To prevent coal mine roof water damage, the water generally needs to be evacuated in advance. It can be mined with the water inrush risk assessed as safe. However, a single index is often employed in the water safety evaluation after the roof drainage, which causes a large gap between the evaluation results and the actual situation. Therefore, the evaluation cannot be effectively used to guide the safety mining in the working face. In this paper, based on the hydrogeological data of the Liangshuijing coal mine, a multifactor water inrush risk assessment model (IAHP-EWM) and multifactor index system are established for assessing the water inrush risk before and after the roof drainage. The improved AHP method and the entropy weight method are adopted in the model to determine the index weight. This combined way avoids the excessive subjectivity and objectivity of the index weight. A″ Fold undulation degree ( F ud )″ is innovatively proposed to quantify the impact of the spatial relief of folds on water inrush in the multifactor index system. The IAHP-EWM model is applied to evaluate the risk of roof water inrush in the 42205 working face of the Liangshuijing coal mine. The evaluation results show that the water inrush risk is ″high″ when the water is not dredged, and the water inrush risk is ″low″ after the water is dredged, which are consistent with the actual water inflow data and evaluation results, which verifies the accuracy of the model. The application results of the IAHP-EWM model in the 42202, 42203, and 42204 working faces verify its universal applicability in the Liangshuijing mining area. It can provide a reference for the evaluation of the roof water damage control effect during coal seam mining.

A combination of geographic information system (GIS) and spatial multicriteria decision making (MCDA) in mine water inrush risk evaluation is widely used, but the randomness in the process of index weight determination and the risk-coping attitude of decision makers are not considered in the decision making process. Therefore, this paper proposes a probability-based roof water inrush risk evaluation method (GIS-MCDA) by combining the Monte Carlo analytic hierarchy process (MAHP) and ordered weighted averaging (OWA) operator. This method uses MAHP to determine the weight of the evaluation indicators, reducing the randomness of the analytic hierarchy process (AHP) to determine the weight of the evaluation indicators using the OWA operator to quantify the five risk-coping attitudes of decision makers and incorporate the risk attitude of decision makers into the evaluation process. Taking the Liangshuijing Coal Mine in northern Shaanxi as an example, the application of the GIS-MCDA method showed that the method makes the risk results of roof water inrush more objective and comprehensive and reduces or avoids the risk of decision making due to human subjective tendency change.

After coal mine wastewater is artificially injected into a groundwater reservoir transformed from a goaf, micron-sized suspended matter in the wastewater is purified by the broken rock mass in the goaf. Existing studies can only analyze the macroscopic changes in the content of suspended solids during the purification process, and it is difficult to explain the microscopic deposition mechanism of the suspended solids in broken rock. This paper studied the microscopic deposition behavior of micron-sized suspended solids inside the broken rock mass via numerical simulation using a coupled CFD-DEM method. In addition, indoor model tests were carried out to verify the accuracy and reliability of the model in comparison. The study results show that suspended solids’ deposition behavior varies significantly under broken rock masses’ different pore sizes (0.47 mm, 1.14 mm, 3.00 mm, and 5.33 mm). Within the goaf, the adsorption of suspended solids by the broken rock mass plays a dominant role. At the same time, suspended particles are mostly collected in the inlet area, and the difference in the number of deposited particles can reach 74% when comparing the first 50 mm range as well as the 50–100 mm range. The number of deposited particles at a flow rate of 0.02 m/s is 14% more than that at a flow rate of 0.06 m/s. This work offers new ideas for studying the purification mechanism of coal mine wastewater within a goaf.