## 2 Engineering Background
### Supporting Parameters and Deformation of Gob-Side Entry Retaining  
A U-shaped steel arch support (U33) with steel mesh was used in the entry. The width and height of the entry were 5.2 m and 3.65 m, respectively. The cross-sectional area of the entry during the excavation stage was 15.1 m\({}^{2}\). The distance between the steel arch frames was 0.67 m. After coal mining in the longwall face, an artificial filling wall was built to maintain the gob-side entry. Figure 3a shows the original design of the support scheme. However, at a longwall retreat with a distance of 200 m, the width and height of the headgate of the 12-panel longwall were 2.6 m and 1.29 m, respectively. The total vertical convergence was about 64% of the initial roadway height. The average floor uplift was 1.04 m, and the average roof lowering was 1.32 m. The headgate deformed asymmetrically. The steel arches were critically bent and irreversibly deformed. The yielding nodes failed, and the steel mesh was disrupted. The entry required repair. The failure of the headgate support system and the floor have consequences are shown in Figure 3b. To increase the load-bearing capacity of the steel arch frames, wooden pillars were installed. Floor restoration was carried out with a Hasemag EL160 loader machine to ensure the required cross-sectional area in the gob-side entry retaining. This practice is  
Figure 2: The geological and engineering conditions of a mine: (**a**) strata histogram; (**b**) layout of longwall panels. typical for coal mines in Ukraine [41]. Scholars from other countries report similar cases of critical floor heave [16; 18; 27; 42; 43]. Floor heave monitoring was performed in the headgate of the 12 panels. Measurements were carried out at three monitoring stations. The distance between stations was 9.6 m. Each station consisted of 4 marker points installed in the roof, floor, and both wall sides of the gateroad. The measurements were carried out over 4 months. The graphs of floor heave evolution in the center of the headgate span in front of the longwall face and behind it are presented in Figure 3c. The floor uplift in front of the longwall influence zone was 95 mm (9% of the total floor heave) and occurred during the roadway excavation stage. The monitoring results show that the main part of the floor uplift occurred at a distance of +40 m in front of the longwall face and \(-\)50 m behind it. In total, 35% of the floor uplift occurred at a distance of \"+40\" m in front of the longwall face to the intersection of the headgate with the face. Another 28% of floor uplift appears in the section of the headgate \"0\"-\"-50\" m behind the longwall face. The floor uplift has a damping tendency and stabilizes at a distance of 260-300 m behind the longwall face. At the stage of maintaining the headgate behind the longwall face, 56% of the total floor uplift occurs. An analysis of the floor heave dynamic monitoring showed that this phenomenon evolved with different intensities at different stages of the gateroad's life. This is generally consistent with previous studies [15; 17; 27; 41]. The gateroad that was an object of study had no water inflows. Therefore, the swelling mechanism of heaving is not typical for it. The greatest increase in gateroad floor heave was associated with the longwall face influence. The abutment pressure changed the equilibrium state of rock masses, increased vertical stress concentration and led to post-elastic deformation of rocks. In this case, the immediate floor lost its continuity and became discontinued. This was visually confirmed after rock excavation during floor restoration, similar to previous studies [41]. Post-elastic deformation (pseudoplastic flow) and dilatancy are the main causes of floor heave. Floor heave in the gob-side entry is complicated by the asymmetrical stress-strain state. In this case, the heaving mechanism is close to bearing capacity in failure cases. However, due to the stress asymmetry, failures of the floor strata underneath the coal body and the filling wall body are different.