The Material Mix Proportion of Roadside Backfill Body (RBB) Based on Spatiotemporal Law of Ground Pressure: A Case Study

The law of ground pressure behavior can accurately guide the material proportion and performance of the roadside backfill body (RBB) in gob-side entry retaining (GER), thereby reducing the waste of materials and the cost of retaining roadway. In this study, a similar material modeling is used to verify the spatiotemporal law of the ground pressure in the engineering case of solid dense backfilling mining in Xingtai Mine, China. Based on that law, the theoretical requirements for the bearing performance of the RBB are proposed. Finally, a material mix proportion that meets the theoretical requirements is obtained by compression test, and the deformation and failure characteristics of the backfill body with that mix proportion are analyzed. The results show that the maximum pressure of the backfill body measured in Xingtai Mine is 5.5 MPa, which is about 40 m away from the coal face; after 40 m, the force on the backfill body will not increase anymore. The physical simulation experiment also proved that the ground pressure behind the coal face increases gradually and tends to be during the backfilling process, which shows certain spatiotemporal characteristics. Through the proportioning experiment, it is determined that the optimal material mix proportion of the RBB is gangue:fly ash:cement = 10:3:1, which meets the theoretical requirement that the strength of the RBB at any position is not less than the ground pressure at that position. The research results provide theoretical support for the field practice of GER in solid dense backfilling mining.