Experimental Study On Mechanical Properties Of Coal Gangue Fly Ash Filling Material Affected By Mine Water

Filling mining is a mining method that fills the goaf behind the working face with filling materials,which can effectively control the surface subsidence and improve the coal recovery rate.Based on the idea of energy-saving and efficient development,the filling material prepared by mixing coal gangue and fly ash can not only save filling cost,but also achieve the purpose of waste reuse.Because the mechanical balance of the overlying strata in goaf is broken,and the strata crack under the action of stress,leading to groundwater inflow,the goaf often contains groundwater in varying degrees.Because the filling material is saturated for a long time,its mechanical properties and durability have changed greatly compared with the normal state.In the process of coal mining,because of the contact between groundwater and coal seam,human activities and stratum lithology,the composition of mine water also changes greatly.There are more SO42-,HCO 3-,Cl-,Na+ and Mg2+plasma in the water.The filling body in mine water will be decomposed under the erosion of these ions for a long time,which will lead to filling material decomposition.The material is unstable or destroyed.Firstly,the factors affecting the strength of coal gangue fly ash filling material are analyzed,and the proportion scheme is determined to make the test block and test the strength of the test block for 28 days under dry condition.Then,the same proportion of the test block is soaked to measure the water absorption performance of the test block and the strength change after water saturation under different influencing factors.Finally,the performance of the filling material is improved by stimulating the fly ash.Through experimental research,it is found that:(1)The slurry concentration has a great influence on the slump and strength of the backfill for 28 days,and the ash-to-aggregate ratio has a great influence on the slump and strength of the backfill.The larger size aggregate will increase slump to a certain extent,while the larger size aggregate will increase water consumption and reduce slump.(2)When the sample is immersed in water for 1 day,the water absorption is the largest,and reaches the equilibrium state basically until 14 days.The water absorption decreases with the increase of slurry concentration,and increases with the decrease of ash ratio and gangue powder ratio.The water absorption rate of the sample with large particle size gangue as aggregate is obviously higher than that of other groups.(3)The strength change of the specimen after water absorption decreases with the increase of slurry concentration,and increases with the increase of ash-to-powder ratio.The larger the waste-to-powder ratio,the smaller the strength change of the specimen after water absorption.The strength change of the two groups of large-size aggregates with the largest water absorption is not the biggest after water absorption.The two groups of small-size aggregates with smaller water absorption are similar to the groups with similar water absorption.Comparing with the strength of rigid saturation,the strength of the specimen after immersion for 30 days basically did not change,and the strength of the specimen after immersion for 60 days was slightly reduced compared with that of the specimen under rigid saturation,but the degree of reduction was not obvious.The strength of the specimen after immersion for 120 days was increased compared with that after immersion for 60 days,and a group of changes of large ash-to-aggregate ratio were more obvious.(4)Na2SO4 addition of 0.5%and 1%respectively improved the water absorption capacity and strength of the sample best.