Strength model and its application of downward drift filling roof based on thick plate theory

As the direct roof of the stope using the downward drift cut and fill mining method,the stability of the artificial roof formed by backfill is the key to the successful application of the method. The strength required for filled artificial roof is taken as the research object,and the typical technological characteristics of the downward approach mining method are analyzed. Meanwhile,the dangerous mechanical state of artificial roof is determined and simplified to a thick plate model with four sides simply supported. Based on the Vlasov's basic solution to the thick plate theory,the tensile stress distribution of filled artificial roof is analyzed,and the strength model of filled artificial roof in downward drift is established. According to the measured value of overburden pressure of backfill body in the downward approach stope of the Datun tin mine,the ultimate tensile stress at the bottom of artificial roof is determined to be 0.23 MPa based on the maximum monitoring result of 0.35 MPa as the basic calculation parameter. In order to ensure the stability of the artificial roof,the tensile strength of the artificial roof is designed as 0.345 MPa,considering the safety factor of 1.5. The stope physical model of 3-1 ore body is constructed with FLAC3D,and the stress distribution and stability state of filled artificial roof in the process ofore body mining are simulated and analyzed under the condition of designed strength parameters. When the ore body is recovered to the last layer,the tensile stress of artificial roof is distributed between 0.10 MPa and 0.23 MPa,and the maximum value is 0.23 MPa,which is consistent with the theoretical analysis results that no plastic damage is found until the end of delamination stoping. With the results of model calculation and numerical simulation analysis,the optimal ratio satisfying the strength index is recommended as waste rock:tailings=8:2, cement content 210 kg/m³, mass concentration 85%, whch guides the completion of 110 000 m³ filling practice in the downward approach stope of 3-1 ore body in the Datun Tin Mine. There is no safety accident caused by instability in this process,which provides strength guarantee for the safe mining of ore body. Compared with the original mine design,the strength of the model design is more reasonable and economical. The recommended ratio of waste rock and copper slag tailings paste save 32.30 yuan/m³ compared with the original one,and the cumulative saving of filling cost is 3 553 000 yuan.