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Catastrophic events in underground coal mining usually originate from weak structures such as bedding and fractures. This study investigated the failure characteristics of coal samples with different bedding orientations by employing acoustic emission (AE) technology. Analysis of the AE time series, including ringing counts, amplitude, b -value, and the AF-RA relationship, was performed to characterize the failure behavior of the bedded coal. The synergistic effect of bedding and in-situ stress on the failure mechanism was also examined. The anisotropy of strain energy during the deformation and failure process was analyzed. The results indicate that bedding significantly influences the AE activity of coal during the failure process. Before failure, various AE parameters exhibit distinct precursory signals. Specifically, the sensitivity is found to be: b -value > cumulative ringing counts > amplitude > ringing counts. With increasing bedding orientation, the proportion of tensile cracks decreases initially, reaching a minimum at 60°. Conversely, the proportion of shear cracks exhibits an opposite trend. Microcrack development within the coal samples is primarily concentrated in the unstable crack extension and post-peak failure stage. The total strain energy, elastic strain energy, and dissipated energy display of coal sample show a V-shaped variation trend and reach their minimum values when bedding orientation is 60°. The degree of anisotropy for total strain energy, elastic strain energy, and dissipated energy exhibited a tendency to increase initially and then decrease with increasing stress.The research results can provide a scientific theoretical foundation for the stability assessment and prediction of underground mining engineering.

The aim of this study was to investigate the energy evolution characteristics and an ontological model of the deformation of coal under different water contents. Uniaxial compression tests were conducted for coal with different water contents, and the analyses were based on the energy principle and the principle of minimum energy dissipation. The results showed that the physical properties of the coal specimens were different under different water contents, the peak strain was positively correlated with water content, and the compressive strength and elastic modulus were negatively correlated with water content. Additionally, the compressive strength and elastic modulus of the coal specimens showed a steep and subsequent slow-change trend. From an energy perspective, the higher the water content of the coal specimens, the higher their energy dissipation at the peak; the smaller the limiting elastic strain energy, the lower the absorbed energy. The principle of minimum energy dissipation was used to deduce the energy evolution and mechanical properties of coal body damage under different water contents, deriving the initial and critical values of damage. The water content of the coal specimens was positively correlated with their initial and critical values of damage, and the relationship with water content was nonlinear. This result was used to establish a stress–strain ontology model for coal rocks with different water contents under uniaxial compression. The model is an improvement over traditional ontology models, addressing the problem of low accuracy in simulations of materials at the compaction stage.

The rapid growth of China’s economy has greatly accelerated the process of urbanization during China’s reform periods. Urbanization has significantly caused land use and land cover (LULC) changes and thus has impacts on the local climate and ecosystem. This study chooses Quanzhou, a fast-developing city of southeast China, as an example to detect and quantify the LULC and ecological changes from 1989 to 2018 by using the remotely sensed technique. The LULC of Quanzhou was derived from the four Landsat images taken in 1989, 1999, 2007 and 2018, and the land-use-degree ratio index and land-use–change method were used to estimate the change of land use. The remote sensing based ecological index (RSEI) was used to detect the ecological changes of the city. The built-up land expansion intensity and annual built-up land expansion rate were carried out for seven districts of Quanzhou. The results show that the urban area of Quanzhou has drastically grown by 192.99 km 2 at the expense of forest, water, and cropland land during the 1989~2018 period. Moreover, the built-up land of seven districts had expanded at the average rate of 0.027~0.154 per year and the built-up expansion intensity was higher than 0.59. The average RSEI value of Quanzhou city dropped from 0.78 in 1989 to 0.34 in 2018, which suggested an overall decline in ecological quality. The proportion of areas with an RSEI rating good decreased from 30.84% to 11.52% while the proportion of areas with rating bad increased from 4.73% to 19.11% during the past 29 years. This study has shown the built-up land expansion intensity is negatively correlated with the ecological quality change, and the increase in built-up land can greatly accelerate the decline of the ecological quality. Government policies play a profound impact on land use changes, urbanization and eco-environment changes. Therefore, the policy decision-makers should take enough action and consider integrating the concept of ecology to enable the healthy and sustainable development of the city.

With increasing coal mining depths, water-rock interactions exacerbate the mechanical degradation of coal-rock masses and geological disaster risks. Investigating the mechanical properties and energy evolution mechanisms of water-bearing sandstone is crucial for ensuring safe mining operations. To address the existing research gap in analyzing energy evolution mechanisms of water-saturated rock masses from a macroscopic perspective and the lack of exploration into energy mechanisms at critical failure points at the mesoscale, this study employs the particle discrete element software PFC3D to establish numerical models of sandstone with varying water contents. Combined with uniaxial compression tests and energy calculation principles, the mechanical degradation laws and energy evolution characteristics of sandstone under water-rock interactions are systematically investigated. The results indicate that the mechanical properties of sandstone exhibit significant degradation with prolonged immersion time, where compressive strength and elastic modulus gradually decrease with increasing water content. Energy evolution during sandstone deformation and failure can be divided into three stages: elastic energy storage, crack propagation energy dissipation, and sudden energy release at failure. Water immersion significantly reduces energy absorption efficiency during the elastic storage stage and increases energy dissipation rates during crack propagation. Mesoscale crack development analysis reveals that water accelerates the extension of initial fractures and the initiation of new cracks, while higher water content promotes a transition from localized to diffuse crack distribution. Additionally, the energy thresholds at critical failure points and failure modes of samples with different water contents show significant correlations, revealing the dynamic regulatory mechanism of water-induced weakening effects on energy accumulation and release in sandstone. These findings provide theoretical support for safe mining and dynamic disaster prevention in deep water-rich coal seams.

A uniaxial compression test was conducted on sandstone specimens at various inclination angles to determine the energy evolution characteristics during deformation and damage. Based on the principle of minimum energy dissipation, an intrinsic model incorporating the damage threshold was developed to investigate the mechanical properties of sandstone at different inclination angles, and the energy damage evolution during deformation and damage. This study indicated that when the inclination angle of the structural surface remained below 40°, sandstone exhibited varying mechanical properties based on different inclination angles. The peak strain was positively correlated with the inclination angle, whereas the compressive strength and modulus of elasticity showed negative correlations. From an energy perspective, the deformation and damage of sandstone under external loading entail processes of energy input, accumulation, and dissipation. Moreover, higher inclination angles of the structural surface resulted in a smaller absorbed peak strain and a reduced proportion of dissipated energy relative to the energy input, thereby affecting the evolution of energy damage throughout the process. As the inclination angle of the structural surface increased, the absorbed total strain at the peak value decreased, whereas the proportion of the dissipated energy increased. Additionally, the damage threshold and critical value of the rock specimens increased with the inclination angle. The critical value, a composite index comprising the peak strain, compressive strength, and elastic modulus, also increased accordingly. These findings can offer a novel perspective for analyzing geological disasters triggered by fissure zones within underground rock formations.

The present aims to investigate the mechanical characteristics and energy evolution in rock masses containing weak structural planes under conventional triaxial loading conditions. Using a fluid–solid coupling test system of coal rock, numerous conventional triaxial compression tests were performed on rock masses at various dip angles of the structural plane. The obtained empirical outcomes revealed that the deviatoric stress–strain curve of the weak structural plane rock mass with an inclination angle greater than 20° rises step-by-step. On the macro level, slip-stability occurs on the upper and lower parts of the rock mass on the weak structural plane. Then mechanism of the slip-stability phenomenon is explored by analyzing the stress level in the rock mass with various inclination angles. It is found that the energy evolution during deformation and failure reflects the damaged state of the rock. Accordingly, the concept of ‘slip dissipation energy’ is proposed, and the values of each energy are calculated. The results have a good correspondence with the deviatoric stress–strain curve. Furthermore, it was found that the energy evolution of rock mass with a weak structural plane can be primarily classified into four stages, including storage of the initial energy, slip dissipation, abrupt increase in the pre-peak dissipation energy, and sudden drop in post-peak energy. Rock masses with various levels of dip angles exhibit similar elastic strain energy and dissipation energy at the peak point, demonstrating that energy evolution is dominated by energy storage and dissipation. At the same time, a negative correlation is observed between the structural plane dip angle and the occurrence of instantaneous impact instability failure in rock masses, indicating that a greater dip angle makes the rock mass less prone to experiencing instantaneous impact instability failure. This article provides a new idea for analyzing the geological disasters caused by external disturbances.

With increasing mining depth, the coal pillars of a coal mine will be in a stressful environment characterized by high gas pressures and unidirectional loading. To investigate the damage evolution characteristics and energy evolution mechanism of coal pillars loaded in a gas pressure environment, a uniaxial compression test was performed on a coal body under different gas pressures using a load testing apparatus for gas-containing coal rocks. The obtained results showed that the mechanical properties of the coal body varied with the gas pressure. Specifically, the peak strain, compressive strength, and elastic modulus decreased with increasing gas pressure; the higher the gas pressure, the lower the conversion rate of the elastic strain energy in the elastic deformation stage of the coal body and the lower its total input energy. With increasing gas pressure, the damage threshold of the coal body decreased, whereas the damage variable corresponding to the peak value, as well as the damage threshold value, increased. According to the theory of continuous damage mechanics, an ontological damage model of the coal body under different gas pressures was established based on the principle of minimum energy dissipation, and the rationality of the model was verified through a comparison between the theoretical and experimental data. Our findings can be useful in ensuring the safety of coal mining in terms of preventing gas disasters.

The rapid growth of China's economy has greatly accelerated the process of urbanization during China's reform periods. Urbanization has significantly caused land use and land cover (LULC) changes and thus has impacts on the local climate and ecosystem. This study chooses Quanzhou, a fast-developing city of southeast China, as an example to detect and quantify the LULC and ecological changes from 1989 to 2018 by using the remotely sensed technique. The LULC of Quanzhou was derived from the four Landsat images taken in 1989, 1999, 2007 and 2018, and the land-use-degree ratio index and land-use-change method were used to estimate the change of land use. The remote sensing based ecological index (RSEI) was used to detect the ecological changes of the city. The built-up land expansion intensity and annual built-up land expansion rate were carried out for seven districts of Quanzhou. The results show that the urban area of Quanzhou has drastically grown by 192.99 km2 at the expense of forest, water, and cropland land during the 1989~2018 period. Moreover, the built-up land of seven districts had expanded at the average rate of 0.027~0.154 per year and the built-up expansion intensity was higher than 0.59. The average RSEI value of Quanzhou city dropped from 0.78 in 1989 to 0.34 in 2018, which suggested an overall decline in ecological quality. The proportion of areas with an RSEI rating good decreased from 30.84% to 11.52% while the proportion of areas with rating bad increased from 4.73% to 19.11% during the past 29 years. This study has shown the built-up land expansion intensity is negatively correlated with the ecological quality change, and the increase in built-up land can greatly accelerate the decline of the ecological quality. Government policies play a profound impact on land use changes, urbanization and eco-environment changes. Therefore, the policy decision-makers should take enough action and consider integrating the concept of ecology to enable the healthy and sustainable development of the city.

An accurate description of the mechanical properties and deformation characteristics of a structural plane of a rock mass with a large chamber or slope under the ultimate stress with periodic stress disturbances is of great significance to ensure the stability and safety of underground rock engineering. By theoretically analysing the strength effect of a structural plane of a rock mass under dynamic disturbance, a criterion for the occurrence of shear damage on a structural plane of a compressed rock mass under dynamic disturbance is proposed. The results of the cyclic disturbance kinetic test show that there is a disturbance threshold for the shear failure of the structural plane under different disturbance stresses. When the disturbance stress is lower than the disturbance threshold, the cumulative plastic strain stabilizes with an increasing number of cycles; when the disturbance stress is higher than the disturbance threshold, an S-shaped curve of cumulative plastic strain versus the number of cycles is observed, revealing the progressive damage process and mechanism of such a rock structure plane under periodic dynamic disturbance. Based on perturbation concept theory, the relationship between the accumulated plastic strain and the number of cyclic loadings is similar to the relationship between strain and time, the creep curve. A new nonlinear viscous element is proposed, and the nonlinear element and the deformation element considering structural plane closure and sliding are combined with the Burgers model to form an 8-element nonlinear viscoelastic‒plastic creep constitutive model. Using the global optimization algorithm of 1stOpt, model validation and parameter identification are performed on the experimental data, and the results show that the model curve has a very good agreement with the experimental data. The model can accurately reflect the deformation characteristics of a structural plane of a rock mass under periodic dynamic disturbance. These research results provide a new idea for analysing disturbance-induced geohazards.

In this paper, in the deformation and damage process under different confining pressures, the energy evolution characteristics and damage mechanism of coal–rock combinations with different inclination angles are studied. Based on the brittleness indexes of coal rock combinations, the evolution rules between brittleness indexes and the inclination are explored, as well as the confining pressure of coal rock combinations; then, the influence mechanism of the inclination angle of coal rock combinations on the plastic yielding degree, energy dissipation level, crack extension and fracture speed in the pre-peak stage is revealed. The composite specimens are mainly damaged due to oblique shear and accompanied by tensile damage; In the deformation and damage, various energies of coal rock composites are distributed as a negative exponential function of the inclination angle, which is significantly affected by the change of the confining pressure.