## 4 Conclusions  
In this study, a loading simulation system of grouting backfilling materials was used to conduct uniaxial confined compression tests on gangue slurry with five different fluidities. The main conclusions are as follows:  
1. Under instantaneous loading conditions, the compression rate of gangue slurry changes with stress, which can be divided into rapid the deformation stage, slow deformation stage, and deformation stable stage. The lower the fluidity, the greater the corresponding stress when the slurry reaches the deformation stable stage, the smaller the extreme value of compression rate, and the stronger the deformation resistance  
Figure 14: Stress-strain curves of compacted solid with different fluidities: (**a**) 230 mm, (**b**) 240 mm, (**c**) 250 mm. and bearing capacity. Under creep loading conditions, the maximum compression rate of the slurry is generally low, while the deformation resistance and bearing capacity are strong. The entire bearing process also shows three stages: rapid deformation, slow deformation, and stable deformation. 2. The bleeding rate of the gauge slurry with a fluidity of 220-260 mm under a static state does not exceed 10%. However, after instantaneous and creep loading, more than 60% and 50% of the water passively leaks out of the slurry, respectively. The gauge particles in the slurry play the main bearing role. The compressive bleeding rate of the slurry has a threshold, and the entire bearing process can be divided into the supersaturated drainage stage, compressive bleeding stage, and no bleeding stage. The solid-water ratio of the compacted body after loading is mainly affected by the fluidity and loading mode. 3. The self-bearing and deformation process of gauge slurry is manifested in three stages: the rapid compression and drainage stage, pore compaction and water bleeding stage, and particle crushing and elastic-plastic deformation stage. In the first stage, the slurry is rapidly discharged with supersaturated water, its deformation rate is fast, and the pore water is mainly subject to pressure. The deformation resistance and bearing capacity of the slurry are poor at this stage. In the second stage, the pores in the slurry are reduced due to the sliding backfilling of gauge and the crushing and compaction under the action of water wedges and dissolution, and the deformation resistance and bearing capacity of the slurry gradually increases. In the third stage, the slurry gradually forms a compacted solid with a stable solid-water ratio, and the gauge particles undergo elastic-plastic changes after being compressed, gradually transforming into a continuous medium. As a result, the bearing capacity is further strengthened, and the mechanical strength of the compacted body is affected. 4. After creep loading, the compacted body undergoes the elastic stage, yield stage, reinforcement stage, and crushing stage during uniaxial compression, and the compressive strength of the compacted body with different fluidities under the 3 h creep loading reaches the maximum value. However, stress damage occurs after the 3 h loading. At the same time, the compressive strength of the compacted body of the 240 mm fluidity slurry under different loading schemes is the maximum, and the optimal scheme for the later mechanical strength of the backfilling material is obtained as a fluidity of 240 mm and creep loading of 3 h.
5. In summary, for the mine with a mining depth of 800 m, when using the grouting backfilling process with a fluidity of 240 mm of gauge slurry, the maximum compression rates of the slurry are 45% and 47.7%, respectively, when the overlying rock strata collapse instantly and sink slowly. As the mining depth decreases, the pressure on the overlying rock decreases, and the compression rate of the slurry decreases, resulting in better control of overlying rock deformation. Conceptualization, J.X. ; Methodology, N.Z. and Z.L. ; Data curation, Y.Z. ; Writing--original draft, S.L. ; Writing--review & editing, C.D.