## 1 Introduction
With the Chinese government's emphasis on safety and environmental protection, the shrinkage method is gradually being replaced by the green and efficient backfilling method. The new policy advocates accelerating the upgrading and transformation of mines and promoting the mechanization of small and medium-sized mines. At the same time, it stipulates that the backfilling method shall be adopted in principle for the construction, reconstruction or expansion of metal and non-metal mines; if there are special circumstances where it cannot be applied, it must go through a strict argumentation procedure. The backfilling method is a mining method that uses filling slurry to manage goals, filling as a part of mining, filling slurry filling into the mining area to provide a stable working platform for miners, and the filling body can also play a role in supporting the role of the mining goat, preventing the collapse of the mining room, and the safety hazards brought by the goat can be effectively eliminated [17]. At the same time, the backfill method can fully recover the ore pillars and increase the recovery of ore, and it also reduces the dilution of the ore to a certain extent due to the flexibility of the backfilling method during the process of ore recovery. Finally, most of the mines are using tailings as filling aggregate to fill the goat. This filling allows a large amount of tailings to be stored underground (more than 50%), which largely reduces the operating costs of tailings storage, relieves the pressure of day-to-day management, and reduces the environmental impact of the tailings surface stockpile, which is very good at avoiding the impacts of the use of the shrinkage method. Meanwhile, the use of trackless equipment such as drill jumbos, LHDs and scaling rigs can greatly improve the safety and efficiency of the operation and reduce the labor intensity of the workers in the process of applying the filling method. Therefore, the filling method is a very good transformation direction for the shrinkage method. With the development of technology, China has made good breakthroughs in the research on the filling process, filling material preparation and conveying technology, and the low-cost filling mining process has become more mature [18; 19; 20; 21; 22; 23; 24; 25; 26; 27]. Since the 1960s, China's filling technology has passed through different stages, including water-sand filling, graded tailings filling, and full tailings filling. With the gradual increase in the concentration of the filling slurry and the addition of cement, the strength of the backfill increases. At the same time, the development of high-concentration paste filling has also been realized [28]. Moreover, the long-distance transportation theory, pipeline materials, and filling equipment of the filling slurry that are highly matched with the high-concentration filling slurry have been developed [19; 29]. In addition, a large number of researchers have studied the stress distribution in the filling body. [PERSON] and [PERSON] used the improved Marston method to propose an analytical solution of the vertical stress \(\sigma_{\text{v}}\) and horizontal stress \(\sigma_{\text{h}}\) of the backfill in the near-vertical backfill slope [30]. [PERSON] and [PERSON] used FLAC2D software (FLAC 6.0) to simulate the effects of stope inclination, backfill material characteristics and filling sequence on the stress distribution of the backfill [31]. [PERSON] et al. proposed an analytical solution to the vertical stress of the backfill for an inclined stope with non-parallel walls on both sides [32]. [PERSON] et al. (2015) used numerical simulation to study the stress distribution and interaction of two adjacent vertical filling slopes [33]. [PERSON] studied the backfilling time using the backfill CAD Model [34]. At the same time, with the increase of depth, waste rock filling has also shown its own transportation advantages, and a large number of scholars have studied the research law of waste rock filling.