Spatial-temporal Evolution Mechanism And Control Technology Of Air Leakage Fissures In High-intensity Mining Of Shallow Thick Coal Seam

Mining area in Western China generally has geological characteristics of shallow burial depth,thin bedrock and thick coal seam.Overburden fracture fissures concatenate surface fissures during intensive mining activities.The ground surface destruction caused by shallow seam mining activities may lead to severe air leakages,thus disturbing underground ventilation and increasing the concentration of carbon monoxide and the risk of spontaneous combustion.Surface air leakage fissures formed in shallow coal seam mining have serious impact on safety mining.This paper proposes a novel approach to study strata structure movement and air fluid movement in overburden fissures based on the geological occurrence and production technology conditions of the Chuancao Gedan Coal Mine in Inner Mongolia.This approach combines field tests,similar material simulation,numerical simulation,theoretical analysis and site industrial test.The content of this article has carried on the system research for overlying strata movement and dynamic development and distribution of fracture fissures,formation mechanism and spatial-temporal evolution of air leakage fissures,and air leakage characteristics of mining face and air flow field in goaf under influence of air leakage fissures.Ultimately,security mining technology based on control of air leakage fissures is found in intensive mining activities of shallow thick seam mining This study serves as a good theoretical and practical reference for strata control and safety mining of high-intensity mining in shallow coal seam of Western mining area.Based on the geologic conditions of the shallow coal seam in the Chuancao Gedan Coal Mine,spatial-temporal distribution and dynamic development characteristics of surface fissures and their main controlling factors are measured.The intensity of surface air leakage and goaf gas concentration distribution and their correlation are also studied.The types of surface mining-induced fissures and their influence on safety mining of different geological occurrence conditions are analyzed and classified.Mechanics analysis model of deep beam structure is established to study failure characteristics,movement forms and influencing factors of loading key strata initial and periodic breaking.The formation mechanism of overburden mining-induced fissures through ground surface is also studied.The influencing factors on spatial-temporal evolution of overburden fracture fissure in shallow thick seam mining are analyzed.And the influencing factors are loading key strata location,bedrock thickness,loose cover layer thickness,mining face advancing speed and surface topography.Dynamic spatial-temporal evolution characteristics,types and distribution of overburden fracture fissures are determined.The air flow dynamics model of overburden air leakage fissures in shallow coal seam mining is established.The air transmission mechanism and air transmission characteristics of overburden air leakage fissures are analyzed.Ultimately,The distribution characteristics and air permeation conditions of overburden air leakage fissures are discussed.The calculation formula of the air leakage flow volume(q?)and the average air leakage speed(m?)of overburden air leakage fissures based on equivalent fissures width are obtained.Through the combination of field measurement and computational fluid dynamics analysis,the spatial-temporal distribution of overburden air leakage fissures in the mining face advancing direction is obtained.The evolution model of overburden air leakage fissures is established,which lay a theoretical foundation for predicting the spatial-temporal distribution of air flow field in goaf under the influence of air leakage fissures.Security mining technology based on control of air leakage fissures and safety technical way in Shallow Thick Seam Mining are determined and put forward.Including air leakage fissures plugging and ground surface recovery,preventing airflow of air leakage fissures by pressure ventilation,preventing spontaneous combustion by grouting and nitrogen injection in goaf,preventing spontaneous combustion by guaranteeing a certain advancing speed.