Table 2 - available via license: Creative Commons Attribution-NonCommercial 4.0 International
Content may be subject to copyright.
Source publication
This open access book focuses on investigating predicting precursor information and key points of rockburst in mining engineering through laboratory experiment, theoretical analysis, numerical simulation and case studies. Understanding the evolution patterns for the microstructure instability of rock is a prerequisite for rockburst prediction. The...
Citations
... Contrary to standard shapes like squares or circles, the diverse contours observed in this study indicate intricate and irregular mine pit boundaries, holding significant implications for mining methods and potential environmental impacts. Firstly, it indicates that mining operations might be influenced by the natural topography of the area, as irregular shapes could result from following the contours of the land or adapting to geological formations (Carranza, 2008;Wang, 2018). Secondly, different mining methods might be employed for pits of varying shapes, with some methods being more suitable for elongated pits while others for wider ones; this diversity in mining techniques could stem from the varying mineral deposits, accessibility, or other logistical considerations (Mouflis et al., 2008). ...
Osun River, a UNESCO heritage site is
currently under threat to unregulated mining activity
along its course. Through remote sensing techniques,
this study aimed to evaluate mining severity (number
and size of mine pits) which was acquired and used
to quantify landscape changes and degradation in
water quality (turbidity) along the river. Studies were
carried out using data for years 2020–2022 covering
2-km and 5-km bufer areas of the river’s watershed.
High-resolution Google Earth imagery and Landsat
8 imagery (OLI) were used for land-use land-cover
assessment and computation of the Normalized Difference Water Index (NDWI) respectively. The mining severity assessment for 2022 revealed a total of
32 mining pits within the 5-km bufer zone, where
21 mining pits (65.63%) of the total mining activities
occurred within the 2-km bufer zone. The severity
assessment in terms of both the number of mines and
the land area covered revealed an extensive physical mining activity, with severe impacts on surface water
quality. The predominantly irregular shapes of the
mine pits, indicated by the mean perimeter-to-area
ratio (X̅=0.22), linear regression (y = 0.1351x +
0.6102), and coefcient of determination (R2
=0.88),
portend challenges for post-mining reclamation,
including erosion control and terrain stabilization.
The declining trend in the upper limit NDWI values
over the 3 years, 2020, 2021, and 2022 (0.053, 0.017,
and −0.084476 respectively), indicates a signifcant
reduction in water quality, plausibly associated with
the heightened mining activity within the 2-km bufer
areas of the river. The escalating habitat degradation
and imminent efects on drinking water quality and
biodiversity health underscore the pressing implications of unchecked mining, eroding the ecological
and cultural signifcance of the Osun-Oshogbo Sacred
Grove, a UNESCO World Heritage Site. Urgent governmental action is crucial to enforce mining regulations, curbing these threats, and preserving the site’s
ecological and cultural importance.
... In a global-wise record, more than 54,722 rockburst incidents were reported in the period from 2002 to 2016. In 2016, the death toll from coal mines alone due to rock bursting in China exceeds 538 [64]. In addition to the above, rockburst and its related incidents were reported in many countries around the globe including Australia as shown in Fig. 3. ...
As the global push towards clean energy intensifies, the demand for critical minerals has driven deep excavation in hard rock formations, posing significant challenges related to rockburst and spalling. Spalling refers to explosion-like rock fractures under high geo-stresses. Despite several successful studies and practical models, the mechanisms governing spalling propagation under polyaxial stress states remain inadequately understood, particularly in weaker and high-porosity rocks. This study introduces a novel Crack Mode-Changing Stress (CMCS) concept, which defines the minimum principal stress required to change the crack mode from shear to tensile failures when rock spalls. The concept was validated using cubed sandstone samples containing centric circular holes subjected to a range of loading conditions including uniaxial, biaxial, generalized triaxial compression, generalized triaxial tensile, and true triaxial loading stress states. Our results highlight the significance of the out-of-plane minor principal stress on the crack initiation threshold and the CMCS, emphasizing the need for careful consideration when designing openings in highly stressed environments.
... Therefore, the energy density of rock materials increased nonlinearly under different loading/unloading rates; it is also worth noting that the loading and unloading speed has a considerable effect on the dissipated energy density [37][38][39]. In actual projects, rock materials are usually loaded/unloaded repeatedly, such as in coal mining, tunnel excavation and roadway support [40]. The strength and deformability are closely related to the stress state and loading history. ...
Coal failure is often the precursor of dynamic disaster. The energy evolution behaviour at different stress values was analysed under the gradation of equal amplitude cyclic loading/unloading. Based on the energy dissipation behaviour, the energy evolution model of the coal specimen was established. The multi-parameter energy behaviour predicting model was proposed. Then, the energy storage factor criterion, the energy tangent factor criterion, the energy dissipation growth factor criterion and the energy damage factor criterion of the coal specimen were proposed during the coal fracture process. The energy density and the energy storage status showed different evolution patterns under cyclic loading/unloading. The energy behaviours and status were different in fracture stages of coal specimens, and the dissipated energy behaviour had a sudden response during the failure process. The energy storage and energy dissipation mechanism were related to their respective limits. The energy storage mechanism showed a growth pattern of “low energy promotion, high energy suppression and dissipation promotion, cumulative suppression”. The damage evolution equation and the energy behaviour evolution criterion were established under the cyclic loading/unloading.
... It is known that the original openings inside the rock are dislocated under loading, and the released energy during rupture propagates through the rock in the form of elastic waves, monitored as AE [8]. It has been widely used in rock mechanics and engineering for damage assessment and hazard warning [9][10][11]. ...
... AE monitoring was performed on rock failure experiments with different loading methods and paths, and the microcrack distribution results successfully indicated the real rupture location and the coincident damage shape [12][13][14][15][16][17][18]. As a result, the microcracks were found to be more prevalent in severely damaged zones in the laboratory and the field [9]. Therefore, for a better visualization of the damage zone directly by the microcrack, the density estimation method was adopted on the microcrack distribution results to find severely damaged areas [19,20]. ...
... The loading test was implemented by uniaxial loading controlled by displacement, and the loading speed was set at 0.1 mm/min. Based on previous experimental experience and lead break tests [9,24,25], in this AE monitoring test, the acquisition threshold was set to 45 dB for minimizing the environmental noise effect, the sampling frequency was set to 1 MHz, and the preamplifier gain was set to 40 dB. ...
To further understand the rock damage zone, an approach based on microcrack distribution was proposed to characterize the crack space of rock specimens in this research. Acoustic emission (AE) technology was utilized on sandstone to obtain the spatial distribution of microcracks in which uniaxial compression forms the single-cracked fracture. The proposed theoretical distribution pattern space (TDPS), 3D convex hull, and the minimum volume enclosing ellipsoid (MVEE) algorithms were adopted to analyze the geometric features of the crack space. It was found that the 3D convex hull method returned the smallest results in both area and volume of the crack space, and the largest results were provided by the proposed TDPS method. The difference between the results of the proposed TDPS method and the MVEE method became smaller after 85%. The deviation angle of the principal axis of the cracked space gradually decreased as the spatial scale decreased, while the other two major axes exhibited a tendency to increase at the 65% scale. The results indicate that a spatial scale from 65% to 85% is a reliable range for the characterization of crack space.
... Moradian [14] used collision parameters to describe the dynamic process from microcrack nucleation to macro-fracture formation. Wang [15] analyzed the failure of granite under uniaxial compression by observing the changing AE energy. Wang [16] also investigated the frequency spectrum characteristics of coal mass during fracturing induced by uniaxial compression. ...
The dynamic evolution characteristics of fracture are crucial to analyzing the development of coal and rock mass instability, gas diffusion law, and dynamic disaster prediction. These characteristics affect coal rock fractures and gas-induced disaster channels. Based on the experimental results, we found the following: In areas rich in both coal and oil, the coal mass damage due to high-pressure oil diffusion was inversely correlated with the distance of the coal mass from the disaster source. Moreover, as the coal mass became closer to the disaster source in the abandoned oil well, the average CT number reduced, mechanical performance diminished, fracture volume ratio increased, and capacity of the oil and gas storage improved. The four-dimensional analysis of the rock evolution and strength grade showed that coal mass stress, fracture propagation, and AE incidents were characterized by a low-strength compression stage featured by tensile fractures, medium-strength elastic stage with shear fractures replacing tensile fractures, and high-strength rapid fracture stage with rapid growth in shear fracture quantity and intensity. The dynamic conversion between coal mass instability disaster in coal and oil resources co-storage areas and oil and gas disaster was clarified. We propose high strength, high RA, and low AF of AE incidents in the rapid fracturing stage as the qualitative warning factors for the fracture of coal mass and the occurrence of oil and gas disaster.
... Besides, the coordinate dataset finally obtained is relatively incomplete. Not only because there are cracks that weaken and block the propagation of the signal wave (Moradian et al. 2016), but also some microcrack signals are artificially excluded when the threshold was set to reduce the effects of the ambient noise (Wang 2018;Wang et al. 2019b). It is likely that some very small signals representing microcracks go unrecorded and unidentified herein (Baud et al. 2017;Faillettaz et al. 2016;Meier et al. 2019;Rouet-Leduc et al. 2017). ...
... The characteristics of macrocracks under complex fracturing failure were obtained, such as the crack quantity, locations, directions, sizes, and proportions. From the perspective of the accurate and refined study of rock failure, this research provides a new approach to further understand the propagation of a crack and the development of rock fracturing, such as crack size analysis of the fracture zone (Granger et al. 2007) and the mechanical behavior of a single macrocrack (Katsaga et al. 2007) in rock mechanics, and the stability of potential cracks regions and rockburst prediction in rock engineering (Wang 2018). Complying with the conventional consideration of visual observation and understanding the distribution of cracks, the relationship between macrocracks is assumed to be a linear combination in this study. ...
... Moreover, some microcrack signals may be artificially excluded in AE experiments, when the threshold is set to filter out a specific range of signals for reducing the effect of ambient noise, such as voices and machine noise (Wang 2018;Wang et al. 2019b). It is likely that some small signals representing microcracks go unrecorded and are thus unidentified herein (Baud et al. 2017;Faillettaz et al. 2016;Meier et al. 2019;Rouet-Leduc et al. 2017). ...
Many macrocracks are usually generated during the fracturing of rocks. Elucidating the spatial distribution of cracks provides the basis for understanding crack nucleation and fracture formation in rock mechanics. Considering either a single microcrack or all the microcracks provides a limited interpretation of rock mass failure that is often induced by different macrocracks. Here we recognize macrocracks based on a three-dimensional (3D) crack model, implemented using an unsupervised machine learning algorithm and microcrack coordinates. This approach recognized microcracks that coalesce to form a macrocrack in three dimensions. Rock fracturing was performed using a triaxial loading test, and the coordinate data were obtained via the acoustic emission (AE) technique. The results show that the main macrocracks are distributed throughout the whole granite specimen, and smaller macrocracks form near the unloading surface. The AE-recognized crack pattern was found to be consistent with the actual cracks. The adaptability of the proposed method and the potential research and applications were discussed. This approach provides a means to understand the formation and distribution of rock fractures.
... Strain burst disasters have seriously threatened the safe and efficient development of deep resources and the rational and effective utilization of underground space (Cook 1963;Ortlepp et al. 1994;Helmut et al. 2003;He et al. 2010;Stacey et al. 2016;Feng et al. 2017). To date, scholars in various countries have performed a large amount of research on strain burst (He et al. 2012a(He et al. , 2015aKaiser and Cai 2012;Singh 1989;Fortin et al. 2006;Lee and Haimson 2011;Li et al. 2012;Su et al. 2017a;Wang 2018). Presently, there are two main methods for conducting strain burst research: field studies and laboratory experiments. ...
This paper introduces a new high-pressure servo true triaxial rockburst experimental apparatus that can realize multi-face rapid unloading in the horizontal direction. The apparatus is used to simulate different types of strain burst phenomena in deep underground engineering, such as those at roadways, roadway intersections, and pillars with three and four free faces. In the research and development process, apparatus technologies were included to overcome five key challenges: rapid unloading under high pressure, loading gap removal fixture, three-way loading alignment, symmetrical loading, and system stability after unloading. The apparatus is used to carry out multi-face unloading strain burst experiments and can fully satisfy the experimental requirements. The entire strain burst process is recorded using a high-speed camera. The apparatus can provide experimental support for strain burst mechanism research and an experimental basis for different types of strain burst research.
... In the early 1900s, this phenomenon came into sight and brought more attention (Blake & Hedley 2003). Since then, incidents have been recorded in many places around the globe such as Sweden, Australia, Norway, Japan, USA, South Africa, Canada, China and Brazil (Martna 1972;Hargraves 1980;Selmer-Olsen 1988;Fujii et al. 1997;Whyatt et al. 2002;Brown & Hudyma 2017;Wang 2018). There are over 23 countries in which the rockburst phenomenon has been observed, including France, Russia, Ukraine, and others (Zhu et al. 2019). ...
Due to the huge demands for natural resources and minerals at a global scale, mining depths have progressively increased over the past decades to 1,000 m and deeper. However, despite many successes, deep mining operations are now facing new challenges never experienced before, including rock spalling and unwanted slabbing failures. This phenomenon is characterised as a sudden explosion-like fracture, which can affect the long-term viability and stability of deep underground mining. According to the literature, the most indicative predictir of the spalling strength at laboratory scale is the determination of the crack initiation point, which is defined as the onset of stress-induced damage in low-porosity rocks after the closure of pre-existing cracks. Hence, many methods have been developed to identify this critical design parameter, based mainly on the measurement of vertical, lateral or volumetric strains. That is, an accurate measurement of strain is deemed critical in determining the onset of the crack initiation threshold in the study of rock failure. Nevertheless, it remains difficult to determine the actual sample deformation in many geotechnical test apparatuses (i.e., multi-stage triaxial, Hoek-cell, true triaxial, etc.), in which the measured deformation by Linear Variable Differential Transformers (LVDTs) is the cumulative deformation of the load frame itself, the loading platens and the sample. As a result, relying on these deformation measurements can lead to erroneous estimation of the material’s strain behaviour. This work presents a qualitative study on how to measure the actual sample deformation in a multi-functional true triaxial testing apparatus recently commissioned at the Geotechnical Engineering Centre (GEC) within the School of Civil Engineering at The University of Queensland (Brisbane, Australia).
... Liu et al. (2014) derived a damage evolution equation of rock salt and obtained the stress levels leading to the initiation and acceleration of damage. Wang (2014Wang ( , 2018 proposed the views of the relative quiet period and the warning key point of rock bursts. Kong et al. (2016) indicated that the changing trends of AE counts can be used to describe the rock deformation and failure process, and predict the direction of rock cracking accurately. ...
... Therefore, a rock damage law can be proposed if the energy change is analysed in detail during the process of rock deformation and destruction and if the strength theory is used to establish the damage criterion on the basis of the energy change. To date, many scholars have studied the mechanical behaviour characteristics of rocks under dynamic loads (such as rockburst) from different viewpoints and have obtained many valuable results (Blake et al. 1974;Brady and Leighton 1977;Ortlepp and Stacey 1994;Linkov 1996;Kirzhner and Rosenhouse 2000;Yu et al. 2002;Dou et al. 2009;Kabiesz and Makówka 2009;Brady and Brown 2013;Stacey 2013;Wang et al. 2015;Wang 2017). All of these authors have played a guiding role in the practice of rock engineering. ...
To investigate the quantification of the extent of damage by considering the energy during rock failure, the pattern of energy dissipation and energy conversion, and the stress–energy mechanism for induced rock failure were analysed under cyclic loading/unloading. Based on damage mechanics, rock mechanics, and energy conservation theory, the test data were analysed. The results showed that the characteristics of hard rock compression are small deformation, high energy, and sudden failure; an elastic–plastic damage constitutive model and a stress–energy–rigidity–damage multi-criteria model for rock failure were established for hard rock. We compared the numerical curves and the experimental curves and found that they coincide. Rock failure is a combination of the results of elastic strain accumulation and dissipation by stress propagation. The key to inducing the energy storage capacity of rock before failure is closely related to the rock damage evolution. The pattern of energy release and dissipation through stress during rock failure was revealed from the perspective of energy using the constitutive model and multi-criteria model established for rock failure; these theoretical studies are very helpful in elucidating the mechanism of rock failure.
