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The management of rock mass deformation in high-stress roadways is a pivotal aspect of deep geotechnical engineering. Given the fruitful outcomes of research in rock mechanics regarding traditional confining pressure control methods, scholars have increasingly turned their attention to exploring pressure-relieving techniques, including borehole pressure relief and blasting pressure relief. However, there is limited research on pressure relief methods for deep-buried hard rock tunnels. This article commences with an overview of pressure relief in the roadway and conducts a detailed study on the parameters and methods of pressure relief in the roadway. To address safety and mining efficiency challenges, such as severe deformation leading to support failures, this study conducted a parameter analysis using the Sanshandao Gold Mine as a case study. Based on existing support methods, a strategy for arranging pressure relief roadways at varying distances from the main roadway is proposed, significantly enhancing the stress environment there. Numerical simulation software was employed to model two scenarios: (1) excavating the pressure relief roadway, main roadway, and maintenance roadway simultaneously and (2) first excavating the pressure relief roadway, followed by the main roadway and the maintenance roadway simultaneously. Simulation results indicated that the first pressure relief approach outperforms the second. The optimal position for both pressure relief roadways is 15 m from the main roadway, resulting in maximum deformation of the main roadway within 100 mm. These findings align with on-site stress monitoring data and satisfy safety production criteria. The research offers a theoretical foundation for similar pressure relief techniques in deeply buried, high-stress roadways. [ABSTRACT FROM AUTHOR]

Investigating the correlation between acoustic emission (AE) parameters and damage mechanisms in rock mechanics can help understand rock damage evolution under loading and provide a theoretical basis for engineering support and safety detection. Therefore, this paper presents experimental works on the correlation between AE and failure mechanisms of rock mass under uniaxial compression stress, with the aim of capturing the damage evolution leading to a new damage constitutive model. The experimental results indicate that the uniaxial compression process of shale can be divided into four stages according to AE characteristics. AE signals are minimal during the crack compaction and elastic stages. The crack initiation strength σci, which is approximately 55% of the uniaxial compressive strength, is identified when the cumulative AE counts and damage factor begin to increase slowly. When axial stress reaches the damage strength σcd, which is approximately 80% of the uniaxial compressive strength, a significant number of AE signals are generated. AE phenomena can be observed during the unstable crack development and post-crack stages. Considering the initial damage to the rock, the damage factor D initially decreases and then increases with increasing cumulative ring-down counts rather than exhibiting a monotonic increase. The damage factor D is proportional to the cumulative AE counts N in the stage before rock failure. [ABSTRACT FROM AUTHOR]

In order to solve the problem that the broken rock mass is easy to collapse and fall during the excavation of a submarine gold mine, two kinds of bolt-mesh-concreting combined support schemes are designed by means of field engineering geological investigation, indoor rock mechanics test, rock mass quality classification, and theoretical analysis. We use the numerical simulation for verification and carry out the field industrial test. The results show that the stability grade of broken surrounding rock is III–IV; both schemes can effectively control the deformation and failure of surrounding rock. Compared with the unsupported scheme, the maximum roof displacement in the scheme using roadway roof and sidewall support is reduced by 26.9%, the maximum thickness of the roof plastic zone is reduced by 58.2%, and the volume of the surrounding rock plastic zone is reduced by 26.32%. The bolt-mesh-shotcrete support has good control effect on the loose deformation of surrounding rock, which can effectively prevent the roof collapse and sidewall spalling of roadway. The field industrial test of support scheme meets the stability control requirements of broken rock mass in mines, and the application effect is obvious. The research results presented in this study provide valuable technical guidance and essential insights for the design of support systems in other similar mining projects, contributing to the effective control and stability of broken rock masses during excavation. [ABSTRACT FROM AUTHOR]

Rock grain size parameter is the key parameter of reservoir rock physics analysis. The study found that the relationship between the NMR T 2 spectrum and rock grain size distribution curve is directly related to NMR T 2 distribution and grain size distribution of rock, so you can use T 2 to retrieve the size distribution of rock NMR spectral data. Based on the calculation of the rock core experiment results of grain size distribution by NMR T 2 distribution using the conversion method of piecewise nonlinear calibration for each core, adjusting the calibration parameters to make the grain size distribution calculated with the core analysis of grain size distribution approximation, the error is minimum to obtain each core scale parameter conversion. In the end, the core parameters are classified according to the parameters of pore and permeability. Finally, according to the actual NMR T 2 distribution curve inversion of underground rock granularity, the inversion results contrast with the core analysis results, and the reliability of the method is verified to provide accurate, continuous rock size distribution profile analysis of geological reservoir rock physics. [ABSTRACT FROM AUTHOR]

The mechanical property of deep complex jointed rock mass is a hot topic in rock mechanics. In order to grasp the deformation and damage rules of through-going variable dip joint rock masses, the triaxial compression test and joint surface morphology scan test were conducted on cylindrical specimens in dry and wet conditions under 0, 5, 10, and 20 MPa water pressure. Through these tests, the deterioration law of rock samples under different pore water pressure in dry and wet conditions was studied. The effect of pore water pressure on the strength of saturated jointed rock sample is nonlinear. The imposed pore water pressure can significantly increase the axial deformation of rock samples, and higher pore water pressure can facilitate the deformation deterioration of samples. When the pore pressure is high, the rock samples show the characteristics of sliding shear failure. Under different pore pressure, the compressive strength of dry jointed rock is significantly higher than that of saturated jointed rock, and the saturated rock is more susceptible to sliding in the joint plane than dry rock. Dry jointed rock samples have stronger deformation ability than saturated jointed rock samples. The change rate of the morphologic parameters and the distribution of the failure cracks indicate that the stress concentration is evident in the middle of the joint plane. [ABSTRACT FROM AUTHOR]

To study the effect of saturation on the freeze-thaw damage of fractured rocks in cold regions, five prefabricated oval double-hole red sandstones with different saturations were prepared. Three-dimensional images of rock fractures were obtained by CT technology. The freeze-thaw damage mechanism and critical saturation of the red sandstone were explored through the fracture propagation evolution and quantitative characterization of the pore structure. The experimental results show that the pore size distribution can reflect the complex pore structure. Pores can be divided according to their sizes: small pores, mesopores, and macropores; mesopores account for the largest proportion and more than 70% of the total, and the proportion of mesopores in high-saturation sandstone (90% or 100%) increases under the action of freeze-thaw cycle. This is also accompanied by a small increase in the proportion of macropores. An 80% critical saturation of the sandstone was obtained. In addition, prefabricated cracks make the ice separation mechanism more likely to occur. The low-saturation sandstone mainly damaged the fracture area during freeze-thaw cycles, while the prefabricated cracks provided a good seepage channel for high-saturation sandstone. The corresponding rock bridge area eventually demonstrated a connectivity trend. This study more realistically reflects the freeze-thaw damage of actual rock masses in cold regions and provides a theoretical basis for the prediction of rock mass engineering disasters in cold regions. [ABSTRACT FROM AUTHOR]

Based on similar model tests and finite element simulations, inversion study of the mechanical parameters of the tunnel surrounding rock by combining artificial fish swarm algorithm (AFSA) and digital scattering correlation method is carried out. The inversion of the mechanical parameters of the tunnel surrounding rock is carried out by iterating the optimization algorithm to minimize the objective function value through similar model test with the displacement measurements obtained by the digital scattering correlation method as the known quantity and the nodal displacement simulation values obtained by numerical simulation as the unknown quantity. The results show the following: (1) The new research idea proposed in this paper is effective and feasible and can perform the inversion calculation of the parameters of the soft and weak tunnel surrounding rock. (2) Through the inversion calculation, the parameters related to the surrounding rock show a wave-like change: the parameters increase in the initial and final compaction stages due to the small deformation rate of the tunnel and decrease in the continuous loading stage due to the increasing deformation rate of the tunnel. (3) The displacement field calculated by DSCM in the test is basically the same as the displacement distribution characteristics of the numerical simulation displacement cloud map, and the error of nodal displacement value is within 3%. [ABSTRACT FROM AUTHOR]

The southeast region of Tibet in China is prone to earthquakes at high seismic levels. Since the construction of tunnels in this region faces a seismic hazard, it is necessary to explore the seismic responses of related construction areas there. In this study, a high-precision finite model of a mountain in a construction area was established based on a deep-buried tunnel in Southeast Tibet. Core specimens were obtained through on-site drilling, with the initial tectonic stress in the tunnel area measured by using the hydraulic fracturing method. Dynamic mechanical parameters of the rocks were acquired through in-situ testing. Moreover, indoor tests were conducted to obtain the physical and mechanical properties of the rocks. The tectonic stress, identified through multiple linear regression inversions, was used as the initial condition for dynamic calculation. The dynamic responses of the tunnel-engineering area under seismic action were calculated, followed by an analysis of the dynamic response characteristics. In addition to dramatic fluctuations in mountain topography, complex dynamic response characteristics of the mountain structure in earthquake environments were also revealed. Although the displacement time-history curve of each observation point displayed a consistent fluctuating pattern, the dynamic displacement extremes in different areas of the mountain varied significantly when the time arrived for their appearance. A maximum dynamic displacement of 0.53 m was observed at the observation point with the highest elevation (5,265.8 m). The acceleration amplification effect inside the mountain body was obvious, with the acceleration increasing as the elevation rose. The time for the occurrence of PGA (acceleration extreme) of each observation point in different directions differed substantially. The extreme value of dynamic stress along the tunnel axis conformed to the distribution pattern of the initial tectonic stress. Compared to the initial tectonic stress, the dynamic stress increased significantly at all observation points along the tunnel axis, with the dynamic stress increasing at a larger rate in the areas at a greater buried depth. Horizontal dynamic stress Sx at the maximum buried depth and Sy increased to 13.86 MPa and 10.32 MPa, respectively, and vertical dynamic stress Sz increased to 4.30 MPa. Variations in horizontal stress became more apparent as the elevation rose, in contrast to weakened variations in vertical stress as the elevation dropped. This study aims to explore the dynamic responses of mountains and the variation law of tectonic stress in deep-buried tunnels in earthquake environments in Tibet through qualitative analysis. The results revealed drastic changes in acceleration, dynamic displacement, and ground stress in the tunnel-engineering area. It is hoped that the contents of the study will contribute to the prevention and control of seismic geological hazards in the tunnel-engineering region and render technical support for the design and construction of similar projects in this region. [ABSTRACT FROM AUTHOR]

To investigate the energy evolution and storage characteristics of the rock during the mixed-mode fracture failure, several single loading-unloading tests under preset different unloading levels were conducted on the cracked straight-through Brazilian disc (CSTBD) red-sandstone specimen with crack inclination angles of 10° and 20°. The input energy, elastic energy, and dissipated energy parameters were obtained by calculating the area integral of the load-displacement curve. Test results display that the total input energy, elastic energy, and dissipated energy of rock specimens increase in quadratic function with the increase of unloading level at different unloading levels. It was found that there are significant linear energy storage and dissipation laws of rock during the mixed-mode fracture process. The concepts of fracture energy storage coefficient (FESC) and fracture energy dissipation coefficient (FEDC) were proposed to express the energy variation of rock in the prepeak stage. Under the same loading conditions, FESC and FEDC remain unchanged regardless of crack inclination angles, indicating that the linear energy storage and dissipation laws are an inherent property of the rock. Besides, the peak fracture elastic-dissipation index W ed (the ratio of peak elastic energy to peak dissipation energy) was obtained through quantitative analysis and demonstrated its invariant feature. [ABSTRACT FROM AUTHOR]

In order to establish prediction models for the mechanical parameters of rock freeze-thaw damage based on nuclear magnetic resonance (NMR) technology, with reference to the laboratory test of rock mechanical parameters after freeze-thaw, combined with low-field NMR and multivariate analysis methods, PLSR and PCR prediction models for the peak stress, peak strain, and elastic modulus of frozen-thawed rocks were established. The results show that the correlation coefficient of calibration set ( R 2 cal ) and validation set ( R 2 val ) of the PLSR and PCR prediction models are both greater than 0.9, and the residual prediction deviation (RPD) of each model is greater than 3, indicating that the established prediction models have good stability, small relative error, and high prediction accuracy. The application evaluation results show that the peak stress and peak strain of frozen-thawed rocks can be accurately predicted using these models. In this paper, only the NMR tests are performed on the frozen-thawed rocks, and no rock mechanics experiments are performed. The research results provide a new method for the research of rock freeze-thaw damage. [ABSTRACT FROM AUTHOR]

Rock burst is one of the most sophisticated and threatening problems in the process of mining activities of underground coal mines, which can evolve into phenomena such as gas outburst, violent ground pressure behavior of surrounding rock of stope roadway, and high dynamic load energy event of roof overburden fracture through the interaction between various influencing factors. This paper deeply studies the causes, consequences, and disaster mechanism of "2–2 rock burst accident" in Xinjulong coal mine, gives the network diagram of the relationship between the main influencing factors of fault type rock burst and high-energy events, establishes a mechanical model on this basis, and explores the influence and evolution law of fault influencing factors on the elastic strain energy field of surrounding rock of stope roadway. [ABSTRACT FROM AUTHOR]

The size effect on the bulk modulus of rocks has been reported by previous studies. The accuracy in selecting the parameter for the rock mechanics analysis determines further accuracy of the calculation results. Moreover, given the influence of the size effect and joint spacing, the rock bulk modulus often changes. Thus, it is essential to examine the size effect on the bulk modulus. This study elucidated the influence of rock size and parallel joint spacing on the bulk modulus using the regression analysis and 12 sets of numerical plans. The results demonstrated that the bulk modulus decreased with an increase in rock size, and the curve represents an exponential function. The bulk modulus linearly increased as the parallel joint spacing increased. Furthermore, the characteristic size of the bulk modulus linearly decreased as the parallel joint spacing increased. In contrast, the characteristic bulk modulus linearly increased as the parallel joint spacing increased. The specific forms of these relationships were also elucidated in this study. [ABSTRACT FROM AUTHOR]

The depth of shale oil of Fengcheng Formation in Mahu of Junggar Basin, China, is 4500-5000 m. The horizontal principal stress difference of deep shale reservoir is high, which makes it difficult to form complex fractures during fracturing reconstruction. In order to fully understand the law of hydraulic fracture propagation in the formation during fracturing construction, the anisotropy characteristics and basic reservoir physical parameters (mineral composition and rock strength parameters) of rock were obtained through mineral composition test and indoor rock mechanics test (Brazil splitting test), and it was found that the heterogeneity was strong. The true triaxial fracturing simulation experimental system is used to carry out experimental research on full-diameter core rock samples, and the propagation patterns of hydraulic fractures under the influence of different geological factors (in situ stress difference and natural fractures) and engineering factors (pumping rate and fracturing fluid viscosity) are compared and analyzed. The results show that the in situ stress is the most important factor affecting fracture propagation, which determines the direction and shape of fracture propagation. The natural weak surface (lamina/bedding and natural fractures, etc.) in shale reservoir is an important reason for complex fractures. The nature of the weak plane, occurrence, and in situ stress jointly determine whether the fracture can extend through the weak plane. With the increase of pumping rate (18 mL/min to 30 mL/min), the ability of hydraulic fractures to penetrate layers is continuously enhanced. The horizontal principal stress difference of deep shale reservoir is high, and the low viscosity fracturing fluid (10 mPa·s) tends to activate the horizontal bedding, while the high viscosity fracturing fluid (80 mPa·s) tends to directly penetrate the bedding to form the vertical main fracture. Therefore, the fracturing technology of alternating injection of prehigh viscosity fracturing fluid and postlow viscosity fracturing fluid can be adopted to maximize the complexity of fracturing fractures in deep shale reservoirs. The research results are designed to provide theoretical guidance for prediction of hydraulic fracturing fracture propagation in shale reservoir and have certain reference significance for field construction. [ABSTRACT FROM AUTHOR]

In recent years, the phase field fracture model has been widely studied and applied. It has good convergence in crack propagation simulation. Comparing with other methods, the phase field method has advantages in simulating crack intersection, bifurcation, and three-dimensional propagation. Based on the phase field method, the influence of excavation disturbance on crack initiation of rock mass is realized in this paper. The phase field fracture variational model is built by using user-defined element interface (UEL) and user material subroutine (UMAT) in ABAQUS. Firstly, the prefabricated crack propagation simulation is carried out to verify the algorithm. The fracture initiates in a butterfly shape and then expands along the horizontal direction. The results show that the maximum support reaction decreases with the gradual increase of l , which is compared with the results obtained by Miehe et al. The result proved the correctness and reliability of the algorithm. In this paper, the phase field fracture model of a flat plate with a reserved small hole under the upper tension is established. The results show that the crack finally produces a crack in the lower left and upper right directions of the square hole and continues to extend to the model boundary, which proves the feasibility of crack independent initiation and propagation by the phase field method. The stress formed a butterfly region until the fracture occurs. And the butterfly stress distribution was still present at the end of crack propagation. The maximum vertical stress was 1.7 × 103 MPa. Based on the South-to-North Water Transfer Project, the simulation of tunnel crack propagation under excavation disturbance is realized for the first time, which is based on the phase field method. The results show that the influence area of excavation disturbance will increase after considering crack development. Comparing the simulation results without considering crack propagation with the simulation results considering crack propagation, it is found that the stress level in the excavation disturbance area around the tunnel is greatly affected by cracks. When the crack is not considered, the maximum vertical stress is 2.16 × 105 Pa, and the maximum horizontal stress is 9.35 × 105 Pa, which occurs at the waist of the tunnel on the horizontal axis. When the crack is considered, the maximum vertical stress is 2.53 × 105 Pa, and the maximum horizontal stress is 1.10 × 106 Pa. It shows that the stress at the dome increases greatly. The vertical stress reaches 3.68 × 105 Pa, and the horizontal stress is up to 3.07 × 103 Pa. For the rock mass far away from the excavation disturbance area, because part of the elastic strain energy is absorbed by the surface crack, the stress level considering the crack is lower than that without the crack. But it is basically similar, indicating the accuracy of the phase field fracture model. This paper realizes the simulation of crack propagation under excavation disturbance and provides a way for the application of phase field fracture model in rock mechanics. This paper proves that phase field method has broad prospects in simulating rock crack propagation and provides the possibility for the popularization of phase field method. [ABSTRACT FROM AUTHOR]

The constitutive equation of rock and soil has always been the core problem in rock and soil mechanics. Up to now, the nature of nonlinear shear strength of rock and soil has not been revealed. In many engineering practices, it is still considered that the failure mode of rock and soil is always shear failure, and Coulomb linear constitutive equation is adopted, or Mohr envelope is fitted by data. However, the constitutive equation of rock mass is nonlinear, and its failure mode is not only shear failure. A large number of single triaxial tests show that there is not only shear stress, but also tensile stress in the failure process of rock and soil. Theoretical and experimental research on failure mode of rock mass under pressure are one of the important means to improve and develop soil mechanics. It is important to understand the nonlinear nature of rock and soil constitutive equation to explore the energy variation and the distribution of tensile stress and shear stress in different failure modes of rock and soil. [ABSTRACT FROM AUTHOR]

As a major hidden danger of mine safety production, the impact resistance tendency of rock seriously restricts the safety and high yield of coal mine. At the same time, as one of the puzzles of rock mechanics, it has been perplexing many domestic and foreign scholars since the recorded rock burst in South Stafford coal mine in 1738. At present, this research is relatively weak; so, it is different for economic and social benefits. The study of the impact resistance law and the antishock measures of water-bearing rocks are extremely meaningful. In order to deeply explore the impact resistance law of rock with different water content and the antishock support measures after roadway excavation, based on the previous research results of the previous research, the impact tendency of different coal samples was firstly tested by coal uniaxial compression experiment, judging and then calculating the damage characteristics of rock with different water content according to the obtained data, as one of the judgment basis of the impact law of coal mine. Secondly, according to the experimental data, the energy evolution characteristics are calculated and analyzed with the graph. Finally, the impact tendency of the rock under different moisture conditions is obtained. [ABSTRACT FROM AUTHOR]

In this study, based on the example of the ground vibration damage response of a thick and hard rock layer fracture type mine quake, and by applying the theories of mine pressure, rock mechanics and vibration energy principle, the concept of "vibration damage boundary" of mine quake ground, which uses particle vibration velocity to evaluate the vibration damage, is proposed. In addition, the quantitative prediction method of the ground vibration damage boundary is preliminarily established. The research results reveal that the elastic deformation of the fixed support end of the thick and hard rock layer structure in the stope is the main energy source for the formation of mine quakes, and that the particle vibration velocity caused by the propagation of focal energy to the ground can reasonably reflect the response degree of vibration damage. The proposed prediction method considers the "instantaneous" motion characteristics of mining thick and hard rock layer and the dynamic load effect of "mine quakes." The method can deepen our understanding of mining ground damage prediction, and increase the reliability of ground damage boundary prediction. Finally, the results are used to predict the ground vibration damage boundary of limestone primary fracture in the longwall 16101 face of the Fuping Coal Mine. [ABSTRACT FROM AUTHOR]

A rock creep constitutive model is the core content of rock rheological mechanics theory and is of great significance for studying the long-term stability of engineering. Most of the creep models constructed in previous studies have complex types and many parameters. Based on fractional calculus theory, this paper explores the creep curve characteristics of the creep elements with the fractional order change, constructs a nonlinear viscoelastic-plastic creep model of rock based on fractional calculus, and deduces the creep constitutive equation. By using a user-defined function fitting tool of the Origin software and the Levenberg–Marquardt optimization algorithm, the creep test data are fitted and compared. The fitting curve is in good agreement with the experimental data, which shows the rationality and applicability of the proposed nonlinear viscoelastic-plastic creep model. Through sensitivity analysis of the fractional order β2 and viscoelastic coefficient ξ2, the influence of these creep parameters on rock creep is clarified. The research results show that the nonlinear viscoelastic-plastic creep model of rock based on fractional calculus constructed in this paper can well describe the creep characteristics of rock, and this model has certain theoretical significance and engineering application value for long-term engineering stability research. [ABSTRACT FROM AUTHOR]

Current energy to "release" after accumulating + first for the mechanism of rock bursts occurred in analysis of the strategy is accepted by many scholars, based on the existing means of prevention and control of percussive ground pressure, from the angle of the prevention and control of design of the mechanism of impact ground pressure energy regulation, namely, "weakened after the first release +" softened water injection measures and "lead after the first release +" drilling pressure relief measures, for the study of mining under the action of a strong shock tendentiousness rock energy regulatory mechanism; based on rock mechanics experiment, the analysis under different modification measures should be variant energy storage mechanisms of induced damage evolution of rock energy. The mechanism of energy evolution in the modification of strong bursting liability roof rock is revealed. The results show that different modification regulation measures can effectively change the physical and mechanical parameters of target rock samples and realize "hard rock softening or soft rock hardening." Samples under different modification measures are classified as initial consolidation stage, elastic stage, stage of plastic deformation, yield failure stage, and late stage, the energy evolution is roughly the same as the sample complete natural condition, but the yield failure stage and the destruction of late stage have an obvious difference, which provides favorable conditions for impact ground pressure to prevent. With the help of three characteristic energy indexes of total strain, elastic strain energy, and dissipative strain energy of rock samples, the evolution law of energy indexes under different modification control measures is analyzed. The index of elastic energy consumption ratio is introduced as a precursor feature of rock instability and failure, which indicates the rock impact tendency to a certain extent. The energy regulation mechanisms of "first release+then weakening" water injection softening measures and "first release+then guidance" drilling pressure relief measures are explained theoretically, respectively. However, we should focus on the defects of the corresponding control measures and finally try to make a reasonable combination of different modification measures. Finally, the gradient pressure relief scheme should be considered in order to avoid large stress drop caused by large-scale pressure relief in the region and aggravate the instability of rock mass. The instability of rock mass is further aggravated. [ABSTRACT FROM AUTHOR]

A discrete element method code was used to investigate the damage characteristics of jointed rock masses under repetitive impact loading. The Flat-Joint Contact Model (FJCM) in the two-dimensional particle flow code (PFC2D) was used to calibrate the microparameters that control the macroscopic behavior of the rock. The relationship between macro- and microparameters by a series of uniaxial direct tension and compression numerical tests based on an orthogonal experimental design method was obtained to calibrate the microparameters accurately. Then, the Synthetic Rock Mass (SRM) method that incorporates joints into the calibrated particle model was used to construct large-scale jointed rock mass specimens, and the repetitive drop hammer impact numerical tests on SRM specimens with different numbers of horizontal joints and dip angle joints were carried out to study the damage evolution, stress wave propagation, and energy dissipation characteristics. The results show that the greater the number of joints, the greater the number of cracks generated, the greater the degree of damage, and the more energy dissipated for rock masses with horizontal joints. The greater the dip angle of joints, the less the number of cracks generated, the less the degree of damage, and the less energy dissipated for rock masses with different dip angles of joints. The impact-induced stress waves will be reflected when they encounter preexisting joints in the process of propagation. When the reflected stress waves meet with subsequent stress waves, the stress waves will change from compressional waves to tensile waves, producing tensile damage inside rock masses. [ABSTRACT FROM AUTHOR]

In situ stress is the natural stress existing in the stratum without engineering disturbance, also known as initial stress, absolute stress, or original rock stress. In order to master the in situ stress of the Manmushu Tunnel and Mamo Tunnel in Southwest China, the casing stress solution method is adopted in this paper. Through the combination of field measurement and laboratory test, the basic data such as initial strain during stress relief are collected, and the in situ stress values are analyzed in combination with indoor temperature compensation test, confining pressure calibration, and relevant rock mechanics tests. The measured results show the following: (1) the maximum horizontal principal stress σh.max ranges from 6.44 MPa to 19.74 MPa; the vertical principal stress σ v ranges from 4.11 MPa to 13.48 MPa; and the minimum horizontal principal stress ranges from 4.32 MPa to 11.22 MPa. (2) The maximum horizontal principal stress directions of the five measuring points are all located in the NW direction, which is basically consistent with the maximum principal stress direction of the regional tectonic stress field. The maximum horizontal principal stress (σh.max), the minimum horizontal principal stress (σh.min), and the vertical principal stress ( σ v ) all increase with the increase of buried depth, and the relationship is approximately linear. It is suggested that, in the actual construction process, the construction method and construction parameters should be optimized scientifically and reasonably to reduce the disturbance of blasting on the tunnel surrounding rock. After tunnel excavation, support measures should be taken quickly, timely, and scientifically to reduce and control the deformation of the surrounding rock. [ABSTRACT FROM AUTHOR]

In order to obtain the mechanical behavior and permeability characteristics of coal under the coupling action of stress and seepage, permeability tests under different confining pressures in the process of deformation and destruction of briquette coal were carried out using the electrohydraulic servo system of rock mechanics. The stress-strain and permeability evolution curves of briquette coal during the whole deformation process were obtained. The mechanical behavior and permeability coefficient evolution response characteristics of briquette coal under stress-seepage coupling are well reflected. Research shows that stress-axial strain curve and the stress-circumferential strain curve have the same change trend, the hoop strain and axial strain effect on the permeability variation law of basic consistent, and the permeability coefficient with the increase of confining pressure and decreases, and the higher the confining pressure, the lower the permeability coefficient, the confining pressure increases rate under the same conditions, and the permeability coefficient corresponding to high confining pressure is far less than that corresponding to low confining pressure. The confining pressure influences the permeability of the briquette by affecting its dilatancy behavior. With the increase of the confining pressure, the permeability of the sample decreases, and the permeability coefficient decreases with the increase of the confining pressure at the initial stage, showing a logarithmic function. After failure, briquette samples show a power function change rule, and the greater the confining pressure is, the more obvious the permeability coefficient decreases. [ABSTRACT FROM AUTHOR]

As the scale and depth of mines increase, large deformations of high-steep slopes progressively become prominent. Compared with the ordinary cables, negative Poisson's ratio (NPR) cables can provide a constant resistance force and high deformation inhibition during slope deformation, avoiding the occurrence of slope instability hazards. Consequently, the control effects on the toppling failures of slopes were necessary to be researched. Changshanhao open-pit gold mine was taken as an example; based on the field geological investigation and rock mechanics testing, a three-dimensional engineering geological model of open-pit mine was constructed. Subsequently, the stability of open pit in current situation and final boundary situation was estimated with FLAC3D software, for the potential slope vulnerable areas to be comprehensively identified. Finally, the control effects of ordinary cables and NPR cables on the instable W13 slope section were compared and studied through FLAC3D simulations, and the reinforcement effects of NPR cable on the anti-dip slope were proved as significant; meanwhile, the corresponding reinforcement methods in the failure mine areas were proposed, laying a reference for the instability failure control and reinforcement of similar anti-dip slopes. [ABSTRACT FROM AUTHOR]

The rockburst disaster in the hard rock caused by excavation and unloading of deep underground caverns threatens the safety of engineering construction. In recent years, the microseismic monitoring technology, which can dynamically monitor the whole process of progressive failure of rock mass in real time, has been widely used in rockburst monitoring and early warning of underground engineering. In view of the slight rockburst in local surrounding rock during the excavation of underground powerhouse of Huanggou Pumped Storage Power Station, a rockburst microseismic monitoring system is constructed. And through the analysis of the temporal and spatial activity of microseisms during the monitoring period, the potential risk areas of rockbursts are identified and delineated. The monitoring results show that the microseismic system can effectively capture the blasting and microseismic signals during construction. The microseismic activity is closely related to the intensity of field blasting disturbance. The potential risk areas of rockburst are the upstream side arch shoulder and the intersection between lower drainage corridor and workshop installation room. The research results can provide technical support for later excavation and support of underground powerhouse caverns of Huanggou Hydropower Station. [ABSTRACT FROM AUTHOR]

To investigate the strength characteristics of mudstone in deep-buried coal-measure formation, four types of experiments have been conducted: (i) the X-ray diffraction (XRD) test; (ii) the scanning electron microscope (SEM) scanning test; (iii) the point load strength index test; and (iv) the uniaxial compressive strength test. It was concluded that the mudstone of the deep-buried coal measures in the Longtan Formation is dominated by chlorite, quartz, and albite using the XRD test, of which chlorite is primary, accounting for 74.3%. It was found that the three minerals in the mudstone are unevenly distributed using the SEM scanning test, albite is irregularly distributed in chlorite, and quartz is present in the albite and chlorite. Sixty-five specimens were tested for the point load strength index. After processing the data using the method suggested by the International Society for Rock Mechanics and Rock Engineering(ISRM), it was found that the maximum value of Is(50) was 6.10 MPa, the minimum is 0.14 MPa, and 53% of the specimens' Is(50) values are below 2.0 MPa. The RMT-150C rock mechanics testing machine was used to conduct uniaxial compression tests on six specimens. The maximum uniaxial compressive strength (UCS) value is 59.26 MPa, the minimum value is 31.77 MPa, and the average is 45.64 MPa. Linear fitting and logarithmic fitting are carried out for the correlation between UCS and Is(50). The goodness of fit R2 of the linear fitting is 0.863, and that of the logarithmic fitting is 0.919, indicating a strong correlation between them. When it is challenging to make standard specimens, Is (50) can be used to estimate UCS. [ABSTRACT FROM AUTHOR]

Fracability evaluation is the basis of reservoir fracturing and fracturing zone optimization. The tight sandstone reservoir is characterized by low porosity and low permeability, which requires hydraulic fracturing to improve industrial productivity. In this study, a systematic model was proposed for the fracability evaluation of tight sandstone reservoirs. The rock mechanics tests and sonic tests demonstrated that tight sandstone reservoir is characterized by high brittleness, high fracture toughness, and weak development of natural fractures. Numerical simulation was used to analyze the change of reservoir parameters during hydraulic fracturing and the influence of in situ stress on fracture propagation. The results showed that when the horizontal stress anisotropy coefficient is small, natural fractures may lead hydraulic fractures to change direction, and complex fracture networks are easily formed in the reservoir. The horizontal stress anisotropy coefficient ranges from 0.23 to 0.52, and it is easy to produce fracture networks in the reservoir. A new fracability evaluation model was established based on the analytic hierarchy process (AHP). The fracability of tight sandstone reservoir is characterized by the fracability index (FI) and is divided into three levels. Based on the model, this study carried out fracability evaluation and fracturing zone optimization in the study area, and the microseismic monitoring results verified the accuracy of the model. [ABSTRACT FROM AUTHOR]

With the gradual depletion of shallow resources, deep mining has become an inevitable trend and has become an important part of the world mining industry. The high stress concentration caused by redistribution of original stress field will lead to stress-driven failure of surrounding rock; conventional methods, such as point-location stress measurement, analytical analysis, numerical simulation, and physical modeling, are not able to completely reflect the distribution and evolution characteristics of the mining-induced stress field in real time and at mine scale, so it is difficult to fully understand, control, and prevent mining-induced injuries and fatalities. In the past decades, microseismic monitoring technology, velocity tomography, numerical simulation, and laboratory test technology have been successfully applied to better understand mining-induced stress and rock mass failures. The combination of these methods has led to innovative ways to investigate the mining-induced stress field, surrounding rock failure, and hazard prevention. This review focuses on the mining-induced stress and velocity tomography based on microseismic monitoring data. Research progress in analysis and measurement methods of mining-induced stress, rock mechanics for mining, and velocity tomography practices are presented. [ABSTRACT FROM AUTHOR]

Rock excavation has been the hot spot and frontier of scientific research. Rock excavation research is in a period of rapid development. The bibliographies included in ISI Web of Knowledge database from 1999–2020 were used as data samples, and the collected data were analyzed by literature co-citation and cluster analysis using CiteSpace and VOSviewer information visualization techniques and dynamic network analysis tools. A knowledge map of the evolution of bibliometric research development is drawn to reveal the representative literature in the field of bibliometrics. The hot areas of bibliometric research are introduced. The development trend of bibliometrics is proposed. The results of the study show that the amount of the literature on rock excavation is growing rapidly. A large amount of the foreign literature is available in China, the United States, Australia, Canada, France, and other countries. The main included journals are Tunnelling and Underground Space Technology, International Journal of Rock Mechanics and Mining Sciences, "Rock Mechanics and Rock Engineering," "Engineering Geology," and "Bulletin of Engineering Geology and the Environment." Keyword co-occurrence analysis includes the following contents: rock damage constitutive model, excavation damage area, numerical simulation, stability analysis support, and prediction technology of rock. [ABSTRACT FROM AUTHOR]

To study the lateral deformation characteristics of coal under different confining pressures, coal compression experiments with confining pressures of 0 MPa, 3 MPa, 5 MPa, and 7 MPa were conducted under the same loading rate by using the TAW-2000 electrohydraulic servo rock mechanics experimental machine. The results of the study showed the following: at the initial stage of loading, the lateral strain of coal was about 12.22%–46.9% of the axial strain at the elastic deformation stage and 41.18%–64.96% of the axial strain at the inelastic deformation to peak stress stage. Compared with the experiment under 0 MPa confining pressure, the growth rate of the lateral strain of the coal under 3 MPa, 5 MPa, and 7 MPa confining pressures was much smaller than that of the corresponding axial strain. When the coal was damaged under different confining pressures, the lateral strain was maintained at about 0.6 × 10−2. Based on the field verification, we proposed that the lateral strain during the coal failure and the nonlinear region of the lateral axis ratio changing with time can be used as potential parameters for predicting the coal failure. [ABSTRACT FROM AUTHOR]

A mathematical equation of water drive physical simulation of pressure-sensitive fractured reservoirs was established based on previous research results. In this study, the similarity criteria of water drive physical simulation of pressure-sensitive fractured reservoirs were derived according to the similarity theory. First of all, based on the three-dimensional differential equation of rock mechanics, a dimensionless analysis was conducted to determine the similarity relationship between the displacement of oil by water of pressure-sensitive fractured reservoirs, the similarity criterion was obtained, and the similarity criteria were formed. Secondly, according to the similarity criterion, the similar relationship between the stress-strain fields of the real object and the simulated object was worked out. Thirdly, the finite element software COMSOL Multiphysics was applied to model and calculate the multifield coupling process in the percolation of pressure-sensitive fractured reservoirs, verifying the correctness of the established similarity criteria and similarity relationship. The verifying results shows that the similarity between the physical model and the actual model can be realized by magnifying the geometric size N times in a certain direction and adjusting the load and boundary conditions according to the similarity principle, which can be used for the design of the pressure-sensitive fractured reservoir simulation model for a physical indoor test. [ABSTRACT FROM AUTHOR]

Water injection in coal seams will lead to the increase of moisture content in coal, which plays an essential role in the physical and mechanical properties of coal. In order to study the influence of moisture content on the mechanical properties of soft media, the forming pressure (20 MPa) and particle size ratio (0-1 mm (50%), 1-2 mm (25%), and 2-3 mm (25%)) during briquette preparation were firstly determined in this paper. Briquettes with different moisture contents (3%, 6%, 9%, 12%, and 15%) were prepared by using self-developed briquettes. Uniaxial and triaxial compression tests were carried out using the RMT-150C rock mechanics test system. The results show that the uniaxial compressive strength and elastic modulus of briquette samples increase first and then decrease with the increase of briquette water, while Poisson's ratio decreases first and then increases with the increase of briquette water. When the moisture content is around 9%, the maximum uniaxial compressive strength is 0.866 MPa, the maximum elastic modulus is 1.385 GPa, and Poisson's ratio is at the minimum of 0.259. The compressive strength of briquettes increases with the increase of confining pressure. With the increase of moisture content, the cohesion and internal friction angle of briquettes first increased and then decreased. [ABSTRACT FROM AUTHOR]

Uncertainty is an essential property of rock mechanics and engineering, which is of great significance to excavation, design, and control of rock engineering. In this study, an innovative framework of the reliability-based design was developed for the rock tunnel under uncertainty. The convergence-confinement method is used to characterize the interaction mechanism between the support structure and surrounding rock mass. Artificial bee colony (ABC) was adopted to solve the optimization problem in the reliability-based design. The probabilistic properties of rock strength and failure envelope were obtained based on the triaxial compression test data using the Bayesian method. The reliability of the tunnel and support structure was evaluated based on the abovementioned probabilistic properties of rock strength using the reliability analysis method. A circular tunnel was used to illustrate the developed framework, and the procedure was presented in detail. The time of rockbolt installed, the thickness of the shotcrete, length of rockbolt, circumferential space, and longitudinal space of rockbolt were determined and met the constraints of reliability index. Results show that the developed framework can consider the uncertainty for support design in the tunnel. It provides a good and promising way to support design considering the uncertainty of test data using the reliability-based design. [ABSTRACT FROM AUTHOR]

In order to reveal the influence of prophase stress levels on the fatigue damage characteristics of granite, uniaxial fatigue tests of granite with different prophase stress levels were carried out on the basis of the MTS 815.04 rock mechanics test system. The results show that, under the same number of cycles, the failure degree increases with the increase of the prophase stress level. Under the low upper limit of cyclic stress, the tangent modulus and dissipated energy increase significantly with the increase of prophase stress level at the early stage of the cycle loading, while the increasing trend is not obvious with the increase of prophase stress level at the late stage. Under the high upper limit of cyclic stress, the tangent modulus and dissipated energy are less affected by the prophase stress level. The development trend of elastic release energy is not obvious with the increase of prophase stress level, which is less affected by the number of cycles. From the damage parameters defined by dissipative energy, under the low upper limit of cyclic stress, the initial damage is less affected by the prophase stress level. With the increase of the number of cycles, the influence of the prophase stress level on the development trend of the damage variable increases gradually. And the development trend of damage variables shows "C-shaped" damage. [ABSTRACT FROM AUTHOR]

To accurately obtain the tensile strength of rock and fully understand the evolution process of rock failure is one of the key issues to the research of rock mechanics theories and rock mass engineering applications. Using direct tensile, Brazilian splitting, and three-point bending test methods, we performed indoor and numerical simulation experiments on marble, granite, and diabase and investigated the tensile strength and damage evolution process of several typical rocks in the three different tests. Our experiments demonstrate that (1) the strength is about 10% greater in the Brazilian splitting than in the direct tensile, while the tensile modulus is lower; it is the highest in the three-point bending, which is actually subjected to the bending moment and suggested as one of the indexes to evaluate the tensile strength of rock; (2) the strength in splitting tests is strikingly different, while the strain law is basically similar; the direct tensile test with precut slits is more attainable than that with no-cut slits, with an uninfluenced strength; (3) the failure modes of rocks using different methods are featured by different lithology, while their final modes are basically the same under the same method; (4) PFC and RFPA numerical simulation tests are effective to analyze the internal crack multiplication and acoustic emission changes in the rock as well as the damage evolution process of rock in different tests. [ABSTRACT FROM AUTHOR]

Zonal disintegration refers to the special phenomenon whereby fractured zones and intact zones appear alternately in deep-buried surrounding rocks under high stress conditions, which are different from that of the shallow rock mass. Because the divisional rupture law in engineering practice is closely related to the force characteristics of the bolt body, this paper analyzed stress distribution rules of the same bolt body at different times and that of different bolt bodies at the same time in the case of zonal disintegration based on coordination deformation between the bolt body and surrounding rock. The nonlinear rheological mechanics model of rock mass on the elastic-plastic interface under the maximum support pressure was established. It puts forward the theoretical calculation formula about the mechanics criterion and breakdown moment of the zonal disintegration. Using the mechanics model of interaction between a bolt and the surrounding rock, the distribution locations along the bolt body of the anchor neutral points and its maximum axial forces were discussed with the multiple theoretical neutral points. Furthermore, the location and width of each fracture zone were back analyzed. The results show that the rock mass on the elastic-plastic interface of the surrounding rock has a significant creep effect after the excavation of the deep underground cave. While maximum deviator stress of the rock mass is more than its long-term strength, the rock mass will fracture along a radial direction and come into the fractured zone. The multiple redistribution of the surrounding rock stress will generate alternate distribution phenomena of the fractured zone and intact zone. Meanwhile, the distribution regularity of the peaks and troughs interval of the displacement of surrounding rock leads to multiple neutral points along the anchor length direction. The computed results of zonal disintegration through the back analysis can reflect the actual space-time evolution laws of zonal disintegration in deep underground caves. [ABSTRACT FROM AUTHOR]

The aim of this study is to obtain movement laws of overlying strata above a fully mechanized coal mining face backfilled with gangue and solve the problem of surface subsidence during coal mining. This study was carried out based on gangue backfilling mining of Jiulishan Coal Mine (Jiaozuo City, Henan Province, China) from the perspectives of deformation of backfilled gangue under compaction, surrounding rock of a stope, and activities of key strata. The method combining with rock mechanics, viscoelastic mechanics, control theory of rock mass under mining, and numerical simulation was used based on physical and mechanical characteristics of backfilled gangue. On this basis, the research analyzed the temporal-spatial relationships of activities of surrounding rock of the stope, compressive deformation of backfilling body, failure depth of the floor, deformation characteristics of the main roof with laws of surface subsidence. The movement characteristics of overlying strata above the fully mechanized coal mining face backfilled with gangue and the traditional fully mechanized mining face were compared. It is found that, under the same conditions of overlying strata, movement laws of overlying strata are mainly determined by the mining height of coal seams and the heights of a caving zone and a fracture zone are nearly linearly correlated with the mining height. Through analysis based on thin-plate theory and key stratum theory, the location of the main roof of the fully mechanized coal mining face backfilled with gangue in coal seams first bending and sinking due to load of overlying strata was ascertained. Then, it was determined that there are two key strata and the main roof belongs to the inferior key stratum. By using the established mechanical model for the main roof of the fully mechanized coal mining face backfilled with gangue and the calculation formula for the maximum deflection of the main roof, this research presented the conditions for breaking of the main roof. In addition, based on the theoretical analysis, it is concluded that the main roof of the fully mechanized coal mining face backfilled with gangue does not break, but bends. The numerical simulation results demonstrate that, with the continuous increase of strength of backfilled gangue, the stress concentration degree of surrounding rock reduces constantly, so does its decrease amplitude. Moreover, the compressive deformation of backfilling, failure depth of the floor, and bending and subsidence of the main roof continuously decrease and tend to be stable. The mechanical properties of backfilling materials determine effects of gangue backfilling in controlling surface subsidence. Gangue backfilling can effectively control movement of overlying strata and surface subsidence tends to be stable with the increase of elastic modulus of gangue. [ABSTRACT FROM AUTHOR]

In deep engineering, the initial damage point of host rock has become an important concern. Nowadays, there are many methods which can work out the initial damage point. However, each existing method introduces some significant subjective or parametric errors. In this paper, a new determination method of initial damage point employing step cyclic loading tests was designed and a series of tests were conducted on deep granite. After analyzing the peak strength and effect of cyclic loading, the turning point of initial damage was confirmed. The testing results show that the turning stress of initial damage was about 45% peak strength and will present a little decrease with the confining pressure increasing. These calculated damage points are much more scientific, accurate, and intuitive, which provides a new method for the study on rock mechanics in deep mining. [ABSTRACT FROM AUTHOR]

Many problems are encountered in the construction of bifurcated tunnels due the abrupt change in section, small clear distance, and large section. Progress in the direction of tunnel construction is limited by the large-span section; therefore, a special method of construction that involves constructing a guiding tunnel first followed by reverse excavation was adopted to construct the large-span bifurcation section of the Liantang tunnel of Shenzhen Eastern Transit Expressway in China. The stability criterion of the surrounding rock of the middle wall in the section of multiple arch and small clear distance is studied by theoretical analysis, and the internal stress and corresponding ultimate strength of the middle wall under different buried depths and widths of the middle wall are calculated by the stability criterion. In this study, 3D finite-difference software was used to simulate the excavation process under forward and reverse excavation conditions. The results show that the displacement field and internal force field distribution are similar for both excavation methods, and the tunneling first and reverse excavation construction method is safe and reliable. [ABSTRACT FROM AUTHOR]

The great threat and destructiveness brought by a rock burst make its prediction and prevention crucial in engineering. The rock burst hazard evaluation at project locations is an effective way of preventing rock burst since currently real-time prediction is not available. Since different control factors and discrimination conditions of rock burst were accepted by conventional risk determination methods, the rock burst risk determination in the same area may produce conflicting results. In this study, Naive Bayes statistical learning models based on different model prior distributions representing highly complicated nonlinear relationship between rock burst hazard and impact factors were built to evaluate the rock burst hazards. The results suggested that the Bayes statistical learning model based on a Gaussian prior has the strongest performance over four preset prior distributions. Combining the rock mechanics parameters measured in the laboratory and the stress data collected on the project sites, the proposed model was successfully employed to evaluate the kimberlite rock burst risk of a diamond mine in Canada. The Bayes statistical learning model exhibits its robustness and generalization in rock burst hazard evaluation, which can be generalized for similar engineering cases with enough supported data. [ABSTRACT FROM AUTHOR]

The common failure forms in the uniaxial compression test of standard cylindrical rock specimens are symmetric cone failure and splitting failure. In the past, two kinds of failure forms were explained from the plane problems of elasticity theory. However, there was a lack of research based on space problems. In this paper, based on spatial axisymmetric elastic mechanics theory, three-dimensional stress function is constructed for the cylindrical rock specimen under uniform axial compression by adopting the semi-inverse method. According to the stress function, the stress components and the principal stress are deduced when considering the end effect. The failure form is speculated, which can well explain the two common types of damage in uniaxial compression. This work may enrich the basic research of rock mechanics. [ABSTRACT FROM AUTHOR]

In most mining areas of China, coal seams are characterized by low gas pressure, poor permeability, and high gas adsorption capacity, all of which have brought considerable difficulties to coal seam mining and coalbed methane (CBM) extraction. According to the multiyear scientific research and production practice of China, gas is migrated in quantity only after the coal body is directly mined, and the surrounding rocks deform and fracture under the mining influence. Thus, the key to effective control of gas migration and the coal and CBM comining technology lies in investigating the gas resolution, permeation, migration, and accumulation laws in the coal seams under the unloading confining pressure during mining. The MTS815.02 rock mechanics testing system and its supporting equipment are combined to test the permeability characteristics of coal and rock mass (postpeak fractured coal and sandstone specimens) under the loading and unloading of confining pressure using the steady method, and then, the permeation laws of the fractured coal and rock mass are obtained. Results show that after the postpeak rock crack propagation reaches a stable state, the confining pressure gradually increases, and the gas permeability presents an approximately linear reduction; in the postpeak unloading phase, the opening and coalescence degree of rock cracks gradually increase as the deformation extends. Thus, permeability reaches a peak value. The strain softening phase follows, where the cracks are closed and permeability declines to a certain extent. Moreover, the unloading step size of confining pressure has bearing on gas permeability. Specifically, as the unloading step size of confining pressure decreases, the change of gas permeability increases in stability. [ABSTRACT FROM AUTHOR]

In order to evaluate the coal pillar stability in recovery of residual room pillars under different mining rates, this paper studies the influence of loading rate on the mechanical properties of the coal body. The uniaxial compression tests of coal samples in Yangcheng area at different loading rates were carried out with the MTS815 electrohydraulic servo rock mechanics test system. The stress-strain curves and the evolution characteristics of AE signals were analyzed. At same time, the mechanism of damage and failure of specimens are also discussed. The results show the following. (1) With the increase in loading rate, the ultimate stress and ultimate strain of specimens decrease first and then increase. (2) Loading rate has a significant effect on the stability adjustment of specimens. With the decrease in loading rate, the earlier the stress adjustment is, the larger the adjustment range is, and the failure mode changes from shear failure to tensile failure. (3) In addition, when the loading rate increases, the AE evolves from continuous dense to discrete catastrophe, which indicates that the failure of the sample at a larger loading rate is sudden, which is not conducive to the maintenance of the stability of the coal pillar. (4) Finally, the failure mechanism of the specimen structure under different loading rates is obtained, and the improvement measures for the effect of mining velocity of working face on the stability of coal pillar are put forward. The results reveal the loading rate effect of mechanical properties of coal and provide a reference for controlling the stability of the residual coal pillar. [ABSTRACT FROM AUTHOR]

In order to increase the understanding of the strength and failure mechanism of rock mass during tunnel excavation, a series of uniaxial compression tests were conducted on mortar specimen with cracks and holes by using a rock mechanics servo-controlled testing system. And by monitoring the experimental process, the initiation, propagation, and coalescence process of cracks were observed and characterized. According to the experimental results, the influences of the excavation depth on the mechanical parameters and fracture characteristics of mortar specimens with single hole and the ones with single-hole crack were analyzed in detail. In the specimens with single hole, the peak strength decreases with the increase of hole depth, but the peak strain and elastic modulus have no obvious linear correlation with the hole depth. And the position and angle of initial crack change differently with the increase of the hole depth. The position of initial crack moves from the side of the hole to the top of the hole. When the hole depth exceeds 50%, the crack initiation angle is no longer inclined to the axial stress direction, but parallel to the axial stress direction. In the specimens with single prefabricated crack, the wing-shaped secondary cracks are generated at the tip of the precrack, and the antiwing-shaped secondary cracks are generated at the tip when approaching the peak stress. However, in the specimens with single-hole crack, no antiwing-shaped crack appears. And when the hole depth reaches 80%, two wing-shaped cracks appear at the precrack tip. One of the new wing-shaped cracks appears in the direction of the extension line of the precrack. [ABSTRACT FROM AUTHOR]

Poisson's ratio is of crucial importance for the theoretical and numerical analysis of rock engineering. It is an elastic parameter of the material and the ratio of the absolute value of lateral strain and axial strain when the material is under uniaxial tension or compression. However, it was rarely investigated compared with deformation modulus and strength. Rock materials are different from metal materials. The pure elastic deformation stage is usually very short or nonexistent in the process of uniaxial tension or compression. In this paper, in order to explore the behavior of Poisson's ratio, uniaxial compression tests according to The International Society for Rock Mechanics and Rock Engineering are performed on standard specimens of granite, marble, red sandstone, carbonate rock, coral concrete, etc. According to the results, Poisson's ratio, both the secant Poisson's ratio and tangent Poisson's ratio, increase with the externally applied stress. Therefore, regarding it as an elastic constant is worthy of a second thought. If the midpoint of the stress interval is fixed in the 50% of uniaxial compressive strength, the average Poisson's ratio is almost impervious to the varying span of the stress interval. In addition, the average Poisson's ratio is immune to the nonlinear deformation in the early loading stage. Thus, the average Poisson's ratio is a better index than the secant Poisson's ratio in describing the relationship between axial and lateral strains of hard rocks. The determination of Poisson's ratio of soft rocks needs further investigation because Poisson's ratio tends to exceed the theoretical limit in relatively low stress levels. The proposed viewpoint provides a deeper insight into the testing, determining, and using of Poisson's ratio. [ABSTRACT FROM AUTHOR]

To explore the development mechanism of cracks in the process of rock failure, triaxial compression tests with simultaneous acoustic emission monitoring were performed on granite specimens using the MTS rock mechanics test system. The frequency-domain information of the acoustic emission signal was obtained by the fast Fourier transform. The Gutenberg–Richter law was used to calculate the acoustic emission signals and obtain the b -value dynamic curve in the loading process. Combined with the stiffness curve of granite specimens and acoustic emission signal in the time domain and frequency domain, the crack development characteristics in different stages were analyzed. The results showed that the acoustic emission signals of granite samples under triaxial compression can be divided into four stages: quiet period 1, active stage 1, quiet period 2, and active stage 2. b -value attained its maximum value in the active phase 2 when it is close to the sample loss, and then drops rapidly, which means the propagation of cracks and the formation of large cracks. The acoustic emission signal's dominant frequency was not more than 500 kHz, mostly concentrated in the medium-frequency band (100–200 kHz), which accounted for more than 80%. The proportion of signals in each frequency band can reflect the distribution of the three kinds of cracks, while the change in low-frequency signals can reflect the breakthrough of microcracks and the formation time of macrocracks in granite samples. By fully analyzing the characteristics of acoustic emission signals in the time domain and frequency domain, the time and conditions of producing large cracks can be determined accurately and efficiently. [ABSTRACT FROM AUTHOR]

The abrupt rock-related hazards, such as landslide, rock burst, and collapse, seriously threaten the safety and service life of engineering works. Precursory information on critical transitions preceding sudden fracture is of great significance in rock mechanics and engineering. This study investigates the critical slowing down feature of acoustic emission (AE) signals and precursory indicators during the mode I fracture process of brittle rock. Cracked chevron notched Brazilian disc (CCNBD) specimens were utilized, accompanied by acoustic emission monitoring. The principle of critical slowing down was introduced to study AE count sequences, and the variance and autocorrelation coefficient versus loading time curves were analyzed. The results show critical slowing down phenomenon exists during mode I rock fracture. The variance and autocorrelation coefficient of AE counts grow significantly prior to rock fracture, and thus, the significant growth of variance and autocorrelation coefficient of AE signals can act as the precursory indicator of rock fracture. Compared to the autocorrelation coefficient, the precursors determined by the variance are more remarkable. The time interval between the precursory indicator using the critical slowing down theory and fracture moment ranges from 2% to 15% of the entire loading time. The findings in this study could facilitate better understandings on the rock fracture process and early-warning technique for rock fracture-related geological disasters. [ABSTRACT FROM AUTHOR]

Karst cave collapse usually occurs during the process of drilling and reservoir development. Karst cave collapse increases drilling risk and seriously affects oil production. In order to reveal the collapse mechanism of karst caves in fractured-vuggy reservoirs in Tahe oil field, rock mechanic experiments and numerical simulation studies were conducted. In rock mechanic experiments, three types of rock mechanics tests (uniaxial compression, triaxial compression, and Brazilian splitting) were carried out to obtain the basic rock mechanics parameters. In numerical simulation studies, the collapse conditions of a single karst cave and a cave system were studied. Numerical simulation results indicate that for a single karst cave, the size and geometrical features of karst caves are the main factors influencing collapse condition. For a cave system, a combination pattern and distance between caves are two main factors affecting collapse condition. In order to facilitate the application of these research results, the authors present formulas for calculating the critical conditions of karst cave collapse by means of multivariate linear regression method. The calculation formulas and prediction chart were verified as consistent with actual field results. The research results in this paper have great theoretical and practical value for revealing the mechanism of karst cave collapse in fractured-vuggy carbonate reservoirs. [ABSTRACT FROM AUTHOR]

Rocks in deep coal mines are usually in varying degrees of damage state before they are destabilized by impact loads such as rock bursts. For the problem of the mechanical properties and energy evolution of damaged rocks under impact loads, the authors use static loads with different cyclic load thresholds to act on sandstone specimens to make them in distinct degrees of damage. Then, the rock mechanics system (MTS-816) and the Split Hopkinson pressure bar (SHPB) are employed to perform uniaxial compression and impact dynamics tests on sandstones with different degrees of damage. The results show that, from the perspective of mechanical properties, the uniaxial compressive strength and dynamic compressive strength of the damaged sandstone gradually decrease with the increase of the upper limit of the cycle threshold and both obey the growth law of the quadratic function, and the dynamic strength increase factor (DIF) also decreases with the increase of the cyclic load threshold. In terms of energy, with the increment of the cyclic load threshold, the number of cracks in the damaged sandstone is large and the scale is enormous. Due to the effect of cracks, when the incident energy is a fixed value, the transmission energy decreases with the increase of the damage degree and the change law of the reflection energy is the opposite. The systematic study of the dynamic mechanical properties and energy evolution law of the damaged sandstone provides some reference for the prevention and mechanism research of rock bursts. [ABSTRACT FROM AUTHOR]

In this study, considering the scale effect of rock mass, the influence of different height-to-diameter ratios on rock mechanics and acoustic emission characteristics was studied by using PFC2D software. The damage constitutive model of rock was established, and the damage evolution characteristics of rock with different height-to-diameter ratios were further analyzed. The results showed that, with the increase of height-to-diameter ratio K, the uniaxial compressive strength and peak strain of rock exhibited a gradual decrease; however, the elastic modulus gradually increased. Moreover, rock failure modes exhibited different characteristics under different K values. The scale effect showed little influence on the acoustic emission characteristics in the elastic stage; nonetheless, in the plastic deformation stage and the residual damage stage, with the increase of the rock's height-to-diameter ratio, the maximum number of impacts of acoustic emission increased, the range of strong strain of acoustic emission decreased, and the maximum time of acoustic emission impacts increased gradually. The height-to-diameter ratio of the rock slightly influenced the zero-damage stage of the rock, but the damage affecting the rock increased slowly and accelerated the development stage. The damage evolution law was found to be similar when the K values varied from 1.0 to 2.0; however, when the K was greater than 2.0, the damage evolution law exhibited the characteristics of slowing down in the acceleration phase. [ABSTRACT FROM AUTHOR]

This paper focuses on improving the blasting effect of the drilling and blasting method in the deep rock mass and solves the problems of blasthole collapse and misfire accident in the process of drilling and blasting construction of heading face. FEM software, ABAQUS, is used to simulate the stress distribution around the blasthole by extending a certain depth in the vertical direction of the shaft heading face. The sensitivity of different depths, different heading face sizes, and different lithologies on the horizontal stress distribution is analyzed by using a six-factor four-level orthogonal analysis method. The results show that the change of the radius of the heading face has the most considerable influence on the distance of the distressed zone and the stress concentration zone, followed by the lithology and the excavation depth. Also, the excavation depth has the most significant influence on the peak stress value. Through the industrial field experiment, the in situ stress of the shaft heading face is tested, and the numerical simulation results are consistent with the field monitoring results. The results reveal the law of stress distribution near the heading face, which can provide some reference for the design of blasthole depth in the drilling and blasting construction scheme. [ABSTRACT FROM AUTHOR]