Metal mineral resources play an indispensable role in the development of the national economy. Dynamic disasters in underground metal mines seriously threaten mining safety, which are major scientific and technological problems to be solved urgently. In this article, the occurrence status and grand challenges of some typical dynamic disasters involving roof falling, spalling, collapse, large deformation, rockburst, surface subsidence, and water inrush in metal mines in China are systematically presented, the characteristics of mining-induced dynamic disasters are analyzed, the examples of dynamic disasters occurring in some metal mines in China are summarized, the occurrence mechanism, monitoring and early warning methods, and prevention and control techniques of these disasters are highlighted, and some new opinions, suggestions, and solutions are proposed simultaneously. Moreover, some shortcomings in current disaster research are pointed out, and the direction of efforts to improve the prevention and control level of dynamic disasters in China’s metal mines in the future is prospected. The integration of forward-looking key innovative theories and technologies in the abovementioned aspects will greatly enhance the cognitive level of disaster prevention and mitigation in China’s metal mining industry and achieve a significant shift from passive disaster relief to active disaster prevention.
Rockburst has perennially posed a formidable challenge to the stability of underground engineering works, particularly under conditions of deep-seated high stress. This paper provides a comprehensive review of recent advancements in on-site research related to rockburst occurrences, covering on-site case analyses, monitoring methodologies, early warning systems, and risk (proneness) evaluation. Initially, the concepts and classifications of rockburst based on on-site understanding were summarized. The influences of structural planes (in various spatial distribution combinations), in-situ stress (particularly magnitude and direction of the principal stress), dynamic disturbances, and excavation profiles on rockburst were thoroughly assessed and discussed through the analysis of published rockburst cases and on-site survey results. Subsequently, a compendium of commonly employed on-site monitoring techniques was outlined, delineating their respective technical attributes. Particular emphasis is accorded to the efficacy of microseismic monitoring technology and its prospective utility in facilitating dynamic rockburst early warning mechanisms. Building upon this foundation, the feasibility of assessing rockburst propensity while considering on-site variables is verified, encompassing the selection and quantitative evaluation of pertinent indicators. Ultimately, a comprehensive synthesis of the paper is presented, alongside the articulation of prospective research goals for the future.
The mechanical properties of residual coal pillars under the influence of upward mining disturbances significantly affect the safety of residual mining activities on working faces. This study conducted low-frequency disturbance dynamic uniaxial compression tests on coal specimens using a self-developed dynamic-static load coupling electro-hydraulic servo system, and studied the strength evolutions, surface deformations, acoustic emission (AE) characteristic parameters, and the failure modes of coal specimens with different static preloading levels were studied. The disturbance damage is positively correlated with the coal specimen static preload level. Specifically, the cumulative AE count rates of the initial accelerated damage stage for the coal specimens with static preloading level of 60% and 70% of the uniaxial compressive strength (UCS) were 2.66 and 3.19 times that of the 50% UCS specimens, respectively. Macroscopically, this behaviour manifested as a decrease in the compressive strength, and the mean strengths of the disturbance-damaged coal specimens with 60% and 70% of UCS static preloading decreased by 8.53% and 9.32%, respectively, compared to those of the specimens under pure static loading. The crack sources, such as the primary fissures, strongly control the dynamic response of the coal specimen. The difference between the dynamic responses of the coal specimens and that of dense rocks is significant.
Four key stress thresholds exist in the compression process of rocks, i. e., crack closure stress (σcc), crack initiation stress (σci), crack damage stress (σcd) and compressive strength (σc). The quantitative identifications of the first three stress thresholds are of great significance for characterizing the microcrack growth and damage evolution of rocks under compression. In this paper, a new method based on damage constitutive model is proposed to quantitatively measure the stress thresholds of rocks. Firstly, two different damage constitutive models were constructed based on acoustic emission (AE) counts and Weibull distribution function considering the compaction stages of the rock and the bearing capacity of the damage element. Then, the accumulative AE counts method (ACLM), AE count rate method (CRM) and constitutive model method (CMM) were introduced to determine the stress thresholds of rocks. Finally, the stress thresholds of 9 different rocks were identified by ACLM, CRM, and CMM. The results show that the theoretical stress - strain curves obtained from the two damage constitutive models are in good agreement with that of the experimental data, and the differences between the two damage constitutive models mainly come from the evolutionary differences of the damage variables. The results of the stress thresholds identified by the CMM are in good agreement with those identified by the AE methods, i.e., ACLM and CRM. Therefore, the proposed CMM can be used to determine the stress thresholds of rocks.
Backfill mining is one of the most important technical means for controlling strata movement and reducing surface subsidence and environmental damage during exploitation of underground coal resources. Ensuring the stability of the backfill bodies is the primary prerequisite for maintaining the safety of the backfilling working face, and the loading characteristics of backfill are closely related to the deformation and subsidence of the roof. Elastic thin plate model was used to explore the non-uniform subsidence law of the roof, and then the non-uniform distribution characteristics of backfill bodies’ load were revealed. Through a self-developed non-uniform loading device combined with acoustic emission (AE) and digital image correlation (DIC) monitoring technology, the synergistic dynamic evolution law of the bearing capacity, apparent crack, and internal fracture of cemented coal gangue backfills (CCGBs) under loads with different degrees of non-uniformity was deeply explored. The results showed that: 1) The uniaxial compressive strength (UCS) of CCGB increased and then decreased with an increase in the degree of non-uniformity of load (DNL). About 40% of DNL was the inflection point of DNL-UCS curve and when DNL exceeded 40%, the strength decreased in a cliff-like manner; 2) A positive correlation was observed between the AE ringing count and UCS during the loading process of the specimen, which was manifested by a higher AE ringing count of the high-strength specimen. 3) Shear cracks gradually increased and failure mode of specimens gradually changed from “X” type dominated by tension cracks to inverted “Y” type dominated by shear cracks with an increase in DNL, and the crack opening displacement at the peak stress decreased and then increased. The crack opening displacement at 40% of the DNL was the smallest. This was consistent with the judgment of crack size based on the AE b-value, i.e., it showed the typical characteristics of “small b-value-large crack and large b-value-small crack”. The research results are of significance for preventing the instability and failure of backfill.
Toppling failure of rock mass/soil slope is an important geological and environmental problem. Clarifying its failure mechanism under different conditions has great significance in engineering. The toppling failure of a cutting slope occurred in a hydropower station in Kyushu, Japan illustrates that the joint characteristic played a significant role in the occurrence of rock slope tipping failure. Thus, in order to consider the mechanical properties of jointed rock mass and the influence of geometric conditions, a simplified analytical approach based on the limit equilibrium method for modeling the flexural toppling of cut rock slopes is proposed to consider the influence of the mechanical properties and geometry condition of jointed rock mass. The theoretical solution is compared with the numerical solution taking Kyushu Hydropower Station in Japan as one case, and it is found that the theoretical solution obtained by the simplified analysis method is consistent with the numerical analytical solution, thus verifying the accuracy of the simplified method. Meanwhile, the Goodman-Bray approach conventionally used in engineering practice is improved according to the analytical results. The results show that the allowable slope angle may be obtained by the improved Goodman-Bray approach considering the joint spacing, the joint frictional angle and the tensile strength of rock mass together.
In practical engineering applications, rock mass are often found to be subjected to a triaxial stress state. Concurrently, defects like joints and fractures have a notable impact on the mechanical behavior of rock mass. Such defects are identified as crucial contributors to the failure and instability of the surrounding rock, subsequently impacting the engineering stability. The study aimed to investigate the impact of fracture geometry and confining pressure on the deformation, failure characteristics, and strength of specimens using sand powder 3D printing technology and conventional triaxial compression tests. The results indicate that the number of fractures present considerably influences the peak strength, axial peak strain and elastic modulus of the specimens. Confining pressure is an important factor affecting the failure pattern of the specimen, under which the specimen is more prone to shear failure, but the initiation, expansion and penetration processes of secondary cracks in different fracture specimens are different. This study confirmed the feasibility of using sand powder 3D printing specimens as soft rock analogs for triaxial compression research. The insights from this research are deemed essential for a deeper understanding of the mechanical behavior of fractured surrounding rocks when under triaxial stress state.
The damage and failure law of rock mass with holes is of great significance to the stability control of roadways. This study investigates the mechanical properties and failure modes of porous rock masses under cyclic loading, elucidates the acoustic emission (AE) characteristics and their spatial evolution, and establishes the interrelation among AE, stress, strain, time, and cumulative damage. The results reveal that the rock mass with holes and the intact rock mass show softening and hardening characteristics after cyclic loading. The plastic strain of the rock mass with holes is smaller than that of the intact rock mass, and the stress - strain curve shows hysteresis characteristics. Under uniaxial compression, the pore-bearing rock mass shows the characteristics of higher ringing count, AE energy, b-value peak, and more cumulative ringing count in the failure stage, while it shows lower characteristics under cyclic action. At the initial stage of loading, compared with the intact rock mass, the pore-containing rock mass shows the characteristics of a low b-value. The AE positioning and cumulative damage percentage are larger, and the AE positioning is denser around the hole. The specimen with holes is mainly shear failure, and the complete specimen is mainly tensile shear failure.
During the construction and operation of the abandoned mine pumped storage power station, the underground space surrounding rock body faces the complex stress environment under the action of mining disturbance, frequent pumping, water storage and other dynamic disturbances. The stability of the abandoned mine surrounding rock body is the basis for guaranteeing the safety and effectiveness of water storage in the underground space of the abandoned mine. By considering the two main factors of different stress levels and disturbance amplitudes, the mechanical properties, damage characteristics and acoustic emission characteristics of the abandoned mine perimeter rock body under dynamic disturbance were investigated using a creep-disturbed dynamic impact loading system. The experimental results show that: 1) The stress level is considered to be the major contributing factor of the failure of muddy sandstone, followed by the amplitude of the disturbances; 2) The time required for the destruction of muddy sandstone decreases with the increase of amplitude. When the stress level is 80%, the sandstone specimens have a decreasing number of cycles as the disturbance amplitude increases. The disturbance amplitude is sequentially increased from 4 MPa to 5, 6, 7, and 8 MPa, the number of cycles required for specimen destruction decreases significantly by 96.71%, 99.13%, 99.60%, and 99.93%, respectively; 3) Disturbance amplitude and stress level have a significant effect on muddy sandstone damage and damage occurs only after a certain threshold is reached. With the increase of stress level and disturbance amplitude, the macroscopic damage of muddy sandstone is mainly conical, with obvious flake spalling and poor damage integrity; 4) According to the time-dependent changes in AE energy and ringing counts, the acoustic emission activity during the failure process could be divided into three phases, namely, weakening period, smooth period, and surge period, corresponding to the compaction phase, elastic rise phase and post-peak damage phase. The research results are of reference significance for the damage evolution analysis of muddy sandstone under dynamic disturbance and the safety and stability of abandoned mine perimeter rock body.
Rock fracture warning is one of the significant challenges in rock mechanics. Many true triaxial and synchronous acoustic emission (AE) tests were conducted on granite samples. The investigation focused on the characteristics of AE signals preceding granite fracture, based on the critical slowing down (CSD) theory. The granite undergoes a transition from the stable phase to the fracture phase and exhibits a clear CSD phenomenon, characterized by a pronounced increase in variance and autocorrelation coefficient. The variance mutation points were found to be more identifiable and suitable as the primary criterion for predicting precursor information related to granite fracture, compared to the autocorrelation coefficient. It is noteworthy to emphasize that the CSD factor holds greater potential in elucidating the underlying mechanisms responsible for the critical transition of granite fracture, in comparison to the AE timing parameters. Furthermore, a novel multi-parameter collaborative prediction method for rock fracture was developed by comprehensively analyzing predictive information, including abnormal variation modes and the CSD factor of AE characteristic parameters. This method enhances the understanding and prediction of rock fracture-related geohazards.
Understanding the physical, mechanical behavior, and seepage characteristics of coal under hydro-mechanical coupling holds significant importance for ensuring the stability of surrounding rock formations and preventing gas outbursts. Scanning electron microscopy, uniaxial tests, and triaxial tests were conducted to comprehensively analyze the macroscopic and microscopic physical and mechanical characteristics of coal under different soaking times. Moreover, by restoring the stress path and water injection conditions of the protective layer indoors, we explored the coal mining dynamic behavior and the evolution of permeability. The results show that water causes the micro-surface of coal to peel off and cracks to expand and develop. With the increase of soaking time, the uniaxial and triaxial strengths were gradually decreased with nonlinear trend, and decreased by 63.31% and 30.95% after soaking for 240 h, respectively. Under different water injection pressure conditions, coal permeability undergoes three stages during the mining loading process and ultimately increases to higher values. The peak stress of coal, the deviatoric stress and strain at the permeability surge point all decrease with increasing water injection pressure. The results of this research can help improve the understanding of the coal mechanical properties and seepage evolution law under hydro-mechanical coupling.
Pillar is closely related to the stability and reliability of underground spaces in closed/abandoned mines. The present research introduced a new technique to strengthen square cement mortar columns via fiber-reinforced polymer (FRP) strips to verify the strengthening effect of FRP on pillars. Compared to a fully wrapped FRP jacket, the advantages of FRP strip are cost-effective and easy-to-construct. A series of compression tests as well as theoretical analysis were carried out to explore the mechanical behavior of square cement mortar specimens partially strengthened with FRP strips. The results verified the effectiveness of FRP strips in enhancing the stress and strain of cement mortar. Different from unconfined cement mortar specimens, these FRP-strengthened cement mortar specimens are featured with the double-peaked behaviors, mainly attributed to the stress state transformation from a one-dimensional to a three-dimensional stress state. It also indicated that the enhancement of stress increased with the FRP strip width. Moreover, the brittle-ductile transition ductile failure characteristics were also observed in FRP-confined cement mortar specimens. The ultimate ductility of the cement mortar specimen decreases gradually with the growth of the FRP strip width. The main contribution of this research is to enrich the strengthening techniques for residual pillars.
To develop suitable grouting materials for water conveyance tunnels in cold regions, firstly, this study investigated the performance evolution of ferrite-rich sulfoaluminate-based composite cement (FSAC grouting material) at 20 and 3 °C. The results show that low temperature only delays the strength development of FSAC grouting material within the first 3 d. Then, the effect of four typical early strength synergists on the early properties of FSAC grouting material was evaluated to optimize the early (≤1 d) strength at 3 °C. The most effective synergist, Ca(HCOO)2, which enhances the low-temperature early strength without compromising fluidity was selected based on strength and fluidity tests. Its micro-mechanism was analyzed by XRD, TG, and SEM methods. The results reveal that the most suitable dosage range is 0.3 wt%–0.5 wt%. Proper addition of Ca(HCOO)2 changed the crystal morphology of the hydration products, decreased the pore size and formed more compact hydration products by interlocking and overlapping. However, excessive addition of Ca(HCOO)2 inhibited the hydration reaction, resulting in a simple and loose structure of the hydration products. The research results have reference value for controlling surrounding rock deformation and preventing water and mud inrushes during the excavation in cold region tunnels.
Experiments on grouting-reinforced rock mass specimens with different particle sizes and features were carried out in this study to examine the effects of grouting reinforcement on the load-bearing characteristics of fractured rock mass. The strength and deformation features of grouting-reinforced rock mass were analyzed under different loading manners; the energy evolution mechanism of grouting-reinforced rock mass specimens with different particle sizes and features was investigated; the energy dissipation ratio and post-peak stress decreasing rate were employed to evaluate the bearing stability of grouting-reinforced rock mass. The results show that the strength and ductility of granite-reinforced rock mass (GRM) under biaxial loading are higher than that of sandstone-reinforced rock mass (SRM) under uniaxial loading. Besides, the energy evolution characteristics of grouting-reinforced rock mass under uniaxial and biaxial loading mainly could be divided into early, middle, and late stages. In the early stage, total, elastic, and dissipation energies were quite small with flatter curves; in the middle stage, elastic energy increased rapidly, whereas dissipation energy increased slowly; in the late stage, dissipation energy increased sharply. The energy dissipation ratio was used to represent the pre-peak plastic deformation. Under uniaxial loading, this ratio increased as the particle size increased and the pre-peak plastic deformation of grouting-reinforced rock mass became larger; under biaxial loading, it dropped as the particle size increased, and the pre-peak plastic deformation of grouting-reinforced rock mass became smaller. The post-peak stress decline rate Av was used to assess the post-peak bearing performance of grouting-reinforced rock mass. Under uniaxial loading, parameter Av exhibited reduction as the particle size kept increasing, and the ability of post-peak of grouting-reinforced rock mass to allow deformation development was greater, and the bearing capacity was greater; under biaxial loading, Av increased with the particle size, and the ability of post-peak of grouting-reinforced rock mass to allow deformation development was low and the bearing capacity was reduced. The findings are considered instrumental in improving the stability of the roadway-surrounding rock by granite and sandstone grouting.
Underground energy and resource development, deep underground energy storage and other projects involve the global stability of multiple interconnected cavern groups under internal and external dynamic disturbances. An evaluation method of the global stability coefficient of underground caverns based on static overload and dynamic overload was proposed. Firstly, the global failure criterion for caverns was defined based on its band connection of plastic-strain between multi-caverns. Then, overloading calculation of the boundary geostress and seismic intensity on the caverns model was carried out, and the critical unstable state of multi-caverns can be identified, if the plastic-strain band appeared between caverns during these overloading processes. Thus, the global stability coefficient for the multi-caverns under static loading and earthquake was obtained based on the corresponding overloading coefficient. Practical analysis for the Yingliangbao (YLB) hydraulic caverns indicated that this method can not only effectively obtain the global stability coefficient of caverns under static and dynamic earthquake conditions, but also identify the caverns’ high-risk zone of local instability through localized plastic strain of surrounding rock. This study can provide some reference for the layout design and seismic optimization of underground cavern group.
In the process of shield tunneling through soft soil layers, the presence of confined water ahead poses a significant threat to the stability of the tunnel face. Therefore, it is crucial to consider the impact of confined water on the limit support pressure of the tunnel face. This study employed the finite element method (FEM) to analyze the limit support pressure of shield tunnel face instability within a pressurized water-containing layer. Subsequently, a multiple linear regression approach was applied to derive a concise solution formula for the limit support pressure, incorporating various influencing factors. The analysis yields the following conclusions: 1) The influence of confined water on the instability mode of the tunnel face in soft soil layers makes the displacement response of the strata not significant when the face is unstable; 2) The limit support pressure increases approximately linearly with the pressure head, shield tunnel diameter, and tunnel burial depth. And inversely proportional to the thickness of the impermeable layer, soil cohesion and internal friction angle; 3) Through an engineering case study analysis, the results align well with those obtained from traditional theoretical methods, thereby validating the rationality of the equations proposed in this paper. Furthermore, the proposed equations overcome the limitation of traditional theoretical approaches considering the influence of changes in impermeable layer thickness. It can accurately depict the dynamic variation in the required limit support pressure to maintain the stability of the tunnel face during shield tunneling, thus better reflecting engineering reality.
Within the framework of achieving carbon neutrality, various industries are confronted with fresh challenges. The ongoing process of downsizing coal industry operations has evolved into a new phase, with the burgeoning proliferation of abandoned mines posing a persistent issue. Addressing the challenges and opportunities presented by these abandoned mines, this paper advocates for a scientific approach centered on the advancement of pumped storage energy alongside gas-oil complementary energy. Leveraging abandoned mine tunnels to establish pumped storage power stations holds significant ecological and economic importance for repurposing these sites. This initiative not only serves as an effective means to restore the ecological balance in mining regions but also provides an environmentally friendly approach to repurposing abandoned mine tunnels, offering a blueprint for economically viable pumped storage power stations. This article delineates five crucial scientific considerations and outlines seven primary models for the utilization of abandoned mine sites, delineating a novel, comprehensive pathway for energy and power development that emphasizes multi-energy complementarity and synergistic optimization within abandoned mines.
Every year in China, a significant number of mines are closed or abandoned. The pumped hydroelectric storage (PHS) and geothermal utilization are vital means to efficiently repurpose resources in abandoned mine. In this work, the development potentials of the PHS and geothermal utilization systems were evaluated. Considering the geological conditions and meteorological data available of Jiahe abandoned mine, a simple evaluation model for PHS and geothermal utilization was established. The average efficiency of the PHS system exceeds 70% and the regulatable energy of a unit volume is over 1.53 kW·h/m3. The PHS system achieves optimal performance when the wind/solar power ratio reaches 0.6 and 0.3 in daily and year scale, respectively. In the geothermal utilization system, the outlet temperature and heat production are significantly affected by the injection flow rate. The heat production performance is more stable at lower rate flow, and the proportion of heat production is higher in the initial stage at greater flow rate. As the operating time increases, the proportion of heat production gradually decreases. The cyclic heat storage status has obvious advantages in heat generation and cooling. Furthermore, the energy-saving and emission reduction benefits of PHS and geothermal utilization systems were calculated.
Rockburst is a common geological disaster in underground engineering, which seriously threatens the safety of personnel, equipment and property. Utilizing machine learning models to evaluate risk of rockburst is gradually becoming a trend. In this study, the integrated algorithms under Gradient Boosting Decision Tree (GBDT) framework were used to evaluate and classify rockburst intensity. First, a total of 301 rock burst data samples were obtained from a case database, and the data were preprocessed using synthetic minority over-sampling technique (SMOTE). Then, the rockburst evaluation models including GBDT, eXtreme Gradient Boosting (XGBoost), Light Gradient Boosting Machine (LightGBM), and Categorical Features Gradient Boosting (CatBoost) were established, and the optimal hyperparameters of the models were obtained through random search grid and five-fold cross-validation. Afterwards, use the optimal hyperparameter configuration to fit the evaluation models, and analyze these models using test set. In order to evaluate the performance, metrics including accuracy, precision, recall, and F1-score were selected to analyze and compare with other machine learning models. Finally, the trained models were used to conduct rock burst risk assessment on rock samples from a mine in Shanxi Province, China, and providing theoretical guidance for the mine’s safe production work. The models under the GBDT framework perform well in the evaluation of rockburst levels, and the proposed methods can provide a reliable reference for rockburst risk level analysis and safety management.
Granite is usually composed of quartz, biotite, feldspar, and cracks, and the variation characteristics of these components could reflect the deformation and failure process of rock well. Taking granite as an example, the video camera was used to record the deformation and failure process of rock. The distribution of meso-components in video images was then identified. The meso-components of rock failure precursors were also discussed. Moreover, a modified LSTM (long short-term memory method) based on SSA (sparrow search algorithm) was proposed to estimate the change of meso-components of rock failure precursor. It shows that the initiation and expansion of cracks are mainly caused by feldspar and quartz fracture, and when the quartz and feldspar exit the stress framework, rock failure occurs; the second large increase of crack area and the second large decrease of quartz or feldspar area may be used as a precursor of rock failure; the precursor time of rock failure based on meso-scopic components is about 4 s earlier than that observed by the naked eye; the modified LSTM network has the strongest estimation ability for quartz area change, followed by feldspar and biotite, and has the worst estimation ability for cracks; when using the modified LSTM network to predict the precursors of rock instability and failure, quartz and feldspar could be given priority. The results presented herein may provide reference in the investigation of rock failure mechanism.
This work investigated the effect of process parameters on densification, microstructure, and mechanical properties of a nickel-aluminum-bronze (NAB) alloy fabricated by laser powder bed fusion (LPBF) additive manufacturing. The LPBF-printed NAB alloy samples with relative densities of over 98.5% were obtained under the volumetric energy density range of 200–250 J/mm3. The microstructure of the NAB alloy printed in both horizontal and vertical planes primarily consisted of β′ martensitic phase and banded α phase. In particular, a coarser-columnar grain structure and stronger crystallographic texture were achieved in the vertical plane, where the maximum texture intensity was 30.56 times greater than that of random textures at the (100) plane. Increasing the volumetric energy density resulted in a decrease in the columnar grain size, while increasing the amount of α phase. Notably, β1′ martensitic structures with nanotwins and nanoscale κ-phase precipitates were identified in the microstructure of LPBF-printed NAB samples with a volumetric energy density of 250 J/mm3. Furthermore, under optimal process parameters with a laser power of 350 W and scanning speed of 800 mm/s, significant improvements were observed in the microhardness (HV 386) and ultimate tensile strength (671 MPa), which was attributed to an increase in refined acicular martensite.