To review the rockburst proneness (or tendency) criteria of rock materials and compare the judgment accuracy of them, twenty criteria were summarized, and their judgment accuracy was evaluated and compared based on the laboratory tests on fourteen types of rocks. This study begins firstly by introducing the twenty rockburst proneness criteria, and their origins, definitions, calculation methods and grading standards were summarized in detail. Subsequently, to evaluate and compare the judgment accuracy of the twenty criteria, a series of laboratory tests were carried out on fourteen types of rocks, and the rockburst proneness judgment results of the twenty criteria for the fourteen types of rocks were obtained accordingly. Moreover, to provide a unified basis for the judgment accuracy evaluation of above criteria, a classification standard (obtained according to the actual failure results and phenomena of rock specimen) of rockburst proneness in laboratory tests was introduced. The judgment results of the twenty criteria were compared with the judgment results of this classification standard. The results show that the judgment results of the criterion based on residual elastic energy (REE) index are completely consistent with the actual rockburst proneness, and the other criteria have some inconsistent situations more or less. Moreover, the REE index is based on the linear energy storage law and defined in form of a difference value and considered the whole failure process, and these superior characteristics ensure its accuracy. It is believed that the criterion based on REE index is comparatively more accurate and scientific than other criteria, and it can be recommended to be applied to judge the rockburst proneness of rock materials.

Core discing often occurs in deep rocks under high-stress conditions and has been identified as an important characteristic for deep rock engineering. This paper presents the formation mechanism of core discing firstly. Then, the interaction between diamond drill bits and rock was analyzed based on numerical modeling. A novel drill bit with an inner conical crown for the mitigation of core discing was designed and verified by simulation experiments. The mitigation method was applied in the cavern B1 of CJPL-II and satisfactory results had been achieved. The percentage of core discing had been obviously decreased from 67.8% when drilling with a rectangular crown drill bit, to 26.5% when an inner conical crown drill bit had been adopted. This paper gives full insight into core discing characteristics and provides a new method for core discing mitigation; it will potentially contribute to stress measurement in deep rock engineering.

Rockburst is a dynamic phenomenon accompanied by acoustic emission (AE) activities. It is difficult to predict rockburst accurately. Based on the fast Fourier transform (FFT) method and the information entropy theory, the evolution model of dominant frequency entropy was established. The AE energy, frequency and stress were synthetically considered to predict rockburst. Under the triaxial and the single-face unloading tests, the relationship between AE energy and the development of internal cracks was analyzed. Using the FFT method, the distribution characteristics of AE dominant frequency values were obtained. Based on the information entropy theory, the dominant frequencies evolved patterns were ascertained. It was observed that the evolution models of the dominant frequency entropy were nearly the same and shared a characteristic “undulation-decrease-rise-sharp decrease” pattern. Results show that AE energy will be released suddenly before rockburst. The density of intermediate frequency increased prior to rockburst. The dominant frequency entropy reached a relative maximum value before rockburst, and then decreased sharply. These features could be used as a precursory information for predicting rockburst. The proposed relative maximum value could be as a key point to predict rockburst. This is a meaningful attempt on predicting rockburst.

Active fault creep slip induces deformation of rock mass buried deeply in fault zones that significantly affect the operational safety of long linear projects passing through it. Displacement distribution patterns of rock masses in active fault zones which have been investigated previously are the key design basis for such projects. Therefore, a discrete element numerical model with different fault types, slip time, dip angles, and complex geological features was established, and then the creep slip for normal, reverse, and strike-slip faults were simulated to analyze the displacement distribution in the fault rock mass. A disk rotation test system and the corresponding laboratory test method were developed for simulating rock mass displacement induced by creep slippage of faults. A series of rotation tests for soft-and hard-layered specimens under combined compression and torsional stress were conducted to verify the numerical results and analyze the factors influencing the displacement distribution. An S-shaped displacement distribution independent of fault dip angle was identified corresponding to reverse, normal, and strike-slip faults. The results indicated that the higher the degree of horizontal extrusion, the softer the rock mass at the fault core, and the higher the degree of displacement concentration in the fault core; about 70% of the creep slip displacement occurs within this zone under 100 years of creep slippage.

Natural geological structures in rock (e.g., joints, weakness planes, defects) play a vital role in the stability of tunnels and underground operations during construction. We investigated the failure characteristics of a deep circular tunnel in a rock mass with multiple weakness planes using a 2D combined finite element method/discrete element method (FEM/DEM). Conventional triaxial compression tests were performed on typical hard rock (marble) specimens under a range of confinement stress conditions to validate the rationale and accuracy of the proposed numerical approach. Parametric analysis was subsequently conducted to investigate the influence of inclination angle, and length on the crack propagation behavior, failure mode, energy evolution, and displacement distribution of the surrounding rock. The results show that the inclination angle strongly affects tunnel stability, and the failure intensity and damage range increase with increasing inclination angle and then decrease. The dynamic disasters are more likely with increasing weak plane length. Shearing and sliding along multiple weak planes are also consistently accompanied by kinetic energy fluctuations and surges after unloading, which implies a potentially violent dynamic response around a deeply-buried tunnel. Interactions between slabbing and shearing near the excavation boundaries are also discussed. The results presented here provide important insight into deep tunnel failure in hard rock influenced by both unloading disturbance and tectonic activation.

To investigate the acoustic emission (AE) precursors of coarse-grained hard rock instability, an experimental study on the rockburst and slabbing process of granite was carried out using a true triaxial test system. The evolution of the AE signals was monitored and analyzed in terms of the AE hit rate, fractal dimension of the AE hit number, AE count rate, b-value, dominant frequency and microcrack type. The test results show that after rock slabbing occurs, the AE precursors that can be used to predict the final dynamic instability (rockburst) are as follows: indicators such as the AE hit rate and AE count rate suddenly increase and then suddenly decrease; the AE hit rate exhibits a “quiet period”; during the “quiet period”, a small number of high-amplitude and low-frequency hits occur, and the signals corresponding to shear fracture continue to increase. The AE precursors for the final static instability (spalling) are as follows: both the AE hit rate and the b-value continuously decrease, and intermittent sudden increases appear in the high-frequency hits or the AE count rate.

Tensile failure (spalling or slabbing) often occurs on the sidewall of deep tunnel, which is closely related to the coupled stress state of deep rock mass under high pre-static load and dynamic disturbance. To reveal the mechanism of rock tensile failure caused by this coupled stress mode, the Brazilian disc tests were carried on red sandstone under high pre-static load induced by dynamic disturbance. Based on the pure static tensile fracture load of red sandstone specimen, two static load levels (80% and 90% of the pure static tensile fracture load) were selected as the initial high pre-static loading state, and then the dynamic disturbance load was applied until the rock specimen was destroyed. The dynamic disturbance loading mode adopted a sinusoidal wave (sine-wave) load, and the loading wave amplitude was 20% and 10% of the pure static tensile fracture load, respectively. The dynamic disturbance frequencies were set to 1, 10, 20, 30, 40, and 50 Hz. The results show that the tensile failure strength and peak displacement of red sandstone specimens under coupled load actions are lower than those under pure static tensile load, and both parameters decrease significantly with the increase of dynamic disturbance frequency. With the increase of dynamic disturbance frequency, the decrease range of tensile strength of red sandstone increased from 3.3% to 9.4% when the pre-static load level is 80%. While when the pre-static load level is 90%, the decrease range will increase from 7.4% to 11.6%. This weakening effect of tensile strength shows that the deep surrounding rock is more likely to fail under the coupled load actions of pre-static load and dynamic disturbance. In this tensile failure mechanism of the deep surrounding rock, the stress environment of deep sidewall rock determines that the failure mode of rock is a tensile failure, the pre-static load level dominates the tensile failure strength of surrounding rock, and dynamic disturbance promotes the strength-weakening effect and affects the weakening range.

To investigate the influence of loading rate on rockburst in a circular tunnel under three-dimensional stress conditions, the true-triaxial tests were conducted on 100 mm×100 mm×100 mm cubic sandstone specimens with d50 mm circular perforated holes, and the failure process of hole sidewall was monitored and recorded in real-time by the microcamera. The loading rates were 0.02, 0.10, and 0.50 MPa/s. The test results show that the rockburst process of hole sidewall experienced calm period, pellet ejection period, rock fragment exfoliation period and finally formed the V-shaped notch. The rockburst has a time lag and vertical stress is high when the rockburst occurs. The vertical stress at the initial failure of the hole sidewall increases with loading rate. During the same period after initial failure, the rockburst severity of hole sidewalls increased significantly with increasing loading rate. When the vertical stress is constant and maintains a high stress level, the rockburst of hole sidewall under low loading rate is more serious than that under high loading rate. With increasing loading rate, the quality of rock fragments produced by the rockburst decreases, and the fractal dimension of rock fragments increases.

To study the mechanism of rockburst and its spatio-temporal evolution criterion, a rockburst simulation experiment was performed on granite specimens, each with a prefabricated circular hole, under different lateral loads. Using micro camera, acoustic emission (AE) system, and infrared thermal imager, the AE characteristics and thermal radiation temperature migration were studied during the rockburst process. Then, the failure mode and damage evolution of the surrounding rock were analyzed. The results demonstrate that increasing the lateral load can first increase and then reduce the bearing capacity of the hole. In this experiment, the hole failure process could be divided into four periods: quiet, particle ejection, stability failure and collapse. Correspondingly, the AE signals evolved from a calm stage, to have intermittent appearance; then, they were continuous with a sudden increase, and finally increased dramatically. The failure of the surrounding rock was mainly tensile failure, while shear failure tended to first increase and then decrease. Meanwhile, damage to the hole increased gradually during the particle ejection period, whereas damage to the rockburst mainly occurred in the stability failure period. The thermal radiation temperature migration exhibited warming in shallow parts, inward expansion, cooling in the shallow parts with free surface heating, inward expansion, a sudden rise in temperature of the rockburst pits, and finally specimen failure. The initial reinforcement support should fully contribute to surface support. Furthermore, an appropriate tensile capacity and good energy absorption capacity should be established in support systems for high-stress roadways.

The deep fissured rock mass is affected by coupled effects of initial ground stress and external dynamic disturbance. In order to study the effect of internal flaw on pre-stressed rock mechanical responses and failure behavior under impact loading, intact granite specimens and specimens with different flaw inclinations are tested by a modified split Hopkinson pressure bar (SHPB) and digital image correlation (DIC) method. The results show that peak strain and dynamic strength of intact specimens and specimens with different flaw angles (α) decrease with the increase of axial static pressure. The 90° flaw has weak reduction effect on peak strain, dynamic strength and combined strength, while 45° and 0° flaws have remarkable reduction effect. Specimens with 90° flaw are suffered combined shear and tensile failure under middle and low axial static pre-stresses, and suffered shear failure under high axial static pre-stresses. Specimens with 45° and 0° flaws are suffered oblique shear failure caused by pre-existing flaw under different axial static pre-stresses. Besides, based on digital image correlation method, it is found that micro-cracks before formation of macro fractures (include shear and tensile fractures) belong to tensile cracks. Tensile and shear strain localizations at pre-existing flaw tip for specimen with 45° and 0° flaws are produced much earlier than that at other positions.

The core-disk phenomenon has been observed generally in the drilling process under high-stress conditions. This paper presents the in-situ experimental study of the coring-disking failure mechanism of marble in an underground cavens with 2400 m depth. Based on the disk samples in several boreholes with different diameters, both macro- and micro-morphological characteristics of core-disks’ break surface were analysis, using 3D optical scanning and electron microscope scanning. Moreover, the numerical back analysis was also used to simulate the drilling process for demonstrating the development of core disking. The in-situ experiment results showed that the failure types of core disking consisted of tensile break and shear break, i.e., the shear break usually appears in the edge part of break surface, and tensile break appears in the central part. What’s more, the ration of core-disks thickness to borehole diameter is in a relatively stable range. Numerical back analysis indicated this micro asynchronous break of hard marble is induced by high geostress and unloading drill.

To investigate the stability of rock mass in high geostress underground powerhouse caverns subjected to excavation, a microseismic (MS) monitoring system was established and the discrete element method (DEM)-based numerical simulation was carried out. The tempo-spatial damage characteristics of rock mass were analyzed. The evolution laws of MS source parameters during the formation of a rock collapse controlled by high geostress and geological structure were investigated. Additionally, a three-dimensional DEM model of the underground powerhouse caverns was built to reveal the deformation characteristics of rock mass. The results indicated that the MS events induced by excavation of high geostress underground powerhouse caverns occurred frequently. The large-stake crown of the main powerhouse was the main damage area. Prior to the rock collapse, the MS event count and accumulated energy release increased rapidly, while the apparent stress sharply increased and then decreased. The amount and proportion of shear and mixed MS events remarkably increased. The maximum displacement was generally located near the spandrel areas. The MS monitoring data and numerical simulation were in good agreement, which can provide significant references for damage evaluation and disaster forecasting in high geostress underground powerhouse caverns.

In this research, a series of biaxial compression and biaxial fatigue tests were conducted to investigate the mechanical behaviors of marble and sandstone under biaxial confinements. Experimental results demonstrate that the biaxial compressive strength of rocks under biaxial compression increases firstly, and subsequently decreases with increase of the intermediate principal stress. The fatigue failure characteristics of the rocks in biaxial fatigue tests are functions of the peak value of fatigue loads, the intermediate principal stress and the rock lithology. With the increase of the peak values of fatigue loads, the fatigue lives of rocks decrease. The intermediate principal stress strengthens the resistance ability of rocks to fatigue loads except considering the strength increasing under biaxial confinements. The fatigue lives of rocks increase with the increase of the intermediate principal stress under the same ratio of the fatigue load and their biaxial compressive strength. The acoustic emission (AE) and fragments studies showed that the sandstone has higher ability to resist the fatigue loads compared to the marble, and the marble generated a greater number of smaller fragments after fatigue failure compared to the sandstone. So, it can be inferred that the rock breaking efficiency and rock burst is higher or severer induced by fatigue loading than that induced by monotonous quasi-static loading, especially for hard rocks.

Cemented backfill used in deep mines would inevitably be exposed to the ambient temperature of 20–60 °C in the next few decades. In this paper, two types of cemented gravel sand backfills, cemented rod-mill sand backfill (CRB) and cemented gobi sand backfill (CGB), were prepared and cured at various temperatures (20, 40, 60 °C) and ages (3, 7, 28 d), and the effects of temperature and age on the physico-mechanical properties of CRB and CGB were investigated based on laboratory tests. Results show that: 1) the effects of temperature and age on the physico-mechanical properties of backfills mainly depend on the amount of hydration products and the refinement of cementation structures. The temperature has a more significant effect on thermal expansibility and ultrasonic performance at early ages. 2) The facilitating effect of temperature and age on the compressive strength of CGB is higher than that on CRB. With the increase of temperature, the compressive failure modes changed from X-conjugate shear failure to tensile failure, and the integrity of specimens was significantly improved. 3) Similarly, the shear performance of CGB is generally better than that of CRB. The temperature has a weaker effect on shear strength than age, but the shear deformation and shear plane morphology are closely related to temperature.

The split-Hopkinson pressure bar (SHPB) and digital image correlation (DIC) techniques are combined to analyze the dynamic compressive failure process of coal samples, and the box fractal dimension is used to quantitatively analyze the dynamic changes in the coal sample cracks under impact load conditions with different loading rates. The experimental results show that the fractal dimension can quantitatively describe the evolution process of coal fractures under dynamic load. During the dynamic compression process, the evolution of the coal sample cracks presents distinct stages. In the crack propagation stage, the fractal dimension increases rapidly with the progress of loading, and in the crack widening stage, the fractal dimension increases slowly with the progress of loading. The initiation of the crack propagation phase of the coal samples gradually occurs more quickly with increasing loading rate; the initial cracks appear earlier. At the same loading time point, when the loading rate is greater, the fractal dimension of the cracks observed in the coal sample is greater.

Hydraulic fracturing, as a key technology of deep energy exploitation, accelerates the rapid development of the modern petroleum industry. To study the mechanisms of hydraulic fracture propagation and rock failure mode of the vertical well hydraulic fracturing, the true triaxial hydraulic fracturing test and numerical simulation are carried out, and the influence of the principal stress difference, water injection displacement, perforation angle and natural fracture on fracture propagation is analyzed. The results show that the fracture propagation mode of limestone is mainly divided into two types: the single vertical fracture and the transverse-longitudinal crossed complex fracture. Under high displacement, the fracturing pressure is larger, and the secondary fracture is more likely to occur, while variable displacement loading is more likely to induce fracture network. Meanwhile, the amplitude of acoustic emission (AE) waveform of limestone during fracturing is between 0.01 and 0.02 mV, and the main frequency is maintained in the range of 230–300 kHz. When perforation angle θ=45°, it is easy to produce the T-type fracture that connects with the natural fracture, while X-type cracks are generated when 0=30°. The results can be used as a reference for further study on the mechanism of limestone hydraulic fracturing.

Evaluation of the performance of existing support in underground tunnels is of great importance for production and interests. Based on field investigation, the shape and number of joints and fractures were investigated in the mining area. Then, the stability of each structural blocks is analyzed by 3D wedge stability analysis software (Unwedge). Moreover, a new analysis method based on critical block theory is applied to analyze the stability of excavated laneways in continuous and discontinuous rock and monitor the stress changes in a fractured tunnel rock mass. The test results indicate that the 3D wedge stability analysis software for underground excavation can evaluate deep tunnel support. Besides, there is no direct relation between the size of the block and the instability of the tunnel. The support method, on large and thick key blocks, needs to be improved. In a broken tunnel section, U-shaped steel support can effectively promote the stress state of the surrounding rock. By monitoring the surrounding rock, it is proven that the vibrating string anchor stress monitoring system is an efficient and real-time method for tunnel stability evaluation.

To investigate the influence of confining pressure and pore water pressure on strength characteristics, energy storage state and energy release intensity at peak failure of deep sandstone, a series of triaxial compression tests under hydraulic coupling conditions are carried out. By analyzing the process of rock deformation and failure, the stress thresholds of the rock are obtained. The change trend of total energy density, elastic energy density and dissipated energy density of deep sandstone in the pre-peak stage is obtained by the graphical integration method. By comparing the dynamic energy storage level of rocks under different confining pressures, the influence of pore water pressure on the energy dissipation at stress thresholds of crack closure stress, crack initiation stress, crack damage stress and peak stress is analyzed. Based on the ratio of pre-peak total energy density to post-peak total energy density, the interaction mechanism of confining pressure and pore water pressure for the rock burst proneness of deep sandstone is studied. The experimental results show that the peak stress of sandstone increases with the increase of confining pressure, while the existence of pore water pressure can weaken the peak stress of sandstone. In the stress stage from crack closure stress to peak stress, the dynamic energy storage level of rock presents a trend of the inverse “check mark”. Meanwhile, the larger the confining pressure, the higher the energy storage level of rock. However, the pore water pressure increases the degree of energy dissipation of rock and reduces the energy storage capacity of rock, and the degree of dissipation is linear with pore water pressure. The increase of confining pressure aggravates the instability and failure of deep sandstone, while pore water pressure has the opposite effect. The research results will provide necessary data support for the stability analysis of rock mass excavation in sandstone stratum under high stress and high pore water pressure.

Rock is more sensitive to tensile loading than compressive loading, since the tensile strength of rock is much lower than compressive strength. The fracture characteristics of rock in the tensile state are of great significance to the understanding of rock failure mechanisms. To this end, we have conducted numerical simulation researches on mode I cracking process of rock with varying homogeneity, using the Realistic Failure Process Analysis program. With the increase of homogeneity, cracks are concentrating to the ligament area with a decreasing number of crack bifurcations, and the main crack path is becoming smooth. Crack behaviors and mechanical properties are influenced significantly when the homogeneity index is in the range of 1.5 to 5. When the homogeneity index is greater than 30, they are not affected by rock homogeneity and the rock can be considered as essentially homogeneous. It is considered that the global and local strengths are affected by the distribution of rock mechanical properties at mesoscale, which influence the crack behaviors and mechanical characteristics.

Microseismic monitoring system is one of the effective methods for deep mining geo-stress monitoring. The principle of microseismic monitoring system is to analyze the mechanical parameters contained in microseismic events for providing accurate information of rockmass. The accurate identification of microseismic events and blasts determines the timeliness and accuracy of early warning of microseismic monitoring technology. An image identification model based on Convolutional Neural Network (CNN) is established in this paper for the seismic waveforms of microseismic events and blasts. Firstly, the training set, test set, and validation set are collected, which are composed of 5250, 1500, and 750 seismic waveforms of microseismic events and blasts, respectively. The classified data sets are preprocessed and input into the constructed CNN in CPU mode for training. Results show that the accuracies of microseismic events and blasts are 99.46% and 99.33% in the test set, respectively. The accuracies of microseismic events and blasts are 100% and 98.13% in the validation set, respectively. The proposed method gives superior performance when compared with existed methods. The accuracies of models using logistic regression and artificial neural network (ANN) based on the same data set are 54.43% and 67.9% in the test set, respectively. Then, the ROC curves of the three models are obtained and compared, which show that the CNN gives an absolute advantage in this classification model when the original seismic waveform are used in training the model. It not only decreases the influence of individual differences in experience, but also removes the errors induced by source and waveform parameters. It is proved that the established discriminant method improves the efficiency and accuracy of microseismic data processing for monitoring rock instability and seismicity.

The rock mass in nature is in most cases anisotropic, while the existing classifications are mostly developed with the assumption of isotropic conditions that not always meet the engineering requirements. In this study, an anisotropic system based on China National Standard of BQ, named as A-BQ, is developed to address the classification of anisotropic rock mass incorporating the anisotropy degree as well as the quality of rock mass. Two series of basic rating factors are incorporated including inherent anisotropy and structure anisotropy. The anisotropy degree of rock mass is characterized by the ratio of maximum to minimum quality score and adjusted by the confining stress. The quality score of rock mass is determined by the key factors of anisotropic structure occurrence and the correction factors of stress state and groundwater condition. The quality of rock mass is characterized by a quality score and classified in five grades. The assessment of stability status and probable failure modes are also suggested for tunnel and slope engineering for different quality grades. Finally, two cases of tunnel and slope are presented to illustrate the application of the developed classification system into the rock masses under varied stress state.

In order to explore the control effect of backfill mining on dynamic disasters under special geological mining conditions of overlying thick magmatic rock (TMR), a three-dimensional numerical model of a panel of one side goaf in Yangliu coal mine with double-yield backfill material constitutive model was developed. The simulation results were then compared with field monitoring data. The dynamic disaster control effect of both caving and backfill mining was analyzed in three different aspects, i.e., displacement field, stress field and energy field. The results show that in comparison to the full caving mining method, the bearing capacity of the goaf after backfilling was enhanced, the backfill mining can effectively reduce the stress and energy accumulated in the coal/rock body, and the backfill mining eliminates the further moving space of TMR and prevents its sudden rupture. Before TMR fracture, the subsidence displacement of TMR was reduced by 65.3%, the front abutment stress of panel decreased by 9.4% on average and the high energy concentration zone around panel was also significantly reduced. Overall, the results of this study provide deeper insights into the control of dynamic disasters by backfill mining in mines.

In this study, the effect of loading rate on shale fracture behaviors was investigated under dynamic and static loading conditions. Cracked straight through Brazilian disc (CSTBD) shale specimens were tested with a split Hopkinson pressure bar (SHPB) setup and INSTRON1346 servo-testing machine under pure mode I loading conditions. During the test, the crack propagation process was recorded by high-speed (HS) camera, and the acoustic emission (AE) signal generated by the fracture was collected by acoustic emission (AE) system. At the same time, crack propagation gauge (CPG) was used to measure the crack propagation velocity of the specimen. The results show that the crack propagation velocity and fracture toughness of shale have a positive correlation with the loading rate. The relationship among the crack propagation velocity, the fracture toughness and the loading rate is established under the static loading condition. In addition, the characteristics of AE signals with different loading rates are analyzed. It is found that the AE signals generated by microcrack growth decrease with the increase of loading rates. Meanwhile, the turning point of cumulative counting moves forward as the loading rate increases, which shows that the AE signal generated by shale fracture at low loading rate mainly comes from the initiation and propagation of microcracks, while at high loading rate it mainly comes from the formation of macro large-scale cracks. The fracture mechanism that causes shale fracture toughness and crack propagation velocity to vary with loading rate is also discussed based on the analysis results of AE signals.

Dongjiahe Coal Mine belongs to the Carboniferous Permian coal field which has a high degree of karst and fissure development. This paper takes the working face of Dongjiahe Coal Mine as an example; through the microseismic(MS) monitoring system arranged on the working face, the moment tensor theory was used to invert the focal mechanism solution of the anomalous area of the floor MS event; combining the numerical simulation and field data, the underlying floor faults were identified by the stress inversion method. The results show that: 1) Moment tensors were decomposed into three components and the main type of rupture in this area is mixed failure according to the relative criterion; 2) The hidden fault belongs to the reversed fault, its dip angle is approximately 70°, and the rupture length is 21 m determined by the inversion method of the initial dynamic polarity and stress in the focal mechanism; 3) The failure process of the fault is divided into three stages by numerical simulation method combined with the temporal and spatial distribution of MS events. The results can provide a reference for early warning and evaluation of similar coal mine water inrush risks.

In the context of deep rock engineering, the in-situ stress state is of major importance as it plays an important role in rock dynamic response behavior. Thus, stress initialization becomes crucial and is the first step for the dynamic response simulation of rock mass in a high in-situ stress field. In this paper, stress initialization methods, including their principles and operating procedures for reproducing steady in-situ stress state in LS-DYNA, are first introduced. Then the most popular four methods, i.e., explicit dynamic relaxation (DR) method, implicit-explicit sequence method, Dynain file method and quasi-static method, are exemplified through a case analysis by using the RHT and plastic hardening rock material models to simulate rock blasting under in-situ stress condition. Based on the simulations, it is concluded that the stress initialization results obtained by implicit-explicit sequence method and dynain file method are closely related to the rock material model, and the explicit DR method has an obvious advantage in solution time when compared to other methods. Besides that, it is recommended to adopt two separate analyses for the whole numerical simulation of rock mass under the combined action of in-situ stress and dynamic disturbance.