The Comprehensive Identification of Roof Risk in a Fully Mechanized Working Face Using the Cloud Model

Comprehensive Identification of Surface Subsidence Evaluation Grades of Mines in Southwest China

Due to their complex geological structure, it is difficult to systematically analyze the surface subsidence of coal mines in southwest China, and the factors that cause surface subsidence are also different from other coal mines. Focusing on the problem of surface subsidence caused by mining in southwest China’s mines, a grade evaluation system for surface subsidence of southwest mines is constructed based on the analytic hierarchy process, and ten evaluation indicators are established from the perspectives of mining disturbance and geological structure. A matter–element model of surface subsidence based on matter–element extension theory and a cloud model of surface subsidence based on cloud theory are then constructed. A coal mine in Anshun, Guizhou, is taken as an example to calculate the evaluation level of surface subsidence and thus verify the scientificity of extension theory and cloud theory. The results show that the main factors that affect the surface subsidence of southwest mines are the number of coal seam layers, mining height and comprehensive Platt hardness of rock, similar to that of northern plain coal mines. Surface slope and subsidence area are also very important. The comprehensive correlation degree of each grade of the coal mine is −0.29836, 0.192232, −0.1093 and −0.46531, and the coal mine is concluded to be in grade 2. The calculated similarity of the overall index evaluation cloud map of the coal mine and each grade is 0, 0.3453, 0.7872 and 0, respectively. The coal mine is in grade 2, which is a relatively safe state. Consistent with the calculation results of the extension model and in line with the field situation, the extension matter–element model and cloud model built in this paper can verify each other and have a certain scientificity.

Study on Failure Characteristics and Control Technology of Roadway Surrounding Rock under Repeated Mining in Close-Distance Coal Seam

In this study, taking the Sheng’an coal mine as an engineering background, the failure characteristics of the surrounding rock of a roadway under repeated mining in a close-distance coal seam is comprehensively illustrated through field measurements (e.g., drilling imaging), theory analysis and numerical simulation (finite difference method (FDM)). The results show that although the return airway 10905 remains intact, the apparent failure of the roadway’s roof and the coal pillar can be observed. In addition, the expression of floor failure depth caused by upper coal seam mining is obtained through elastic-plastic theory. Meanwhile, the deformation of the surrounding rock of the roadway increases with the increase of repeated mining times, especially for the horizontal displacement of the roadway on the coal pillar side. Moreover, the cracks’ evolution of surrounding rock in the roadway can be observed as asymmetric characteristics. Finally, the stability control technology of “asymmetric anchor net cable + I-steel” is proposed to prevent potential mining disasters, and the feasibility of this support scheme is verified by numerical simulation and field practices. It can meet the requirement of safe mining and provide guidelines to effectively solve the failure of a roadway in close-distance coal seam mining.

Using Fuzzy Comprehensive Evaluation to Assess the Competency of Full-Time Water Conservancy Emergency Rescue Teams

Drought and flood disasters are common events threatening the safety of human lives, and full-time water conservancy emergency rescue teams play an important role in fighting against these disasters. In this paper, a competency assessment indicator system full-time water conservancy emergency rescue teams was first constructed by the Delphi Method. Four first-level, seventeen second-level and sixty third-level competency assessment indicators are proposed. Secondly, the weights of assessment indicators for a full-time water conservancy emergency rescue team at all levels were obtained by an analytic hierarchy process. Thirdly, based on that established assessment indicator system, the competency of the water conservancy emergency rescue team in Province A was assessed using a fuzzy comprehensive evaluation. Finally, the assessment results for the full-time water conservancy emergency rescue team in Province A were obtained. This study concludes by noting some practical implications of the results.

Research on Dynamic Assessment Method of Earthquake Scene Rescue Performance Based on AHP and Cloud Model

In view of the ambiguity and randomness of the assessment of earthquake scene rescue performance, this paper proposes an integrated assessment method considering quantitative and qualitative influencing factors from three levels: search, rescue and medical treatment. Firstly, this study constructs an assessment index system of rescue performance at the earthquake scene based on the International Search and Rescue Advisory Group (INSARAG) guidelines set by International Search and Response. Secondly, the subjective weights and objective weights of each index were calculated using the hierarchical analysis process (AHP) and cloud model, respectively. The comprehensive weights were calculated using weighted analysis, and the performance assessment results were visually expressed by cloud model images. Finally, the study was applied to an earthquake rescue case with an initial assessment of 4.0065, and its performance was improved by 4.36% when the rescue process was optimized. The assessment results show that earthquake rescue performance can be estimated, and the rationality and effectiveness of the method was validated.

Study on Mechanical Characteristics and Failure Modes of Coal–Mudstone Combined Body with Prefabricated Crack

There are normally pre-existing cracks that can be observed in the coal seam and immediate roof that influences the stability of the rib spalling and the movement law of overlying strata. In this study, comprehensive research methods (e.g., theory analysis, experimental tests and numerical simulations) were adopted to reveal the mechanical characteristics, acoustic emission behaviors and failure modes of a coal–mudstone combined body with a single prefabricated non-penetrating crack. The results show that the influence of the crack angle on the elastic modulus of the coal–mudstone combined body samples was limited. With the increase in the crack angle, the unconfined compressive strength of samples decreased first and then increased in a V-shaped trend. In addition, the minimum unconfined compressive strength could be observed at a crack angle of 45°. Moreover, the number of acoustic emissions significantly increased with the process of continuous loading. In addition, the stress reduction zone could be observed in both ends of the prefabricated cracks at the initial stage of loading. The high- and low-stress zones were transformed with the process of continuous loading. Under an unconfined compression test, the failure models of the coal body part in the samples were mainly caused by shear failure, and only a few cracks occurred in the upper tip of the prefabricated cracks of the mudstone part. Therefore, airfoil cracks could be observed in the samples due to the strength difference of the coal mass and mudstone.

Study on Overlying Strata Movement and Surface Subsidence of Coal Workfaces with Karst Aquifer Water

The overlying strata layers of coal workfaces with karst aquifer water normally causes serious safety problems due to the precipitation, drainage and water inrush, such as a wide range and long term of surface subsidence. In this study, by taking 10,301 working faces of the Daojiao coal mine in Guizhou Province as the engineering background, the numerical model of water-bearing strata with fluid-solid coupling was established by using UDEC to illustrate the laws of overlying strata movement and surface subsidence. A theory model was proposed to calculate the surface settlement caused by the drainage of aquifer based on the principle of effective stress modified by the Biot coefficient αb. The results showed that the corresponding maximum value (0.72 m) and the range of the surface subsidence with the occurrence of karst aquifer water were larger than that of the overlying strata without karst aquifer water (e.g., the maximum value of surface subsidence with 0.1 m). Moreover, the surface subsidence caused by the drainage of aquifer accounted for 17.8% of the total surface subsidence caused by coal mining. According to the field monitoring of surface subsidence in 10,301 working faces, the maximum value was 0.74 m, which was highly consistent with the results of numerical simulation and theoretical analysis. It verified the accuracy and reliability of the numerical model and the theory model in this study.