Brittleness is one of the most important mechanical properties of rock: it plays a significant role in evaluating the risk of rock bursts and in analysis of borehole-wall stability during shale gas ...development. Brittleness is also a critical parameter in the design of hydraulic fracturing. However, there is still no widely accepted definition of the concept of brittleness in rock mechanics. Although many criteria have been proposed to characterize rock brittleness, their applicability and reliability have yet to be verified. In this paper, the brittleness of rock under compression is defined as the ability of a rock to accumulate elastic energy during the pre-peak stage and to self-sustain fracture propagation in the post-peak stage. This ability is related to three types of energy: fracture energy, post-peak released energy and pre-peak dissipation energy. New brittleness evaluation indices
B
1
and
B
2
are proposed based on the stress–strain curve from the viewpoint of energy. The new indices can describe the entire transition of rock from absolute plasticity to absolute brittleness. In addition, the brittle characteristics reflected by other brittleness indices can be described, and the calculation results of
B
1
and
B
2
are continuous and monotonic. Triaxial compression tests on different types of rock were carried out under different confining pressures. Based on
B
1
and
B
2
, the brittleness of different rocks shows different trends with rising confining pressure. The brittleness of red sandstone decreases with increasing confining pressure, whereas for black shale it initially increases and then decreases in a certain range of confining pressure. Granite displays a constant increasing trend. The brittleness anisotropy of black shale is discussed. The smaller the angle between the loading direction and the bedding plane, the greater the brittleness. The calculation
B
1
and
B
2
requires experimental data, and the values of these two indices represent only relative brittleness under certain conditions. In field operations, both the relative brittleness and the brittleness obtained from seismic data or mineral composition should be considered to gain a more comprehensive knowledge of the brittleness of rock material.
In this paper, the feasibility of a thermally assisted drilling method is investigated. The working principle of this method is based on the weakening effect of a flame-jet to enhance the drilling ...performance of conventional, mechanical drilling. To investigate its effectiveness, we study rock weakening after rapid, localized flame-jet heating of Rorschach sandstone and Central Aare granite. We perform experiments on rock strength after flame treatments in comparison to oven heating, for temperatures up to 650
∘
C and heating rates from 0.17 to 20
∘
C/s. The material hardening, commonly observed at moderate temperatures after oven treatments, can be suppressed by flame heating the material at high heating rates. Our study highlights the influence of the heating rate on the mechanism of thermal microcracking. High heating rate, flame treatments appear to mostly induce cracks at the grain boundaries, opposed to slow oven treatments, where also a considerable number of intragranular cracks are found. Herewith, we postulate that at low heating rates, thermal expansion stresses cause the observed thermal cracking. In contrast, at higher heating rates, thermal cracking is dominated by the stress concentrations caused by high thermal gradients.
•A numerical model coupling joints, water and microseismicity is proposed to simulate rock mass damage.•An inversion model of rock damage based on microseismic moment tensor was proposed.•The ...integration of microseismic data is beneficial to the prediction of rock damage development.
The behaviour of rock mass is governed by the properties of the intact rock, the joints and the water conditions. Moreover, this behaviour is also influenced by the temporal and spatial damage evolution patterns of the rock. Thus, in this study, an approach that couples joints, water and microseismicity is proposed to model rock engineering problems. Joints are used to reduce the global properties of the rock mass, water is used to reduce the local properties of the rock mass, and microseismicity are used to reduce the point properties of the rock mass. Using data from the Shirengou iron mine, the effects of water and joints on the properties of rock masses were investigated, and a representative elementary volume of rock mass was determined. Then, a coupled fluid–solid numerical model was established to simulate the evolution of rock mass damage while considering the effects of joints and water. Finally, an inversion model of rock damage based on microseismic moment tensor was proposed. A numerical simulation of rock mass damage that couples joints, water and microseismicity was performed. The rock mass damage mechanism was then analysed. Joints and water were found to significantly affect the damage zones. The rock mass damage estimate would not be accurate without considering the effects of joints and water. Thus, water was the critical factor in the studied damage pattern. Further integration of microseismic data aided in modifying the numerical results and in predicting the damage development. The proposed approach can efficiently assess rock mass damage evolution and provide a basis for rock support.
During the mining process of deep mines, the instability of surrounding rock caused by rock creep has occurred from time to time. However, it is difficult to study the accelerating creep phase of ...rock with the classical Nishihara model. Due to the influence of water seepage and different stress, rock creep exhibits non-linear characteristics. For this reason, on the basis of the Nishihara model, the dashpot in the Kelvin model was replaced by the Abel dashpot, and the dashpot in the plastomer model was modified to non-linear dashpot, and the modified Nishihara model and its constitutive equation were established. Based on the creep experimental data of granite, the experimental results of granite under different stress and different osmotic pressures were analyzed. The typical experimental data were fitted by using MATLAB software, and the fitting results showed that the modified Nishihara model was verified. The model can better describe the whole process (decelerating creep phase, stable creep phase, accelerating creep phase) and non-linear characteristics of rock creep. Especially when the load on the rock is greater than the long-term strength, the accelerating creep phase of rock is more obvious. The modified Nishihara model has five parameters, and the method for determining each parameter is simple and has wide applicability. It better reflects the damage and failure process of the surrounding rock subjected to stable creep phase and accelerating creep phase after excavation, which can provide theoretical basis for further revealing the objective law of rock creep.
There is a growing demand of knowledge on the behavior of rock masses after thermal treatment in both academic and practical aspects due to the high demand of construction of underground structures ...under the high-temperature environment. The peak shear strength of rock joints has a significant role in evaluating the stability problems of surrounding rocks. However, there is a lack of information about the temperature-dependent nature of the basic friction angle of rock joints, which serves as an essential parameter to evaluate the peak shear strength. The present study experimentally investigates the influences of temperature magnitude (20, 200, 400, 600, and 800 °C) on the basic friction angle of granite, marble, and red sandstone joints. The basic friction angles of the three kinds of rock joints exhibit linear trends with the increase in the treatment temperature. The basic friction angles of granite and red sandstone joints increase with the increase in the treatment temperature, while the values for marble joints continually decrease. The mechanisms for the thermally altered variations in the basic friction angle of rock joint are mainly related to dehydration process, uneven expansion of mineral grains, thermally weakened asperities distributed on the surfaces, and change in physical and mechanical properties of minerals. In addition, other test conditions, including tilting rate, specimen size, repetition number, and cooling rate, are also analyzed. The present study provides useful data in establishing a peak shear strength criterion for rock joints by considering the temperature effect.
The tectonic regime and melting conditions of adakitic tonalitic‐trondhjemitic leucosomes and tonalite plutons from the North Qaidam terrane are evaluated through petrology, whole‐rock major, trace ...element and Sr‐Nd isotopic data and zircon U‐Pb data. Zircons from leucosomes and metabasites preserve distinct U‐Pb age populations: early Ordovician inherited zircon cores record a protolith age of ~470 Ma, whereas zircon rims preserve subsequent HP granulite facies metamorphism, anatexis, and magmatism between 437 and 433 Ma. Whole‐rock geochemistry suggests that three types of leucosomes and tonalite plutons have geochemical features similar to adakites. Type 1 leucosomes record high Sr contents and positive Eu anomalies representing an earlier period of plagioclase accumulation. The flat fractionated rare earth element patterns of type 2 leucosomes correspond to residues of HP mafic granulites, and the steep fractionated rare earth element patterns of type 3 leucosomes correspond to garnet‐ and clinopyroxene‐rich residues. Petrological observations with P‐T paths and experimentally constrained melting curves together infer that melting of the metagabbro were triggered by the breakdown of amphibole ± zoisite under high‐pressure conditions. Therefore, tonalite, trondhjemite, and granodiorite (TTG)‐adakitic magmas in the North Qaidam terrane were produced through partial melting of newly emplaced gabbroic rocks with an arc affinity under high‐pressure, granulite facies conditions in a thickened lower crust during continental collision. This model explains the origin of TTG‐adakitic rocks and related continental growth and crustal differentiation genetically associated with continental collision.
Key Points
TTG‐like magmas in the North Qaidam were produced by partial melting of newly emplaced metagabbros under HP granulite facies conditions
Metagabbros possess a subduction‐related arc signature, whereas leucosomes and tonalite plutons record geochemical features similar to TTGs
TTG‐like rocks and related continental growth genetically are associated with continental collision zones
Discrete element simulation of rock cutting Rojek, Jerzy; Oñate, Eugenio; Labra, Carlos ...
International journal of rock mechanics and mining sciences (Oxford, England : 1997),
09/2011, Volume:
48, Issue:
6
Journal Article
Peer reviewed
Open access
This paper presents numerical modelling of rock cutting processes. The model consists of a tool–rock system. The rock is modelled using the discrete element method, which is suitable to study ...problems of multiple material fracturing such as those involved in rock cutting. Both 2D and 3D models are considered in this work. The paper presents a brief overview of the theoretical formulation and calibration of the discrete element model by a methodology combining the dimensional analysis with simulation of the unconfined compressive strength (UCS) and indirect tension (Brazilian) tests. The rock cutting process with roadheader picks, which is typical for underground excavation, has been simulated. The results of the 2D and 3D analyses have been compared with one another, and numerical results have been compared with the available experimental data.
► Advanced modelling of a complex engineering problem using the discrete element model. ► Calibration of the discrete element model. ► Successful validation of the numerical model using experimental results of rock cutting.
Owing to the importance of serpentinites for planetary geochemical and geodynamic processes, there has been much work discerning the origins of their parent rocks, including distinguishing between ...serpentinites derived from a subducting plate versus overlying mantle in exhumed subduction complexes. The island of New Caledonia (SW Pacific Ocean) provides a rare window into Cenozoic Pacific subduction processes. The island is unique in exposing both an exceptionally preserved high‐pressure, low‐temperature subduction complex and one of the largest supra‐subduction zone ophiolites in the world. Previous studies disagree on the origin of serpentinites in the subduction complex. In this study, we analyze 23 serpentinites from this complex for whole‐rock major and trace element geochemistry and stable isotope (δD, δ18O) compositions. Our data reveal two distinct groups of serpentinites: Group I samples in the northern portion of the complex are pervasively serpentinized, and exhibit enriched heavy rare earth element (REE) compositions and δ18O values between +6.7‰ and +10.2‰. In contrast, Group II serpentinites in the south preserve relict orthopyroxene and olivine, and show depleted trace element compositions and comparatively lower δ18O values between +5.1‰ and +8.0‰. We interpret Group I serpentinites to derive from downgoing plate mantle, whereas Group II serpentinites derive from overlying mantle wedge, exhibiting remarkable similarity to the REE geochemistry of the structurally overlying New Caledonia ophiolite. Our results establish the subduction complex in New Caledonia as an unusual natural record of the entrainment and exhumation of mantle from both the overlying mantle wedge and the downgoing plate in an oceanic subduction zone.
Plain Language Summary
The hydration of Earth's mantle produces rocks called serpentinites that are important to chemical cycling within the Earth system. This process, a form of metamorphism, occurs in several types of tectonic settings on Earth. Serpentinites formed in these different settings are imparted with unique geochemical “fingerprints” due to different types of fluids and varied compositions of the original mantle material. In metamorphic complexes that preserve remnants of subduction zones, serpentinites can offer clues to the original tectonic setting and subsequent mechanics of subduction. We analyze stable isotope and whole‐rock compositions to determine the origin of the mantle that produced serpentinites found in the metamorphic complex preserved in New Caledonia (SW Pacific). We discover two distinct groups of serpentinites: one group in the northern portion of the complex likely formed on the ocean floor prior to subduction, and experienced high degrees of fluid alteration as it was metamorphosed. In contrast, a second group of serpentinites in the southern portion of the complex resembles material from the mantle overlying the subducting plate and is less altered. This locality represents an uncommon example, globally, where material from the overlying mantle was entrained and then preserved at the surface in an exhumed subduction complex.
Key Points
Two compositionally distinct types of serpentinites are identified in the New Caledonia subduction complex
Some serpentinites derive from the subducting plate, others from the overlying mantle wedge
New Caledonia preserves evidence for incorporation and exhumation of mantle hangingwall via the subduction channel
Brian Eno Albiez, Sean; Pattie, David
2016, 2016-08-11
eBook
On the back of his published diary Brian Eno describes himself variously as: a mammal, a father, an artist, a celebrity, a pragmatist, a computer-user, an interviewee, and a 'drifting clarifier'. To ...this list we might add rock star (on the first two Roxy Music albums); the creator of lastingly influential music (Another Green World; Music for Airports); a trusted producer (for Talking Heads, U2, Coldplay and a host of other artists); the maker of large-scale video and installation artworks; a maker of apps and interactive software; and so on. He is one of the most feted and influential musical figures of the past forty years, even though he has described himself on more than one occasion as a non-musician. This volume examines Eno's work as a musician, as a theoretician, as a collaborator, and as a producer. Brian Eno is one of the most influential figures in popular music; an updated examination of his work on this scale is long overdue. - See more at: http://www.bloomsbury.com/uk/brian-eno-9781441129123/#sthash.CmHDQ6Xy.dpuf
During underground mining, rock deformation may be time-dependent and is reflected in rheological behavior. These changes may be also accelerated by dynamic disturbances, such as rock blasting, which ...can trigger mining-induced hazards such as rockburst and a falling roof. A combined double-rock sample was analyzed to clarify the rockburst mechanism resulting from interaction between roof and pillar. In this work, a double-rock sample was subjected to a combined creep and dynamic loading condition. Based on the results, an ideal mechanical model was developed to describe the interaction between double rock samples loaded in series to simulate interaction between the pillar and roof. To test the model, a double-rock sample composed of granite and sandstone was loaded in series under creep and dynamic loading and the effect of dynamic disturbance on the creep process was quantified. Under the same creep stress, a higher impact dynamic disturbance resulted in shorter failure time. Under the same dynamic disturbance, the specimen failed faster with increased strain energy of rebound of the granite sample under increasing creep stress. The energy dissipation rate and energy transfer efficiency are defined to quantify the energy dissipation of double-rock sample and energy transfer between strong and weak sample. Based on the quantification of energy transfer efficient, it confirms that the ratio of stiffness of the double-rock sample should be a indicator for the energy transfer between strong and weak samples. The granite sample had higher uniaxial compressive strength, so it did not fail during the loading process. For the plaster-granite sample, the granite released most energy to accelerate the unstable failure of plaster. The granite-granite sample failed simultaneously and released most strain energy violently. The results can provide a reference to evaluate the delayed rockburst of rock subjected to creep stress.
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