## 3 Flexible Anti-Hydrofracturing Solution
### Onsite Scheme Construction  
#### 3.2.1 Test  
For the field test, the chosen site is the upstream surface of the No. 13 dam section. Test areas A and B, each encompassing 28 m\({}^{2}\), were designated on this surface (Figure 8a). Test area C was positioned near the corner of the upstream surface and the fillet, as depicted in Figure 8b. Schemes 1 and 2 were assigned to areas A and B, respectively. In consideration of the induced dry joint from the No. 17 to No. 28 dam section, scheme 3 was applied to test area C. This scheme entailed incorporating a GB filler rod (for support), 3-millimeter GB material, a segment devoid of GB lining, and a 7-millimeter-thick layer of sprayed polyurea. Prior to the anti-hydrofracturing treatment, the concrete surface needed to be clean, dry, and free of impurities such as dust and oil. Polyurea could be directly sprayed onto the GB plate.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Crack Width \(b\)/mm** & \begin{tabular}{c} **The Elongation of** \\ **Scheme 1** \\ \end{tabular} & \
\begin{tabular}{c} **The Elongation of** \\ **Scheme 2** \\ \end{tabular} &
\begin{tabular}{c} **The Elongation of** \\ **Scheme 3** \\ \end{tabular} \\ \hline
5 & 0.46 & 0.49 & 0.35 \\
8 & 0.90 & 0.87 & 0.67 \\
10 & 1.17 & 1.21 & 0.83 \\
15 & 1.48 & 1.62 & 1.12 \\ \hline \hline \end{tabular}
\end{table}
Table 5: The elongation under different crack openings.  
Over the next fortnight (two weeks), scrutiny aimed to detect any deformation or detachment between the anti-hydrofracturing system and the concrete during construction. Following this period, adhesion strength tests were conducted, and the thickness of sprayed polyurea underwent assessment.  
The outcomes of the field test exhibit no signs of deformation or detachment between the anti-hydrofracturing system and the concrete throughout the initial 20-day period following polyurea application. Employing an adhesion strength tester (Figure 9), pull-out failures were assessed across the three test regions. Notably, maximum adhesion strength and locations of tensile failure were noted, along with confirmation of sprayed polyurea thickness. Test results, as presented in Table 6, reveal that the sprayed polyurea thickness in all three test zones surpasses the original design, thus meeting the design criteria. In the A test area, the average adhesion strength between the GB plate and concrete exceeds 0.23 MPa, while in the B test area, the average adhesion strength between GB glue and concrete surpasses 0.37 MPa. In the C test area, failure positions occur at junctions between standard blocks and polyurea, indicating robust concrete-polyurea bonding. The average adhesion strength between polyurea and concrete is consistently above 2.31 MPa.  
Figure 8: Location of the field test areas: (**a**) test areas A and B; (**b**) test area C.  
Figure 9: Adhesion strength test of the anti-hydrofracturing system: (**a**) the TJ-10 adhesion strength, tester; (**b**) failure position.  
The aforementioned test outcomes demonstrate the feasibility and suitability of all three schemes for implementation. Among these, scheme 1 stands out with its smooth appearance and enhanced ease of construction quality control, as depicted in Figure 10. Additionally, scheme 1 boasts a thicker, more flexible, and more cost-effective GB plate compared to scheme 2, making it better suited for accommodating significant deformations. Consequently, it is recommended that scheme 1 be prioritized as the primary choice for the official upstream dam surface protection approach, while scheme 3 is advised for application in the corner between the upstream surface and the fillet.