The damage and failure characteristics of layered salt rock under cyclic loading presents critical implications for the stability of underground salt cavern gas storages. This investigation employed an innovative micro-scale loading-observation system to characterize fracture propagation and damage evolution in cyclically loaded salt rock specimens. Through a multidisciplinary methodology combining laboratory mechanical tests, SEM microstructural analysis, and numerical simulation analysis, three progressive failure modes were identified under incremental cyclic stress conditions. The failure mechanism initiates with transverse shear fracture formation, accompanied by a characteristic stress redistribution pattern evolving from circumferential to fan-shaped and ultimately band-like concentration zones. These findings provide significant insights for optimizing the design and operational safety of salt cavern gas storage systems.

Constructing salt caverns in deep formations poses significant challenges due to high geostresses, pronounced creep behavior, and particularly intense pressure fluctuations. This study first conducted mechanical experiments to investigate the long-term creep behavior of salt rock, and to examine the differences in its mechanical response under cyclic loading compared with traditional triaxial loading. The results revealed a confining-pressure-dependent nonlinear creep behavior as well as a degradation mechanism induced by cyclic loading. A numerical model was then developed that incorporate the nonlinear creep law with periodic parameter weakening. Comparative analyses of cavern dilatancy under cyclic versus constant pressure conditions were conducted, validating the necessity of integrating the periodic weakening mechanism into the numerical model. Results indicate that cyclic loading enhances the plastic deformation capacity while lowering its dilatancy threshold; For cyclic gas pressure (CGP) mode, a minimum operational pressure of 9.6 MPa is infeasible due to excessive sidewall convergence and extensive spalling risk zones, with 12 MPa recommended as the lower limit; The constant brine pressure (CBP) mode exhibits superior performance in controlling deformation and damage; For constant gas pressure (GP) mode, a constant pressure of 19.2 MPa results in no significant dilatancy damage zones in salt layer; Critically, neglecting the dynamic weakening of parameters induced by cyclic loading leads to substantial underestimation of long-term deformation, by 20.2

Under complex stress conditions, the spatiotemporal coupling between creep deformation and structural degradation of salt rock remains unclear. Traditional creep models mainly rely on macroscopic strain fitting, neglecting the intrinsic correlation between micro-damage and macroscopic structural evolution, which leads to ambiguous physical meanings, redundant parameters, and limited predictive capability. In this study, the microstructural evolution, acoustic emission response, and strain characteristics of salt rock during creep were analyzed to reveal the staged deformation mechanisms: in the initial stage, pores and microcracks gradually close; in the steady stage, microcracks independently nucleate and slowly propagate, marking the onset of new damage; and in the accelerated stage, deformation shifts from viscoelastic to instantaneous plastic compression. Accordingly, the total creep strain is decomposed into elastic, viscoelastic, and plastic compression components. Based on the fractional derivative Maxwell model, a nonlinear creep model incorporating a damage-attenuated Hookean element and a switch element was established to describe structural degradation and plastic compression. Creep tests on different types of salt rocks under various stress paths verified the model’s capability through staged parameter identification. A parameter sensitivity analysis was conducted for the plastic compressive strain model, further enhancing the convenience of model application. Based on the composition of creep strain, the strain evolution patterns of different types of salt rock under multiple stress levels were systematically analyzed, providing theoretical support for the precise characterization of time-dependent deformation and instability prediction of surrounding rocks in deep salt cavern reservoirs.

Utilizing real-time acoustic emission monitoring data to predict the creep failure of salt rock has emerged as a crucial method for ensuring the smooth operation of salt cavern storage facilities. This article integrated real-time acoustic emission monitoring data from the creep process of salt rock to analyze the dynamic evolution of internal structural damage. It was discovered that the relationship between damage rate Ḋ_t and cumulative strain closely resembles the Weibull distribution function. By incorporating the Weibull probability distribution function and Drucker–Prager strength criterion, a damage evolution model that considers elastic stress threshold and cumulative damage effect was established. Based on the damage evolution characteristics observed during the creep process of salt rock, the linear solution values of the damage evolution model were revised and validated. The cumulative damage D from the salt rock creep-acoustic emission test was integrated into deformation modulus E_D and viscosity coefficient η_D of the Maxwell creep model, thereby creating a new Maxwell creep model that considers compression-creep coupling and mutual feedback damage. This model was then extended to three-dimensional stress conditions. The research findings reveal that the new creep model adeptly describes the entire creep process of salt rock. The derivative order β of the model reflects the geometric structure state and creep strain participation rate ζ of salt rock during the creep process. The sudden increase in strain during the accelerated creep stage of salt rock is attributed to the compressive strain resulting from rapid structural degradation.

With the deepening of coal mining, the frequency and intensity of rock burst accidents are increasing. According to incomplete statistics, there have been over 200 rock burst accidents in tunnels in China alone from 2005 to 2024, resulting in more than 500 deaths and causing extensive damage to tunnel equipment. Therefore, research on tunnel surrounding rock support methods is urgently needed. Based on a large number of previous studies on the surrounding rock support methods and technologies of coal mine roadway, this paper innovatively proposed the in-situ modified support method of roadway surrounding rock, and compared and analyzed the differences between the original rock roadway and the in-situ modified roadway surrounding rock in terms of static stress redistribution, displacement, plastic zone, dynamic stress and kinetic energy dissipation by using numerical simulation and laboratory experiments. The results show that the surrounding rock in the cracked region and reinforced region can redistribute the static stress of the roadway, better transfer the high static stress concentration distribution zone to the outside of the surrounding rock in the cracked region, and the dynamic stress transmitted to the surrounding rock surface of the roadway is reduced by about 1.29 ~ 4.0 times. Under the action of large vertical dynamic load, the displacement of surrounding rock in the roadway reinforcement area is reduced by about 1.9 ~ 4.0 times, the dynamic stress is reduced by about 37%~48%, and the overall plastic zone is significantly reduced. The plastic failure of coal and rock in the cracked region consumes and weakens the impact energy, enhances the dissipation effect of kinetic energy in surrounding rock, and effectively ensures the integrity of coal and rock in the reinforced region. The above research results can provide new support theory and technical ideas for surrounding rock support of roadways prone to rock bursts, prevent roadway rock burst accidents, and ensure mine safety production.

The analysis of historical coal mine safety events and the accurate identification of disaster factors are essential for effective mine safety management. Based on the KeyBERT network model, conducts a coupling analysis of six typical coal mine disaster cases in China between 2013 and 2023: gas explosions, water disasters, fires, roof collapses, coal dust incidents, and rockbursts. It utilizes the 24Model (a theoretical model of accident causation) to systematically analyze the mechanisms of each causative factor. The research reveals that causative factors of coal mine accidents can be classified into three categories: geological factors representing hazardous conditions of materials, serving as prerequisites for disaster occurrences; behavioral and managerial factors reflecting unsafe human behaviors, crucial as trigger conditions for disasters. Moreover, deeply explored the disaster-causing characteristics and action mechanisms of key geological factors such as faults, folds, goafs and overburden structures, and divided behavioral factors into two levels: psychological and executive. It was found that psychological factors play a leading role in accident induction. When psychological factors are superimposed on problems at the executive level, major safety hazards will be formed, seriously threatening coal mine safety production. Based on these findings, we have developed a dual-prevention mechanism integrating hidden danger investigation with safety risk classification control, and proposed an innovative “3LA” coal mine disaster management system, revealing that the inevitability of mine disasters stems from simultaneous failures at three management levels.

Strength anisotropy and heterogeneous rotated anisotropy are prevalent phenomena in natural slopes. Previous studies have underscored their significance in slope stability analysis. However, in previous slope stability analyses, the effects of strength anisotropy and heterogeneous rotated anisotropy on slope stability were studied separately, without considering their coupled effect. This paper aims to propose a probabilistic analysis framework of slope stability considering the coupled effect of strength anisotropy and heterogeneous rotated anisotropy. Through an undrained clay slope case, the proposed probabilistic analysis framework is examined. The influence of strength anisotropy and heterogeneous rotated anisotropy on slope stability is investigated. The results show that the proposed probabilistic analysis framework of slope stability considering the coupled effect of strength anisotropy and heterogeneous rotated anisotropy is effective. Both strength anisotropy and heterogeneous rotated anisotropy have an important influence on slope stability. Furthermore, the statistics of safety factor including mean value, coefficient of variation, and reliability index, vary with the strength anisotropy coefficient, the heterogeneous anisotropy coefficient, and the rotational angle. The smaller the strength anisotropy coefficient, the larger the heterogeneous anisotropy coefficient, and the smaller the reliability index. The rotational angle of strata corresponding to the minimum and maximum values of the slope reliability index is sensitive to the strength anisotropy coefficient, but not to the heterogeneous anisotropy coefficient.

The long-term stability of water-immersed coal pillars in proximity to urban areas is critical for ensuring the safety of urban development. This study investigates the creep damage evolution in strip coal pillars through a comprehensive approach integrating in-situ investigations, laboratory experiments, and numerical modeling based on a real-world case study. The analysis focuses on the evolution of stress distribution, creep damage propagation, and the mechanisms driving continuous damage in coal pillars. Findings indicate that in the studied case, concentrated stress around the elastic-plastic boundary progresses toward the central region of the coal pillar as creep damage expands. Initially, the propagation of creep damage is rapid but decelerates due to the residual strength of damaged coal, which bears the overburden pressure and provides lateral constraint. The state of creep damage expansion in a coal pillar depends on the evolution of triaxial creep strength of coal induced by the stress conditions of the intact coal body, which will be changed by the transferred overburden pressure and increased confining pressure.

This study investigates the mesostructural damage evolution and creep deformation mechanisms in bedded rock salt through integrated scanning electron microscopy (SEM) and multistage creep experiments. Utilizing a self-developed in situ observation system coupled with digital image correlation (DIC) analysis, the microstructural heterogeneity, strain localization, and damage propagation patterns in the rock were systematically characterized. The results revealed distinct microstructural contrasts between rock salt and argillaceous interlayers, with interfacial regions exhibiting pore-rich, interconnected structures due to crystal gradation disparities. Creep damage initiation predominantly occurred in pure rock salt domains, manifesting as transgranular fractures and intercrystalline slip, followed by crack propagation into salt–mudstone interfaces governed by shear dilatancy. The integration of mesoscale structural characterization with macroscopic mechanical behavior establishes a framework for predicting the long-term stability of bedded salt formations under operational loads.

Coal mine underground reservoirs play a significant role in energy utilization while also contributing to energy security. Prolonged immersion in mine water reduces the long-term strength of coal, subsequently leading to continuous creep damage in coal pillars. This manifests as the propagation of damage, ultimately resulting in instability, which affects their load-bearing capacity and impermeability. A multi-faceted approach involving laboratory experiments, similar model tests, and numerical simulations was employed to investigate the mechanical properties of water-immersed coal and the continuous creep damage process in coal pillars. Key findings reveal that water immersion significantly diminishes the long-term strength of coal; for example, initial instantaneous strain rose from 0.16% (non-immersed) to 0.25% (8-week immersion), with final creep strain reaching 1.15% versus 0.78%, respectively. The combined modeling methods effectively replicated the creep damage process, demonstrating that when concentrated stress exceeds the reduced long-term strength of coal, damage propagates toward the center of the pillar, forming continuous creep damage extending approximately 3.8 m within 7 years. This study contributes to our understanding of the creep damage mechanism in coal pillars and supports the long-term stability evaluation of CMURs.

Fluctuations in gas pressure within salt cavern storage and the creep behavior of salt rock are key factors influencing the deformation of surrounding rock and the stability of salt caverns. Considering the operational characteristics of salt cavern storage, this study conducted triaxial graded loading creep tests on an impurity-containing salt rock to systematically analyze its creep deformation, strength characteristics, and failure modes under different confining pressures. The findings reveal that as axial stress increases, creep strain gradually becomes the dominant deformation component in an impurity-containing salt rock, while the proportion of instantaneous compressive strain decreases. When axial stress levels are similar, increasing confining pressure reduces both instantaneous compressive and steady-state creep strain rates. Under similar deviatoric stress conditions, a higher confining pressure leads to varying degrees of increase in instantaneous elastic strain, creep strain, and total strain of an impurity-containing salt rock. Under different confining pressures, the evolution of the steady-state creep strain rate and the viscosity coefficient follows an inverse function relationship. Based on the creep characteristics of salt rock and the geometric features of creep models in the nonaccelerated creep stage, a nonlinear integer-order viscous dashpot is proposed to describe the strain surge in the accelerated creep stage. A nonlinear viscoelastic-plastic creep model capable of capturing the entire creep process of salt rock is developed and further extended to a three-dimensional stress state. Comparative analysis demonstrates that the proposed creep model effectively describes the full creep process of different types of salt rock, particularly the accelerated creep stage.

Progressive deepening of coal extraction has directed attention to the objective transmission of floor stresses beneath inclined remnant pillars. Physical analogue experiments, three-dimensional finite-difference analyses (FLAC3D) and a semi-space elastic solution were jointly employed to quantify stress redistribution after panel extraction. The results reveal a bilateral arch-shaped failure zone within the roof strata and identify two characteristic floor-stress patterns that are governed by seam dip. For inclinations of 15-30°, near-floor stress exhibits quadratic decay from approximately 70 MPa to 25-30 MPa; for dips of 30-60° the decay is effectively linear, declining from 45 to 50 MPa to 15-20 MPa. The compiled data furnish a quantitative framework for panel layout and laminated-roof control in deep inclined seams.

Similar material simulation experiments on grouting in the goaf, aiming to investigate the damage characteristics of the overburden and the movement behavior both before and after grouting were conducted. The results demonstrate that after grouting the goaf, large fissures, fractures, holes, and other cavities are effectively sealed by the slurry. Compared to untreated goaf, grouting significantly reduces subsidence, with a reduction rate of up to 92.3%. The slurry grouting compacts the residual voids in the goaf, slowing the further subsidence of the collapsed area. It also provides lateral support and a barrier to water infiltration in the residual coal pillars. Additionally, the slurry improves the stress conditions of these coal pillars, transforming the initial unidirectional (or bidirectional) stress state into a bidirectional (or triaxial) stress state. This significantly enhances the support strength and stability of the coal pillars.

Addressing the insufficient pressure relief in the deep coal mass and the deterioration of the surrounding rock bearing structure due to increased borehole diameter in conventional borehole pressure relief techniques, a static expansive fracturing method for pressure relief in coal seam boreholes is proposed. A critical stress model for static expansive fracturing in coal seam boreholes is established through theoretical analysis, and numerical simulations are conducted to compare and analyze the differences between this method and conventional borehole pressure relief techniques in terms of roadway pressure relief effect and surrounding rock stability control. The results indicate that using a 150 mm borehole with a 75 MPa expansive stress achieves a comparable state of full pressure relief in the rib coal as a 250 mm borehole, while increasing the pressure relief range in the deep coal mass by a factor of approximately 3.6. Although conventional borehole pressure relief methods can enhance pressure relief by increasing the borehole diameter, they significantly expand the plastic zone in the shallow surrounding rock, aggravating surrounding rock deformation. In contrast, the static expansive fracturing method for pressure relief in coal seam boreholes actively directs fractures in the deep high-stress coal mass, promoting the expansion and interconnection of its plastic zone to form a deep structural weakening zone, while markedly reducing the disturbance and damage to the shallow surrounding rock. This method breaks through the limitations of passive borehole for pressure relief, offering dual advantages of efficient deep pressure relief and shallow surrounding rock stability protection, and providing a new approach for rockburst prevention.

The sealing performance of coal mass is of significant importance for converting abandoned mines into geological repository. This study presents a novel approach to enhancing the sealing of the pore structure in coal seams, such a technique utilizes mined water as the primary substance and additive solution based crystalline. Sequent tests are implemented, including saturation test, ion chromatography test , permeability test and scanning electronic microscope observations. It was suggested that the produced crystalline decrease the porosity and permeability of the coal, with different crystal morphologies due to various ions of additive solutions. The produced rod-shaped crystals has the most remarkable impact on closing the pores in the coal exhibiting the columnar crystals which distributed uniformly within the joints and pores of the coal, and reducing the effective radius and tortuosity of the coal pores to a significant extent. Improving the sealing ability of the abandoned mines. Thus, the sealing ability of abandoned mines is improved.

During coal mining operations, the coal will be deformed and damaged due to multiple mining disturbances (MMD), often resulting in disasters, like rock burst. To understand the evolution rules of coal deformation under MMD and its final fracture characteristics after impact dynamic load loading, reduce the adverse effects of mining disturbances, and improve disaster prevention and control capabilities, quasi-static uniaxial cyclic loading-unloading (L-U) and dynamic axial compression tests were conducted on large-sized coal-like samples. During the tests, three-dimensional (3D) laser scanning and acoustic emission (AE) monitoring technology were utilized to accurately capture the full-field deformation and AE response data, facilitating a systematic analysis of deformation and fracture characteristics. The results show that: (1) Under the cyclic L-U effect induced by MMD, each loading cycle causes compression deformation with partial recovery during unloading, presenting an overall “wavy” variation trend. (2) The maximum load is the most critical factor affecting the damaged coal deformation, with smaller load resulting in less overall sample deformation. (3) After the impact dynamic loading, the damaged samples suffered large-scale impact splitting failure, with the compressive-shear layer failure mainly occurred inside the holes. (4) Lower loading during cyclic L-U process correlate with reduced damage degree, and smaller debris particles with a higher fractal dimension when impact failure occurs, indicating a more severe impact failure. (5) With multiple cycles of L-U, the cracks inside the sample gradually extend and expand from around the hole to the outside. The greater the load and the number of cycles, the more serious the crack damage will be. (6) In the practical mining process, it is crucial to reinforce roadway interiors while minimizing low-loading cyclic disturbances induced by MMD. The study has obtained the deformation evolution rules and failure characteristics of coal under MMD, providing a theoretical basis for the prevention and control of corresponding engineering disasters.

The existing prevention and control of rockbursts in mining mainly focus on the production phase, making it challenging to fundamentally curb rockburst disasters. Based on the concept of lifecycle management, the lifecycle of coal mines can be divided into four stages: exploration, construction, production, and closure. "Source" prevention and control measures are implemented during different stages of the mine to address rockbursts. During the exploration stage, the emphasis is on assessing the rockburst proneness and predicting the risk of rockbursts in the newly developed coal seams. In the construction stage, the focus is on identifying the dynamic tendencies and evaluating the risk of rockbursts considering all minable coal seams, as well as the roof and floor strata. This involves conducting a rockburst identification for the mine, establishing a sound prevention mechanism, improving management systems, determining mine capacity, and implementing rockburst prevention designs. In the production stage, rockburst prevention and control measures are implemented in three stages: pre-mining, during mining, and post-mining. During each stage, specific measures are undertaken to mitigate the risks associated with rockbursts. During the closure stage, safety assessments are conducted regarding the recovery of coal pillars to prevent rockbursts. Special prevention measures are developed based on the assessment results. By implementing these measures throughout the entire lifecycle of the mine, from exploration to closure, it becomes possible to address the issue of rockbursts comprehensively and effectively. This approach ensures that preventive actions are taken at the early stages of mine development and continues to manage and control rockburst risks during the operational phases, ultimately enhancing safety and reducing the impact of rockburst disasters.

Underground coal gasification is currently the highest-temperature(over 1200℃)unconventional development method for fossil energy.Underground gasification of coal in the medium-deep(refer to the depth of 800～1500 m in this paper)has obvious advant-ages in improving the gasification pressure and reducing the geological safety risks.Scientific prediction of safe width of gasification cav-ity is important to ensure stable gasification operation.Since the method of calculating the safe width of gasification cavity based on Con-trolled Retreat Injection Point(CRIP)process has not yet been established,targeted research is needed to ensure the smooth implementa-tion of field tests.Once the top plate of the gasification cavity is"exposed"to high temperature behind the gasification cavity.The genera-tion position of thermal stresses inside the rock and the influence law of differences in the thermal expansion coefficient of particles and matrix on the magnitude of thermal stresses were studied by numerical simulation under compressive stress constraints.the thermal dam-age mechanism of rock under high temperature was clarified combined with the scanning electron microscope results of rock after high temperature treatment.According to the characteristics of CRIP gasification process,a thin plate model of gasification cavity roof consid-ering the influence of high temperature was established,and a method for calculating the safe width of the gasification cavity was pro-posed in combination with the theory of"key layer".The study revealed that,rock thermal damage was caused by the interaction and syn-ergy of rock physicochemical reactions and thermal stress,and the rock undergone irregular deformation at high temperatures.Microstruc-tural changes of rock caused by the thermal damage were the fundamental cause of changes in rock mechanical and physical properties.The maximum tensile thermal stress in rock occurred at the grain interfaces or in grains with small coefficient of thermal expansion.The maximum tensile thermal stress increased rapidly with decreasing the thermal expansion coefficient of the grain when the ratio of the thermal expansion coefficient of the grain to that of the matrix is in the range of[0.01-1).The microcracks of mudstone was developed when heated to 200℃,the crack development was more obvious when heated to 400℃,which mainly along the edge of the particles rup-ture.The number of cracks was increased and the size was larger when heated to 600-800℃.The larger cracks and numerous pores were formed when heated to 1000℃.The crack connectivity increased significantly at 1200℃,and the stomatal development was larger.Due to the effect of high temperature,the step constant for the thin plate model is no longer a constant,and specific values need to be determ-ined based on the extent of thermal damage to the roof of gasification cavity and the location of the hard rock layer on the top plate.The safe width of gasification cavity was affected by temperature.In the study,the calculated safe widths of sandstone roof at 35 and 1000℃ were 34.3 m and 14.1 m,respectively,with a difference of 58.9%.while the safe widths at 35 and 1000℃ were 16.7 m and 15.9 m,re-spectively,with a 4.8%difference.Lastly,a method of determining the longitudinal target area of coal seam was proposed from the per-spective of reducing the risk of roof collapse and improving gasification control.When the coal seam thickness exceeded half of the gasi-fication cavity safe width,it was suggested to design the longitudinal target area of horizontal well at a location not more than half of the safe width of gasification cavity from the top of the coal.

Underground water reservoirs (UWR) of coal mine plays a significant role in enhancing the ecological environment and safeguarding water resources. The water stored in UWR, known as brine solution, seriously damages the mechanical properties of the coal pillar. However, the mechanical degradation characteristics of coal under the action of different concentration solutions are still unclear. In this paper, we propose a novel coal corrosion device to simulate the real environment, designed to ensure the effective dissolution of the solution to the samples. Here we show the results of brine solution corrosion tests, considering ion composition changes, microscopic CT imaging, and mechanical properties. The solution ion composition experiences significant changes after the corrosion test. The variation in Mn2+ ion content can reflect the reaction degree and trend of water-rock interaction; CT test visually demonstrates the microstructural changes, allowing for direct observation of dissolution, generation, and attachment phenomena. The specimen’s overall porosity increases after corrosion; Triaxial compression tests were conducted, and both solution concentration and corrosion time can cause varying degrees of mechanical parameters degradation. Our results demonstrate how solution concentration affects coal and the extent of its impact. We anticipate our research will contribute to the construction and long-term safety of UWR.