Search

China is the country with the most complicated coal-forming and occurrence conditions in the world. The roof water disaster, caused by the diversity and complexity of the hydrogeological conditions of the coal seam roof, the mutuality and time-varying coupling of the mining overburden fracture field and the seepage field, and the uniqueness and harmfulness of the coal mine roof water inrush, is one of the main mine disasters in China, especially in the western coal mining area. In order to better understand the roof water disaster, promote the existing technology and explore new technologies to prevent and control such mine disasters, based on the comprehensive analysis of the law of roof water disaster accidents in China’s coal mines in recent years and the occurrence conditions, water inrush mode, dynamic characteristics and mechanical behavior of roof water-filled aquifers, the types and characteristics of roof water disasters are systematically divided. The disaster mechanism of the main categories and the existing prevention and control technologies of roof water disasters are reviewed, and the future development direction of roof water disaster prevention and control is prospected. The study found that: ① The main structure of roof water disaster includes five types: gushing (leaching) water in thick bedrock aquifer, water-sand coupling inrush in weak cementation layer of thin bedrock, water storage and energy storage water inrush in abscission layer space, skylight recharge water inrush, and surrounding rock burning and permeability enhancement. They are concentrated in the north of the Qinling Mountains-Huaihe River. Shaanxi, Inner Mongolia and Ningxia are the main gathering places of roof water disasters. ② Mining-induced “Z” -type separation space is developed in the primary fractures of overlying strata under the super-thick bedrock aquifer, resulting in a large area of water gushing (leaching) in the stope. The fracture conditions of composite key strata are established, and the power source of water-sand coupling inrush disaster in weak cemented layer of thin bedrock is clarified. The critical criterion for assessing the instability of water inrush from bed separation is constructed, and the water inrush from bed separation is divided into three modes: static load disturbance, “dynamic+static” load composite disturbance and repeated disturbance of composite coal seam mining. The lack of laterite aquiclude and the mining-induced deterioration damage in the weak area of laterite are the main causes of skylight leakage recharge. The surrounding rock is burnt to increase permeability and porosity, and a new water-bearing structure is formed after receiving water supplement from adjacent water sources. Under the induction of mining, burnt rock water pours into stope and causes water disaster accidents. ③ The current prevention and control technology system of coal mine roof water disaster “exploration-discharge-treatment” is evaluated, and the future development direction is put forward, such as the conjugate linkage of upper and lower wells, the drilling-mining (excavation) high-level collaborative geological exploration system, the geological guarantee work guided by the “three zones” division of water prevention and control, the green mining and water prevention concept of “coal-water-ecology” multi-objective co-management, and the digital intelligence and transparent mine hydrogeological disaster information maintenance system.

Regarding the issue of determining the thickness of the protective layer for waterproof and safe coal (rock) pillars in mining near water bodies, Appendix 4-3 of the “Code for Retaining and Mining Coal Pillars in Buildings, Water Bodies, Railways, and Main Tunnels” (hereinafter referred to as the “Three Underground Mining Code”) is only applicable to coal mining under “loose aquifers”. As for how to determine the thickness of the protective layer for coal mining under bedrock aquifers and mining under goaf water bodies, it is not involved; The main content of commonly used roof water hazard risk assessment techniques and methods includes water abundance evaluation, conductivity evaluation, and water filling strength evaluation. When the water abundance of the aquifer is known, only “conductivity” can be evaluated, and the evaluation method can be further simplified. Based on the above two points, this article attempts to construct a simple criterion similar to the coefficient of water inrush from the bottom plate to evaluate the risk of roof water damage, starting from the “Three Underground Mining Standards”. Firstly, based on the scientific connotation of the term “protection”, it is proposed that the impermeable rock layers between the top interface of the water conducting fracture zone and the overlying aquifer have protective functions and should be collectively referred to as the protective layer (Hb); Based on the practice of selecting a certain multiple of mining height (A) for the thickness of the protective layer in the “Three Lower Mining Standards”, the concept of protection coefficient (Bs) is proposed, which is the ratio of the thickness of the protective layer to the mining height (Bs=Hb/A). Secondly, based on the provisions of Appendix 4-3 of the “Three Underground Mining Specification” regarding the thickness of the protective layer for waterproof coal pillars, the threshold value of the protection coefficient zoning for coal mining under loose aquifers is proposed to be Bi=(0，2、3、4、5、6、7); The coal bearing strata under the bedrock aquifer are generally composed of sand and mudstone interbedded sedimentary formations, where mudstone has a water blocking function (equivalent to the cohesive soil layer under the loose layer), and the total thickness of mudstone is generally greater than the cumulative mining thickness. The thickness of the protective layer can be selected according to the condition of “the thickness of the cohesive soil layer at the bottom of the loose layer is greater than the cumulative mining thickness” in Appendix 4-3 of the “Three Underground Mining Specifications” and selected according to the maximum value, Therefore, the threshold value of the protection coefficient zoning for evaluating the bedrock aquifer is Bi=(0,4). According to the protection coefficient and zoning threshold, the evaluation area can be divided into water inrush zone (Bs≤0), danger zone (0

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Taking 307 working face of Tingnan Coal Mine as the engineering background, in order to verify the reliability of real-time monitoring of water flowing fractured zone height by micro-seismic monitoring data, the mechanical numerical simulation software is used. In order to analyze the relationship between micro-seismic events and roof water inflow, the mathematical statistics method is used to establish the correlation between them. The results show that the micro-seismic events in 307 working face are concentrated in the areas with serious overburden damage under different driving distances, which can reflect the overburden damage and the development height of the water conducting fracture zone; the numerical simulation results of working face mining are basically consistent with the change rules of micro-seismic monitoring events. The highly developed water conducting fracture zone is characterized by “rapid growth in the early stage, slow growth in the middle stage, and balance in the later stage”. The number of micro-seismic monitoring data events in 307 working face has a significant correlation with the water inflow in the same time period. The occurrence of water inflow events and micro-seismic events has a specific lag effect, and the accuracy of water inflow prediction can be better improved by using appropriate lag micro-seismic data for prediction.