The meso-structural changes of rocks during repeated cycles of water invasion are the fundamental cause of macroscopic physical property damage. In this paper, based on the computed tomography scan images of rock samples under different numbers of water invasion cycles, a three-dimensional pore network model was constructed to analyze the changes in pore structure under the action of water invasion. The damage variable was introduced to quantitatively characterize the parameter damage of each pore and reveal the evolution of rock meso-damage. The results show that 81% of the pore radius is less than 10 μm under 0 water invasion cycles and that 76% of the pore radiuses are less than 10 μm after 10 water invasion cycles. After 10 water invasion cycles, the peak range of the pore radius distribution enlarged from the initial range of 2–4 μm to that of 4–6 μm and the proportion of pore throats with a radius less than 10 μm decreased from an initial 82–72%. With an increase of water invasion cycles, the proportion of large pores increased and the connectivity among pores enhances gradually. The damage variable of each pore parameter changed the most during 2–5 water invasion cycles. After 10 water invasion cycles, the maximum degree of damage that the pore volume reached was up to 41.44% and the minimum degree of damage of the pore coordination number was 5.80%. The test results helped to reveal the pore structure changes and the damage of rock samples during water invasion cycles.

To prevent serious shaft deflection disasters under asymmetric mining conditions, it is urgent to solve the problem of designing shaft protection rock pillar (SPRP) sizes in thick soil and thin rock strata. In this paper, based on the parallel mining model and the perpendicular mining model, a dynamic prediction model that can describe the horizontal movement of the shaft was established by the probability integration method and the Knothe time function. Next, according to the measured data of the shaft deflection in the Guotun Coal Mine, a back analysis was used to calculate the prediction parameters that were suitable for the deep soil strata. Based on the mining model, the variation law of the horizontal deflection displacement of the shaft and SPRP size was obtained. The results showed that the final displacements of the shaft under the two ideal mining models were equal, while the parallel mining model was superior to the perpendicular mining model at the initial stage of mining. The horizontal displacement of the shaft head had a nonlinear negative correlation with the SPRP, and the SPRP size in thick soil and thin rock strata calculated by the parallel mining model was more reasonable. For the Guotun Coal Mine, when the soil movement angle was 57.8% of the actual value, the horizontal displacement of the main shaft head was reduced by 87%. The results have important theoretical and practical value in preventing shaft deflection in thick soil and thin rock strata.

As a common geological disaster, surface subsidence caused by mining underground resources has always been a hot and difficult topic in the civil engineering field. Aimed at the shortcomings of existing time function models in predicting mining subsidence in deep soil strata, a more accurate and reasonable time function model, called the composite function model, was established based on an inverted analysis of measured data. The results showed that the composite function model could describe the whole subsidence process of a deep soil surface and agreed well with the measured data. The model parameters were calculated by specific formulas, which improved the reliability of the subsidence prediction results under different mining conditions. The new model provided important guiding significance for preventing subsidence geological disasters and determining the coal mining time under the buildings, the railways, and the water bodies in deep soil strata.

Indentation hardness and brittleness are the important factors to be considered in the study of rock-like materials’ mechanical crushing behaviors. The brittleness of rock-like materials is defined as the ratio of uniaxial compressive strength to tensile strength in this paper. In order to investigate the influences of hardness and brittleness on rock-like materials’ crushing behaviors, quartz sand and high strength α-hemi-hydrated gypsum were used to prepare rock-like materials with different hardness and brittleness through different mass ratios. The artificial rock-like materials can eliminate the effects of natural rock’s weak structure plane on experimental results. The indentation test, Uniaxial compressive test, and Brazilian tensile test were conducted for characterizing the indentation hardness and brittleness of this artificial rock-like materials. The experimental results showed that brittleness increased with the increase of indentation hardness with high correlation coefficient. The confining stress presented a positive impact on the indentation hardness of the rock-like materials. Based on those mechanical properties, the numerical rock models were calculated to study rock crushing behaviors using discrete element method (DEM). A series of rock crushing tests were conducted to investigate the influences of hardness and brittleness of rock-like materials on rock crushing behaviors using a conical pick cutter. The numerical results showed that the normalized specific energy was negatively correlated with indentation hardness index (IHI). The normalized specific energy decreased with the increase of brittleness index (BI) with a high correlation coefficient. This study is beneficial in utilizing IHI and BI to evaluate the mechanical properties, failure patterns, and mechanical crushing efficiency of rock-like materials.