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In order to study the effect of water-rock interactions on shear strength characteristics, we performed shearing tests under varying hydrochemical environments. Moreover, a custom meso-shear test equipment for coal rock was used for the tests. Through 3D scanning of the shear fractures and scanning electron microscope imaging, we studied the effect...
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Context 1
... custom meso-shear test device was adopted to conduct nonrestrictive shear tests 30 . Figure 3 shows the actual specimen installation and labels the forces exerted. After the test, a 3D laser scanner was employed to scan the three dimensions of the upper and lower shear-fracture surfaces (Fig. 4). Furthermore, We then used Matlab and other software to collect statistics and analyze the morphology characteristic parameters of the three-dimensional maps of the shear-fracture ...
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... features of fracture surface and analysis of the SEM graph. A three-dimensional scanning system (Fig. 4) was used to scan the stereometric and three-dimensional structure of the shear-fracture surface of the sandstone. The scanning results are shown in Fig. 9. Figure 9 clearly shows that compared with the shear-fracture surface of sandstone etched in solutions, the shear-fracture surface of dry sandstone has a steeper topography (color ...
Citations
... Luo et al. (2021) analyzed variation in crack surface parameters of limestone under acid corrosion by 3D laser scanning and found that the surface roughness and height distribution of cracks increased their dispersion after chemical corrosion. Chen et al. (2019) examined the influence of different pH environments on the shear fracture morphology of sandstone by 3D scanning. Similarly, Liu et al. (2021) scanned the fracture surface morphology of granite under constrained tensile loading, revealing the close correlation of fracture roughness with the macroscopic fracture patterns. ...
The hard rock roof in coal mines is prone to failure, causing catastrophic disasters due to highly concentrated stresses. Acidification can effectively degrade the resulting mechanical properties of hard rocks. Therefore, quantitative assessment and understanding of the tensile properties and microscopic characteristics of acidified limestone is essential for rock engineering. In this work, Brazilian splitting tests (BSTs) were carried out on acid-immersed limestone specimens and the resulting properties were determined by digital image correlation (DIC), 3D scanning, and nanoindentation. The effects of varying pH values on tensile properties, splitting surface morphology, and nanoindentation characteristics were investigated. The results indicate the tensile strength decreases with the decrease in pH value, while the splitting failure mode gradually transitions from I-shaped tensile to Y-shaped tensile-shear failure mode. Further, DIC results indicate that the maximum principal strain increases gradually. The evaluation of the splitting surface also showed that the roughness, relative fluctuation height, angle, area ratio of the splitting surface, and the range of indentation depth increase as the pH value decreases, while the relative fluctuation height increases the most. Nanoindentation confirms that the micromechanical parameters (hardness, modulus, and fracture toughness) degrade to varying degrees due to the acidification. Finally, the correlation between tensile strength and micromechanical parameters was developed for a better understanding of the microscopic deterioration mechanism in acidified limestone.
... Few studies have been conducted on the effect of water content on fracture characteristics under shear loading [11]. Shear loading is frequently observed in the rock fractures. ...
The water content of a rock affects its fracture characteristics, such as strength and fracture toughness. In this study, the effect of water content on the fracture characteristics, such as strength, fracture toughness and subcritical crack growth index under shear loading for Coconino sandstone was investigated. Here, experiments were conducted in two cases: completely dry and fully saturated. In particular, a short-beam compression specimen was employed to examine the fracture characteristics due to shear; in addition, the shear strength, mode II fracture toughness, and subcritical crack growth index under shear stress were obtained. Consequently, the shear strength and mode II fracture toughness decreased as the water content increased; however, the subcritical crack growth index remained almost the same without significant alterations. The effect of water on the strength reduction of rocks is related to chemical and physical corrosion, pore pressure increase, and frictional reduction. Previous investigations on the deterioration of strength by water have yielded similar results in this research. Under saturated conditions, the shear strength decreased by 15.5%, and the fracture toughness decreased by 11.8%, compared with dry conditions. Regardless of the dry or saturated condition, the subcritical crack growth index n exhibited similar values.
... Pore water is described to have a two-fold impact on faults. On the one hand, the action of pore water pressure can produce a mechanical effect on pre-existing faults, whereby frictional strength of faults is weakened due to a reduction in effective normal stress 42 . On the other hand, pore water can degenerate preexisting faults through chemical interactions. ...
An anomalous seismic sequence of five small (MW < 3) felt earthquakes occurred between 29 August 2020 and 05 December 2020 around the Victoria Reservoir in the central highlands of Sri Lanka that clearly exceeded the established national background seismic rate. Using seismic waveform template-matching and a newly developed single-station earthquake location method based on travel-time back-projection, we detected an additional co-located 23 microseismic events, of which 18 occurred within the same period as the felt events. This hitherto undetected seismic swarm defines a seismogenic zone beneath the western flank of the reservoir between 1.5 and 3 km depths. The reservoir-induced peak stresses, resolved on E-W striking faults, predicted from the poroelastic theory that include both drained and undrained crustal responses are ~ 15 kPa in an area overlapping the seismogenic zone, which, together with the physical and spatio-temporal characteristics of the seismic swarm, establish a causal link between reservoir-induced stresses and the earthquake swarm with implications to seismic hazard. This is the first record of induced seismicity in Sri Lanka. The newly developed efficient computational workflows with minimal operational costs described in our study provide a blueprint for monitoring reservoir-induced seismicity in developing countries with severe resource limitations.
... For example, the peak shear strength of sandstone fractures decreased by 20~24% after 1 day of soaking in deionized water, and decreased by approximately 50% after 32 days of soaking (e.g., Zhao et al., 2017;Tang et al., 2019). In the study of the mechanical properties of jointed rocks in acidic and alkaline solutions, most studies used extreme pH values, such as pH=2 or pH=12 (e.g., Han et al., 2013;Chen et al., 2019). This range of pH is rather large compared to the more typical range of pH values that are encountered in the upper crust of the Earth (i.e., 5.5-8.5). ...
... However, it is difficult to obtain a substantial water-rock interaction effect simply by soaking in water for a long period of time. Therefore, the acidity and alkalinity of the soaking solution, and the ion concentration were enhanced, as proposed by Han et al. (2013) and Chen et al. (2019), to enhance the corrosion effect on the specimen in the short term during the dry-wet cycling. A set of NaSO 4 solutions with different pH values (i.e., 2, 7, and 12) were prepared as follows. ...
The degradation of shear mechanical properties of rock fracture surfaces was determined after applying multiple dry-wet cycles. Artificially fractured feldspathic sandstone specimens were soaked in chemical solutions with pH values of 2, 7, and 12 for 3, 6, 9, 12, and 15 dry-wet cycles, followed by direct shear tests under normal stresses of 3, 6, 9, 12, and 15 MPa. The results showed that the pre-peak shear stiffness and peak shear strength of the fracture surfaces decreased, and the peak shear displacement increased progressively after cumulative dry-wet cycling treatments compared to the behavior of oven-dry rock fractures. Additionally, the pre-peak shear stiffness, peak shear strength, peak shear displacement, and residual shear strength decreased cumulatively as the number of dry-wet cycles increased. However, the chemistry of the wetting solution had little effect on mechanical behavior. Based on the Barton formula for describing the peak shear strength for rock fractures, an empirical formula for peak shear strength for irregular rock fractures under dry-wet cycling conditions is proposed by introducing a proportionality factor to describe the degree of deterioration of the rock fracture surface shear strength. The modified formula has a good fitting accuracy for the test shear strength data of sandstone fractures under dry-wet cycling conditions, which may assist in the practical estimation of the peak shear strength of rock fractures under dry-wet cycling conditions in engineering practice.
... The effects of thermal shock on rocks can be summarized mainly as thermal stress (Chen et al. 2019a), Fig. 14 The influence of multiple factors on rock micromorphology: a, b pH (Mukai et al. 2014); c, d freeze-thaw cycle (Feng et al. 2019); e, f wet-dry cycle ; g, h high temperature (Tao et al. 2019) Geomech. Geophys. ...
To reveal the connection between the microscopic morphological characteristics of rock fractures, crack nucleation, extension, fracture modes, and rock damage processes, this paper systematically reviews the scanning electron microscopic (SEM) morphological characteristics of rock specimens using seven different testing methods. The characteristics of the microscopic fracture morphology of specimens under triaxial extension were experimentally investigated and the relevant factors affecting the microscopic morphology of rock materials were summarized. It was found that the fracture surfaces of rocks fracturable at a low energy are usually intergranular, and those of rocks fracturable at high energy are usually trans-intergranular; the transition from intergranular fractures to trans-intergranular fractures can be observed due to the increase of confining pressures during triaxial extension. In addition, except for the structure of the rock specimen itself, external conditions such as temperature can also affect the microscopic fracture characteristics of the rock to varying degrees. In addition, the analysis of specific microstructural compositions and grain fracture surface patterns will be more effective in providing an understand the microfracture mechanics mechanisms of the specimens. The results of this study will help establish a bridge between microscopic damage mechanisms and macroscopic fracture analyses.
Article highlights
The microscopic characteristics of rock specimens under different loading methods were reviewed
The cross-sectional microscopic characteristics of three typical rocks after triaxial extension were analyzed
The factors affecting the microfracture characteristics of rocks are discussed
... A higher water absorption value leads to negatively impact the various properties of rocks [33]. When rock is exposed to water, it will soften and crystallize, which will result in a loss of strength [34]. On the other hand, in soundness test, the cycles of immersion and drying processes are affected and it's taken into consideration effects. ...
Rocks are the basic materials that are used to strengthen the banks of rivers. Their properties and characteristics play an important role in controlling erosion problems. This paper compares and studies the soundness and erosion rates of several types of rocks collected from four locations in Muthanna Province, southern Iraq. Soundness testing is performed using two experimental approaches (ASTM C88 method and EN 1367-2 (Annex B) approaches). To perform the erosion test, a rotating erosion testing apparatus (RETA) was built in the laboratory. Soundness tests indicated that the rock of South Muthanna sites (SRM2) had a lower resistance to degradation, whereas the rock of West Muthanna sites (WMA1) had a higher resistance. Both ASTM C88 and EN 1367-2 techniques yield similar results, but the EN 1367-2 method yields greater mass loss than ASTM C88. As well, it was discovered that the porosity of the rock and its capacity to absorb water directly affect the soundness test results. Tests conducted with the erosion function apparatus (EFA) indicated that the erosion rate value is higher than those obtained from the rotating erosion testing apparatus (RETA). High water salinity decreases erosion rates; whereas higher water velocity leads to increase it.
... Machinability studies on HEAs by non-contact type processes like mechanical erosion, [220][221][222] electrochemical machining, [223][224][225] chemical machining [226,227] and thermoelectric machining [228] are yet to be fully revealed. Tsao et al. [229] studied the joining performance of Al 0.3 CrFe 1.5 MnNi 0.5 high entropy alloy with a traditional alloy system of 6061-Al using Sn-Ag-Ti active solder. ...
High entropy alloys (HEAs) are an emerging class of engineering materials with excellent mechanical, thermal, chemical and electrical properties due to constituent alloying elements and type of synthesis/processing criteria. This literature review intends to find product manufacturing aspects from HEAs while relating them to their synthesis and characterisation. A wide range of synthesis modes has been developed for HEAs recently. Methods of synthesis, both bulk and powder-based, are reviewed and discussed at length in this article. Based on the researcher’s results, various characterisation studies like materials, mechanical, chemical, electrical, and magnetic are also discussed. For product manufacturing, it is observed that very few machinability studies have been carried out on HEAs to honour post-machining material properties. Research on HEAs in the manufacturing domain, if done, will lead to their extensive industrial applications. Further, several potential applications have been suggested for specific HEAs based on the composition of constituent elements.
... Liu et al. [30] studied the morphology data and the geometrical statistics of asperities on granite fracture surface under both different confining pressures and tensile loading rates. Chen et al. [4] analyzed the fracture morphology parameters of artificial sandstone before and after hydro-chemical erosion, and analyzed the erosion mechanism. Furthermore, experiments on the rock shear strength degradation under different water contents and different soaking times have been conducted. ...
Hydro-chemical erosion has a great effect on the micro-structure morphology and macroscopic mechanical properties of the rock mass. In this paper, direct shear test system was used to study the hydro-chemical effect on the shear strength characteristics of limestone fractures. Besides, morphology parameters of the fracture under different chemical solutions were also analyzed through three-dimensional laser scanning and electron microscope imaging. Experimental results showed that after hydro-chemical erosion, the profile mean square root deviation Sq, the profile area ratio Rs, the profile peak point density Spd increased, while the slope mean square root Sdq decreased. Combined with scanning electron microscope (SEM) images, it is found that due to the hydro-chemical erosion, the roughness of limestone fracture surface, the discreteness of height distribution of the asperities and the JRC2D values increased, but the slope of asperities decreased. There was a good exponential relation between the decrease percentage of limestone internal friction angle and soaking time, and a logarithmic relation between the decrease percentage of cohesion and soaking time. According to the gray correlation method, the influencing factors were ranked in descending order as follows: normal stress, soaking time and pH values. In addition, the JRC2D value had a negative linear correlation with internal friction angle and cohesion of limestone fracture.
... Both rock fractures and rock bridges are frequently subjected to shear under constant normal stress or stiffness in practice [24], but the normal and shear stresses on the potential failure surface increases gradually in the conventional triaxial test because of the increasing deviatoric stress [28]. Therefore, a number of recent experimental studies performed direct shear tests on intact or pre-flawed rock samples under different normal stress conditions [4,5,8,13,24,28], and showed that the development of a shear zone results from the formation of micro-scale tensile cracks [1]. A power function failure criterion can reasonably estimate the peak shear stress of intact rocks under normal tensile or compressive stress conditions [4]. ...
Shear behaviors of core samples from a deep geothermal exploration well was investigated using direct shear tests. The fracturing process inside the intact rock samples during shear was monitored using acoustic emission (AE) technique. The results show that three shear stages including compaction, quasi-elastic and failure phases can be easily divided based on the shear stress-shear displacement or the cumulative AE parameters-shear displacement curves. Three characteristic stresses in terms of crack initiation stress, crack damage stress and peak strength are defined for intact rock samples undergoing shear. The crack initiation stress is about 0.80 times of the peak strength, and the crack damage stress is about 0.88 times of the peak strength. In addition, the different shear behaviors and AE characteristics between intact rocks and rock fractures are compared. AE events are scattered in the pre-peak stage but are localized around the fracture surface in the post-peak stage, while AE events are located along the shear zone in intact rock samples.
... Atkinson and Meredith investigated the influence of different chemical solutions on the strength and crack propagation rate of quartz and found that increasing environmental OH − concentration resulted in a faster expansion rate of the quartz fracture by means of a crack propagation model [19]. Similar scientific research has been conducted [20,21]. ...
In order to study the mechanical properties of sandstone under the coupling action of chemical erosion and freeze-thaw cycles, the fine-grained yellow sandstone in a mining area in Zigong, China, is collected as the research object. The changes in mechanical properties of yellow sandstone under the coupling action of chemical solution erosion and freeze-thaw cycles are analyzed based on uniaxial compression tests (UCTs) and triaxial compression tests (TCTs). The results show that, with the increase in freeze-thaw cycles, the compressive strength, elastic modulus, and cohesion of the sandstone samples decrease with varying degrees. Under constant freeze-thaw cycles, the most serious mechanical properties of degradation are observed in acidic solution, followed by alkaline solution and neutral solution. Under different confining pressures, the compressive strength and elastic modulus of the sandstone samples decrease exponentially with the increase in freeze-thaw cycles. Under the action of the chemical solution erosion and freeze-thaw cycles, the internal friction angle fluctuates around 30°. For the cohesion degradation, 35.4%, 29.3%, and 27.2% degradation are observed under acidic, alkaline, and neutral solutions. Nuclear magnetic resonance imaging shows that the chemical erosion and freeze-thaw cycles both promote the degradation of rock properties from surface to interior; after 45 freeze-thaw cycles, the mechanical properties drop sharply. To properly design rock tunneling support and long-term protection in the cold region, the impact of both freeze-thaw cycles and chemical erosion should be considered.
