## 1 Introduction
The problem of gob-side entry retaining stability is aggravated by the constant increase in the mining depth and the natural deterioration of geological conditions. The deformation and failure of the roof and wall sides of the entry in most cases are effectively controlled by a multi-level support system (steel arch, rock bolt, cable bolt), while the entry floor often remains free. Therefore, severe floor heave is an unsolved problem in gob-side entry retaining. Floor heave control will significantly increase the application of progressive pillarless mining technologies. Many scholars have studied the floor heave mechanism in gob-side entry retaining [15; 16; 17]. It can be concluded that failure or plastic flow of the immediate floor, caused by stresses exceeding the strength limit of the rock, is a prerequisite for floor heave [18]. [PERSON] et al. [19] pointed out that the key factors of floor heave are changes in the stress-strain state of surrounding rocks after roof failure. This causes an increase in vertical stress in the roadway side walls, which affects the floor strata state. [PERSON] et al. 2023 [16] found that the floor is squeezed by the two sides to form an asymmetric sliding force towards the free face of the floor. Most scientists agree that high horizontal stresses in the immediate floor are one of the main factors that cause severe floor heave. The magnitude of heaving depends on the vertical-horizontal stress ratio [20; 21]. [PERSON] et al. [22] proposed the Horizontal Stress Rating (HSR), which represents the magnitude of horizontal stress by statistical analysis on an Australian database. [PERSON] and [PERSON] [23] found that variations in the horizontal-vertical stress ratio in the floor strata are the main cause of large floor heave. [PERSON] et al. [15] found that horizontal stress in the immediate floor is the root factor that causes floor heave. [PERSON] et al. [24] proved that squeezing and fluid floor heave play an important role in the stable stage of gob-side entry retaining. [PERSON] et al. [25] defined the main role of shear failure in roadway failure. Traditional ideas about floor heave identify three main floor heave mechanisms: bearing capacity failure, swelling, and buckling [26]. Each of these mechanisms is associated with a key factor that causes it. Bearing capacity failure cases are associated with the shear failures of the floor strata underneath the coal pillars when the vertical stress exceeds the bearing capacity of the floor. Swelling occurs in wet rocks containing clay minerals. Buckling occurs under the influence of high horizontal stresses on the floor strata [27]. However, in situ, the mechanisms of heaving are not so clear. In gob-side entry retaining, different factors often have simultaneous influence. In each local case, this leads to different magnitudes of floor heave. In addition, the headgate has different media from the two wall sides (solid coal on one side and filling wall on another); it also has different vertical pressure, which leads to asymmetry in the entry deformation. In this paper, it was accepted that the main cause of floor heave is a change in the stress field in surrounding rocks; moisture is still considered an additional negative factor. Reinforcement and stress-relief methods have the greatest potential for the control of floor heave in gob-side entry retaining. However, despite the significant scientific substantiation of these methods, in practice, they are not widely used. Floor restoration has been widely implemented. Therefore, scientists from different countries have searched for new effective reinforcement schemes. Traditional floor reinforcement schemes with rock bolts are modified by combining them with flexible anchor supports [28], shotcrete and steel frames [29], concrete inverted arches [30], pressure-relief holes [31], etc. [PERSON] et al. [32] proposed the control method of \"bottom lifting + bottom angle bolt + floor bolt\" based on the results of a numerical simulation. [PERSON] et al.