Mechanical Properties Of Coal Slime Based Pre Filling Cementitious Material And Its Application

Based on the pre filling scene of old goaf / roadway and the resource utilization of coal slime,this paper uses coal slime as the main raw material,supplemented by a small amount of sulphoaluminate material,cement and fly ash to prepare coal slime based pre filling cementitious material.Based on the test of the basic physical properties of the material,the key factors affecting the fluidity and strength are determined through orthogonal experimental research,and the material ratio is optimized,Through the combination of numerical simulation and industrial test,the control efficiency of surrounding rock stability is verified,and the supporting application system is constructed.Research findings:(1)The initial setting time of the material can be controlled in the range of 45 ～ 70 min,in which the content of sulphoaluminate material determines the initial setting time of the material slurry;The water precipitation can be controlled in the range of 3 ～ 17%.The water precipitation rate of materials mainly depends on the mass concentration of coal slurry water,and the content of sulphoaluminate plays a secondary role.The diffusivity can be controlled within the range of 40 ～ 80 cm,and the diffusivity is mainly affected by the mass concentration of slime water.The best ratio of fluidity is coal slime: sulphoaluminate,a and B materials: cement: Fly Ash: water = 160:18:48:48:240(mass ratio).(2)In terms of compressive / shear strength,the influence degree of each factor is as follows: Cement > fly ash > slime > sulphoaluminate material.The strength of cement-based filling material is significantly affected by the content of sulfur mud,and the content of aluminate is the lowest.At the same time,it is found that the strength of coal slime based pre filling cementitious material increases slowly,and the strength is relatively stable after 28days;The highest strength ratio group is coal slime: sulphoaluminate A and B material:cement: Fly Ash: water: 160:18:48:48:240,and its 28 d compressive strength is 0.30 MPa and shear strength is 0.37 MPa.(3)The numerical simulation shows that after filling the original roadway in the coal seam with this type of material,it can significantly improve the stress concentration of the newly excavated trench(located below the roadway,with an azimuth difference of 90 °)and the surrounding rock mass and the development of plastic zone.During excavation,the section shrinkage of the measuring point of the trench is reduced by 5.7%(25.0% without filling is reduced to 19.3% after filling),and the stress between the roadway is reduced by 7.8%(from 8.37 MPa to 7.72MPa).When the advancing distance of the working face decreases from 30 MPa to 20 MPa(when the advancing distance of the working face decreases from32.7% to the position of the unmeasured goaf filling point),the stress of the working face decreases by 25.5%(when the advancing distance of the working face decreases from 30 MPa to 20 MPa).(4)In engineering application,equipment selection and matching and process flow design are carried out according to the selected ratio,so as to form a three pipeline filling application system of coal slurry and a dynamic control mechanism of material ratio;The measured results show that the gravity flow distance of this type of material in the roadway with an inclination of 5 ～ 10° exceeds 38 m,and the actual compressive strength and shear strength range are 0.45 ～ 0.50 MPa and 0.37 ～ 0.42 MPa respectively.The maximum section shrinkage of the chute under the filled roadway is 12.3% and 20.6% respectively during excavation and mining.The maximum stress of the roof at the monitoring point is 3.7MPa and 5.6MPa respectively,which can effectively meet the needs of surrounding rock stability control of the chute at the working face.