Feedback mechanism of front abutment stress on filling rate of backfilling body in coal burst mine

High stress is the main reason for high frequency of rock burst in deep coal mines. Backfilling mining serves as an effective method to control roof strata movement, alleviate the degree of stress concentration, and reduce the failure of surrounding rock and the risk of rock burst. To evaluate the controlling ability of the backfilling on mining stress in the gob area, the 1123 longwall panel of the Gucheng mine is taken as the project background. Theoretical analysis, laboratory test and field measurement are used to study the mining-induced stress distribution in the backfilling longwall face, and to reveal the feedback mechanism between the front abutment stress and bearing capacity of the backfilling body, helping to determine the backfilling rate of coal burst mine. The results show that the backfilling ratio in the early stage is lower than 80%, the subsidence of hard roof is serious, the influence area of front abutment stress is more than 30 m, and the degree of stress concentration reaches 1.5. The influence area and concentration degree of mining-induced stress in the fault affected area increase to 60 m and 1.65, respectively. Surrounding rock instability phenomenon, such as rib spalling and roof fall, happens frequently. The whole dynamic evolution characteristics of bearing stress in the backfilling body is measured. The stress distribution curve is divided into five stages, namely rapid decrease, transient stabilization, rapid increase, slow decrease, and secondary stabilization. The stabilization values of the bearing stress in the upper, middle, and lower regions of the gob area under the condition of low backfilling ratio are 1.5, 5.2 and 2.5 MPa, respectively. The backfilling body in the gob area is divided into non-sufficiently compacted zones and sufficiently compacted zones, and the continuous subsidence model of the hard roof under the support of the backfilling body is constructed, and the “ʅ” type subsidence curve of the hard roof is obtained, and the range of the insufficiently compacted area decreases approximately linearly with the backfilling ratio. The test obtains the evolution curves of elastic modulus and uniaxial compressive strength of the back-filling body with time. By combining with the roof subsidence curve and face advance speed, the distribution curve of mining-induced stress in the whole area of the longwall face is obtained. Negative exponential relationship is established for the backfilling rate and the afront abutment stress, which reveals the reverse feedback mechanism between them. Quantitative assessment on the load reduction and burst prevention effect of backfilling mining is realized. The trinity enhancement measures for improving the backfilling ratio of the gob area are proposed, which raises the backfilling ratio of the 1123 working face to more than 90%. The bearing capacity of the backfilling body is strengthened. The trinity measures reduce the separation space under the hard roof to 50 mm. The stress concentration coefficient decreases to 1.3. Correspondingly, the controlling effect of the surrounding rock of the longwall panel is significantly improved.