# Mechanics Model of Floor Heave: Case Study on Thin Coal Seam with Soft Roof and Floor
## 1 Introduction  
Gob-side entry retaining refers to the technique of roadside packing along the edge of the goaf side of the mining roadway as the caving face progresses, retaining the original caving face groove and using it as the next district sublevel caving face groove [1; 2]. It is commonly used in medium thick and thin coal seams. The thinner the coal seam, the stronger the support capacity of the roadway filling body, and the better the overall effect. It is meaningful for thin coal seam mining, and has the advantages of canceling coal pillars, achieving non pillar mining, and improving coal resources recovery [3; 4]. However, it differs from the mining of medium thick or thick coal seam gob-side entry retaining. As the mining height increases, the mining stress and influence range increase, and the filling body is affected by roof subsidence, rotation, etc., resulting in increased deformation and poor stability of the filling body [5]. For thin coal seams with gob-side entry retaining, the effectiveness mainly depends on the stability of the filling body, the properties of the roof and floor surrounding rocks, and for weak floor slabs, floor heave is prone to occur. The floor heave of the gob-side entry retaining is a phenomenon brought on by changes in thesurrounding rock's stress state as a result of mining, excavation, retaining roadways, and other factors, as well as changes in the rock's properties during maintenance. As a result, the rock mass's roof, floor, and two sides are deformed and move towards the roadway, with the floor rising upwards [6; 7; 8]. The phenomenon of floor heave in the gob-side entry of fully mechanized top coal cavity is currently becoming more prevalent. However, it not only harms the roadway but also significantly affects the stability of small coal pillars, filling bodies close to the roadway, and even the entire roadway. Strong floor heaves require considerable maintenance and renovation work, which has a negative impact on the mine's normal output and significantly raises the cost of maintaining and repairing the road [9]. The application requirements for gob-side entrance retention have gradually increased from straightforward to intricate with the advancement of the technology. According to research, the primary factors influencing the floor heave of gob-side entrance include burial depth, the characteristics of the surrounding rocks, coal seam mining height, support form, and strength [10; 11; 12; 13]. In Luan Mining Area, Shanxi Province, [PERSON] et al. studied the auxiliary transportation roadway along the goat in the N2301 fully mechanized caving face of Gucheng Coal Mine. They discovered that the cantilever structure on the roof of the gob-side entry retaining behind the working face and the uneven superposition of high advanced support pressure and horizontal stress in front of the working face are to blame for the asymmetric floor heave of soft rock [14]. In order to develop a mechanical model for the coal-rock roadway's floor rock mass failure, [PERSON] examined the floor heave's deformation characteristics [15]. The thick coal seam roadway floor with soft roof, soft coal, and soft floor is susceptible to significant deformation, according to [PERSON] et al. 's analysis [16]. By analyzing the rock mass's motion characteristics at various depths in the roadway's subgrade, [PERSON] was able to determine that shallow uplift and deep subsidence are the mechanisms responsible for floor heave [17]. [PERSON] et al. [18] took Huafeng Coal Mine as the research object, proposed anti-slide piles control technology for the floor heave problem in the \(-1100\) level, and provided a method for determining the support parameters of anti-slide piles. [PERSON] [19] investigated floor heave analysis in a deep coal mine. [PERSON] [20] studied the floor heave in a western Kentucky mine with localized increase in the thickness of the fireday mine floor.