# Impact of the Mining Dimensions on the Stability of Backfilled Pier-Columns
## 1 Introduction  
The first planned use of the backfill mining technique was performed in 1915. The backfill mining technique has been used for over one hundred years across the globe. In Australia, waste rocks generated during the mining process have been used to fill the mine chambers [1, 2]. In Poland, backfill mining has been widely used [3, 4]. Paste backfill has been applied in metal mines for a long period in the USA [5]. The German mining industry uses different residues for backfilling and stowing [6, 7]. The use of environmental desulphurization and cemented paste backfill technology in Canada has been reported [8]. Backfilling in goat also plays an extremely important role in India [9, 10]. An environmentally friendly technique, involving backfilling the mined-out area with a hardening mixture, has been used in Ukraine [11]. An analysis of the operational parameters of partial backfilling in selective coal mining has been undertaken by [PERSON] et al. [12]. An adaptive neuro-fuzzy inference system has been used to model the uniaxial compressive strength of cemented hydraulic backfill [13]. [PERSON] et al. have studied the experimental characteristics and deformation properties of backfill mass [14]. [PERSON] et al. have performed the geomechanical substantiation of the parameters of technologies for mining salt deposits with a backfill [15]. In China, paste filling has been used in underground coal mines and other metal mines [16, 17]. Solid filling can effectively reduce the deformation of the key layer [18, 19]. Grout injection into the overburden separation is a successful surface subsidence control measure [20, 21]. Some other filling technologies have also been developed [22, 23]. [PERSON] et al. have performed experimental research on the strata movement characteristics of backfill-strip mining using similar material modeling [24]. [PERSON] et al.  
developed a rheometer for high-concentration coal gangue backfill slurry measurements and analyzed the rheological properties of the backfill slurry [25].  
Since 2011, the Zibo Wangzhuang Coal Mine Co., Ltd. has adopted the method of \"pier-column backfilling\" [26]. In this method (as shown in Figure 1), relatively independent backfilled pier-columns arranged at certain intervals in the goat can support the overlying strata, thus achieving the goal of controlling the surface subsidence [27; 28].  
The ability of the backfilled pier-columns to maintain stability is the key to controlling surface subsidence. Therefore, analyzing the factors that affect the stability of the pier-column is critical for the design method. Considering the theoretical research and many mining practices, it has been demonstrated that the geological mining conditions and the parameters of the pier-column itself are the main factors that affect the stability of the pier-column. In addition, the duration of the service time of the pier-column in the goal also affects its stability. In this study, numerical simulations, physical experiments, and field testing were used to analyze the impact of the geological mining conditions. In addition, our main focus was on the changing of the mining thickness and mining width in regard to the stability of the backfilled pier-column.