Theoretical And Experimental Study On The Control Of Overlying Strata Movement In Paste Backfill Mining

Paste backfilling mining technology is an important method to control the subsidence of overburden rock and improve the extraction rate.It has the advantages of green environmental protection,strong applicability and intuitive filling effect,and has been widely used in the mining of medium and thick coal seam.At present,backfilling mining technology is relatively mature,but The theoretical and experimental study of overburden control in backfill mining is not sufficient,which limits the development of this technology.In this paper,2351 filling-mining face of Daizhuang Mine are chosen asthe research objects,and an in-house experiment system of similarity simulation is established in this study.Combined with numerical simulation and digital speckle observation test under uniaxial compression to determine the basic mechanical parameters and deformation characteristics of fly ash geopolymer paste filling material,the movement law and control problems of overburden rock during paste filling mining.The main research contents and results are:(1)The mechanical model of single composite slab with "coal wall-filling support-filling body" cooperative roof control system as elastic foundation with different foundation coefficients and roof rock beam as semiinfinite beam is established.The significance of the influence of various factors on roof subsidence is as follows: The movement of roof > Filling rate >Overburden load >Elastic modulus of filling body.(2)The flyash polymer filling material was prepared by the secondary mixing process and batch feeding method under the condition of optimal mixing ratio.The activation of 1.6-modulus sodium silicate on fly ash was carried out in stages.The results of digital speckle experiment under uniaxial compression(DIC)show that the initial solidification strength of backfill material is0.5MPa,and the 28 d strength is 1.87 MPa.The filling material can be divided into microcrack compression stage,linear elastic stage,microcrack expansion stage and crack expansion charging stage from deformation to failure.The material shows strong plastic characteristics,and the strength decreases slowly after the peak value.(3)In the process of similar material simulation experiment,the combination formed by the bonding of styrofoam and wood board was used as the similar filling material to simulate the"filling-mining" cycle process.The overall structure of the overburden strata of coal seam remained intact instead of the phenomenon of "three zones",and only presented bending subsidence and vertical crack unobviously in the roof.The subsidence of direct roof and basic roof can be classificed as three stages :“slow subsidence,fast subsidence and tending to stability",and the maximum subsidence is 10.8mm and 8.9mm,respectively.There is no obvious tending to stability in the process of main key stratum and sub-key stratum,and the maximum subsidence is less than that of main key stratum.The final subsidence of each layer is as follows: direct top>basic top> sub-key layer > key layer.The closer the vertical distance is to the overburden rock of coal seam,the larger the deformation is and the more intense the activity is;on the contrary,the smaller the subsidence deformation is and the more gentle the activity is.(4)The numerical simulation results show that with the increase of filling ratio,the smaller the vertical displacement of overburden is,the smaller the plastic area is.The existence of backfill body can improve the stress concentration distribution,and its plastic deformation can absorb the elastic energy released by rock mass,realizing the process of "yielding".There are 47 figures,18 tables,and 74 references in this paper.