# Strata Movement of the Thick Loose Layer under Strip-Filling Mining Method: A Case Study
## 1 Introduction  
The strength of the loose layer is far less than that of the ordinary rock layer. The loose layer not only undergoes consolidation and compression deformation but also loads the bedrock surface, aggravating the destruction of rock formations and mining subsidence, resulting in damage to surface buildings (structures) [1; 2; 3; 4]. Therefore, the law of overburden and surface movement and deformation in loose layer mining is quite different from conventional mining. Some scholars have used fractal-related theories to study the mining with thick loose layers and thin bedrock, and they found that the evolution characteristics of overlying rock fractures have good self-similarity and fractal characteristics. Some have studied the mechanical properties of the thick loose layer, and they pointed out that the maximum surface subsidence value increases with the thickness of the loose layer, and decreases with the increase in the friction angle and cohesion of the loose layer [5; 6; 7; 8; 9]. Furthermore, the relevant research across the world is shown as follows. According to the engineering geological conditions of the Shandong mining area, the law of surface movement and deformation in thick loose layers and large mining height mining is studied [10; 11]. Based on the measured data of the Lianghuai mining area, the influence of geological mining conditions on boundary angle and movement angle is analyzed in detail. It is concluded that there is a logarithmic relationship between comprehensive movement angle, comprehensive boundary angle, and the thickness of the Tertiary and Quaternary loose layer [12; 13]. The change characteristics of topographic factors such as slope direction, coefficient of variation, and slope before and after mining subsidence show that all topographic factors are changedby mining subsidence [14, 15]. Under the mining condition of thin bedrock and thick loess layer, the subsidence deformation of loess layer and bedrock subsidence keep moving synchronously. The model of deep wide strip mining under super thick loose layer is established to study the relationship between the change in loose layer thickness, surface movement law, and subsidence coefficient [16]. The calculation of surface rock movement parameters of coal mine under loess gully terrain is based on slope stability analysis and computer inversion simulation. To evaluate surface asymmetric settlement in a mining area with thick bedrock and a thin loose layer, a superposition model is proposed. Time evolution of mining-related residual subsidence monitored over 24 years using InSAR in southern Alsace, France, is also investigated [17]. Others used numerical simulation to study the influence of loose layer thickness/base rock thickness, buried depth/coal thickness, and three mechanical parameters of tensile strength, cohesion, and internal friction on ground subsidence [18, 19, 20, 21, 22]. Some have analyzed the stability of the key water-proof layer of the filling working face through theoretical analysis, numerical simulation, and actual measurement, and they revealed the crack height and change law of the overburdened rock under the thin base rock and thick loose layer [23, 24, 25, 26, 27]. Some researchers have established a mechanical model of the thin bedrock face structure, and they pointed out that a thick clay layer with greater bearing capacity can be combined with a thin bedrock to form a stable structure [28, 29, 30, 31]. Some scholars regarded the thick loose layer and single thin bedrock as the load-bearing structure acting on the solid filling material, and they established a single-layer thin bedrock elastic continuous beam model [32, 33, 34, 35]. The above-mentioned research has enriched the theory and practice of overlying rock movement and deformation in mining under thick loose layers [36, 37, 38]. However, the theory of paste filling mining has not been adopted for the shallow buried extremely thick loose layer and thin bedrock, and there are few cases of paste filling mining under such conditions.