Constructing deep underground tunnels faces severe challenges when the surrounding rock contains weak, unstable layers. This study investigates how the angle and spacing of these weak layers lead to the deformation and collapse of deep tunnel structures. A particle flow simulation, based on a 1,000–m-deep tunnel, was developed to recreate the physical behavior of the surrounding rock and observe how it cracks, shifts, and loses its internal support under various geological conditions. The findings indicate that steeper weak layers cause the rock’s internal support network to break down more severely, resulting in a peak crack density of approximately 1,250 per square meter and a fractal dimension of 1.5848 in the highly fractured zones. Conversely, a larger distance between these weak layers preserves more solid rock, significantly reducing overall damage, restricting the maximum displacement of the roadway roof to between 0.3 m and 0.4 m and maintaining a lower fractal dimension of approximately 1.33. The primary cause of tunnel failure is the widespread internal fracturing which in field conditions led to cumulative floor heaving exceeding 6 m and rib shrinkage exceeding 4 m prior to reinforcement. To control this instability, the injection of a grouting slurry into surrounding rock. This cementing slurry intervention glues the broken rock fragments back together, successfully rebuilding the internal support network and optimizing the fractal dimension of crack distribution. Ultimately, using this grouting reinforcement strategy fundamentally repairs the rock’s internal connections, transforming the broken material back into a stable structure.

Roadways in deep-buried thick coal seams subjected to superimposed excavation–mining disturbance commonly experience surrounding-rock loosening, continuous deformation, and support failure. Taking the −808 m level intake roadway of a coal mine as the engineering background, borehole imaging and cyclic triaxial loading–unloading tests were used to characterize fracture development, surrounding-rock loosening, and mechanical behavior. Based on unified strength theory and rib displacement compatibility, a mechanical model for rib instability was established to reveal the rib-dominated failure mechanism. An integrated bolt–mesh–cable–shotcrete–grouting support technology was proposed and validated using similar model tests and in situ ground pressure monitoring. The results show that the main loosened and fractured range of the surrounding rock was 3.0–3.3 m. Significant fracturing occurred in the roof, arch shoulders, and ribs, and rib fracture propagation and continuous inward convergence were the key processes inducing full-section coupled deformation. The proposed model divides the roadway rib into a residual fracture zone, a plastic damage zone, and an elastic disturbance zone. The model-predicted depth of the residual fracture zone is generally consistent with the loosened and fractured range identified by borehole imaging, providing field-scale support for the reliability of the model. Similar model tests and field monitoring show that rib stress fluctuations were most pronounced under mining disturbance. After applying the proposed support technology, roadway deformation was effectively controlled: deformation stabilized after approximately 60 days, the convergence rate approached zero after 100 days, and bolt and cable loads remained below their ultimate bearing capacities.

Based on uniaxial and triaxial compression tests of coal and sandstone, deformation and strength parameters for the coal-rock-bolt composite structure were determined, providing key inputs for subsequent single free-surface loading simulation. A numerical model characterizing coal-rock composite anchored body with through-going joints was developed using FLAC3D 9.0 integrated with Fish scripting language. By developing a real-time energy density tracking program, multi-factor coupled simulation loading experiments were systematically conducted. The simulations reveal the strength parameter degradation and energy evolution law of the anchored bodies of the coal-rock composite with through-going joints. Results indicate that the ultimate strength of the coal-rock combination depends on the coal mass, the plastic deformation capacity relies more on the rock mass, with the overall stiffness exhibiting intermediate characteristics between coal and rock. Both peak strength and energy storage limits demonstrate positive correlations with interfacial roughness. Furthermore, for the composite geological bodies formed by coal and rock, anchoring reinforcement applied to weaker zones effectively coordinates stress and energy distribution within the composite structure, suppressing localized damage propagation, thereby increasing the energy storage threshold and delaying the catastrophic failure time of the anchored body. Therefore, a "weakness-compensation-first" support strategy is proposed to enhance the overall geomechanical performance of the composite structure.

In this study, triaxial cyclic loading-unloading tests are conducted on sandstone samples under four different confining pressures to examine the energy evolution and distribution characteristics of brittle rocks subjected to cyclic loading. Two methods for energy calculation, namely the integration of single loading-unloading curves and the consideration of cyclic fatigue damage, are employed to elucidate the energy evolution patterns and the effects of confining pressure on loaded rock samples. A criterion for predicting rock instability is developed based on the cumulative impact of dissipated energy. An analysis of energy storage characteristics indicates that the internal energy storage of rocks follows a power function relationship with stress levels and a linear function relationship with confining pressure. By integrating energy conservation principles with elastoplastic analysis, the energy balance mechanism and the transfer-transformation law of tunnel surrounding rock under elastic-brittle-plastic constitutive conditions are derived and examined, facilitating the application of rock energy theory to practical engineering scenarios. Engineering analysis demonstrates that external energy is transmitted from the deeper sections of the surrounding rock to the excavation area of the tunnel through radial stress work. At the elastic-brittle interface, both elastic and dissipated energy experience abrupt changes while strictly conforming to the law of energy conservation. The findings of this research offer a theoretical basis for the support design of rockburst tunnels and impulsive ground pressure tunnels.

The peak strength is a significant parameter in rock engineering, the traditional empirical strength criteria for rocks show good agreement with test results under specific conditions. However, it is not completely accurate for a wide range of loading stress domains and uncorrelated rock types. In this research, porosity, uniaxial compressive strength (UCS) and confining pressure are selected as input variables, and the artificial bee colony (ABC) algorithm is used to optimize the support vector machine (SVM) model. Finally, we validate and comparatively analyze the applicability of the models based on the testing set and the comprehensive evaluation indexes (namely correlation coefficient (R2), root mean square error (RMSE) and mean absolute percentage error (MAPE)). Meanwhile, the cosine amplitude method is applied to analyze the correlation between the peak strength and the input variables. The results indicate that both SVM model and ABC-SVM model are suitable for the prediction of peak strength under triaxial compression. Additionally, the ABC-SVM model obviously has better prediction performance by comparison.

The mining of the working face has a pronounced influence on the floor roadway, resulting in the intensification of deformation of the surrounding rock of the roadway and posing a threat to production safety. To clarify the failure mechanism of the surrounding rock of the dynamic pressure roadway and to understand the development pattern of the plastic zone shape, in this paper, by integrating the stress distribution law of the floor during the mining process of the working face, a mechanical model of the surrounding rock of the floor dynamic pressure roadway is established. An analytical solution for the plastic zone shape of the surrounding rock of the dynamic pressure roadway is proposed and verified through a comparison between analytical calculations and numerical simulation (using FLAC3D 7.0 software). The results indicate the following: (1) when the horizontal distance between the working face and the roadway exceeds 35 m, no obvious changes are observed in the development pattern of the plastic zone of the surrounding rock of the roadway; (2) when the horizontal distance is less than 35 m, the rate of change in the maximum value of f increases from 0.02 MPa/m to 0.205 MPa/m as the vertical distance decreases, and the β value increases from 0.09°/m to 0.79°/m. The maximum development depth increases, the butterfly leaf of the plastic zone deflects towards the working face direction, and the shape gradually transforms from a “circular” shape to a “butterfly” shape. (3) The morphological characteristics of the plastic zone obtained by the analytical algorithm are highly consistent with those obtained by the numerical simulation method, suggesting that the analytical algorithm possesses certain validity. (4) There exist certain errors between the analytical method and the numerical simulation results, and they increase with the increase in the vertical distance (the error range is 19.4%~54.9%), but they can be disregarded within the requirements of engineering accuracy.

The mechanical properties of granular rocks are intrinsically linked to the heterogeneity of mineral grains. In this study, a 3D grain-based model (PFC3D-GBM) incorporating a hybrid contact model was established. Triaxial compression numerical simulations were conducted to investigate how confining pressure and mineral heterogeneity-characterized by spatial distribution, volume fraction, geometric size, and boundary strength of mineral grains-affect the fracture behavior and mechanical properties of coarse-grained limestone. The results show that force chains serve as load-bearing paths that distribute the external load. The orientation of these chains remains uniform, irrespective of the load magnitude. The ratio of high-strength force chains to weak-strength force chains (R HF/WF) and the ratio of high-strength force chains to microcracks (R HF/c) serve as quantitative indicators of bearing capacity and fracture resistance. At lower confining pressure (sigma 3 <= 10 MPa), the specimens exhibit reduced peak strength and increased brittleness, with failure typically occurring along a single macroscopic fracture plane. As sigma 3 increases, the formation of "X"-shaped failure becomes more pronounced. At the grain scale, a higher dolomite volume facilitates the formation of additional high-strength force chains within the specimen, along with an increase in Tran-D-cs at peak stress. As Tran-D-cs require a higher concentration of stress, sigma p increases by 13%. Moreover, stronger grain boundary strength enhances the stress concentration needed for fracture by modifying the proportion of Trans-c, leading to a 70 MPa increase in sigma p. Larger grain sizes, in turn, accommodate more force chains, necessitating a higher sigma p for fracture.

Energy serves as the fundamental driver of material failure, and accurately describing the mechanical properties and energy evolution laws of loaded anchored body is crucial for the stability control of surrounding rock in boltsupported roadways. Based on uniaxial compression tests of rock samples and utilizing the embedded Fish programming language in FLAC3D, numerical models of loaded sandstone specimens and energy models were developed. Through a comparative analysis between FLAC3D numerical simulations and laboratory uniaxial compression test results, the rationality of the energy model was validated, and post-peak strength parameters for the anchored body were established. Employing the PILE and LINER structural elements within FLAC3D, models for pre-stress diffusion in anchor bolts and energy evolution in anchored body were constructed. These models explored the distribution characteristics of tensile and compressive stress zones within anchored body during prestress release, as well as the pressure arch effect. Furthermore, the fracture behavior of anchored body and bolt load characteristics under different support and drilling size and density conditions were analyzed. The study revealed the evolution and distribution patterns of total energy density, elastic energy density and dissipated energy density during both the pre-peak and post-peak stages of anchored body. The mechanical effects and energy evolution laws of anchored body and bolts exhibit distinct stage - specific characteristics.

Convergence-constraint method is a design approach for underground engineering structures that combines theoretical analysis, field measurements, and engineering experience. It is a commonly used method for analyzing the interaction between surrounding rock and support system, as well as for conducting optimized support design. Based on the basic principle of convergence-constraint method, the classical supporting characteristics and supporting structure deformation equations were summarized. The supporting characteristic curves of supporting structures such as shotcrete, bolt (cable) and U-shaped steel were obtained by theoretical calculation. The effects of the geometric size (diameter, length), row spacing and material strength of supporting structure on the support pressure were analyzed. As the thickness and strength grade of shotcrete increase, the support stiffness and support pressure provided by shotcrete gradually escalate. Simultaneously, the support pressure of bolts experiences a significant increase with the augmentation of bolt (cable) diameter, length, material strength, and reduction in row-spacing between them. Furthermore, the support pressure delivered by U-shaped supports intensifies as the row-spacing decreases and the material strength increases. By using the Mohr-Coulomb strain softening constitutive model embedded in FLAC3D, the numerical analysis model of deep soft rock roadway considering the post-peak strain softening and dilatancy characteristics of rock was established. The deformation curves of roadway longitudinal section and the characteristic curves of surrounding rock under different stress states were calculated. The applicability of three kinds of combined support technologies such as bolting shotcrete, bolt (cable) shotcrete and bolting-shotcrete U-shaped steel to the large deformation control of surrounding rock in deep roadway were analyzed. The feasibility of applying the combined support technique of bolting-shotcrete U-shaped steel in deep roadway support projects has been verified. The numerical simulation results of the strain-softening constitutive model considering the post-peak strain-softening and dilatancy characteristics of rocks are quite different from those based on the classical Mohr-Coulomb constitutive model. The numerical simulation results of the Mohr-Coulomb constitutive model are conservative, and the supporting pressure provided by the supporting structure cannot meet the stability control requirements of the deep roadway. After roadway support, the surrounding rock exhibits pronounced deformation, which may give rise to safety incidents such as roof collapse and wall instability.

Most of the rock surrounding deep roadways is in a fractured state; fractured rock has significant rheological properties, and the time-dependent mechanical properties of fractured rock affect excavation construction, support design, and long-term stability of deep roadways. Triaxial compression and mercury intrusion tests are conducted on the bearing characteristics of severely damaged and fractured rock samples, indicating the strength degradation properties of these samples. The evolution of the internal pore structure in damaged and fractured rock samples is analyzed in relation to changes in unloading points (pre-peak stage, peak point, and post-peak stage), leading to the establishment of a quantitative evaluation index for rock damage based on the porosity evolution. Short-term rheological testing is performed on rock samples with varying degrees of damage and fracture, demonstrating the evolution of creep and stress relaxation characteristics. The findings contribute to a deeper theoretical understanding of the post-peak mechanical properties of coal and rock masses, which hold significant theoretical implications and can inform research on long-term stability in underground engineering applications, such as deeply buried roadways, tunnels, and chambers.

The mechanical behavior of cemented gangue backfill materials (CGBMs) is closely related to particle size distribution (PSD) of aggregates and properties of cementitious materials. Consequently, the true triaxial compression tests, CT scanning, SEM, and EDS tests were conducted on cemented gangue backfill samples (CGBSs) with various carbon nanotube concentrations (PCNT) that satisfied fractal theory for the PSD of aggregates. The mechanical properties, energy dissipations, and failure mechanisms of the CGBSs under true triaxial compression were systematically analyzed. The results indicate that appropriate carbon nanotubes (CNTs) effectively enhance the mechanical properties and energy dissipations of CGBSs through micropore filling and microcrack bridging, and the optimal effect appears at PCNT of 0.08wt

AbstractThe deformation and failure of coal walls in front of a working face cause significant difficulties during mining operations. This study reveals the nonuniform distribution of bearing pressure in front of coal walls based on in situ monitoring data and numerical simulation. Therefore, an eccentric compression mechanical model was established to study the deformation and failure characteristics of a coal wall. The slenderness ratio of the compression bar is introduced to define coal walls. The results showed that instability failure occurs when λ > λc and material failure occurs when λ ≤ λc. The instability failure‐type coal wall spalling was related to the mining height, eccentricity of roof pressure, the horizontal force, and the reaction moment of the floor. The material failure‐type coal wall spalling was related to the cohesion, the internal friction angle of the coal, the upper pressure, and the horizontal force of coal walls. Unstable and destructive coal wall peeling usually occurs at a height of 0.5–0.6 times the mining height, while material damage to coal wall peeling is determined to occur within the range of 0.4–0.6 times the mining depth. The findings contribute to the understanding of the deformation and failure of coal walls.

Microseismic technology has been widely used in geological hazard monitoring. However, the effective identification and classification of microseismic events in mines have always been a challenge in hazard monitoring. In this paper, a new method combining the empirical mode decomposition (EMD) algorithm and artificial neural network is proposed for the classification and identification of microseismic waveforms. This is the first study to explore such a model in the microseismic monitoring of coal mines. The data for this study were collected from a coal mine in northern China. A total of 2768 microseismic events and 2435 non-microseismic events were manually selected from a large amount of data. Firstly, the microseismic waveform reconstruction was performed using the 4th to 8th Intrinsic Mode Function (IMF) obtained by the EMD algorithm. Secondly, the peak factor, clearance factor, impulse factor, kurtosis, skewness, and waveform factor of each reconstructed microseismic waveform were used as features. Subsequently, the convolutional neural network (CNN) was used to classify microseismic events. Among them, data from 3600 microseismic events were used as the training set, and data from 1603 microseismic events were used as the test set. Finally, the original waveform data were used as input and compared with the classification results processed with the EMD algorithm. The classification methods of the BP neural network and Radial Basis Function (RBF) neural network were used for verification. The results of the processed features showed a significant increase in accuracy. The classification accuracy of CNN, BP neural network, and RBF neural network are 97.37%, 91.99%, and 94.23%, respectively. The results show that the utilization of the feature processing technique and CNN algorithm in this study demonstrates superior efficacy in microseismic event classification, which can be used in practice.

Energy is the driving force for the failure of rock materials, and the deformation and failure of the surrounding rock of the roadway is the result of energy accumulation, dissipation and release. Based on the theory of elastic-plastic mechanics and the law of energy conservation, the total energy, elastic strain energy, dissipation energy and release energy of the surrounding rock of the roadway are deduced and analyzed, and the relationship between the energy of all the components is revealed. The energy model is developed based on the Fish language embedded in FLAC3D, and the rationality and accuracy of the energy model are verified through elastic and elastic-plastic theoretical analysis; Through the practical engineering application of the energy model, the similarities and differences in the energy calculation results of the surrounding rock of the roadway through the Mohr Coulomb and Mohr-Coulomb strain softening constitutive models are revealed, and it is pointed out that it is more in line with engineering practices to consider the post-peak deterioration of the mechanical parameters of rock. The energy evolution model of the roadway is established, revealing the space-time effect of energy distribution of the surrounding rock of the roadway under different excavation speeds and conditions, and proposing the time lag of energy evolution and the peak circle effect of the elastic strain energy related to rock burst disaster. The research results can provide references for the research of disasters such as impact ground pressure and large deformation of soft rock, and provide some theoretical guidance for the supporting design of the roadway with large deformation of the surrounding rock and impact danger.

The deformation-to-failure process of rock is accompanied by the dissipation and release of energy and is the result of the mutual conversion of energy. The uniaxial compression and uniaxial cyclic loading–unloading testing of rock samples with eight height–diameter ratios (size) was performed using the MTS 816 rock mechanics testing system to determine the effect of the height–diameter ratio on the rock strength, energy accumulation, and dissipation. The influence rules of the height–diameter ratio on the uniaxial compressive strength, deformation parameters, and failure mode of the rock samples were analyzed. The total, elastic, and dissipated energy densities absorbed by the rock samples with various height–diameter ratios were obtained through calculation, and the evolution and distribution rules of the size effect on energy accumulation and dissipation were revealed. The energy density of rock samples with various height–diameter ratios increased nonlinearly with the increase in the cycle index or axial stress, whereas the energy density of the rock sample decreased with the increase in the height–diameter ratio. At the pre-peak stage, the elastic energy accumulated in the rock samples was higher than the dissipated energy, and the proportion of the elastic energy density was greater. With the increase in the height–diameter ratio of the rock sample, the proportion of elastic energy approximately increased, and the proportion of dissipated energy decreased.

The argillaceous surrounding rock of a horsehead roadway under high stress conditions is prone to deformation and failure, and the control of its long-term stability is difficult. Based on the engineering practices that control the argillaceous surrounding rock of a horsehead roadway in the return air shaft in the Libi Coal Mine in Shanxi Province, field measurements, laboratory experimentation, numerical simulation, and industrial tests are used to analyze the main influencing factors and mechanism of the deformation and failure of the surrounding rock of the horsehead roadway. We propose principles and countermeasures to control the stability of the horsehead roadway. The main factors of the surrounding rock failure of the horsehead roadway include the poor lithology of argillaceous surrounding rocks, horizontal tectonic stress, the superimposed influence of additional stress from the shaft and construction disturbance, the small thickness of the anchorage layer in the roof, and the insufficient depth of floor reinforcement. The results show that the shaft’s presence increases the horizontal stress peak and stress concentration range in the roof, and the plastic zone range. The stress concentration and plastic zones and deformations of the surrounding rock increase significantly with the increase in horizontal tectonic stress. The control principles for the argillaceous surrounding rock of the horsehead roadway include increasing the thickness of the anchorage ring, the floor reinforcement exceeding the minimum depth, and reinforced support in key positions. The key control countermeasures include an innovative prestressed full-length anchorage for the mudstone roof, active and passive reinforcement technology with cables, and a reverse arch for floor reinforcement. The field measurements show that the control of the surrounding rock using the prestressed full-length anchorage of the innovative anchor-grouting device is remarkable.

超细水泥的发明主要是为了解决因普通水泥颗粒粒径较大无法有效注入微细裂缝的难题.超细水泥兼具普通水泥的耐久性好和化学浆材的流动性高的优点,成为水泥基材料由传统材料转向高新技术材料发展的重要开端,在工程中受到广泛使用.本文回顾和总结了近20年来国内外学者对于超细水泥研究所取得的主要进展,对比分析了干磨法和湿磨法制作超细水泥的生产工艺及其优缺点;比较了超细水泥区别于普通水泥的流动性、体积稳定性和力学性能;总结了粉煤灰和矿粉等掺料的加入对超细水泥浆液的性能影响,并在此基础上,对超细水泥在加固和封堵技术中的应用进行了总结,旨在为超细水泥的生产工艺、基本性能以及相关工程应用提供相关参考.

受多次开采扰动影响,多中段联合开采过程中采场围岩稳定性差,地压显现剧烈,采矿进路支护难.以白象山铁矿?470,?430和?390 m中段联合开采工程为研究背景,采用大型相似材料模型试验及采场围岩数字照相变形量测技术,揭示多中段联合开采采场围岩应力变化特征及上覆岩层移动规律.研究结果表明:各中段逐分层向上回采对上覆岩层产生了累积叠加扰动效应,导致采场围岩反复承受荷载(多次扰动)而失稳破坏;各分层矿体下沉量随开采步的推进呈先增大后减小的趋势,采空充填区中部位置附近覆岩的下沉量最大,采场围岩变形具有明显的阶段性增长特征.各中段保留矿体(顶柱)对维持采场围岩稳定、减弱相邻中段间的采矿扰动和降低上覆岩层的变形破坏有积极的作用,受多中段联合开采扰动影响较大、完整性破坏严重的中段保留矿体中的应力可突然释放,出现了局部或整体失稳,威胁采场围岩整体稳定性.确定多中段联合开采扰动条件下采矿进路切圆拱断面形式,其拱高为2.0 m,提出锚网索喷联合支护技术,有效控制采矿进路围岩变形与破坏.

The deformation-to-failure process of rocks is accompanied by energy dissipation and release, indicating that it is an energy conversion process. To investigate the influence of lithology as well as the loading and unloading rates on the evolution and distribution of rock energy, the MTS 816 rock mechanics testing system was used for performing uniaxial compression and uniaxial cyclic loading–unloading tests on the 165 samples of four rock types. The total energy density, elastic energy density, and dissipated energy density absorbed by rocks of different lithology were obtained, and the evolution and distribution laws of lithology and loading and unloading rates on the accumulation and dissipation of rock energy were investigated. The results revealed that the energy density of all rock samples increased nonlinearly with the increase in axial stress, and the elastic energy density increased gradually first and subsequently rapidly with the increase in the axial stress. The evolution curves were not affected by the loading and unloading rates. The dissipated energy density increased gradually with the increase in axial stress, and the discrepancy of the evolution curve was large. The proportion of the elastic energy density varied nonlinearly with the increase in axial stress or the cycle index, exhibiting the evolutionary process of increasing, then stabilizing, and finally decreasing. However, the proportion of the dissipated energy density exhibited an opposite trend. The elastic energy accumulated in the rock sample at the pre-peak stage was considerably higher than the dissipated energy, and the proportion of the elastic energy density was large. With the increase in loading and unloading rates, the proportion of elastic energy exhibited an approximate growth trend, and the proportion of dissipated energy exhibited an approximate decreasing trend.