# 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  
#### 2.4.1 Shear Characteristics of UACC  
The ratios of upstream and downstream dam slope are both 1.0:2.0. The width of dam crest is 10 m. The thickness of transition material is 3 m. The thickness of core crest is 0.5 m. The thickness of core base is 1/100 of dam height. The dam heights are 100, 125, 150, 175, 200, 225, and 250 m. The left valley slope ratios are 0.5:1.0, 1.0:1.0, 1.5:1.0, 2.0:1.0, and 2.5:1.0. The right valley slope ratio is 2.0:1.0. The diagram of calculation schemes is shown in Figure 3. ABAQUS is employed for finite element method (FEM) models in this paper. The material regions of FEM standard model (the dam height is 200 m and the left valley slope ratio is 1.0:1.0) are shown in Figure 4. The meshes of FEM standard model are shown in Figure 5. The element type of dam is C3D8R and the element number of dam is 18240 (the element number of ACC is 2000). The element type of bedrock is C3D10 and the element number of bedrock is 27401. The boundary conditions are that the four sides of models are normally constrained and the bottom of models is fully constrained. The hyperbolic model (proposed by [PERSON] [27]) has been well developed for predicting the stress-strain relationship of geo-material in dams. Thus, this model is used in this paper and the characteristic parameters of dam materials are shown in Table 1.  
Figure 4: Material regions of finite element method (FEM) standard model for asphalt concrete core rockfill dams (ACCRDs). Figure 5: Meshes of FEM standard model for ACCRDs. Figure 3: Diagram of calculation schemes. According to Section 2.1, the settlement of ACC is the fundamental reason that the UACC generates high shear stress (high stress level). Thus, the settlement and stress level of UACC are only discussed in the following section. The settlement of UACC toward up is negative, and the settlement of UACC toward down is positive. Figure 6 shows that the settlement of ACC is circularly distributed. The settlement maximum at the center of ACC is 1.24 m, which is approximately 0.6% of dam height and less than 1%. Figure 7 shows that the stress level of ACC is symmetrically distributed. The stress level maximum at the steeper end of ACC is 0.938. Figures 8 and 9 and Table 2 show that the settlement and stress level of ACC increase sharply with dam height. When \(h\) = 100 m, the settlement of ACC is \(-\)0.385 m. The stress level of ACC is 0.558 (the shear safety factor is 1.79), which is far less than the YSFCS. The ACC is safe and will not experience shear failure. When \(h\) = 150 m and \(h\) = 200 m, the settlements of ACC are \(-\)0.704 m and \(-\)1.067 m. The stress levels of ACC are 0.807 and 0.938 (the shear safety factors are 1.24 and 1.05), which are more than the YSFCS and less than the USFCS. The ACC has the probability that experiences shear failure. When \(h\) = 250 m, the settlement of ACC is \(-\)1.508 m. The stress level of ACC is 1.036 (the shear safety factor is 0.97), which is more than the USFCS. The ACC experiences shear failure. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline
**Parameters Materials** & \(K\) & \(n\) & \(R_{\text{f}}\) & \(C/\text{kPa}\) & \(\varphi l^{\circ}\) & \(\triangle\varphi l^{\circ}\) & \(K_{\text{b}}\) & \(m\) & \(K_{\text{var}}\) & \(\rho(\text{g/cm^{3}})\) \\ \hline Rockfill material & 1100 & 0.4 & 0.75 & 75 & 50 & 8 & 550 & 0.25 & 2100 & 2.15 \\ Transition material & 1200 & 0.45 & 0.8 & 20 & 44.5 & 7 & 700 & 0.375 & 2400 & 2.35 \\ Asphalt concrete core & 450 & 0.5 & 0.7 & 300 & 28 & 5.5 & 1200 & 0.4 & 1550 & 2.45 \\ Prism drainage & 1000 & 0.375 & 0.65 & 15 & 52 & 10 & 525 & 0.35 & 2000 & 2.3 \\ Backfill material & 850 & 0.35 & 0.6 & 45 & 47.5 & 8.5 & 475 & 0.3 & 1700 & 2.1 \\ Bedrock & & & & & \(P\) = 2.75 g/cm\({}^{3}\); \(E\) = 12.5 GPa; \(\mu\) = 0.2 & & & & & \\ \hline \end{tabular}
\end{table} 
Table 1: Characteristic parameters of dam materials (E-B model). Figure 6: Settlement contour of ACC (\(h\) =200 m).