part of the field. These results suggest that harder, stiffer, highly compressible and easily fractured rocks are found in the northern and eastern part of the field as opposed to the southern to western part of the field that is ductile.
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Wang, Kelin. "If Not Brittle: Ductile, Plastic, or Viscous?" Seismological Research Letters 92, no. 2A (January 27, 2021): 1181–84. http://dx.doi.org/10.1785/0220200242.
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Abstract Integrating earthquake studies with geodynamics requires knowledge of different modes of permanent deformation of rocks beyond seismic failure. However, upon stepping out of the realm of brittle failure, students find themselves in a zone of terminology conflict. Rocks below the brittle shallow part of the lithosphere are said to be ductile, plastic, or viscous, yet in many papers what is obviously brittle deformation is said to be plastic. In this EduQuakes article, I explain the origin of this conflict and how to handle it. The primary reason for the conflict is that the word plastic is used by one research community to describe viscous deformation but by another community to describe permanent deformation that is not viscous. To the former community, emphasis is on microscopic deformation mechanisms. To the latter community, emphasis is on whether the macroscopic deformation is time dependent. Using a Coulomb continuum to approximate the effects of numerous brittle faults adds another level of complexity. It is futile to expect a unification of terminology any time soon, but with some basic knowledge one can live with this situation without suffering scientific confusion.
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Winhausen, Lisa, Kavan Khaledi, Mohammadreza Jalali, Janos L. Urai, and Florian Amann. "Failure mode transition in Opalinus Clay: a hydro-mechanical and microstructural perspective." Solid Earth 13, no. 5 (May 16, 2022): 901–15. http://dx.doi.org/10.5194/se-13-901-2022.
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Abstract. The way rocks deform under changing stress conditions can be described by different deformation modes, which is fundamental for understanding their rheology. For Opalinus Clay, which is regarded as a potential host rock for nuclear waste, we investigate the failure mode as a function of applied effective stress in laboratory experiments. Therefore, we performed consolidated undrained triaxial tests at different effective consolidation stresses from 2.5 to 16 MPa, in which samples were loaded parallel to bedding, and analysed the deformation structures using ion-beam polishing and electron microscopy. With increasing effective confining stress, the results show a transition from brittle-dominated to more ductile-dominated deformations, localising in distinct shear bands. Both effective stress paths and microstructural analysis indicate a tendency towards less dilation in the shear zones for higher effective stresses. Triaxial test results suggest a non-linear failure envelope. The non-linearity of the failure envelope is associated with decreasing dilation with increasing effective stress accompanied by changes in microstructural deformation processes, which explain the decreasing friction angle. For the first time, we can verify that the observed non-linear failure envelope is due to the gradual transition from brittle- to more ductile-dominated deformation on the microscale controlling the bulk hydro-mechanical behaviour of Opalinus Clay.
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Zhang, Lianying, Xianbiao Mao, Ming Li, Bing Li, Ruixue Liu, and Aihong Lu. "Brittle–Ductile Transition of Mudstone in Coal Measure Rock Strata under High Temperature." International Journal of Geomechanics 20, no. 1 (January 2020): 04019149. http://dx.doi.org/10.1061/(asce)gm.1943-5622.0001549.
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