Intensity Of Rockburst Research Articles

Energy storage and fracture characteristics of brittle rock with rockburst proneness after microwave irradiation

Microwave irradiation has been considered a promising solution for high-temperature cracking rock. Most of the current researches are concentrated on investigating the effects of microwave irradiation on the physical and mechanical properties of rock. However, there is a paucity of reports on the application of microwave irradiation for controlling rockburst disasters. The novelty of this investigation lies in the utilization of microwave irradiation to modify the energy storage capacity and fracture characteristics of brittle rock with rockburst proneness. Based on the phenomenon of overheating in rock under microwave irradiation, the concept of progressive damage in granite was proposed for the first time. The weakening of energy storage capacity due to microwave irradiation was evaluated by defining an energy storage coefficient. A novel index for assessing the rockburst proneness of brittle rock was proposed. By combining this index with the strain energy release rate, the potential value of microwave irradiation in reducing the proneness and intensity of rockburst was explored. This study also introduced the concept of "sensitive stress level" which influences the closure state of cracks, and found that SSL and mechanical properties show high sensitivity to microwave power. A threshold power of 4.5 kW was identified, at which numerous parameters undergo significant changes.

Experimental investigation on fractal characteristics of rockburst fragments for granite experiencing initial temperature damage

To reveal the influence mechanism of initial temperature damage on the failure characteristics of granite rockburst, the true triaxial strainburst experiments were carried out on granite samples experiencing different initial damage temperatures. First, the peak strength and failure intensity evaluated by the rockburst pit volume of the granite samples were investigated. Second, by calculating the fractal dimensions of the rockburst fragments, the impacts of the initial temperature damage on the scale parameters, surface morphology and microscopic cracks of the rockburst fragments were quantitatively analyzed. Finally, on the basis of the crack evolution characteristics inside the samples during rockburst, a link between the peak strength of the rockburst and the fractal dimension of the fragments was established. The results indicated that with increasing initial damage temperature, the peak strength and failure intensity of rockburst for granite samples initially increase and subsequently decrease. The samples experiencing an initial damage temperature of 200 ℃ present the highest fractal dimensions of scale parameters, surface morphology and microscopic cracks of rockburst fragments, indicating that 200 ℃ is the temperature threshold that affects the failure intensity of rockburst and the fragmentation degree of fragments. The peak strength of rockburst failure for granite samples experiencing different initial damage temperatures is positively correlated with the fractal dimensions of rockburst fragments, providing a scientific basis for revealing the incubation and evolution mechanism of granite samples during rockburst.

Experimental Investigation on the Influence of Water on Rockburst in Rock-like Material with Voids and Multiple Fractures.

To investigate the influence of water content on the rockburst phenomena in tunnels with horizontal joints, experiments were conducted on simulated rock specimens exhibiting five distinct levels of water absorption. Real-time monitoring of the entire blasting process was facilitated through a high-speed camera system, while the microscopic structure of the rockburst debris was analyzed using scanning electron microscopy (SEM) and a particle size analyzer. The experimental findings revealed that under varying degrees of water absorption, the specimens experienced three stages: debris ejection; rockburst; and debris spalling. As water content increased gradually, the intensity of rockburst in the specimens was mitigated. This was substantiated by a decline in peak stress intensity, a decrease in elastic modulus, delayed manifestation of pre-peak stress drop, enhanced amplitude, diminished elastic potential energy, and augmented dissipation energy, resulting in an expanded angle of rockburst debris ejection. With increasing water content, the bond strength between micro-particles was attenuated, resulting in the disintegration of the bonding material. Deformation failure was defined by the expansion of minuscule pores, gradual propagation of micro-cracks, augmentation of fluffy fine particles, exacerbation of structural surface damage akin to a honeycomb structure, diminishment of particle diameter, and a notable increase in quantity. Furthermore, the augmentation of secondary cracks and shear cracks, coupled with the enlargement of spalling areas, signified the escalation of deformation failure. Simultaneously, the total mass of rockburst debris gradually diminished, accompanied by a corresponding decrease in the proportion of micro and fine particles within the debris.

Rockburst prediction for deep tunneling near fault based on the PD-BEM method

A multiscale model coupling the peridynamic (PD) and boundary element method (BEM) is proposed to analyze the rockburst in deep tunnels near fault. The entire rockburst processes of the rock masses around the opening are captured by PD while the field conditions and boundary are described by BEM, which can take full advantage of their salient features and model the rockburst problems efficiently. The proposed model is verified by comparing its predictions with those from the field observations in “11.28” rockburst at the Jinping II Hydropower Station in China. Parametric analysis considering the dip angle and location of the fault as well as the ground stress is performed to reveal the rockburst mechanism of deep tunnel near fault. Numerical results indicate that the rockburst intensity of rock tunnel is a function of the distance between the fault and tunnel, the dip angle of fault and ground stress. Different failure modes, including buckling failure, slip failure and local slabbing failure are found in the simulation, which are controlled by the fault near the tunnel. Moreover, a new index for rockburst is proposed to predict the tendency and intensity of rockburst associated with deep tunneling near a fault.

Temperature effect of rockburst in granite caverns: insights from reduced-scale model true-triaxial test

To investigate the influence of thermal treatment on the rockburst in granite caverns, true-triaxial compression tests were conducted on pre-heated granite cubic samples containing a circular through-hole using a true-triaxial test system, and the micro camera was used to monitor and record the rockburst process in realtime. Test results show that the uniaxial compressive strength and elastic modulus first increase and then decrease as the temperature increases, which reach the maximums at 200 °C and sharply decrease at temperatures from 400 to 600 °C. The density and P-wave velocity decrease and the peak strain increases with increasing temperature. The main failure mode is X-shaped shear-tension failure at 25 and 200 °C, and single-slope shear failure at 400 and 600 °C. Thermal treatment exhibits slight effect on the rockburst incubation process in granite caverns. The stress required for rockburst decreases when the temperature increases or decreases from 200 °C. The higher the temperature, the lower the required stress. At 25 and 200 °C, rockburst is violent, and fine particles and large slabs are mainly produced; at 400 and 600 °C, the intensity of rockburst is relatively weak, and fine particles are mainly generated. Thermal treatment exhibits double effects on rockburst. The mechanism of thermal treatment on granite rockburst is the strengthening effect caused by water loss and the weakening effect caused by thermal expansion cracking. This study can provide theoretical guidance for the stability analysis and rockburst prevention of temperature-affected granite caverns.

Experimental study on the effect of unloading rate on gneiss rockburst

Rockburst are often encountered in tunnel construction due to the complex geological conditions. To study the influence of unloading rate on rockburst, gneiss rockburst experiments were conducted under three groups of unloading rates. A high-speed photography system and acoustic emission (AE) system were used to monitor the entire process of rockburst process in real-time. The results show that the intensity of gneiss rockburst decreases with decrease of unloading rate, which is manifested as the reduction of AE energy and fragments ejection velocity. The mechanisms are proposed to explain this effect: (i) The reduction of unloading rate changes the crack propagation mechanism in the process of rockburst. This makes the rockbursts change from the tensile failure mechanism at high unloading rate to the tension-shear mixed failure mechanism at low unloading rate, and more energy released in the form of shear crack propagation. Then, less strain energy is converted into kinetic energy of fragments ejection. (ii) Less plate cracking degree of gneiss has taken shape due to decrease of unloading rate, resulting in the destruction of rockburst incubation process. The enlightenments of reducing the unloading rate for the project are also described quantitatively. The rockburst magnitude is reduced from the medium magnitude at the unloading rate of 0.1 MPa/s to the slight magnitude at the unloading rate of 0.025 MPa/s, which was judged by the ejection velocity.

Rock Burst Intensity-Grade Prediction Based on Comprehensive Weighting Method and Bayesian Optimization Algorithm–Improved-Support Vector Machine Model

In order to accurately judge the tendency of rock burst disaster and effectively guide the prevention and control of rock burst disaster, a rock burst intensity-grade prediction model based on the comprehensive weighting of prediction indicators and Bayesian optimization algorithm–improved-support vector machine (BOA-SVM) is proposed for the first time. According to the main factors affecting the occurrence and intensity of rock burst, the rock stress coefficient (σθ/σc), brittleness coefficient (σc/σt) and elastic energy index (Wet) are selected to construct the rock burst prediction indicator system. On the basis of the research of other scholars, according to the main performance and characteristics of rock burst, rock burst is divided into four intensity levels. The collected and sorted 120 sets of rock burst case data at home and abroad are taken as learning samples, and the T-SNE algorithm is used to perform dimensionality-reduction visualization processing on the sample data, visually display the distribution of samples of different grades, evaluate the representativeness of the sample data and prejudge the feasibility of the machine learning algorithm to distinguish different rock burst intensity levels. The combined improved analytic hierarchy process (IAHP) and Delphi method determine the subjective weight of the indicators; the combined entropy weight method and CRITIC method determine the objective weight of the indicator, and use the harmonic mean criterion of information theory to synthesize the subjective weight and objective weight of the indicator to obtain the comprehensive weight of the indicators. After weighted prediction indicators, a rock burst intensity-grade prediction model is constructed based on the support vector machine, and the hyperparameters of three types of support vector machines are improved by using the Bayesian optimization algorithm. Then, the prediction accuracy of different models is calculated by the random cross-validation method, and the feasibility and effectiveness of the rock burst intensity-grade prediction model is verified. In order to evaluate the generalization and engineering applicability of the proposed model, 20 groups of rock burst case data from the Maluping mine and Daxiangling tunnel are introduced to predict the rock burst intensity grade. The results show that the accuracy of the rock burst intensity-grade prediction model based on comprehensive weighting and BOA-SVM is as high as 93.30%, which is of higher accuracy and better effect than the ordinary model, and can provide warning information with a higher fault tolerance rate, which provides a new way of thinking for rock burst intensity-grade prediction.

Prediction of rock burst intensity based on multi-source evidence weight and error-eliminating theory.

Rock burst is the main geological hazard in deep underground engineering. For the prediction of the intensity of rock burst, a model for prediction of rock burst intensity on the basis of multi-source evidence weight and error-eliminating theory was established. Four indexes including the ratio of rock's compressive-tensile strength [Formula: see text], the stress coefficient of rock [Formula: see text], the elastic energy index of rock Wet, and integrality coefficient Kv were chosen as the prediction variables of rock burst; the index weights are calculated by different weighting methods and fused with evidence theory to determine the final weight of each index. According to the theory of error-eliminating, taking "no rock burst" (I in classification standards of rock burst intensity) as the objective and using the error function to process 18 sets of typical rock burst data and the weight of evidence fusion as the normalized index limit loss value, a model for prediction of rock burst intensity was built. It is verified by the actual situation and three other models. Finally, the model has been applied to rock burst prediction of Zhongnanshan tunnel ventilation shaft. The results show that evidence theory fuses multi-source index weights and improves the method of determining index weights. The index value is processed by error-eliminating theory, and the limit value problem of index value normalization is optimized. The predicted results of the proposed model are consistent with the situation of Zhongnanshan tunnel. It improves the objectivity of the rock burst prediction process and provides a research idea for rock burst intensity prediction index.

Experimental Investigation of Pre-Flawed Rocks under Dynamic Loading: Insights from Fracturing Characteristics and Energy Evolution.

Different fractures exist widely in rock mass and play a significant role in their deformation and strength properties. Crack rocks are often subjected to dynamic disturbances, which exist in many fields of geotechnical engineering practices. In this study, dynamic compression tests were carried out on rock specimens with parallel cracks using a split hopkinson pressure bar apparatus. Tests determined the effects of strain rate and crack intensity on dynamic responses, including progressive failure behavior, rock fragmentation characteristics, and energy dissipation. Based on the crack classification method, tensile-shear mixed cracking dominates the failure of rock specimens under the action of impact loading. Increasing the flaw inclination angle from 0°-90° changes the predominant cracking mechanism from tensile cracking to mixed tensile-shear cracking. The larger the loading rate, the more obvious the cracking mechanism, which indicates that the loading rate can promote the cracking failure of rock specimens. The fragmentation analysis shows that rock samples are significantly broken at higher loading rates, and higher loading rates lead to smaller average fragment sizes; therefore, the larger the fractal dimension is, the more uniform the broken fragments of smaller sizes are. Energy utilization efficiency decreases while energy dissipation density increases with increasing strain rate. For a given loading rate, the energy absorption density and energy utilization efficiency first decrease and then increase with increasing flaw inclination, while the rockburst tendency of rock decreases initially and then increases. We also find that the elastic-plastic strain energy density increases linearly with the total input energy density, confirming that the linear energy property of granite has not been altered by the loading rate. According to this inherent property, the peak elastic strain energy of the crack specimen can be calculated accurately. On this basis, the rockburst proneness of granite can be determined quantitatively using the residual elastic energy index, and the result is consistent with the intensity of actual rockburst for the specimens.

Evolution of the Fracture Characteristics in a Rockburst under Different Stress Gradients

The variation in principal stress ratio and principal stress direction deflection caused by the stress gradient distribution of surrounding rock is one of the reasons leading to different types of strain rockbursts. Two typical rockburst failure modes of brittle gypsum debris are discussed based on the study of the macroscopic and microscopic appearance morphologies under different stress gradients. Based on the acoustic emission characteristic parameter analysis of the Gaussian mixture model (GMM), the evolution of internal crack propagation and the fracture mechanism during the rockburst under different stress gradients were explored. The results are as follows: (1) The generation and intensity of rockburst are related to the loading stress gradient. The larger the stress gradient, the more significant the dynamic phenomenon during the rockburst process. (2) There are obvious differences in the morphology and arrangement of crystals on the fracture surface of rockburst debris under different stress loading paths. The brittle fracture of debris can be divided into flake debris dominated by intergranular tensile fracture and massive debris dominated by transgranular shear fracture. (3) The AE characteristic parameter classification method based on the GMM has good applicability in crack classification. With an increase in the loading stress gradient, the proportion of the shear crack increases gradually, which is the main reason for the enhancement of the rockburst intensity.

Experiments on rockburst proneness of pre-heated granite at different temperatures: Insights from energy storage, dissipation and surplus

Many underground engineering projects show that rockburst can occur in rocks at great depth and high temperature, and temperature is a critical factor affecting the intensity of rockburst. In general, temperature can affect the energy storage, dissipation, and surplus in rock. To explore the influence of temperature on the energy storage and dissipation characteristics and rockburst proneness, the present study has carried out a range of the uniaxial compression (UC) and single-cyclic loading–unloading uniaxial compression (SCLUC) tests on pre-heated granite specimens at 20 °C–700 °C. The results demonstrate that the rockburst proneness of pre-heated granite initially increases and subsequently decreases with the increase of temperature. The temperature of 300 °C has been found to be the threshold for rockburst proneness. Meanwhile, it is found that the elastic strain energy density increases linearly with the total input strain energy density for the pre-heated granites, confirming that the linear energy property of granite has not been altered by temperature. According to this inherent property, the peak elastic strain energy of pre-heated granites can be calculated accurately. On this basis, utilising the residual elastic energy index, the rockburst proneness of pre-heated granite can be determined quantitatively. The obtained results from high to low are: 317.9 kJ/m 3 (300 °C), 264.1 kJ/m 3 (100 °C), 260.6 kJ/m 3 (20 °C), 235.5 kJ/m 3 (500 °C), 158.9 kJ/m 3 (700 °C), which are consistent with the intensity of actual rockburst for specimens. In addition, the relationship between temperature and energy storage capacity (ESC) of granite was discussed, revealing that high temperature impairs ESC of rocks, which is essential for reducing the rockburst proneness. This study provides some new insights into the rockburst proneness evaluation in high-temperature rock engineering. • The temperature does not change the pre-heated granite possess the linear energy storage law. • The peak strain energy of pre-heated granite is quantitatively calculated using the linear energy storage law. • The rockburst proneness of pre-heated granite at different temperatures can be accurately evaluated by the A EF . • The rockburst proneness of pre-heated granite initially increases and then decreases with the temperature increasing. • The rockburst proneness of pre-heated granite at 300 °C is the highest.

Effect of layered joints on rockburst in deep tunnels

The existence of joints in the surrounding rock mass has a considerable effect on tunnel rockbursts. Herein, we studied the effect of layered joints with different inclination angles and spacings on rockburst in deep tunnels and investigated the failure area, deformation process of the surrounding rock mass, stress change inside the surrounding rock mass, velocity of the failed rock, and the kinetic energy of the failure. The failure type of the surrounding rock mass can thus be determined. The results showed that the intensity of rockburst increases as rock quality designation (RQD) decreases, while the deformation rate of the surrounding rock mass first increases and then decreases. The deformation rate exhibits a turning point between RQD = 50 and 70, below which the deformation rate of the surrounding rock mass gradually decreases, ultimately ceasing to be a rockburst. Rockburst always occurs perpendicular to the direction of the joint. When σx = σy, as the joint inclination angle changes from 45° to 90°, the intensity of a rockburst first decreases (from 45° to 60°), and then increases (from 60° to 90°). When combined with the evolution law of stress and strain energy, the rockburst process can be divided into four stages.

Rockburst Precursors and the Dynamic Failure Mechanism of the Deep Tunnel: A Review

With the rapid development of underground caverns in the fields of hydraulic engineering, mining, railway and highway, the frequency, and intensity of rockburst and dynamic instability have gradually increased, which has become a bottleneck restricting the safe construction of deep caverns. This paper presents a review of the current understanding of rockburst precursors and the dynamic failure mechanism of the deep tunnel. Emphasis is placed on the stability of the surrounding rock of the deep tunnel, the rockburst prediction method, and the dynamic failure characteristics of the surrounding rock of the deep tunnel. Throughout the presentation, the current overall gaps in understanding rockburst precursors and the dynamic failure mechanism of deep tunnels are identified in an attempt to stimulate further research in these promising directions by the research community.

Case Study of the Characteristics and Mechanism of Rock Burst near Fault in Yima Coalfield, China

Deep mining near faults may easily cause rock bursts, which seriously threaten mining safety. Based on the engineering background of deep mining near fault in Yima coalfield, by collecting the rock burst events that happened near fault during deep mining, the correlation between fault structure and time-space features of rock burst was analyzed. The results show that the deep rock burst accounts for 84% in Yima coalfield at 600 m and 93% in the mining area within 1000 m from F16 fault. The risk of rock burst is positively correlated with mining depth and negatively correlated with the distance between mining area and F16 fault, and the frequency and intensity of rock burst near F16 fault increase significantly. Rock burst occurs in high stress concentration area, mainly in roadway, releasing energy level of 1.1 × 104 J–3.5 × 108 J, with impact damage range of 60–500 m. The mechanism of rock burst was explained from the view of the distribution of mining stress in surrounding rock. The stress of coal seam in deep mining near fault increases, and the disturbance effect of fault is obvious. Rock burst is easy to be induced under static and dynamic loads. The occurrence and mechanical characteristics of fault have different effects on rock burst and should be considered when evaluating the risk of rock burst.

Rockburst Prediction on the Superimposed Effect of Excavation Accumulation Energy and Blasting Vibration Energy in Deep Roadway

In deep mining, much elastic energy is stored in rock mass due to the high geostress. Rockburst will be induced by accumulated energy during excavation. Meanwhile, because of blasting vibration energy in the host rock, there will be an obvious superimposed effect on the probability and intensity of rockburst. To explore the most reasonable and effective method for understanding rockburst problem under blasting, a deep roadway of Sanshandao gold mine was studied. On the basis of in situ geostress data, the accumulated energy of three-centered arch roadway after quasi-static excavation was derived. Then, a series of in situ blasting vibration were monitored, and the blasting vibration energy was calculated by employing the equivalent theory of elastic vibration boundary. Finally, the tendentiousness of rockburst was evaluated qualitatively with the superimposed energy. The results indicated that the disaster-driven energy was increased by 45.1% and 28.2% on different places of roadway. Also, the probability and intensity of rockburst would be raised.

Mechanical Properties and Control Rockburst Mechanism of Coal and Rock Mass with Bursting Liability in Deep Mining

In order to study the mechanism of the dynamic disaster of rockburst in a deep coal mine and the prevention and control measures of weakening shock, the MTS815.03 servocontrolled rock mechanics test system is used to test the coal, rock, and combined specimens with the buried depth of nearly 1200 m in Xinwen Mining Area. And their mechanical properties, energy evolution, and bursting properties are studied and analyzed. The rationality of the test results is also verified by the in-situ engineering practice. The key conclusions are as follows: (1) There is a relation between the ratio of elastic modulus Ee before peak strength to descending modulus Ed after peak strength and the bursting properties. For the fractured coal, the descending modulus Ed is relatively small, and the Ee/Ed is relatively large and presents progressive ductile failure with low probability and risk of rockburst. For the less fractured rock, the descending modulus Ed is relatively large, and the Ee/Ed is relatively small and presents brittle failure, which is very similar to the characteristics of rockburst. (2) For the same type of rock, with the increase of confining pressure, the Ee/Ed gradually increases, indicating the reduction of rockburst strength. Therefore, the greater the support strength provided to the surrounding rock surface of the roadway, the smaller the failure degree of rockburst. (3) With the increase of confining pressure, after peak strength, the elastic energy of coal specimens decreases slowly, and the dissipated energy increases slowly, indicating that the increase of confining pressure can effectively limit the energy dissipation and release after coal specimen failure. So, in the in-situ engineering practice, it is an important measure to improve the surface restraint and support strength of the coal roadway for reducing the occurrence intensity and probability of rockburst. (4) The combined measures of “the mining of double liberating seam + the implementation of large-diameter pressure relief borehole in advance of working face” is the very effective way to eliminate the rockburst accidents of working face in a protected coal seam and has an important guiding significance for the safe mining of rockburst mine.

Effect of the propagation direction of the weak dynamic disturbance on rock failure: an experimental study

Weak dynamic disturbance caused by drilling and blasting, adjacent rockburst, and machine vibration is a key factor to rock failure/rockburst during underground excavation. Meanwhile, the propagation direction of weak dynamic disturbances varies when different underground constructions are encountered. To investigate the effect of the propagation direction of the weak dynamic disturbance on rock failure, a general true triaxial test (applying a loading state of “six stressed faces”) and a modified true triaxial test (applying a loading state of “one free face and five stressed faces”) are conducted. For the former test, Pd1 (weak dynamic disturbance along the direction of σ1), Pd2 (weak dynamic disturbance along the direction of σ2), and Pd3 (weak dynamic disturbance along the direction of σ3) are involved. For the latter test, only Pd1 and Pd2 are involved due to the limitation of the testing machine used. After testing, the rock strength and macroscopic failure characteristics of the tested specimens are systematically investigated. The experimental results indicate that the rock strength of the tested specimen without weak dynamic disturbance is higher than those with weak dynamic disturbance, indicating a reduction effect of the weak dynamic disturbance on the rock strength. Pd3 has the greatest reduction effect on rock strength due to its greatest promotion effect on crack development, while the reduction effect of Pd1 on rock strength, as well as its promotion effect on crack development, is smallest. In addition, for the tested specimens with a free face, the failure process is observed and investigated. Rockburst characterized by rock fragment ejection occurs during the testing process of these specimens. The kinetic energy of the ejected blocks without weak dynamic disturbance is higher than that with weak dynamic disturbance, showing that the weak dynamic disturbance has a reduction effect on kinetic energy. In addition, the kinetic energy of ejected blocks is lower under the Pd2 condition than that under the Pd1 condition; consequently, Pd2 has a greater influence on the kinetic energy of the ejected blocks, i.e., the intensity of rockburst.

Discussions on the Complete Strain Energy Characteristics of Deep Granite and Assessment of Rockburst Tendency

In deep mining, the rockburst hazard has become a prominent problem. Rockburst is difficult to be predicted, and it gives a severe threat to mining safety. In this paper, the triaxial compressive tests with an acoustic emission (AE) device and full cyclic loading and unloading tests were carried out, respectively, to present characteristics of linear elastic strain energy and peak strain energy. Also, to consider the time-delay strain characteristics of granite found in the abovementioned tests, a new stage loading and unloading test with dual monitoring systems was designed and performed. Through 20 days’ time-delay strain monitoring, the peak-strength strain energy was further modified. The results showed that the peak strain energy is approximate 1.2-1.3 times than linear elastic strain energy under the same confining pressure, and after considering the time-delay strain effect, the modified maximal strain energy value of the deep granite significantly increased. The peak strain energy values are further enhanced from 1.0 × 104 J/m3 to 1.8 × 104 J/m3, respectively. At last, by taking advantage of the strain energy index model of rockburst, the tendency and intensity of rockburst were assessed contrastively.

Computational framework for simulating rock burst in shear and compression

This paper presents results from a series of numerical modeling tests conducted with the objective of developing a computational framework for studying rock burst events. A commercially available distinct element code with its explicit time-stepping scheme is adopted for modeling the initial quasi-static and the subsequent dynamic response of rock burst in compression and shear. Ground reaction curves are introduced to discuss criteria for stability of a failure through stress analyses. Energy balance equations are analyzed for assessing the rock burst intensity by estimating radiated seismic energy once conditions of instability emerge. Two methods are discussed for estimating radiated seismic energy: tracking of the energy conversion during failure; recording the kinetic energy that is damped by mechanical damping schemes. Modeling approach and methodologies for studying compressive-type rock burst are developed and calibrated against available analytical solutions with respect to radiated seismic energy and excavation convergence. Factors participating in the intensity of rock burst in compression are examined by modeling a rectangular tabular excavation supported by a single pillar with ductile, semi-brittle, and brittle failure responses under different compressive loading. A shear-type rock burst along a strike-slip fault model is simulated and modeling approach is calibrated by checking the resulting slip distribution, radiated seismic energy, and seismic moment against analytical solutions. Factors contributing to the occurrence and intensity of shear-type rock burst are explored by simulating different slip scenarios under different loading conditions. With presented analyses, this paper provides a computational framework calibrated for studying rock burst events and, as a reference for treatment of more complex cases, shows how Young's modulus of the rock, failure stress drop, rock brittleness, and slip-weakening behaviors of faults govern the rock burst occurrence and intensity.

Experimental study of the dynamically induced rockburst of a rock wall with double free faces

Dynamic disturbance is regarded as one of the most significant factors that induce rockburst around the boundary of underground excavation, particularly in high confining pressure conditions. In the present study, three types of dynamic loading tests are conducted to investigate the dynamically triggered rockburst behavior of a rock wall with double free faces. The three types of dynamic loading considered are the large stress single-pulse loading (mild-disturbance), the middle stress low-frequency cyclic loading (modest-disturbance), and the small stress high-frequency cyclic loading (weak-disturbance). The experimental results are analyzed and the damage evolution process during the dynamic disturbances is described. The tests reveal that the failure strain (i.e., the strain at unstable failure) of the dynamically triggered rockburst is greater than that of the self-initiated rockburst. The intensity of rockburst depends not only on the initial static stress level but also on the dynamic disturbance type. The rockburst induced by the mild-disturbance is mainly related to large amounts of disturbance energy imported. The rockburst caused by the modest-disturbance is contributed by the disturbance degradation of ultimate energy-storage capacity of specimen. The rockburst in a weak-disturbance specimen is primarily due to the disturbance aggravation of the damage in specimen and the elastic strain energy release. In particular, the rockburst hazard from the double free faces is more likely to be triggered and its result more serious than that of the rock structure with only one free face because the increasing free face decreases the rock strength. The fragmentation of the dynamically induced rockburst is larger than that of the self-initiated rockburst. With increasing time of dynamic loading, the damage induced by the modest-disturbance and the weak-disturbance first increases continually, subsequently increases steadily, and finally increases drastically. By contrast, the damage of the specimen under the mild-disturbance condition has a linearly increasing trend.