## 3 Results and Discussion
### Later Mechanical Strength of Compacted Body  
The compacted solid obtained from slurries with different fluidities under pressure has differences in height. As a result, some samples do not meet the requirements of the standard sample (GB/T50266-99). The parameters obtained from the test are standardized according to the height-to-diameter-ratio formula (Equation (5)).  
\[\sigma_{1}=\frac{8\sigma_{2}}{7+2\frac{D}{H}} \tag{5}\]  
where \(\sigma_{1}\) is the uniaxial compressive strength of the standard specimen, Mpa; \(\sigma_{2}\) is the uniaxial compressive strength of non-standard specimens, Mpa; \(D\) is the non-standard sample diameter, mm; \(H\) is the height of the non-standard specimen, mm.  
According to the experimental data, the compressive strength of the compacted body is calculated using Equations (4) and (5), as shown in Figure 13. Since the specimens were not drilled from the compacted body with slurry fluidities of 220 mm and 260 mm, Figure 14 shows the uniaxial compressive stress-strain curve of the compacted body with a fluidity of 230-250 mm.  
As shown in Figure 13, when the fluidity is constant, the compressive strength of the compressed solid increases with the increase of loading time in the range of \(x=1\)-3. When \(x=3\), the compressive strength is 3.06 MPa, 3.77 MPa, 4.98 MPa, 4.62 MPa, and 4.54 MPa, respectively. When \(x=4\), the backfilling material undergoes stress damage after prolonged loading, resulting in a decrease in the strength of the compacted body, but it is not lower than that when \(x=1\)-2. Moreover, the greater the fluidity, the more significant the degree of strength loss. The loss proportion of the compacted body with a fluidity of 230-260 mm is 8.5%, 13.1%, 18.2%, and 18.7%, respectively. When the loading scheme is the same, the compressive strength of the slurry increases first and then decreases as the flow increases, and the compressive strength with a fluidity of 240 mm is the maximum value. This indicates that when the fluidity is 240 mm and the creep loading scheme is \(x=3\), the mechanical properties of the compacted body in the later stage are the best. In addition, when the fluidity increases to 250 mm, \(C_{\text{u}}\) is the maximum value and \(C_{\text{c}}\) is the minimum value, there are fewer small particle sizes and more large particle sizes of gangue. When \(x=1\)-2, as well as the short compression time of the slurry, there are more pores in the compacted body, resulting in lower strength and a significant decrease in the strength of the compacted body. As illustrated in Figure 14, the overall trend of stress-strain changes of the  
Figure 13: Compressive strength of compacted body.  
compacted body before and after fragmentation is consistent. The entire loading process can be divided into four stages. (1) Elastic stage (OA section): in this stage, the stress increases linearly with strain. (2) Yield stage (AB section): in this stage, the stress continues to increase with increasing strain, but the degree of increase is significantly lower than that in the elastic stage. (3) Reinforcement stage (BC section): in this stage, stress increases rapidly with increasing strain, and the degree of increase is higher than that in the elastic stage. (4) Crushing stage: in this stage, the stress begins to drop after reaching its peak, and residual stress exists after the peak. During the entire pre-peak (OC section) loading process, the proportion of the reinforcement stage (BC section) is higher and exhibits a linear growth curve similar to the elastic stage. At this time, the compacted body undergoes local plastic failure, causing stress to redistribute until the stress peak is reached.