# Experimental Study on Hydraulic Fracturing of High Asphalt Concrete Core Rock-Fill Dam
## 6 Conclusions  
The scarcity of voids in the impervious asphalt concrete will not allow the entrance of reservoir water to the core wall, thus creating a pore pressure. Meanwhile, the fluid medium of bitumen in the asphalt concrete under normal temperatures has a viscosity so high that it does not behave like a fluid and does not move inside hydraulic asphalt concrete. Since the main preconditions of pore water pressure and pressure transmission do not exist, the hydraulic fracturing of asphalt concrete can be ignored [15]. However, some impervious asphalt concrete tends to dilatancy under the applied shear stress, thus increasing its voids content. This shear dilatancy has occurred in Finstertal ACRD with the behavior of the widening of its core wall during operation [19]. According to the numerical analysis of the Quxue ACRD, the shear dilatancy may also appear in the left upper zone of its core wall. Whether the hydraulic fracturing will occur under such shear dilatancy, no research result could be found in the references at present. In this paper, a feasibility model test was first made to the dilatant asphalt concrete of Quxue ACRD with a 3.5% voids content. This confirmed the occurrence of hydraulic fracturing in the core wall under the action of local tensile stress and water pressure. Furthermore, detailed model tests under water pressure have been conducted to investigate the hydraulic fracturing of the asphalt concrete with different voids contents. Conclusions can be drawn as follows:  
1. For asphalt concrete with a voids content not smaller than 3.4%, hydraulic fracturing will occur under the action of 0.13 MPa water pressure. The smaller the voids content, the longer it will take to hydraulic fracture. 2. For asphalt concrete with a voids content of 3.0%, hydraulic fracturing will not appear under 0.13 MPa water pressure. The test period lasted for 477 h without any sign of a hydraulic fracture. The threshold requirement of a 3% voids content to the impervious asphalt concrete may be confirmed to the concern of hydraulic fracturing. 3. Because the averaged stress of the ligament area of the specimen is smaller than its tensile strength during fracturing, the theory of fracture mechanics should be applied to explain the hydraulic fracture of the asphalt concrete with a 3.4%-4.0% voids content, which behaves during hydraulic fracturing like a quasi-brittle material, similar to a concrete with compressive strength of 56 MPa. Based on the above test and numerical analysis results, the hydraulic fracturing of an asphalt concrete with a void content higher than 3.0% could be the result of a series of gradual fracturing. If this fracturing process could be hindered by a vertical compressive stress, even though it is smaller than the applied water pressure, the hydraulic fracturing would not happen as a result. This conjecture can be further verified by future studies. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Material** & \(\alpha_{\text{I}}\)**/MPa** & \(K_{\text{IC}}\)**/MPa**\(\cdot\)**m**\({}^{\text{1/2}}\) & \(R\)**/mm** \\ \hline High-strength steel-12 Ni [21] & 1500 & 142 & 1 \\ No.45 forging steel & 299 & 89.6 & 10 \\ Concrete (compressive strength of 56 MPa) & 3.65 & 0.803 & 5 \\ Asphalt concrete of this paper & 0.156 & 0.032–0.034 & 4.6–5.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Plastic zone radius \(R\) of different materials. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Voids** & **Critical** & **Crack Disc** & \multirow{2}{*}{**K\({}_{\text{IC}}\)/MPa**\(\cdot\)**m**\({}^{\text{1/2}}\)} & **Averaged Stress of** & **Plastic Zone** \\
**Conten/\%** & **Force/N** & & **Diameter/mm** & **Ligament Area/MPa** & **Radius/mm** \\ \hline
3.4 & 131 & 66.7 & 0.0344 & 0.074 & 5.33 \\
4.0 & 93 & 58.8 & 0.0321 & 0.051 & 4.64 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Mechanical parameters of the model test.