Enlai Zhao

Hydraulic supports serve as crucial equipment in a fully mechanized coal mining face, and the performance degradation assessment is a core topic for the prevention of roof disasters. Existing support degradation assessment is empirical, and transferable approaches from other machinery suffer from inadequate representation of fault-induced degradation behaviors and overlook multi-parameter correlations. This paper proposes a novel predictive performance degradation assessment approach using multivariate statistical fusion. An attention-enhanced TCN-BiLSTM model is developed to predict the future evolution of multiple operating parameters of a hydraulic support. Multi-domain features are then extracted and selected to characterize the support behavior under various fault-induced degradation conditions. Two statistics are constructed to quantify the deviation from the healthy state by evaluating both amplitude deviations and correlation changes in multiple features. A novel overall degradation indicator DI is then proposed, and the baselines at different degradation levels are determined by evaluating the probability density function using adaptive kernel density estimation. Multiple fault-induced degradation experiments are carried out on a support test rig at different severity levels. Results show that the proposed indicator achieves a degradation assessment accuracy above 85% for all fault types and above 95% for most fault types.

In order to study the explosion suppression characteristics of LPG/air mixture by CO₂ synergistic inert powder, explosion suppression experiments were conducted in a 20 L explosion device. The results show that the explosion suppression effect of NaHCO₃ powder is prior to Al(OH)₃ powder under the condition of no CO₂ synergy. As the mass concentration of inert powder increases, the peak value of explosion pressure P_ex and the peak value of the pressure rise rate (dP/dt)_ex decrease, and the explosion suppression effect gradually enhances. Gas–solid two-phase inhibitors exhibit more significant inhibitory effects than single-phase inhibitors. Increasing the volume fraction of CO₂ or the mass concentration of inert powder can improve the explosion suppression effect. The explosion suppression effect of CO₂/NaHCO₃ is significantly better than that of CO₂/Al(OH)₃. The research results have certain significance for the prevention and control of LPG explosion accidents.

This paper conducts impact dynamics experiments on coal measures sandstone in a deep mine via the established dynamic load and temperature split Hopkinson pressure bar (SHPB) experimental system. Firstly, the experimental conditions for the impact dynamics of fine sandstone were determined, with temperatures of 18, 40, 60, 80, and 100 °C, an axial static load range of 1–9 MPa, and a preset bullet incidence velocity of 1.0–5.0 m/s. Secondly, based on the analysis of the basic parameters and physical composition, the dynamic stress and strain responses of fine sandstone under different experimental conditions were obtained, and the change mechanism of its dynamic mechanical process was theoretically analyzed. When the temperature rose from 18 °C to 100 °C, the dynamic peak stress of fine sandstone increased from 36.04 MPa to 73.41 MPa, with an increase of 103.7%. At a temperature of 40 °C, when the axial static load increased from 1 MPa to 9 MPa, the dynamic stress peak of fine sandstone increased from 57.25 MPa to 80.01 MPa, and the corresponding peak strain also showed an increasing trend. The experiment analyzed the variation characteristics of dynamic stress in fine sandstone under the combined action of different strain rates or bullet incidence velocities and different temperatures. In the strain rate range of 47.1 s⁻¹ to 140.9 s⁻¹, there was a significant strain rate effect on the dynamic peak stress and peak strain of fine sandstone, which increased with the increase of strain rate. The study found a polynomial relationship between the dynamic mechanical parameters of fine sandstone and the impact of experimental parameters, with a coefficient of determination greater than 0.9. A dynamic stress constitutive model for fine sandstone under one-dimensional stress state under dynamic load and temperature action was established, and the model validation and parameter determination of dynamic stress changes in fine sandstone under different temperature conditions were carried out. The research results provide a new experimental method for the static and dynamic mechanical analysis of coal and rock masses under complex geological conditions and can provide a basic reference for the prevention and control of dynamic disasters in deep mining processes.

Coal and rock dynamic disasters such as rock burst and outburst seriously threaten the sustainable development of the coal mining industry, which are intimately correlated with the nonlinear dynamic response process of the deep coal and rock mass. This study conducts coal dynamic experiments under vibration load from room temperature to 60 °C by using the split Hopkinson bar (SHPB) with a temperature real-time control system and analyzes the variation in stress and strain and the energy dissipation characteristics of coal during the dynamic load process. The expression equation of dissipated energy of coal at different scales is established, and the judgment conditions of the macroscopic mechanical behavior of coal are analyzed theoretically. The stress curves show a multi-stress peak phenomenon when the coal samples are subjected to different temperatures and dynamic loads, and the coal’s dynamic stress and temperature show a polynomial fitting relationship at different stages. When the coal sample is subjected to temperature and dynamic load, the macroscopic changes in incident energy, reflected energy, and dissipated energy are consistent; that is, various energies gradually increase to a fixed value and tend to stabilize with the time of stress wave action. The transmission energy exhibits a rising trend in correlation with the duration of the dynamic load action, but the value is less than 0.1 J. The growth gradients of the different energies, in descending order, are: the growth gradient of incident energy, reflection energy, dissipation energy, and transmission energy. The energy inflection point appears at 60 °C. Based on the linear elastic fracture mechanics and damage mechanics theories, the expression for coal energy dissipation from the nanoscale to the microscale is established, and the relationship between energy dissipation and macroscopic mechanical behavior response of the coal samples is analyzed. The main physical components of the coal sample are calcite and kaolinite. Within the temperature range of 18–60 °C, the macroscopic failure form of the coal is horizontal tensile failure. The study results are introduced into dynamic disaster prevention and control and the surrounding rock system stability evaluation in deep mines.

The complex mechanical environment of deep coal and rock masses leads to obvious changes on their dynamic mechanical properties. However, there are few reports on the dynamic mechanical properties of rocks under the combined action of medium temperature (normal temperature ∼100°C) and static and dynamic loads. In this paper, a dynamic load and temperature combined action Hopkinson pressure bar experimental system is used to experimentally study the impact type of a fine sandstone under temperature conditions of 18°C, 40°C, 60°C, 80°C, and 100°C, an axial static load of 3 MPa, a gas chamber pressure of 0.06 MPa, and a constant temperature time of 4 h. The dynamic characteristics of the change law of the fine sandstone and the energy dissipation characteristics of the load process are analyzed, and the characteristic law of the fine sandstone surface response is analyzed using digital image correlation technology. Our results indicate the following. (1) Under conditions in which the other experimental conditions remain unchanged, the dynamic stress‐strain of the fine sandstone presents a bimodal shape with a “rebound” phenomenon. Increasing temperature causes the peak strength of the fine sandstone to increase; however, the relative strength can increase or decrease. The relative increase in the strength is 1.14 MPa (°C) when the temperature increases from 40°C to 60°C, 0.15 MPa (°C) when the temperature increases from 60°C to 80°C, and 0.62 MPa (°C) when the temperature increases from 80°C to 100°C. (2) The digital image correlation results show that, under the action of a dynamic load stress wave, the fine sandstone experiences a displacement vector change on the sample surface; furthermore, under the combined action of the temperature and dynamic and static loads, the fine sandstone experiences macroscopic shear failure. The surface strain in the propagation direction of the stress wave is obviously higher and can even reach values of more than 10 times that of the strain in other directions. (3) From the perspective of energy dissipation, the incident energy, reflected energy, and dissipated energy of the fine sandstone under an impact load have the same change law. After being affected by a dynamic load, the energy rapidly increases to a certain value and then remains relatively stable. The transmitted energy is relatively small and can be approximated as a horizontal line. As the temperature increases, the incident energy, reflected energy, and dissipated energy tend to first decrease and then increase, and most of the incident energy in the fine sandstone is dissipated in the form of reflected waves.