# Improvement Methods for Reduction of the High Stress of Ultra-High Asphal Concrete Core Dams
## 2 Investigation on the Shear Stress Feasibility of UACC
### Reasonable Value Ranges of the Strength Parameters of UACC
#### 2.4.2 Value Ranges of the Strength Parameters of UACC That Independently Meet YSFCS  
The _\"Improvement method that reduces the high stress level of UACC\"_ shows that the stress level of ACC can be reduced by the increases of the strength parameters of ACC. Thus, the value ranges of the strength parameters (failure ratio R\({}_{\text{f}}\), cohesion \(C\), and internal friction angle \(\varphi\)) of ACC that independently meet the YSFCS are back-calculated. It is assumed that other material parameters are unchanged and only the failure ratio R\({}_{\text{f}}\), cohesion \(C\), and internal friction angle \(\varphi\) of ACC are independently changed. The stress level of UACC satisfies: \(S\leq 0.77\) (YSFCS).  
Figures 12-14 and Table 4 show that the failure ratio, cohesion, and internal friction angle of ACC that meets the YSFCS increase with dam height. The area above the curve shown in Figure 12 represents  
Figure 11: Relationship between stress level maximum of ACC and valley slope ratio.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Valley Slope Ratio** & **0.5:1.0** & **1.0:1.0** & **1.5:1.0** & **2.0:1.0** & **2.5:1.0** \\ \hline Settlement (m) & \(-1.098\) & \(-1.074\) & \(-1.070\) & \(-1.067\) & \(-1.066\) \\ Stress level & \(0.852\) & \(0.938\) & \(1.030\) & \(1.120\) & \(1.216\) \\ Shear safety factor & \(1.17\) & \(1.07\) & \(0.97\) & \(0.89\) & \(0.82\) \\ \hline \hline \end{tabular}
\end{table}
Table 3: Settlement, stress level, and shear safety factor of ACC with different valley slope ratios.  
Figure 10: Relationship between settlement maximum of ACC and valley slope ratio.  
the safe value range of the failure ratio of ACC, when other material parameters are unchanged. The failure ratio minimum of UACC that meets the YSFCS is \(0.75\leq R_{\text{f}}\leq 1.2\), when \(150\) m \(\leq h\leq 250\) m. The area above the curve shown in Figure 13 represents the safe value range of the cohesion of ACC, when other material parameters are unchanged. The cohesion minimum of UACC that meets the YSFCS is \(0.34\leq C\leq 0.89\), when \(150\) m \(\leq h\leq 250\) m. The area above the curve shown in Figure 14 represents the safe value range of the internal friction angle of ACC when other material parameters are unchanged. The internal friction angle minimum of ACC that meets the YSFCS is \(29.5^{\circ}\leq\varphi\leq 39^{\circ}\), when \(150\) m \(\leq h\)\(\leq 250\) m. The high stress level of UACC can be reduced apparently by the increases of the strength parameters of ACC, which shows that the \"_Improvement method that reduces the high stress level of UACC\"_ is correct. However, it is impossible for the failure ratio, cohesion, and internal friction angle of ACC to reach the values that independently meet the YSFCS, when \(200\) m \(\leq h\leq 250\) m. Thus, the contribution of the failure ratio, cohesion, and internal friction angle of ACC that reduces the stress level of ACC is comprehensively considered in the following section.  
Figure 12: Relationship between failure ratio of ACC that meets YSFCS and dam height.  
Figure 13: Relationship between cohesion of ACC that meets YSFCS and dam height.