## 2 Studied Site
### Hydrogeological Conditions  
There are mainly three layers of medium-thick limestone in the dam site with the stratigraphic symbols of T\({}_{2}\)g\({}^{3\text{-}2\text{-}1}\), T\({}_{2}\)g\({}^{3\text{-}2\text{-}2}\), and T\({}_{2}\)g\({}^{3\text{-}2\text{-}3}\) (Figure 2). The total thickness is 103.4 m. The underlying strata are medium-thick limestone interbedded with thin-bedded shale (T\({}_{2}\)g\({}^{3\text{-}1\text{-}2}\)). In addition, the overlying strata are medium-thick limestone with mudstone shale (T\({}_{2}\)g\({}^{3\text{-}3}\)) with a thickness of 33.6 m and thick dolomite with dolomite limestone (T\({}_{2}\)g\({}^{3\text{-}4}\)). (1) Permeability analysis of rock mass  
The permeability of rock mass is closely related to its weathering integrity. Rock mass in weathering and unloading zones around the valley has good permeability. It decreases obviously with the increase of rock mass integrity (Table 1). The Lu values in Table 1 are obtained by water pressure test, which is defined as the inflow rate per meter in unit time, when the maximum pressure of the test section is 1 MPa. The test was proposed by [PERSON] from France in 1933 to estimate the necessity of grouting in rock mass of dam foundation. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Weathered Zones** & **5–10 Lu** & **1–5 Lu** & **<1 Lu** \\ \hline Weak weathered zone & 28 & 4 & 6 \\ Slightly weathered zone & 44 & 13 & 6 \\ Intact rock mass & 28 & 83 & 88 \\ Weak weathered zone & 28 & 4 & 6 \\ \hline Lu is equivalent to 10\({}^{-5}\) cm/s. & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Percentage of Lu values for different weathering zones (%). Figure 1: Location of study area. Because of the different lithology in the dam site, the development of karst is different, which constitutes a multi-level aquifer system. For example, the T\({}_{2}\)g\({}^{2}\) layer belongs to relative aquicude. The T\({}_{2}\)g\({}^{3\text{-}1\text{-}1}\), T\({}_{2}\)g\({}^{3\text{-}1\text{-}2}\), and T\({}_{2}\)g\({}^{3\text{-}3}\) layers are the fractured weak permeable layers. The T\({}_{2}\)g\({}^{3\text{-}2\text{-}1}\), T\({}_{2}\)g\({}^{3\text{-}2\text{-}2}\), and T\({}_{2}\)g\({}^{3\text{-}2\text{-}3}\) are the moderate permeable layers in karst-fractured systems. In addition, T\({}_{2}\)g\({}^{3\text{-}4}\) is the strong karst permeable layer. Therefore, the permeability of rock mass has heterogeneous anisotropy and is controlled by karst development, weathering, and fragmentation degree of rock mass. The zones with high permeability are mainly distributed in three geological bodies: (1) Strong and fractured dissolution weathering zone near the surface; these zones were disclosed in the adits PD-4, PD-12, and PD-13 in the left bank and PD-9 and PD-10 in the right bank (We edited the adits found in the study area as PD-1, PD-2..., PD-N). Serious dripping occurred in these zones. (2) Karst pipe and corrosion fracture zones; serious dripping was found in the section of 53.2-55.3 m in the adit PD-10 and 53.3-57.5 m in the adit PD-11. (3) Fractured and bedding dissolution zones; there are the dripping phenomenon in the section of 74.3-74.7 m in the adit PD-9 and 43-49 m in the adit PD-10. Owing to the influences of weathering and unloading, the permeability of rock mass decreases obviously with the increase of burial depth of rock mass (Table 2). At the depth of 0-60 m, the permeability of local rock mass is moderate. About 120 m below the surface, the rock mass is basically impermeable (Lu \(<\) 1). \begin{table}
\begin{tabular}{c c c c} \hline
**Burial Depth (m)** & **5–10 Lu** & **1–5 Lu** & **\textless{1 Lu**} \\ \hline
20 & 13 & 45 & 42 \\
40 & 2 & 66 & 32 \\
60 & 1 & 66 & 33 \\
80 & 0 & 75 & 25 \\
100 & 0 & 59 & 41 \\
120 & 0 & 29 & 71 \\ \textgreater{}120 & 0 & 0 & 100 \\ \hline \end{tabular} \(1\) Lu is equivalent to \(10^{-5}\) cm/s.  
\end{table} 
Table 2: Percentage of Lu values for different burial depths (%). Figure 2: Geological profile of dam axis.