## 4 Floor Heave Control with Anti-Shear Pile Technology
### Effectiveness of Anti-Shear Pile Method  
First simulation stage. In the first simulation stage, the search for the best floor control scheme was carried out while installing one pile. The distributions of vertical strain and shear strain around the entry before and after pile installation are shown in Figures 8 and 9. It can be seen that the installation of the pile in any of the positions significantly reduces the size of the post-peak strain zone on the immediate floor. Pile installation does not significantly affect the distribution of compressive stresses; however, the zone of tensile stresses underneath the entry span is reduced. The smallest dimensions of this zone are for the 1 pile 4 scheme (4) (Figure 8c). The pile installed in the entry corner (scheme 1 pile 5 (4)) bends at a depth of 1-2 m in the zone of high horizontal stresses. This pile orientation effectively restricts floor delamination on the side of the filling wall, but practically does not restrain expansion on the side of the coal seam body (Figure 8b). Pile installation in the center of the entry span (scheme 1 pile 3 (4)) restricts floor delamination on the side of the coal seam body, but on the side of the filling wall, vertical delamination remains significant (Figure 8d). Figure 8: The vertical strain distributions in surrounding rock in gob-side entry retaining: (**a**) before pile installation; after pile installation with schemes (**b**) 1 pile 5 (4); (**c**) 1 pile 4 (4); (**d**) 1 pile 3 (4). Pile installation has a similar effect on shear strain in the geometric sense. The smallest dimensions of the post-peak shear strain zone are for the 1 pile 4 (4) scheme (Figure 9c). The pile in the center of the entry span (scheme 1 pile 3 (4)) does not reduce the floor heave by the anti-shear (anti-slide) effect (Figures 8d and 9d). It is more likely that such pile installation halves the entry span, which ensures a reduction in floor delamination. The discussed stress-strain distributions are in accordance with the results of the floor heave analysis. The floor heave before and after pile installation at the first simulation stage is shown in Figure 10a. The smallest contour uplifts among schemes with piles 4 m long are noted for the 1 pile 4 (4) scheme. In this case, the smallest dimensions of the horizontal compression zone on the entry floor are observed (Figure 10b). However, the smallest dimensions of the horizontal post-peak expansion zone are observed in scheme 1 pile 5 (4) (Figure 10b). This scheme is worthy of interest since the post-peak horizontal strain is the key factor of the floor heave in the gob-side entry, which was discussed in the previous section. The vertical strain distributions around the gob-side entry retaining after installation of 2 m long piles are shown in Figure 11. Reducing the length of the piles to 2 m for schemes 1 pile 4(2) and 1 pile 3(2) led to a significant decrease in the efficiency of counteraction to immediate floor delamination. The 1 pile 3(2) scheme affects only the local maximum of floor heave in the center of the entry (Figure 10a) and the vertical floor delamination in the central part of the entry span (Figure 11c). The size of the post-peak strain zone in the immediate floor does not decrease significantly compared to the case before pile installation (Figure 8a). Pile installation with the 1 pile 4(2) scheme reduces the size of the vertical post-peak strain zone on the filling wall body side (Figure 11b), which leads to a decrease in floor heave on the filling wall side (Figure 10a). However, the length of the pile is insufficient to counteract the delamination of the floor from the side of the coal seam body  
Figure 9: The shear strain distributions in surrounding rock in gob-side entry retaining: (**a**) before pile installation; after pile installation with schemes (**b**) 1 pile 5 (4); (**c**) 1 pile 4 (4); (**d**) 1 pile 3 (4).