The downward drift cemented filling mining method has been widely used in the green mining of metal mines in China.The influence of different number of layers,layer angles,backfill thickness and the span-height ratio of the goaf on the stability of the backfill roof was studied by FLAC3D numerical simulation software.The results show that the number of layers,layer angles and the span-height ratio of the goaf are positively correlated with the subsidence displacement of the backfill roof.In particular,when the span-height ratio increases to 1.75,the maximum displacement of the backfill roof in 2-layer reaches 24.56 cm.The backfill thickness and its subsidence displacement are negatively correlated.The maximum principal stress of the backfill roof exists in the form of compressive stress under different number of layers,and the more the number of layers,the greater the compressive stress.With the increase of the layer angle and the span-height ratio of the goaf,the maximum principal stress of the backfill roof gradually changes from compressive stress to tensile stress.Especially when the layer angle is 10°,the maximum tensile stress of the backfill roof in 2-layer reaches 140 kPa.With the reduction of the thickness of the backfill roof,the concentration area of the compressive stress of the roof gradually changes from"scmi-circular"to"saddle-shaped"with both ends raised and the middle depressed.The research results can provide reference for the design and application of backfill in downward drift filling mining.
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