Study On Mechanism Of Water And Sand Inrush In Weakly Cemented Strata And Prediction Method In Yibei Mining Area

Water and sand inrush in coal mine is a type of disaster that has occurred frequently in the western region of China in recent years,and has a great threat to coal mine safety production.Xinjiang Yili Coalfield has large reserves of coal resources.Paleogene weakly cemented strata are generally deposited in the Yibei mining area of the Yili coalfield.The bottom of the weakly cemented strata is a moderately waterrich glutenite aquifer.The sand and water source are integrated,and it has the basic geological conditions for water and sand inrush.In the process of coal mining,when the overlying bedrock destroys and communicates the aquifer,there is a possibility of causing water and sand inrush disasters.Therefore,it is of great theoretical and practical significance to carry out research on the prevention and control of water and sand inrush disasters for weakly cemented strata in northern mining area of Yili.This paper takes northern mining area of Yili as the research object,takes the power source,provenance and channel as the main breakthrough point in weakly cemented strata which happens water and sand inrush,and applies basic subject theories like the foundations of geology,coal mining,hydrogeology,rock mechanics,sedimentology,etc.Using basic theoretical research,test analysis,similar materials and numerical simulation,experimental research and other means,the regional sedimentary environments and the characteristics of the Paleogene weakly cemented strata were studied,the laws of overburden damage and fracture formations in coal seam mining were mastered,the starting conditions of water and sand inrush in the coal seam mining process were determined,the relationships between the factors affecting the occurrence of water and sand inrush were identified,the risk assessment methods were proposed and the corresponding preventive technical engineering measures were formulated,the major achievements are shown as follow:(1)The study on the sedimentary environment and sedimentary characteristics of weakly cemented strata was carried out,7 types of sedimentary microfacies were identified,the main lithological characteristics and diagenetic mineral components of the weakly cemented strata were analyzed,and it was found that the dissolution in the late diagenetic stage is an important reason for the weak cementation of the Paleogene.Through experiments,the characteristics of weakly cemented strata were mastered,which had weak disintegration resistance and were easily disintegrated in contact with water.(2)The coupling effect of four main influencing factors,such as coal seam mining thickness,aquifer water pressure,water-conducting sand channel and clay content,was studied.The research results showed that with the increase of mining thickness,the development range of fissures gradually expanded and the fissures were connected with each other,and the maximum opening degree of fissures also increased;the fissures were mainly distributed at about 28～33m directly above the goaf of the working face.This position was at the junction of the Jurassic bedrock and the weakly cemented stratum,and the possibility of water and sand inrush was high;the increase of mining thickness increased the probability of the water and sand mixture entering the mining space.Once it entered the mining space,the water pressure of the aquifer showed a rapid downward trend.(3)The experimental study on the starting conditions of water and sand inrush was carried out,and the results showed that water pressure and channel size were positively correlated with the severity of water and sand inrush disasters,the possibility was greatly increased,and there was a significant negative correlation between the content of viscous cement and water and sand inrush;the starting conditions of water and sand inrush were studied and the critical hydraulic gradient of the study area was determined.(4)10 objective factors were used as the main evaluation indexes of water and sand inrush risk,and the assessment prediction of water and sand inrush risk were carried out;the technical engineering measures suitable for water and sand inrush disaster prevention in weakly cemented strata were proposed,and no water and sand inrush disaster occurred after the field engineering application.