# 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
#### 2.4.3 Value Ranges of the Strength Parameters of UACC That Comprehensively Meet YSFCS  
The value ranges of the strength parameters (failure ratio \(R_{f}\), cohesion \(C\), and internal friction angle \(\varphi\)) of ACC that comprehensively meet the YSFCS are back-calculated. It is assumed that other material parameters are unchanged and only the failure ratio \(R_{f}\), cohesion \(C\), and internal friction angle \(\varphi\) of ACC are comprehensively changed. The stress level of UACC satisfies: \(S\leq 0.77\) (YSFCS).  
The area above the curved faces shown in Figure 15 represents the safe value ranges of the cohesion and internal friction angle of ACC, when \(R_{f}\) = 0.6, 0.7, and 0.8. Figure 15 and Table 5 show that the cohesion and internal friction angle of ACC that meet the YSFCS increase with dam height, when the failure ratio of ACC is unchanged. The failure ratio and cohesion of ACC that meet the YSFCS increase with dam height, when the internal friction angle of ACC is unchanged. The failure ratio and internal friction angle of ACC that meet the YSFCS increase with dam height, when the cohesion of ACC is unchanged. The cohesion and internal friction angle of ACC that meet the YSFCS decreases with the failure ratio of ACC, when the dam height is unchanged. The failure ratio and cohesion of ACC that meet the YSFCS decrease with the internal friction angle of ACC when the dam height is unchanged. The failure ratio and internal friction angle of ACC that meet the YSFCS decreases with the cohesion of ACC when the dam height is unchanged.  
The data of Maopingxi asphalt concrete core rockfill dam is referred. The failure ratio of ACC is [0.49, 0.91], the cohesion of ACC is [0.16 MPa, 0.51 MPa], and the internal friction angle of ACC is [28.4\({}^{\circ}\), 36.2\({}^{\circ}\)] with the triaxial test under different mixture formulas of ACC. Therefore, the following value ranges of the failure ratio, cohesion, and internal friction angle of ACC for the suitable construction of UACCDs are recommended: \(R_{f}\geq 0.75\), \(C\geq 0.30\) MPa, and \(\varphi\geq 28.5^{\circ}\) (\(h\) = 150 m), with the growth gradient adjusted by 5%, 15%, and 5%/25 m. The stress levels of ACC under different dam heights are shown in Table 6. Table 6 shows that the stress levels of ACC under different dam heights are less than or equal to the YSFCS, i.e., the shear safety factors of ACC under different dam heights are more than or equal to the yield shear safety factor 1.30. The UACC is safe and will not experience shear failure. Thus, the recommended strength parameters of ACC are reasonable.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Dam Height (m)** & **150** & **175** & **200** & **225** & **250** \\ \hline Failure ratio & 0.75 & 0.95 & 1.08 & 1.15 & 1.20 \\ Cohesion (MPa) & 0.34 & 0.47 & 0.60 & 0.74 & 0.89 \\ Internal friction angle (\({}^{\circ}\)) & 29.5 & 33.0 & 35.5 & 37.5 & 39.0 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Failure ratio, cohesion, and internal friction angle minimums of ACC that independently meet YSFCS with different dam heights.  
Figure 14: Relationship between internal friction angle of ACC that meets YSFCS and dam height.