Nalysis Of Stress And Seepage Field Changes In Goaf Floor Based On Multi-Physical Field Coupling

The Heshan coalfield is a typical karst water-filled deposit,and the extraction work of some working faces is deeply affected by the downward pressure of the underlying water,facing great risks.This paper combines the geological data of the 4106 working face of the Heshan No.3 mine.Based on the "stress-seepage-damage" coupling theory and the equivalent continuous porous media model framework,using the numerical simulation software COMSOL Multiphysics,the extraction model of the working face is constructed.The variations of the bottom stress field,water-blocking ability,and seepage field during the extraction process under different water head pressures and different roof collapse heights are studied.This helps to ensure the safe extraction of the 4106 working face and similar working faces,and provides numerical simulation results for extraction methods and waterproof measures during the extraction process.The main research results are as follows:(1)Through the analysis of the process from seepage to outburst of the floor of the goaf affected by the confined aquifer,it is found that the water head pressure provides expansion stress to the rock layer pores of the floor.It not only relieves the stress concentration of the surrounding rock but also slows down the development of the floor damage zone.The wedge effect promotes the development of the confined water uplift zone and reduces the effective thickness of the water barrier.It damages the water-blocking ability of the floor,and the water head pressure is positively correlated with the water inrush volume of the goaf floor.(2)By comparing the numerical simulation results of the extraction process of the working face under different roof collapse heights,it is found that after the collapse of the goaf roof,on the one hand,it reduces its own load and reduces the stress concentration of the surrounding rock floor of the goaf;on the other hand,the collapsed rock fills the goaf,and there is downward pressure on the floor of the goaf,reducing the vertical upward displacement of the floor.Under the joint action of the two,the development of the floor damage is slowed down,which protects the water-blocking ability of the floor and can effectively reduce the water inrush volume of the goaf.(3)By comparing the two situations of the collapse filling area connecting with the roof and not connecting with the roof,it is found that when the collapsed rock fills the goaf and connects with the roof,the mining pressure is transmitted to the floor of the goaf through the collapsed rock.The floor of the goaf is continuously affected by the increasing vertical stress as the working face advances,which significantly inhibits the development of the confined water uplift zone,and the stress concentration of the surrounding rock floor of the goaf is significantly reduced.After the extraction to the depth of 200 m,it tends to be stable.After the extraction to the depth of 260 m,the maximum damage depth of the floor no longer increases,the effective thickness of the water barrier no longer decreases,and the water-blocking ability of the floor is well protected,which significantly reduces the water inrush volume of the goaf and has a positive effect on the prevention and control of floor outburst.