Contamination is a common scenario of intracrustal magmatic processes that may significantly change the compositions of involved anatectic melts. Here, we present major element and B isotope analyses ...on tourmalines from the Guowu leucogranite and their host rocks, which allow us to unravel the potential contaminations of the Himalayan leucogranites by metapelite host rocks. Three types of tourmaline have been identified in our samples. Tur-M in the host schist has the highest Mg/(Mg+Fe) ratio (0.52-0.62) and low Al content, suggesting its metamorphic character. Tourmalines in the leucogranite (Tur-L) and in the contact zone between leucogranite and schist (Tur-C) have an identical core-rim texture, and their cores are characterized by the lowest Mg/(Mg+Fe) ratio (0.13-0.18) and high Al content, which are consistent with the composition of magmatic tourmaline in the Himalayan leucogranites. The rims of Tur-L show higher Mg/(Mg + Fe) ratio (0.32-0.45) and moderate Ca, Ti, F contents, reflecting the contribution of the host schist via contamination. The composition of Tur-C rims is similar to that of Tur-M, suggesting a more significant contribution from contaminated schist than that for Tur-L. The different types of tourmaline share consistent B isotope compositions with δ
11
B ranging from −14 to −12‰. The compositional characteristics of the contaminated tourmaline and the mineral assemblage in the contaminated zone suggest that the involved components derived from the host schist, probably produced by the decomposition of tourmaline, biotite, plagioclase, primarily include Ca, K, Mg, Ti, B and F. In addition, contamination by tourmaline-bearing metapelite may be an alternative interpretation responsible for the peraluminous character of the Himalayan leucogranites. The occurrence of contaminated tourmaline in leucogranites suggests that contamination of host rocks is a possible way promoting the formation of tourmaline in the Himalayan leucogranites, and tourmaline is useful for deciphering the related contamination processes.
The acoustic emission (AE) signals generated during direct shear test were evaluated on different types of joints (rock–rock, rock–concrete and concrete–concrete). Several boreholes were cored from a ...dam body, rock mass and interface between dam and rock mass, and the samples were prepared and tested under direct shear test. A laser profilometer scanner was used for scanning the joint surfaces in order to assess surface roughness. By correlating the AE signals with the shear graphs one can predict the starting point of shearing during direct shear test. Count and energy parameters were analyzed in two different methods to monitor the shear behavior of the joints: a graph of the count and energy rates, and a graph of cumulative count and energy. Four separated periods were observed for bonded and non-bonded joints: linear pre-peak period, non-linear pre-peak period, post peak period and residual period. This study showed that AE has enough accuracy to monitor the shear behavior of the joints and it can be used in site confidently.
The fluid flow in fracture porous media plays a significant role in the assessment of deep underground reservoirs, such as through CO2 sequestration, enhanced oil recovery, and geothermal energy ...development. Many methods have been employed—from laboratory experimentation to theoretical analysis and numerical simulations—and allowed for many useful conclusions. This Special Issue aims to report on the current advances related to this topic. This collection of 58 papers represents a wide variety of topics, including on granite permeability investigation, grouting, coal mining, roadway, and concrete, to name but a few. We sincerely hope that the papers published in this Special Issue will be an invaluable resource for our readers.
The fluid flow in fracture porous media plays a significant role in the assessment of deep underground reservoirs, such as through CO2 sequestration, enhanced oil recovery, and geothermal energy ...development. Many methods have been employed—from laboratory experimentation to theoretical analysis and numerical simulations—and allowed for many useful conclusions. This Special Issue aims to report on the current advances related to this topic. This collection of 58 papers represents a wide variety of topics, including on granite permeability investigation, grouting, coal mining, roadway, and concrete, to name but a few. We sincerely hope that the papers published in this Special Issue will be an invaluable resource for our readers.
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.
The prehistoric hunter-gatherers of the Lower Pecos Canyonlands of Texas and Coahuila, Mexico, created some of the most spectacularly complex, colorful, extensive, and enduring rock art of the ...ancient world. Perhaps the greatest of these masterpieces is the White Shaman mural, an intricate painting that spans some twenty-six feet in length and thirteen feet in height on the wall of a shallow cave overlooking the Pecos River. In The White Shaman Mural, Carolyn E. Boyd takes us on a journey of discovery as she builds a convincing case that the mural tells a story of the birth of the sun and the beginning of time—making it possibly the oldest pictorial creation narrative in North America.Unlike previous scholars who have viewed Pecos rock art as random and indecipherable, Boyd demonstrates that the White Shaman mural was intentionally composed as a visual narrative, using a graphic vocabulary of images to communicate multiple levels of meaning and function. Drawing on twenty-five years of archaeological research and analysis, as well as insights from ethnohistory and art history, Boyd identifies patterns in the imagery that equate, in stunning detail, to the mythologies of Uto-Aztecan-speaking peoples, including the ancient Aztec and the present-day Huichol. This paradigm-shifting identification of core Mesoamerican beliefs in the Pecos rock art reveals that a shared ideological universe was already firmly established among foragers living in the Lower Pecos region as long as four thousand years ago.
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.
•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.
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.
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