Study on the pressure relief energy dissipation law of variable-diameter boreholes in roadway surrounding rock under dynamic and static loads.

To address the conflict between pressure relief and support effectiveness caused by large-diameter boreholes in roadway surrounding rock, this paper proposes a method involving variable-diameter boreholes for pressure relief and energy dissipation. With a typical rock burst coal mine as the engineering context, the study establishes a mechanical model for variable-diameter boreholes through theoretical analysis to examine the elastic stress distribution around boreholes within the coal body. Physical similarity simulation tests are conducted to investigate the influence of conventional borehole and variable diameter borehole on the transmission pattern of dynamic load stress waves. Furthermore, numerical simulations are employed to explore the effects of reaming diameter, depth, and spacing on pressure relief, energy dissipation, and attenuation of dynamic stress wave transmission in roadway surrounding rock. The results demonstrate that stress within the coal surrounding the variable-diameter borehole correlates with the borehole radius, lateral pressure coefficient, and distance from the point to the borehole center, the extent of the plastic zone is influenced by borehole diameter, spacing, and depth. Increased diameter, reduced spacing, and greater depth of deep reaming holes exacerbate the transfer of stress concentration from the surrounding rock of the roadway to the deeper regions, facilitating the formation of stress double peak areas. Moreover, the variable diameter position should be within the original stress peak position of the surrounding rock in the roadway, with deep reaming passing through the stress concentration area for optimal results. This study offers guidance on the prevention and control technology for rock bursts in deep coal mining operations.

Stability evaluation of open-pit mine slope based on Bayesian optimization 1D-CNN.

As mechanized open-pit coal mining intensifies, assessing and predicting slope stability has become increasingly important. To address the limitations of traditional mechanical calculations, numerical simulations, and physical experiments, this paper identifies the key factors impacting slope stability in open-pit mines and develops a multi-parameter sample data set. The study employs hyperparameters optimized using a Bayesian algorithm, introduces additional convolutional layers, and combines the Adam optimizer with dropout techniques to enhance the feature extraction and performance of one-dimensional convolutional neural networks (1D-CNN). This leads to a Bayesian-optimized one-dimensional convolutional neural network (B-1D MCNN) model for predicting slope stability.The study evaluates the classification performance and accuracy of various models for slope stability, including BP neural networks, genetic algorithm-optimized convolutional neural networks, 1D-CNN, and B-1D MCNN, using accuracy, precision, and F1-score as metrics. The analysis also examines the influence of factor indicators and training set length on the model's output to assess its generalization capabilities.The research findings suggest that: (1) the B-1D MCNN model for evaluating slope stability demonstrates the capability to accurately depict the nonlinear correlation between influencing factors and slope stability. (2) Compared with other models, the B-1D MCNN model has shown enhancements of 10.96% to 27.85%, 10.26% to 28.55%, and 8.98% to 25.05% in terms of Accuracy, F1-Score, and Precision, respectively. (3) As the length of the training dataset increases, the performance of the model improves accordingly. (4) The B-1D MCNN model shows a generalization power of 87.5%.

Study on time-frequency features of induced charge signals during the damage and failure process of coal medium.

Monitoring and preventing coal-rock dynamic disasters are vital for safe mining. To investigate the time-frequency features of induced charge signals with coal damage and failure of roadways, the generation mechanism of free charge in loaded coal is analyzed and the induced charge monitoring test is conducted. According to the stress-induced charge-time curves, the time-domain features of charge signals at each loading stage are obtained. The wavelet threshold denoising approach and generalized Morse wavelet transform method are applied to denoise the raw signals and study the frequency-domain features. Further, the quantitative relationship between the de-noised induced charge signals and the degree of coal damage is established. The results show that the event number, amplitude and fluctuation degree of available induced charge signals are all at a low level in the compaction and elastic stages of the coal, which are mainly generated by the piezoelectric effect and predominantly represent discreteness. When entering the plastic and failure stages, the available signals are primarily produced by the crack propagation and triboelectric effects, with a significant increase in the event number, amplitude, and fluctuation degree. Then the induced charge signals gradually transit from discrete to continuous. Generally, the dominant frequency of the available induced charge signals during the coal damage process is concentrated at 0 ~ 11 Hz. The available induced charge is positively correlated with the degree of coal damage, which can perform the damage degree of coal mass, providing a new approach to evaluate the stability of roadway surrounding rocks.

Analysis of the impact of the combined use of rebar bolts and FRP bolts in the roadway enclosure.

In order to investigate the support effect of the combination of FRP bolts and rebar bolts in the roadway, taking a coal mine as the background of the project, research and analysis of the engineering geological conditions of the mine and the layout of the mining roadway, stress analysis of the roadway peripheral rock, and put forward the combination of rebar and FRP bolts in the roadway peripheral rock support program. Based on different scenarios, FLAC3D was applied to simulate and analyze the distribution of axial force, maximum principal stress of the surrounding rock, yield damage of the surrounding rock, and displacement of the surrounding rock under three conditions: no support, full rebar bolt support, and combined rebar and FRP bolt support. The results show that (1) In the pre-action period between the bolt and the surrounding rock of the roadway, the FRP bolt carries the force first; in the late action period, the rebar bolt and the FRP bolt carry the force together. (2) From the analysis of the stress concentration degree of the maximum principal stress of the roadway surrounding rock, the horizontal displacement of the roadway surrounding rock and the distribution characteristics of the plastic zone of the roadway surrounding rock, it can be concluded that the support strength of FRP bolts is slightly lower than that of rebar bolts. (3) Under the state of combined support of FRP and rebar bolts, the range of plastic zone of surrounding rock in the roadway is analyzed in comparison with the effect of full rebar bolt support, and the range of reduction of plastic zone of surrounding rock is not obvious, and the effect of full rebar bolt support and combined support of FRP and rebar bolts on controlling the damage of surrounding rock is similar. (4) The side part of the roadway perimeter rock mining adopts FRP bolts instead of rebar bolts, and if the FRP bolts are not damaged, the combination of FRP and rebar bolts can be used for support, which can maintain the stability of the roadway perimeter rock.