Study On The Formation Mechanism Of Water Inrush From Roof Aquifer In Fully Mechanized Top Coal Caving Mine In Yonglong Mining Area

The Yonglong mining area in Shaanxi Huanglong coalfield is characterized by thick coal seam,deep buried and thick overlying aquifer.In order to realize high-efficient mining,most of the mines in this area adopt the Fully mechanized top coal caving technology,and the Total caving method of roof management,which damages the overlying strata structure greatly and easily causes all kinds of water-inrush accidents.Therefore,in order to ensure the safety and efficient mining of the mine,it is urgent to conduct a comprehensive study on the formation mechanism of water inrush from the roof in fully mechanized top coal caving mine.Based on the geological and hydrogeological conditions of overlying strata in Yonglong Mining Area,this paper studies the undisturbed geological and hydrogeological conditions of aquifer and aquiclude in the overlying strata through the detailed analysis of the roof structure of coal seam.Then,conducted a comprehensive study on the development characteristics of water-flowing fractured zone,and the formation mechanism of bed-separation and water in bed separation under the influence of mining by means of measured data analysis,mathematical statistical analysis and numerical simulation,and an empirical formula for calculating the height of water-flowing fractured zone was obtained under the condition of soft to medium hard overlying strata in the study area.It is considered that fissure separation is mainly developed in Zhiluo Formation and cavity separation is mainly developed in Anding Formation.Cavity separation water in Anding Formation is the key point of water inrush control in this area because of its large quantity and scale.Comprehensively discussed the formation mechanism of water inrush from roof aquifer in the study area,divided it into sandstone water outburst mechanism and bed separation water outburst mechanism.Sandstone water outburst mechanism: Under the influence of mining,aquifer water outburst into the mine through natural channels such as fault structural zone and sedimentary missing zone,as well as artificial channels such as caving zone and water-conducting crack zone.Bed separation water outburst mechanism: Bed separation occurs in overburden rock in the process of the coal mining,surrounding groundwater gathers into the bed separation,along with the increase of mining areas,the area of separation water was enlarged,shaped like the "water bag" hanging in the gob area,when the bed separation closed,the extrusion results in the rupture of the "water bag",and the water in bed separation penetrates into the working face through the water flowing channel.According to the formation mechanism of water inrush from roof aquifer in the study area,the relevant prevention and control measures are put forward,that is,use the underground drainage hole to reduce the threat of roof sandstone water outburst,and use the surface drainage hole to reduce the risk of bed separation water concentrated outburst.