Clay minerals are the common insoluble cementing substances in soil. To study the mechanical effect of montmorillonite under the action of acid rain, the variation law and mechanism of the cohesive force and internal friction angle were discussed by immersing montmorillonite‐quartz remolded soil in HNO₃ solution with pH = 3. It was found that, under acidic conditions, the cohesive force increased after the first drop and subsequently decreased again, while the internal friction angle remained basically unchanged. Considering the vertical pressure of soil landslide, the change in the shear strength of cohesive soil under acid rain is consistent with the change in the cohesive force. The X‐ray diffraction (XRD) results showed that the acid could erode the cement‐montmorillonite, and no new substance was generated, which caused a decrease in cohesion. In addition, based on the microcementation nature of montmorillonite and the change mechanism of cohesion under acid rain, the cohesive force model of saturated montmorillonite‐quartz remolded soil under acid rain was established. The change trend of calculated cohesion values was consistent with the one of measured values, and the error was small.

To clarify the activity patterns and source characteristics of coal mining–induced microseismicity, this study analyzed the spatial distribution characteristics of microseismic events in the Datong coal mining area based on records from the regional digital seismic network. We conducted a detailed characterization of the depth distribution characteristics of microseismic events using the double-difference localization method. Additionally, the source parameters, including corner frequency ( fc), source rupture radius ( r), seismic moment ( M₀), source radiated energy ( E_s), and stress drop (Δσ), were calculated for 136 mine-induced earthquakes with magnitudes ranging from M_L1.3 to M_L3.2. The results show that M_L ≥ 2.0 mining-induced seismic events occur mainly within numerous microfractures in the Datong mining area. The depth of the seismic sources in the mining area is concentrated at 200∼500 m, with significant north–south differences and a close correlation with the mining depth. The displacement spectra of microseismic sources show agreement with the Brune source model [ ] attenuation pattern. As M₀ gradually increases, r, Δσ, and E_s show an increasing trend, while fc gradually decreases, exhibiting characteristics similar to those of tectonic earthquakes. Compared to tectonic earthquakes, coal mining-induced earthquakes have lower corner frequencies and stress drop levels mainly because mining activities alter the originally stable geological structure and stress state, leading to weakened rock strength, decreased elastic modulus, and shallower source depths. These factors contribute to the reduction in corner frequencies. As mining operations continue, microfracturing occurs in the coal and surrounding rock mass, intensifying the dynamic instability of the rock mass that was already under high stress conditions. This situation triggers larger-magnitude, mining-induced seismic events under lower stress conditions.

To study the mechanical effect of clay under acidic and basic conditions, typical clay minerals, montmorillonite and illite, were taken as the main research objects in this study. The variation law and mechanism of the cohesive force and internal friction angle were studied by immersing the remoulded soil in HNO₃ solution with pH = 3 and NaOH (alkaline waste liquid) with pH = 13.5, respectively. It was found that, under acidic conditions, a corrosion reaction between clay minerals and nitric acid occurred. Except for the medium-term, the cohesion generally shows a decreasing trend, and the internal friction angle has little change. Under alkaline conditions, the cohesion of montmorillonite-quartz sand remoulded soil decreased briefly in the early immersion stage of and increased in the middle and late stages. The internal friction angle increases steadily with the extension of immersion time. The cohesion of illite-quartz sand remoulded soil also decreased first and then increased, while the internal friction angle changed little. X-ray diffraction analysis shows that montmorillonite and illite will corrode under acidic conditions, and no new material will be generated, resulting in a decrease in soil cohesion. Under alkaline conditions, montmorillonite was seriously depleted, resulting in the formation of zeolite minerals (zeolite X, garronite) and new cement hydrated calcium silicate CSH (xonotlite). Strong alkali reacts with illite to generate sodium metaaluminate (NaAlO₂) and liquid cement Na₂SiO₃ (sodium silicate). The formation of new cements is the main reason for the increase in cohesion under acid-base conditions, and chemical corrosion and ion exchange cause a decrease in cohesion.

In situ thermal injection modification is an effective approach to address issues such as low production efficiency and poor safety in deep coal mining. During pyrolysis, the pore structure of coal significantly changes, which in turn alters the permeability of pyrolyzed coal seams. Research on porosity evolution models during pyrolysis is crucial for evaluating oil and gas production efficiency and assessing groundwater environmental impacts in mining areas. To address the current limitations of experimental methods that cannot achieve real-time continuous measurement and quantitative description, a universal porosity evolution model for coal during pyrolysis is established in this study. The model is based on the mechanism of organic matter decomposition and is combined with pyrolysis reaction kinetics. Taking the No.2 coal seam of Cixi Mine in Fengfeng Mining Area and the No.12 coal seam of Zhaogezhuang Mine in Kailuan Mining Area, both with a burial depth of over 1000 m, as the research objects, the calculated values were compared with the measured data. The error was relatively small, and the simulated curve of coal porosity variation during pyrolysis was highly consistent with the measured curve, which proves that the established model can accurately and quantify the porosity evolution process of pyrolyzed coal.

To determine the source characteristics of mining-induced earthquakes, the corner frequency fc, rupture radius r, seismic moment M0, radiated seismic energy Es, and stress drop Δσ of 80 micro-earthquakes with 1.0≤ML≤3.3 in the Datong coal mine were calculated based on waveform records from the regional digital seismic network. The Scaling relationships between these parameters and M0 were studied, and the reasons for the lower levels of corner frequency and stress drop in mining-induced seismicity were analyzed. The results show that the displacement spectrum of the source of mining-induced earthquakes in the Datong coal mining is consistent with the Brune model ω-2 attenuation pattern. Using this ω-2 model, the source parameters of micro-earthquakes in the Datong coal mine were estimated. The fc ranges mainly from 0.82 to 4.64 Hz, the r ranges from 67.89 to 382.65 m, and the Δσ from 0.03 to 0.85 MPa. The M0 estimated from the zero frequency limit ranges from 5.85e+10 to 7.66e+13 Nm, and the Es ranges from 7.34e+4 to 7.07e+8 J. With the increase of M0, the source parameters of r, Δσ, and Es show an increasing trend, while the fc decreases gradually, exhibiting characteristics similar to tectonic earthquakes. Mining-induced earthquakes in the Datong coal mining area have lower corner frequencies and stress drop levels than tectonic earthquakes. This is mainly due to the artificial alteration of the initially stable geological structure and stress state during mining. This leads to deformation and micro-fracturing of the coal and rock mass in the roof and floor, approaching or reaching a critical, unstable state. With the continuous mining operation, mining-induced earthquakes occur in a lower-stress environment under the multiple coupling effects of the self-weight stress of the coal and rock mass and mining-induced stress disturbance.