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Supporting and controlling rockburst hazards is a great challenge for deep rock engineering. A new cable, the negative Poisson's ratio (NPR) cable, exhibits excellent mechanical properties, including high energy absorption and resilience to impacts. To investigate its control effect on rockburst, a series of true triaxial strainburst experiments were conducted on sandstone specimens under different anchoring conditions (no support, ordinary support, NPR cable support). The model NPR cables were developed based on similar principles. In addition, the acoustic emission response and fragmentation characteristics were analysed. The experimental results indicate that the NPR cables are capable of co-deforming with the rock and absorbing energy, increasing rock strength and promoting internal rock tensile fracture. The rapid response of the NPR cables during rockbursts provided effective support, exerted better impact resistance and significantly reduced the mass and fractal dimension of the ejected fragments. Thus, NPR cables can reduce kinetic energy release and effectively control rockburst hazards compared to ordinary cables. The aim of this paper is to provide a reference for the design of rockburst support in engineering. [ABSTRACT FROM AUTHOR]

To explore the energy evolution characteristics of rockbursts and the mechanism of excess energy in rockbursts, a self-developed rockburst experimental system was used. We performed true triaxial rapid unloading rockburst simulations and triaxial experiments based on the complete stress-displacement surface (CSDS) model prediction of the post-peak curve of rock uniaxial compression. By analyzing the characteristics of stress–strain curve and energy evolution of the rockburst experiment and comparing the energy storage characteristics of the two experiments, we arrived at the following conclusions Unlike the static failure of rock due to uniaxial compression, the occurrence of rockburst is mainly due to the generation of excess energy, which depends on the elastic strain energy stored before rock failure, outside energy input after rock failure and residual elastic strain energy. The intermediate principal stress of the rockburst experiment stored considerable residual elastic strain energy after the rockburst, resulting in an insufficient release of the elastic strain energy stored before the rockburst. The intensity of the rockburst is closely related to its excess energy release rate (EERR). With an increase in the EERR value, the cumulative energy of acoustic emission (AE) during rockbursts, the fractal dimension of rockburst fragments, and the rockburst intensity gradually increase. Highlights: The energy evolution and energy storage characteristics of true triaxial single-sided rapid-unloading rockburst experiment were studied using the graphic area method. The excess energy mechanism of the rockburst was discussed by comparing the energy storage characteristics of the true triaxial rockburst experiment and the static failure of the uniaxial compression rock. The correlation between rockburst intensity and EERR value was explored. [ABSTRACT FROM AUTHOR]

In this study, a series of impact-induced rockburst experiments were carried out by applying multilevel cyclic stresses on a cubic sandstone with a circular opening. Information on rockburst evolution was monitored using video and AE techniques together. Experimental results show that the opening in the sandstone sample was observed to undergo rock grain ejection, rock spalling and buckling in sequence. AE activity under the lower cyclic stress level followed the Kaiser's effect, while the Felicity's effect of AE was also involved at the higher cyclic stress level. Multi-axial cyclic loading can shorten the fatigue life and fatigue strength of the sandstone sample. However, the multi-axial cyclic loading can obviously reduce the AE hits and its energy rate, in which case the proportion of the AE single with low frequency is less than those under the uni-axial cyclic compression. It is also found that the failure zone in the sandstone is characterized by V-shaped notch. The depth of the failure zone is reduced sequentially under uni-axial, bi-axial, and tri-axial cyclic compression, respectively. In contrast, the extent angle of the failure zone will increase. According to the observed profiles of the failure zone, the changes of friction angle of the sandstone are interpreted by the Mohr–Coulomb strength criterion, as well as movement of the failure line due to the fatigue damage. These findings can provide insights into the study of rock failure mechanisms under various dynamic disturbances. Highlights: Impact-induced rockburst in laboratory was simulated by applying uniaxial, bi-axial, and tri-axial cyclic loadings, respectively to cubic sandstone samples with an opening. The opening in the sandstone sample was observed to undergo rock grain ejection, rock spalling and buckling in sequence. AE activity under the lower cyclic stress level can be explained by the Kaiser's effect, while the Felicity's effect of AE was also involved at the higher cyclic stress level. Failure zone around the opening in the sandstone was characterized by V-shaped notch, whose depth of the failure zone was reduced sequentially under uni-axial, bi-axial, and tri-axial cyclic compression. [ABSTRACT FROM AUTHOR]

To explore the effect of rapid excavation unloading under high pressure on delayed rockburst, a true triaxial double-sided rapid unloading rockburst experiment and a biaxial compression failure experiment without unloading were carried out. The results show that the rapid unloading of excavation before the occurrence of rockburst will cause unloading damage, and the axial strain, acoustic emission (AE) count, and AE energy will suddenly increase at the unloading point. The AE source shows that the rapid unloading produces many tensile cracks, mainly distributed near the free surface. The axial peak stress of the rockburst and the stored strain energy before failure are higher than those of biaxial compression, so the ejection velocity of free surface fragments is also higher at failure. [ABSTRACT FROM AUTHOR]

This study aims to simulate the process of rockburst and spalling failure of roadway surrounding rock under three-dimensional stress in deep rock engineering. Utilizing an independently developed true triaxial rockburst experimental setup, the failure process of a circular tunnel under initial in-situ stress at a depth of 500 m was investigated using red sandstone with prefabricated holes. A miniature camera device and acoustic emission (AE) monitoring system were used to monitor and record the experimental process in real time. Using the collected data, the process of rockburst and spalling failure of the circular tunnel was reproduced. Finally, the difference between rockburst and spalling failure was analyzed and compared based on four aspects of stress characteristics, acoustic emission characteristics, fragment characteristics, and V-shaped notch morphology characteristics. The experimental results show that the failure of surrounding rock was more likely to occur under dynamic disturbance load, resulting in particle ejection. The spalling failure was found to be a slow and gradual static failure process. The mechanism of rockburst was more complex involving tension-shear coupling failure, whereas, the mechanism of spalling failure was simple involving a tensile failure. Compared with spalling failure, rockburst was more intense, producing more debris, and the V-shaped notch was narrow and deep. Highlights: Failure process of rockburst and spalling is reproduced in a laboratory. The stress characteristics of rockburst and spalling failure are calculated based on elastic theory. Frequency-amplitude characteristics and crack types based on acoustic emission are analyzed. The failure intensity of rockburst and spalling is investigated based on the rock fragments and morphology of V-shaped notch. The failure process of rockburst and spalling is discussed along with strain energy. [ABSTRACT FROM AUTHOR]

Rockburst warnings are a significant problem in the field of rock engineering. In this study, a rockburst experimental system was developed to conduct a true triaxial single-side rapid unloading rockburst experiment. The rockburst process and time were recorded using a high-speed camera. Based on the critical slowing-down theory, the acoustic emission (AE) RA/AF, duration, and rise time in the rockburst process were studied to obtain rockburst precursor information. The main conclusions of the experiment are as follows. (1) In the early stage of rockburst, the AE signal appears to be a critical-slowing phenomenon at the critical point, which is manifested as an increase in the variance and autocorrelation coefficient, and it also appears in the increase in the variance and autocorrelation coefficient during rapid unloading. A recording made using a high-speed camera shows that the rockburst occurrence time does not necessarily correspond to the peak stress point of the stress–strain curve. (2) The variances in the AE RA/AF value, duration, and rise time are the same. The sudden change time of the precursor signal is the same, the waveform fluctuation is similar, and they all appear before the rockburst. At this time, the AE localization event shows that many high-energy events occur in the sandstone, and cracks appear on the sandstone surface. (3) The autocorrelation coefficient fluctuates considerably compared with the variance; therefore, the variance can be considered the main criterion for rockburst precursors. This study provides a theoretical basis for predicting rockbursts. [ABSTRACT FROM AUTHOR]

Rockburst may cause damage to engineering equipment, disrupt construction progress, and endanger human life. To this day, the occurrence of rockburst remains complex and difficult to predict. This study proposes the D-P-Transformer algorithm to address this issue by improving the embedding structure of the Transformer for specific applications to rockburst data. To reduce the computational requirement, sparse self-attention is adopted to replace self-attention. A distilling operation and multiple layer replicas are simultaneously used to enhance the robustness and speed up the algorithm's process. Taking all relevant rockburst factors into consideration, multiple experiments are conducted on seven large-scale rockburst datasets with different training ratios to verify the reliability of the proposed D-P-Transformer rockburst prediction algorithm. As compared to the original algorithm, the proposed algorithm shows average reductions of 24.45%, 46.56%, 17.32%, and 48.11% in the mean absolute error (MAE), mean square error (MSE), root mean square error (RMSE), and mean absolute percentage error (MAPE), respectively. The results indicate that the novel D-P-Transformer rockburst prediction algorithm is superior to the Transformer prediction algorithm, and could be used for coal mine rockburst prediction analysis. [ABSTRACT FROM AUTHOR]

• The key distinction between rockburst and spalling failure is whether the fragments possess kinetic energy at the time of final failure. • Spalling failure is attributed to static tensile failure, while rockburst is attributed to dynamic tensile-shear mixed failure. • Energy dissipation and accumulation behavior of the rock unit jointly determine the failure characteristics of the rock mass. • The excess energy within the rock unit is the source of energy that causes the violent ejection of fragment during rockburst. To reveal the differences in the failure characteristics and mechanisms between rockburst and spalling failure, the comparison experiment between spalling failure and rockburst occurred in a circular cavity were carried out. Experiment results reveal that rockburst is accompanied by the intense ejection of fragments, whereas spalling failure features with the slow detachment of fragments. Additionally, besides the plate and flaky fragment, the rockburst fragment exhibits more pronounced blocky features. In terms of strength and deformation characteristics, the peak stress for rockburst is 1.04 times that of spalling failure, whereas the plastic deformation of spalling failure is 1.75 times that of rockburst. Furthermore, considering the micro failure and energy evolution process, three interpretations were proposed to elucidate the distinct mechanisms between rockburst and spalling failure, including: (i) The swift invasion of shear cracks triggers the buckling failure of pre-existing plate-like fractures, causing the fragment ejection observed in rockburst. When shear cracks not substantially contribute to the evolutionary process, the continuous penetrating of the pre-existing tensile cracks will culminate in the gradual delamination and spalling failure of the sidewall. (ii) The energy dissipating behavior determines the distinct mechanisms of rockburst and spalling failure. Almost all of the energy input preceding rockburst is converted into the elastic strain energy of rock units, whereas the energy input preceding spalling failure results in greater energy dissipation (about 1.85 times that of rockburst). (iii) under the framework of Mohr-Coulomb strength criterion, it has been revealed that the rock units of spalling failure adhere to the minimum failure energy criterion. However, the energy accumulated by the rock units prior to rockburst surpasses the minimum energy necessary for failure. This residual energy provides the fractured rock mass with kinetic energy, ultimately leading to a violent ejection phenomenon of rockburst. [ABSTRACT FROM AUTHOR]

In this study, a new strain burst test system was used to conduct two types of strain burst experiments by rapidly unloading single and double faces (in one direction), to simulate the strain burst occurring in surrounding rock of tunnel or double tunnel faces during the opposite tunneling. A high-speed image recording system and an acoustic emission system were used to monitor the failure process of strain burst of red sandstone. The commonalities of these two types of strain burst are as follows: failure stress and percentage of dissipation energy due to crack propagation were approximately equal; the evolution of mean velocity of free face was similar, which suddenly increased first and then decreased, then the gradient increased to the extremum value, and finally decreased to zero. Subregions of the fracture were consistent, and both showed shear, buckling, splitting, and ejection zones. However, the strain burst intensity for unloading double faces was larger than that for unloading single face, as demonstrated by a larger initial ejection velocity, larger volume of burst pit, and lower peak frequency. Furthermore, when double faces were unloaded, the flaky and massive features of fragments obtained due to strain burst were more obvious than the fragments obtained from the unloading of single face. Moreover, from yield to burst, when double faces were unloaded, the sandstone strain burst contained more shear microcracks, whereas the strain burst when unloading single face contained more tensile microcracks. [ABSTRACT FROM AUTHOR]

Zonal disintegration widely exists in the excavation roadways and caverns in deep rock masses. Ultra-low friction can be generated in the deep fractured rock masses, which reduces or disappears under dynamic loading. In this paper, granite blocks were processed into cube specimens with a cylindrical hole in center. Static loads and sinusoidal disturbances were applied to study the sliding phenomenon between blocks. During the experiments, real-time images, and acoustic emissions were recorded. Results indicate blocks above the cylindrical hole slide during the second half of the sinusoidal disturbance, and block sliding is caused by a reduction of friction between the blocks. The existence of ultra-low friction can be inferred from this experiment. [ABSTRACT FROM AUTHOR]

Rockburst disaster is one of the prominent problems faced by deep underground engineering. In this study, rockburst in four elliptical holes with different axial ratios in sandstone under biaxial loading is studied as an analogue for underground roadways. Video and acoustic emission (AE) equipment is used to monitor the biaxial loading tests. Experimental results indicate that each of the elliptical holes goes through four stages: quiet period, small particle ejection, spalling, and rockburst. The duration of quiet and spalling periods increased with increasing axial ratio of ellipse. The duration of the ejection and rockburst periods remains unchanged. All the four elliptical holes have V-shaped pits after rockburst occurs. The fragments produced during rockburst are divided into coarse, medium, fine, and micro grains. The quantity of coarse and medium grains increases with increasing axial ratio. The mass ratio of coarse and medium grains increases and that of fine and micro grains decreases. The depth, angle, and area of the V-shaped pits decrease with increasing axis ratio. Tensile cracks play an important role in rockburst failure. Tensile cracks are the dominant crack types formed during rockburst and account for over 70% of all cracks in the samples. The number of tensile cracks increased and the number of shear cracks decreased. This paper has some reference value for practical engineering design and prevention of rockburst. [ABSTRACT FROM AUTHOR]

Rockburst poses a great threat to the construction safety of deep tunnels under high geostress conditions. Recently, numerous deeply buried tunnels have been constructed in China, especially in the Sichuan–Tibet railway area. In this study, two rockburst experiments (strainbursts and impact-induced rockbursts) were conducted under different initial geostresses using the strainburst experimental apparatus and impact-induced rockburst experimental apparatus equipped with an acoustic emission (AE) monitoring system. A video acquisition system was used to capture the rockburst process. The results demonstrated that the rockburst process is similar under different initial geostresses, including grains ejection, rock plates spalling/buckling, and fragments ejecting violently. Based on the result of the AE characteristics, the large- amplitude AE signals were concentrated in the lower frequency band and the rockburst intensity was increased gradually with increase in the initial geostress. The b -value and β t -value fluctuated slightly at first, subsequently increased steadily, and then decreased abruptly when rockburst occurred. Furthermore, the displacement and divergence fields on the specimen surface were calculated using digital image correlation (DIC) technology. The result shows that the zone of large deformation and high divergence is consistent with the rockburst zone. Moreover, 80%σ peak is a critical stress state where rocks begin experiencing slight damage. • Failure process of strainbursts and impact-induced rockbursts is reproduced in laboratory. • Frequency-amplitude characteristics of AE under different geostress are analyzed. • Evolution of b -value and β t -value during the experiments is investigated. • Deformation and divergence fields are calculated, and microcracks begin to initiate and propagate at 80% of the peak stress. [ABSTRACT FROM AUTHOR]