## 1 Introduction  
In the process of mine production, the sublevel caving method is preferred because of its simple structure, high efficiency, low cost, etc. [1; 2; 3]. It was first applied to the Kiruna mine in Sweden, and it achieved good economic benefits. By 1954, the mines in Sweden using this method accounted for 20%, and then it increased year by year, and in the early 1960s, the mines using this method increased to 60% in Sweden [1; 4]. Subsequently, this mining method was introduced in China and widely used in metal mines, especially iron mines, such as Dagushan Iron Mine [5], Chengchao Iron Mine [6; 7], and Xiaoguanzhuang Iron Mine [8]. In recent years, with the gradual exhaustion of shallow resources, mining has gradually shifted to the deeper parts of the mine, and the goal generated by the sublevel caving method has become more and more difficult to control and predict and has caused geological disasters such as surface subsidence and landslides [9; 10; 11; 12; 13; 14]. Surface collapse, landslides, and other geological disasters have been caused. To address this phenomenon, many scholars have carried out a lot of research on the collapse zones generated by the sublevel caving method and achieved many research results. For example, [PERSON] et al. used large-scale models and numerical simulation methods to study the step failure caused by block collapse and visualized the fracture mechanics and the evolution process of the pressure equilibrium arch during the caving process [11]. [PERSON] used RFPA2D to numerically investigate the effect of rock structure on fracture evolution and settlement and emphasized the importance of stress-balanced arches and their geologic features in settlement prediction and repair [15]. Despite this, the potential hazards to mining and the surrounding ecological environment from using the sublevel caving method in the mining process still exist, which shows that the transformation of the sublevel caving method is imperative. Compared with the sublevel caving method, although the backfilling method requires more complex processes and equipment, the backfilling method has advantages that the sublevel caving method does not have, such as timely management of the goal, control of the rate of ore loss, maintenance of the stability of the surrounding rock, etc. [16; 17; 18; 19; 20]. Up to now, many scholars have conducted research on the backfilling method and obtained many research results, for example, [PERSON] et al. discussed the research of green fill mining technology and its application in the working face of a coal mine [21]. [PERSON] et al. believed that the backfilling method can effectively solve the environmental and safety problems brought by mining and is the key technology to realize green mining. [22] [PERSON] et al. argued that the backfilling method is one of the most commonly used methods in global mining because it can maximize the recovery of mineral resources and protect the underground and surface environment [23]. [PERSON] combined laboratory tests and computer-aided design to determine the BackfillCAD model, which provides a basis for determining the backfilling time. Additionally, [PERSON] conducted comparative laboratory strength tests on three-point and four-point wooden crib models. It was found that filling these cribs with gangue significantly increases their maximal load several times compared to the empty cribs [24; 25]. The above studies show that the application of the backfilling method is an ideal alternative to the sublevel caving method, both in metal mines and coal mines, for increasing the recovery rate of mineral resources in mines and improving the environment around mines.