Kinds Of Rocks Research Articles

Evolution and Characterization of Uniaxial Compression Damage of Coal Measure Rock

In order to study the evolution law of uniaxial compression damage and its characterization method, three kinds of rocks with different lithology that commonly exist in coal measure rock were taken as the research objects to explore the relationship between their mineral composition, microstructure and mechanical properties, and the feasibility of acoustic emission (AE) characteristic parameters and AE spatial location to characterize the evolution process of uniaxial compression damage of rocks was compared and analyzed. A damage constitutive model based on AE cumulative ringing count was established and verified by numerical simulation. The results show that the differences in the micromorphology and mineral composition of coal measures with different lithology directly affect their physical and mechanical properties and load damage characteristics. AE characteristic ringing count can effectively represent the damage evolution process of rock during loading. Based on rock porosity characteristics and AE cumulative ringing count during loading, a constitutive model considering initial damage and cumulative damage was established. The theoretical analysis results of the damage constitutive model are in good agreement with the results of laboratory experiments and numerical simulation, which can be used to analyze the damage process of coal measure rock under load.

A new improved 3D Hoek-Brown criterion

The Hoek-Brown strength criterion has been widely used to estimate the strength of intact rocks and rock masses, and has been continuously developed. However, in the latest version of the standard, the criterion still ignores the influence of the intermediate principal stress. To study the different effects of intermediate principal stress on rock failure under triaxial or multiaxial stress states, this paper proposes a modified three-dimensional H-B strength criterion, which can be reduced to the H-B criterion, three-dimensional Priest criterion, Jiang’s (2012) criterion, and the Cai criterion. Multiaxial test data of six intact rocks were used for validation and applicability analysis. The results show that the proposed criterion can well describe the trend of multi-axial test data of six kinds of rocks, and the average mismatch of the six types of rocks is controlled within 10 MPa, which is much smaller than the fitting error of the original H-B criterion, Mogi criterion and Jiang’s criterion, indicating that the criterion has a good prediction effect on rock strength. The proposed criteria can provide a basic theory for the future construction of in-situ rock mass strength.

Study on the size effect of rock burst tendency of red sandstone under uniaxial compression

The study of rock burst tendency of rock masses with different sizes plays a key role in the prevention of rock burst. Through theoretical analysis, it is proposed that uniaxial compressive strength and deformation modulus ratio are the key mechanical parameters affecting rock burst occurrence. In order to find out the size effect of uniaxial compressive strength and deformation modulus ratio, theoretical analysis and uniaxial compression experiment are carried out on rock samples with different heights, different cross-sectional areas and different volumes. The results show that the smaller the uniaxial compressive strength is, the larger the deformation modulus ratio is, and the more likely rock burst are to occur. On the contrary, rock burst is still not easy to generate. The uniaxial compressive strength of rock samples with different heights, different cross-sectional areas and different volumes increases with the increase of rock sample size. The deformation modulus ratio of rock samples with different heights and different volumes shows an upward trend on the whole, while that of rock samples with different cross-sectional areas shows a downward trend on the whole. The fracture forms of rock are analyzed using the energy conversion law in the process of deformation and failure for three kinds of rock with different shapes and sizes.

Study of slope stability analysis method based on equivalent Mohr‐Coulomb strength parameters of three‐dimensional stress state

AbstractMost rock slope stability analysis methods are based on the Hoke–Brown criterion under a two‐dimensional state of stress, which somewhat ignores the effect of intermediate principal stress. In this paper, by introducing the improved three‐dimensional H‐B criterion into the Meridian plane, the tangent line of a point on the H‐B strength envelope is regarded as its instantaneous equivalent M‐C parameter. Based on this, a formula for solving the equivalent M‐C strength parameters under a three‐dimensional stress state is established to describe the shear strength parameters of rock mass, considering different stress states. Taking three kinds of rocks as examples, the influence of the intermediate principal stress on their strength parameters is analyzed. On this basis, the realization scheme of the nonlinear strength reduction method is established, the stability of the slope is studied, and an example verifies the feasibility of this method. This method fully considers the nonlinear characteristics of rock slope strength parameters under a three‐dimensional stress state and provides a solid basis for slope stability analysis.

Modification of a hybrid fluoro-surfactant containing double fluorocarbon chains on the carbonate and shale rocks for the wettability reduction of water and oil

An original hybrid fluoro-surfactant DHE with double fluorocarbon chains was synthesized. This surfactant aimed to reduce significantly the wettability of water and oil on the carbonate and shale rocks and adapt to the high salinities of the formation water. This could enhance the imbibition and injection of water in the matrix of carbonate reservoirs and the fracturing flowback in shale reservoirs. DHE showed good interface activities in salt-free and brine solutions, and remarkable water- and oil-wettability reduction on the two kinds of rocks. Moreover, its tolerant-NaCl concentrations were not below 80 g/L. The diameters of DHE mono-molecules were 1.5–4 nm and innumerable worm-like micelles were observed by TEM at the critical micelle concentration of 1.2 g/L in water. After being modified only using the 0.03 g/L DHE saline with 30 g/L NaCl for the carbonate rock, the surface energy was reduced substantially, so the primary water- and oil-wetting (θ: 43–50.6°) on the rock changed to nearly intermediate wetting (θ: 85.0−87.4°), which was the most ideal wetting state for oil and gas production in reservoirs. Moreover, the modifying effect of DHE on the rocks became stronger with the DHE and salt concentrations in the DHE brines. Therefore, it was found that the capillary pressure could be changed to zero using very small amounts of hybrid fluoro-surfactants such as DHE because the rocks could be altered to intermediate wetting for water and oil phases. Consequently, the oil recovery in the water-flooding of carbonate reservoirs and the fracturing flowback in shale reservoirs would be improved significantly.

Research on the Application of THz-TDS in Coal–Rock Interface Recognition

The recognition of coal–rock interface is very crucial for research in the intelligent production of coal mines. To this end, the study investigated the application of terahertz time-domain spectroscopy in the recognition of coal–rock interface, including the identification of coal–rock and coal–rock mixtures, as well as the accurate characterization of coal seam thickness. Terahertz detection was used to obtain the optical parameter information of pressed pellets prepared by mixing two different kinds of coal and two kinds of rock. Based on the experiment’s results, a database was established for the identification of coal–rock interfaces for coal mining machines. The terahertz detection was performed on 10 different kinds of sheet anthracite with different thicknesses, and the terahertz spectra of coal seams with different thicknesses were simulated and calculated using simulation software. By comparing the two effective mining thicknesses, parameters can be provided for coal seam mining. The experiment and simulation show that the terahertz time-domain spectroscopy technology has a promising application prospect in the identification of coal–rock interface.

Potential tourmaline reference materials for microbeam B and Sr isotopic analyses

Tourmaline reference materials for in situ B and Sr isotopic analyses.

Research on crack classification method and failure precursor index based on RA-AF value of brittle rock

The mechanical and AE information of the whole process of rock damage and fracture are obtained by uniaxial compression test, Brazil splitting test and improved shear test on marble, granite, limestone and sandstone. The internal relationship between the damage and failure mechanism of brittle rock and AE signal is revealed based on these tests. Moreover, in this paper, the improved shear test is used to replace the traditional direct shear test to avoid the interference of the traditional direct shear test on AE signal acquisition. The experimental results show that the rock fracture process has an obvious piecewise variation characteristic and a significant increasing period. A variety of AE signals are screened by coupling the main frequency and its amplitude, and the values of b and CV (r) can be used as the precursor signals of rock critical failure. Based on KDE method and K-means algorithm, the AE data (RA-AF values) collected in Brazil splitting test and improved shear test are coupled to determine the tensile and shear crack boundaries of four kinds of rocks. Based on the determined boundary of AE data between tensile and shear cracks, the corresponding precursor index CV (r) of rock failure is proposed. When the value of CV (r) increases to more than 1, the rock is close to failure or failure has occurred.

Numerical Study on the Damage Characteristics of Layered Shale Using 3D DEM

Layered shale is a kind of rock with obvious anisotropy, which is significantly influenced by the inclination angle of the rock. In this study, the influence of bedding dip on the strength characteristics, failure mode, and internal fracture evolution of layered shale was investigated through laboratory triaxial compression tests and three-dimensional discrete element numerical simulations. Results show that the numerical model of layered shale constructed using the bonded block model can simulate the layered shale in terms of U-shaped strength variation and failure modes very well. Based on the distribution of cracks and failure characteristics of layered rocks, the failure modes of layered rocks are classified as follows: Shear failure across the bedding plane, slip failure along bedding planes, combined tensile splitting and shear failure. The development of microcracks damage in the slip failure model is controlled by interlayer joints, while in other failure modes, it is jointly controlled by the rock matrix and interlayer joints. The relationship between microscopic joint parameters and the variations of Young's modulus and peak strength has been proposed.

Experimental comparison between dynamic and static parameters for volcanic rocks in Sulcis basin (Italy)

This work compares the results of expensive and time-consuming destructive tests and cheap non-destructive ultrasonic analyses for the assessment of rock parameters (i.e. uniaxial compressive strength, Young's modulus, Poisson's ratio, etc.), with the aim to geologically characterize the site and to find correlations between the mechanical and acoustic properties of rocks for applications in the field of the monitoring of CO2 leakage. The assessment considers 60 samples, 10 per each of the six formations of the Sulcis Miocene volcanic sequence. Samples have been initially subjected to non-destructive tests for the measurement of density and compressional and shear wave velocity and then mechanically tested to determine the uniaxial strength. As it happens for other kinds of rock, a linear direct correlation has been found between uniaxial compressive strength and compressional wave velocity, as well as between dynamic and static Young's moduli and for the dynamic and static Poisson's ratios, with a correlation coefficient R2 significantly affected by the nature of the pyroclastic formation. Helpful information on the pyroclastic rocks have been obtained, collecting parameters currently not available in the literature for this kind of geological formations.

Experimental and Analytical Study on Optimal Spacing for Hard-Rock Breaking under Double-Indenter Impact

Abstract Rock breaking by double hydraulic hammers has a wide application prospect in hard-rock roadway excavation because of its environmental protection and strong rock-breaking ability, but the optimal spacing under double-indenter synchronous impact is not clear. Based on the rock-breaking experimental system under double-indenter synchronous impact established by combining a detachable double-indenter device and Hopkinson pressure bar, the impact tests of three kinds of rocks are carried out, and a theoretical model of specific energy consumption is derived to determine the optimal spacing. The results show that when the indenter spacing is 28 mm, 42 mm, and 14 mm, respectively—that is, when the cross section of the fragmentation crater is in the shape of a “peanut” with a fine middle and two large ends—the concrete, limestone, and sandstone specimens reach the minimum specific energy consumption, which is reduced by 22.55 %, 30.60 %, and 11.85 %, respectively, compared with single-indenter impact. The theoretical model, which explains and verifies the experimental phenomena and results well, can be divided into four zones, and the optimal spacing is in Zone III. The research can be helpful for actual hard-rock tunneling under double hydraulic hammers.

Rock drillability measurement and grading method for a polycrystalline diamond composite bit

The bit holds paramount importance as a rock-breaking tool in petroleum and natural gas industry drilling, rock drillability grading using a polycrystalline diamond composite (PDC) bit is the key basis for individualized design and selection of a bit and optimization of drilling parameters. This is especially true for formations that are above medium hard. However, the petroleum and natural gas industry standard “rock drillability measurement and gradation method” issued and implemented in China has obvious defects. For rocks above medium hard, the measurement is often invalid and drillability grade data cannot be obtained. Through many drillability measurements on rock samples of various lithologies, it has been found that the main reasons for the ineffectiveness of measurements of rock above medium hard are that the standard weight on the bit (WOB) is too low and that the structural parameters of PDC microbits are unreasonable. To solve these problems, we first studied the influence of the side rake of the microbit cutter on the interference state and proposed an optimal microbit side rake. This eliminates the possibility of interference between the microbit cutter and the rock. Second, we conducted rock drilling experiments on five kinds of rock under various WOB values. The experimental data show that there is a linear relation between the variable-weight drillability level and the WOB. We put forward a new method of drillability measurement and grading, which is based on the measurement of drilling pressure grading, equivalent conversion grading, or independent grading. This method not only effectively solves the problem of drillability measurement of medium-hard and harder rocks but is also compatible with past soft-rock measurement data.

Ductile–brittle quantitative evaluation of rock based on post-peak properties under true triaxial stress

To quantitatively evaluate the influence of high true three-dimensional stresses on the ductile–brittle behaviours of rock in deep underground engineering, a series of true triaxial compression tests with different stress levels were carried out on marble and four kinds of granite. The influences of true triaxial stress states (σ2, σ3) on the post-peak characteristics were analysed, and a new normalized ductile–brittle evaluation index was proposed based on post-peak energy conversion characteristics of rock under true triaxial stresses. The ductile–brittle behaviours of rock were divided into four qualitative levels, namely, ductile-brittleness, transitional, brittleness and super-brittleness, and the influences of true triaxial stress states on the ductile–brittle behaviours of rock were quantitatively investigated. The research shows that as σ2 increases or σ3 decreases (that is, the differential stress between σ2 and σ3 increases), the brittleness of rock increases, and its increase rate gradually decreases and tends to be stable, transforming from ductile-brittleness to transitional, brittleness and super-brittleness and resulting in super-brittleness being easily induced by low-σ3 and high-σ2 conditions. When the differential stress between σ2 and σ3 is small, the intrinsic characteristics of rock itself have an obvious influence on ductile–brittle behaviours. When the differential stress between σ2 and σ3 is large, all kinds of rocks can exhibit super-brittle behaviour. The change of stress controls the evolution of rock ductile–brittle behaviours, and high-stress controls rock brittleness. The rock brittleness under true triaxial stress is significantly higher than that under conventional triaxial stress at the same σ3. σ2 induces an increase in rock brittleness and causes the decay rate of brittleness to decrease with increasing σ3, and σ2 increases the upper limit of σ3 for brittle failure of rock. The enhancement effect of σ2 on rock brittleness must be considered when evaluating the brittle failure of deep surrounding rock under high-stress conditions; otherwise, the risk of brittle failure may be underestimated.

Lithofacies Types and Physical Characteristics of Organic-Rich Shale in the Wufeng-Longmaxi Formation, Xichang Basin, China.

The shale of the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation in the Xichang Basin is the main replacement horizon for the shale gas exploration being conducted in the Sichuan Province, except for the Sichuan Basin. The fine identification and classification of the types of shale facies are important for shale gas exploration and development evaluation. However, the lack of systematic experimental studies on rock physical characteristics and micro-pore structures leads to a lack of physical evidence for the comprehensive prediction of shale sweet spots. Therefore, the present study used different means, such as core observation, total organic carbon content (TOC), helium porosity measurement, X-ray diffraction analysis, and mechanical properties analysis, in combination with the analysis of the whole rock mineral composition and characteristics of shale, for the identification and classification of the lithofacies of the shale layer, the systematic petrology and hardness measurement of the shale samples with different lithofacies, and discussion of the dynamic and static elastic properties of the shale samples and the control factors. It was revealed that nine types of lithofacies existed in the Wufeng Formation- the Long11 sub-member in the Xichang Basin, among which moderate organic carbon content-siliceous shale facies, moderate organic carbon content-mixed shale facies, and high-organic carbon content-siliceous shale facies were the best lithofacies with the optimum reservoir conditions, providing sufficient space for shale gas accumulation. The siliceous shale facies mainly developed organic pores and fractures, and the pore texture was excellent overall. The mixed shale facies mainly developed intergranular pores and mold pores, with a preference toward pore texture. The argillaceous shale facies mainly developed dissolution pores and interlayer fractures, and the pore texture was relatively poor. The geochemical characteristics of the organic-rich shale samples with TOC > 3.5% revealed that the sample was composed of microcrystalline quartz grains as the rock support framework, while the intergranular pores were located between the rigid quartz grains, which exhibited hard pores in the analysis of their mechanical properties. In the relatively organic-poor shale samples with TOC < 3.5%, the quartz source was mainly terrigenous clastic quartz, and the sample was composed of plastic clay minerals as the rock support skeleton, while the intergranular pores were located between argillaceous particles, which exhibited soft pores in the analysis of their mechanical properties. The difference in the rock fabric of the shale samples resulted in an ″initial increase followed by a decrease″ trend of velocity with quartz content, with the organic-rich shale samples exhibiting low velocity-porosity and velocity-organic matter content change rate, and the two kinds of rocks were easier to distinguish in the correlation diagram of the combined elastic parameters such as the P-wave impedance-Poisson ratio and the elastic modulus-Poisson ratio. The samples dominated by biogenic quartz exhibited greater hardness and brittleness, while the samples dominated by terrigenous clastic quartz exhibited lower hardness and brittleness. These results could serve as a basis for logging interpretation and seismic ″sweet spot″ prediction of high-quality shale gas reservoirs in Wufeng Formation-Member 1 of the Longmaxi Formation.

Tracing the human movements of three thousand years ago by volcanic grinding tools in the Final Bronze Age settlement of Monte Croce Guardia (Arcevia-Marche Region, central Italy)

Volcanic rocks were among the most sought-after materials to produce grinding tools in antiquity because lavas lithologies, either mafic or felsic, ensured good wear resistance and grinding capacity with respect to many other kinds of rocks. The interest in findings made of vesciculated lavas, referable to parts of querns, mortars, and/or pestles of the Final Bronze Age site of Monte Croce Guardia (Arcevia) lies in the fact that this settlement was built upon limestones belonging to the sedimentary sequence of the Marche-Umbria Apennines (central Italy) and far away from potential raw materials of volcanic rocks. A petrologic study of 23 grinding tool fragments clearly indicates a provenance from the volcanic provinces of central Italy: Latium and Tuscany Regions. Few leucite tephrites (5) and one leucite phonolite lavas have a clear magmatic affinity with the high-K series of the Roman Volcanic Province (Latium) whereas the most abundant volcanic lithotype (17 samples) is represented by shoshonites (K-series) whose thin section texture, modal mineralogy and major-trace elements contents closely match with the shoshonite lavas from the Radicofani volcanic centre in the Tuscan Magmatic Province. At Radicofani (a volcanic neck in the eastern sector of Tuscany) a Final Bronze Age site coeval to that of Arcevia is present and a potential pathway corridor from that site towards Arcevia (air-line distance of ca. 115 km) is dotted with many settlements of the same age. Through analytical algorithms based on the slope and the different human-dependent cost-functions which can be applied to determine non-isotropic accumulated cost surface, least-cost paths and least-cost corridors, the best route from Radicofani to Monte Croce Guardia, approximately 140 km long, was simulated, with a walking time of 25–30 h, possibly using pack animals and wheel chariots. Three thousand years ago the Apennine Mountains did not thus constitute a barrier for human movements. This study also shed light on some other possible patterns of interactions between Final Bronze Age communities of central Italy through the present-day regions of Tuscany, Umbria and Marche, aimed towards the best performance of strategic economic activities at that time such as that of the transformation of cereals, and accompanied to cultural and social reasons.

Experimental studies on rock failure mechanisms under impact load by single polycrystalline diamond compact cutter

Percussive drilling shows excellent potential for promoting the rate of penetration (ROP) in drilling hard formations. Polycrystalline diamond compact (PDC) bits account for most of the footage drilled in the oil and gas fields. To reveal the rock failure mechanisms under the impact load by PDC bits, a series of drop tests with a single PDC cutter were conducted to four kinds of rocks at different back rake angles, drop heights, drop mass, and drop times. Then the morphology characteristics of the craters were obtained and quantified by using a three-dimensional profilometer. The fracture micrographs can be observed by using scanning electron microscope (SEM). The distribution and propagation process of subsurface cracks were captured in rock-like silica glass by a high-speed photography system. The results can indicate that percussive drilling has a higher efficiency and ROP when the rock fractures in brittle mode. The failure mode of rock is related with the type of rock, the impact speed, and the back rake angle of the cutter. Both the penetration depth and fragmentation volume get the maximum values at a back rake angle of about 45°. Increasing the weight and speed of falling hammer is beneficial to improving the rock breaking effects and efficiency. The subsurface cracks under the impact load by a single PDC cutter is shaped like a clamshell, and its size is much larger than the crater volume. These findings can help to shed light on the rock failure mechanisms under the impact of load by a single PDC cutter and provide a theoretical explanation for better field application of percussive drilling.

Evaluation of Rock Brittleness Index under Dynamic Load

Rock is a typical brittle material, and the evaluation of its brittleness index has important guiding significance for hard rock resource exploitation, unconventional oil and gas resource exploitation, mechanical driving efficiency, rock burst prediction, and dynamic disaster prevention and control. At present, brittleness index often measures the brittleness of rock under static load; thus, whether it is applicable to dynamic load is worth exploring. In this study, static and dynamic uniaxial compression tests and Brazilian splitting tests were carried out on five kinds of rocks, including fine granite, coarse granite, shale, marble, and sandstone, using the INSTRON−1346 test system and split−Hopkinson pressure bar (SHPB), respectively. The brittleness index values of different rocks under static and dynamic load were determined, and the changes in the brittleness of rocks under different loading methods and different strain rates were studied. The definition of brittleness and the applicability of existing brittleness indices were also discussed. It was found that the loading rate amplified the variation of the brittleness characteristics of rock. When static load changes to dynamic load, the brittleness of rocks increases, and the brittleness relationship between different rocks remains unchanged. The more brittle the rock is under static load, the greater the range of brittleness enhancement is under dynamic load. It was also found that the brittleness of sandstone had an obvious effect on the strain rate. The brittleness of rock increases with the increase in strain rate, and the greater the strain rate, the greater the brittleness enhancement degree. These research results can provide reference values for dynamic disaster prevention and safe construction of deep rock projects such as mines and tunnels.

Crushing It: Can Ground‐Up Rock Help Save the Earth?

AbstractNature perfected the carbon cycle a long time ago, and rock weathering plays a key role by helping capture atmospheric carbon dioxide through a chemical reaction that occurs when silicate rocks are exposed to air and water. Crushing up the right kind of rocks and spreading them on land could help humans ratchet up nature’s process significantly, capturing some of the excess carbon dioxide we’ve released into the atmosphere. The promising idea has attracted not only a growing number of scientists, but also environmental entrepreneurs who are turning the research into action, albeit at a pace not everyone is comfortable with. While the scientific and business approaches operate under different rules, there’s room for cooperation, data sharing, and innovation as they target the common enemy of climate change.

Cover Image, Volume 68, Issue 4

CSA NewsVolume 68, Issue 4 p. i-i COVER IMAGEFree Access Cover Image, Volume 68, Issue 4 First published: 29 March 2023 https://doi.org/10.1002/csan.21013AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract Cover: Nature perfected the carbon cycle a long time ago, and rock weathering plays a key role by helping capture atmospheric carbon dioxide through a chemical reaction that occurs when silicate rocks are exposed to air and water. Crushing up the right kind of rocks and spreading them on land could help humans ratchet up nature's process significantly, capturing some of the excess carbon dioxide we've released into the atmosphere. The promising idea has attracted not only a growing number of scientists, but also environmental entrepreneurs who are turning the research into action, albeit at a pace not everyone is comfortable with. While the scientific and business approaches operate under different rules, there's room for cooperation, data sharing, and innovation as they target the common enemy of climate change. Cover photo courtesy of UNDO. Volume68, Issue4April 2023Pages i-i RelatedInformation

Experimental and Numerical Studies on Splitting Fracture of Rocks Using Different Bit Heads

A hydraulic splitting method was recently developed to reduce the generation of noise and vibration in urban underground construction. However, research on optimizing the method considering the shape of the hydraulic splitting machine or the rock type has yet to be conducted sufficiently. Herein, experimental and numerical investigations were conducted to identify the crushing performance of six types of bit heads on three kinds of rocks (granite, marble, and sandstone). The uniaxial and triaxial compressive test, Brazilian test, and semicircular bend (SCB) test were conducted to investigate the physical properties of the rocks. Simultaneously, the splitting fracture of the rocks was investigated depending on the shape of the bit head. The test results showed that the failure of the specimens was controlled by the tensile strength of the rock, while the failure mode was governed by the type of the bit heads. Based on the test results, a damage-plasticity model was used to simulate the failure test by introducing double damage variables. Consequently, the numerical simulations effectually replicated the failure modes of the splitting fracture of the rock samples by the different bit heads.