No abstract

Physical simulation is one of the effective methods to study mining problems, but the selection and proportion of simulation materials are greatly affected by the regional environment. This paper is based on a multilevel orthogonal design test scheme using sand, lime, and gypsum as the materials in the Shangwan coal mine in the Shendong coalfield, with the sand to cement ratio, paste to ash ratio, and maintenance days as variables. The effect of the polar difference method on the strength and density of gypsum was used as a reference for physical simulation in the Shendong coalfield. The sensitivity analysis of each factor was carried out by the polar difference method, and the influencing factors on density were, in descending order, sand to mortar ratio, mortar to ash ratio, and the number of maintenance days; the influencing factors on strength were, in descending order, mortar to ash ratio, maintenance days, and sand to mortar ratio. The sand cement ratio was negatively correlated with strength and density, the paste to ash ratio was positively correlated with strength and density, and the number of maintenance days was positively correlated with strength and negatively correlated with density. The multivariate non-linear regression analysis of sand to cement ratio and paste to ash ratio identified similar material proportioning test equations for the Shendong coalfield, which can improve the accuracy of physical simulation and be used to guide physical simulation experiments in the Shendong coalfield.

The remote sensing ecological index (RSEI) has been widely used in the rapid monitoring and evaluation of the regional ecological environment; however, the research on the main factors that cause changes in RSEI and the impact of human activities in the mining area on RSEI is not often explored. To this end, this paper selected the Landsat (TM/OLI) series of remote sensing images from 1986 to 2022; extracted the four important indicators of the normalized difference vegetation index (NDVI), the wetness component of the tasseled cap transformation (WET), normalized difference built-up and soil index (NDBSI), and land surface temperature (LST); calculated the remote sensing ecological index (RSEI) based on the principal component analysis method; monitored and evaluated the ecological environment changes in the Shendong Mining Area for a period of 36 years; and analyzed the driving forces that cause these ecological environment changes. The results show the following: (1) The ecological status of the study area has shown an overall upward trend during the 1986–2022 period. (2) From 1986 to 2022, the area of RSEI with a grade of 0.4–0.6 increased by 1142.74 km2, that with a grade of 0.6–0.8 increased by 124.09 km2, and that with a grade of 0.8–1.0 increased by 0.73 km2. (3) In the past 36 years, the proportion of RSEI with a positive grade difference was 97.52%, and the proportion of regions with a negative grade difference was 6.20%. (4) Rainfall is the main factor that causes changes in the regional ecological environment. By analyzing the main driving factors of ecological environment change and the relationship between human activities and RSEI, reference can be provided for the formulation of environmental protection policies and environmental planning in mining areas.

The temporal pattern of water−rock interaction is significant in predicting the ion concentration of the effluent in coal mine underground reservoirs. This study used the roof-caved rock samples and main incoming water (mine water and fissure water) of the Daliuta coal underground reservoir as the research object and designed four groups of dynamic simulation experiments of the water−rock interaction. Based on the main ion concentrations in the water sample at different reaction times, Q-type hierarchical cluster analysis (HCA) was used to classify the stages of water− rock interaction. The types and intensities of water−rock interaction in each stage were identified by combining the ion ratio and principal component analysis (PCA). Q-type HCA shows that the dynamic simulation experimental water samples can be divided into three categories according to the reaction time, representing the early, middle, and late stages of the water−rock interaction process. The influence of water quality on the division of the water−rock interaction stage is greater than that of rock characteristics. The ion ratio and PCA show that the dissolution of pyrite minerals, cation exchange reaction, and mineral adsorption mainly occur in the early stage of water−rock interaction, in which the cation exchange reaction plays a leading role in the change of ions in water. In the middle stage, the cation exchange reaction and the dissolution of carbonate minerals, such as calcite and dolomite, mainly occur, in which mineral dissolution is the main. In the late stage, the water−rock interaction is relatively weak, and the change of ion concentration in water is not obvious. This study proves the temporal patterns of water−rock interaction between caved rock and mine water (or fissure water) and differences in the types and intensities of water−rock interaction in each stage. The results can provide a theoretical basis for the optimization of the operation cycle of coal mine underground reservoirs and the prediction of effluent ion concentration.

Coal mining subsidence leads to reductions in soil fertility. In order to improve soil physical and chemical properties and to promote vegetation restoration, a nitrogen-fixing bacterium named S1 was isolated from the coal mining subsidence area in the Shendong mining area, and a zeolite-immobilized nitrogen-fixing bacterium was studied to improve the soil in the subsidence area. The results show that the immobilized nitrogen-fixing bacteria can significantly improve the ammonium nitrogen and nitrate nitrogen of soil by 50 times and 0.6 times, respectively, at 20 days, and it can also improve organic matter. In pot experiments, it was found that immobilized microorganisms can improve germination rate, plant height and the dry and fresh weight of maize. The results of the above soil culture tests and pot experiments were then compared and analyzed. It was found that plants made obvious use of soil ammonium nitrogen and nitrate nitrogen, and planting the plants was conducive to increases in soil organic matter.