During the exploitation of deep resources, rocks are often in a high-temperature, high-pressure environment. It is of great significance to study the acoustic emission (AE) characteristics of thermal damaged rock under load to improve the accuracy of monitoring in practical engineering. In this paper, sandstone was heated at different temperatures, before a uniaxial compression test was performed and the AE in the process was monitored. The results show that the strength and AE energy of sandstone decrease gradually with an increase in heating temperature. Through frequency domain analysis of the AE waveform at the time of failure, it was found that the frequency and intensity of AE also showed a downward trend with an increase in temperature. In addition, multifractal theory is introduced to deconstruct the waveform data. The multifractal characteristics of the waveforms decrease with an increase in temperature. It provides new parameters for waveform analysis, which can be combined with frequency analysis as parameters to more accurately identify rock failure in engineering practice. The attenuation of AE of thermally damaged sandstone may be related to an increase in porosity and a decrease in elastic energy release.

The majority of water inrush accidents in coal mines are caused by mining engineering activities. To avoid water inrush accidents, the Time-lapse Electrical Resistivity Tomography (TLERT) is applied to monitor water migration in fractured zone. A great challenge for the application of TLERT monitoring is the huge and numerous time series data sets generated by monitoring systems, which are difficult to process manually. This research proposed a distributed fuzzy clustering algorithm based on kernel function estimation to analyze TLERT images automatically. The resistivity date can be classified with different cluster centroids. The fuzzy c-means algorithm was chosen to display resistivity change. The algorithm was validated using a floor water inrush model. The results indicate that the water migration in the fractured zone can be monitored automatically and the edge of the resistivity changing area can be shown clearly.

Seismic wave propagation in complex terrains, especially in the presence of air layers, plays a crucial role in accurate subsurface imaging. However, the influence of different boundary conditions on seismic wave propagation characteristics has not been fully explored. This study employs the finite element method (FEM) to simulate and analyze seismic wavefields under different boundary conditions, including perfectly matched layer (PML), Neumann free boundary conditions, and air layer conditions. First, the finite element solution for the 2D frequency-domain acoustic wave equation is introduced, and the correctness of the algorithm is validated using a homogeneous model. Then, both horizontal and undulating terrain interfaces are designed to investigate the kinematic and dynamic characteristics of the wavefields under different boundary conditions. The results show that PML boundaries effectively absorb seismic waves, prevent reflections, and ensure stable wave propagation, making them an ideal choice for simulating open boundaries. In contrast, Neumann boundaries generate significant reflected waves, particularly in undulating terrains, complicating the wavefield characteristics. Introducing an air layer alters the dynamics of the wavefield, leading to energy leakage and multi-path effects, which are more consistent with real-world seismic-geophysical models. Finally, the computational results using the Overthrust model under different boundary conditions further demonstrate that different boundary conditions significantly affect wavefield morphology. It is essential to select appropriate boundary conditions based on the specific simulation requirements, and boundary conditions with an air layer are most consistent with real seismic geological models. This study provides new insights into the role of boundary conditions in seismic numerical simulations and offers theoretical guidance for improving the accuracy of wavefield simulations in realistic geological scenarios.

Coal rupture in coal mining is prone to cause rockburst dynamic hazards. To investigate the effect of joint structure characteristics on the mechanical behavior and the fracture mechanism of coal sample. In this study, uniaxial compression numerical simulation experiments were carried out on coal sample with joint spacings (JSs) of 3 mm and 6 mm and joint angles (JAs) of 0°, 30°, 60°, 90°, respectively, by using the discrete element method (DEM) method. The combined effect of JS and JA on the mechanical properties of coal and its damage mechanism is investigated. The results show that: (1) By increasing JA, the uniaxial compressive strength (UCS) of the specimen first decreased and increased, and the UCS was minimized at θ = 60°. The cracks in the coal sample were transformed from “X”-shaped distribution to “V”-shaped distribution and were dominated by shear cracks. (2) The enlargement of JS contributed to increasing the UCS of the coal sample. At the same time, the crack length remarkably expanded, and the crack distribution broadened. (3) A smaller JA favors the development of tensile cracks and the aggregation of tensile chains towards the end of the specimen. The cracking inclination of the coal sample showed an inverse “N”-type movement with the increase in JA. (4) As the increase in JS benefits the forming of tensile cracks, the extension of cracking inclination of coal sample diminishes. The spread range and accumulation level of tensile chain grows.

In longitudinal ventilation tunnel fires, the thermal characteristics become more intricate due to the presence of blockages. This phenomenon becomes more complex when multiple blockages occur, which results in a unique interaction between the fire and longitudinal ventilation through gaps between the blockages. Most of the previous studies have only considered single obstacles or have only performed qualitative analyses and have not obtained predictive models. To fill this research gap, we conducted numerical simulations using the Fire Dynamic Simulator (FDS) to study the effects of vehicular blockages in three lanes and two fire locations. Our study highlights the differences in the flame behavior, maximum temperature rise, and smoke back-layering length in the presence of multiple blockages and reveals that as the ventilation velocity increases, the flame bifurcation angle increases and the smoke back-layering length decreases. Additionally, when the fire is in the side lane, the flame tilts towards the sidewall, leading to higher maximum temperatures compared to those in the middle lane. Based on these findings, we have developed modified formulas that predict the maximum temperature rise, smoke back-layering length, and maximum temperature ratio at different fire locations and blockage rates, which are linearly related.

The transient electromagnetic (TEM) method is a widely used geophysical technique for detecting subsurface electrical structures. However, its inversion results are typically limited to resistivity parameters, making it challenging to directly infer key petrophysical properties, such as water saturation and porosity. This study proposes a petrophysics parameter inversion approach based on TEM data. By constructing multiple geoelectric models with varying porosities and water saturation values for numerical simulations, the results demonstrated that both the forward and inversion responses of the TEM field maintained errors within 5%. The inversion procedure begins with the reconstruction of the subsurface resistivity distribution, which reliably reflects the true geoelectric model. Based on the inverted resistivity, the water saturation and porosity parameters are subsequently estimated. The inversion results closely match the overall trend of the actual model and exhibit a clear response at the target layer. Finally, the proposed method is applied to a field test at the Tongxin Coal Mine. By integrating subsurface electrical responses with geological data, the spatial distributions of water saturation and porosity within the coal-bearing strata were delineated. This provides a scientific basis for the detailed characterization of the physical properties of coal and surrounding rock, as well as for understanding the development of pores and fractures in underground strata.