## 2 Overviews of In Situ Stress and Fifty-One Underground Powerhouses in China
\begin{table}
\begin{tabular}{c c c c c c} \hline  & **Installation** & **Main Powerhouse Size** & & **Rock** & **In Situ Stress** \\
**Project Name** & **Capacity** & **(Length \(\times\) Width \(\times\) Height)/m** & **Lithology** & **Classification** & **Level (MPa)** \\ \hline Ertan & \(6\times 550\) & \(280.3\times 30.7\times 65.6\) & Svenite, Basalt & II, III & 17.2–38.4 \\ Shuangjiangkou & \(4\times 500\) & \(132.6\times 29.3\times 63.0\) & Granite & II & 16.0–37.0 \\ Houziyan & \(4\times 425\) & \(219.5\times 29.2\times 68.7\) & Limestone & II, III & 21.5–36.4 \\ [PERSON] I & \(6\times 600\) & \(277.0\times 28.9\times 68.8\) & Marble & III & 20.0–35.7 \\ Guandi & \(4\times 600\) & \(243.4\times 31.1\times 76.3\) & Basalt & II, III & 25.0–35.2 \\ Changheba & \(4\times 650\) & \(228.8\times 30.8\times 73.4\) & Granite & II, III & 16.0–32.0 \\ Lianghekou & \(6\times 500\) & \(275.9\times 28.4\times 66.0\) & Sandy slate & III & 21.6–30.4 \\ Lavaiva & \(6\times 700\) & \(311.8\times 30.7\times 75.0\) & Granite & I, II & 14.6–30.0 \\ Pubugou & \(6\times 550\) & \(294.1\times 30.7\times 70.2\) & Granite & II, III & 21.1–27.3 \\ Xiaowan & \(6\times 700\) & \(298.4\times 30.6\times 79.4\) & Gneiss & I, II & 16.5–26.7 \\ Baihetan & \(16\times 1000\) & \(438.0\times 34.0\times 86.7\) & Basalt & III & 19.0–26.0 \\ Jinping II & \(8\times 600\) & \(352.4\times 28.9\times 72.2\) & Marble & III & 10.1–22.9 \\ Xiloudu (left) & \(9\times 770\) & \(439.7\times 31.9\times 75.6\) & Basalt & I, II & 14.8–21.1 \\ Dagangshan & \(4\times 650\) & \(226.6\times 30.8\times 73.8\) & Granite & II, III & 11.4–19.3 \\ Lubuge & \(4\times 150\) & \(125.0\times 18.0\times 38.4\) & Limestone, & II, III, IV & 13.5–18.0 \\ Jiangya & \(3\times 100\) & \(107.0\times 19.0\times 46.5\) & Limestone & II & 17.2 \\ Dchaoashan & \(6\times 225\) & \(233.5\times 26.4\times 63.0\) & Basalt & II, III & 13.0–16.9 \\ Zhouning & \(2\times 125\) & \(66.8\times 17.9\times 42.2\) & Granite & I, II & 14.6–16.4 \\ Silin & \(4\times 262.5\) & \(177.8\times 27.0\times 73.5\) & Limestone & II, III & 9.7–16.0 \\ Yixing & \(4\times 250\) & \(155.3\times 23.4\times 52.4\) & Sandstone & III, IV & 8.3–16.0 \\ Tianlonghu & \(180\) & \(77.0\times 18.0\times 39.6\) & Metasandstone, & III, IV, V & 9.7–15.5 \\ Yangjiang & \(6\times 400\) & \(216.0\times 26.0\times 59.8\) & Biotite granite & I, II & 14.0–15.0 \\ Huizhou & \(8\times 300\) & \(152.0\times 21.5\times 48.3\) & Granite & I, II & 12.0–15.0 \\ Sanbanxi & \(4\times 250\) & \(146.4\times 21.0\times 56.4\) & Sandstone & II, III & 14.5 \\ Pushihe & \(4\times 300\) & \(173.3\times 25.7\times 54.6\) & Migmatic & II, III & 14.4 \\ Guangzhou I & \(4\times 300\) & \(146.5\times 21.0\times 44.5\) & Granite & II, III & 14.0 \\ longtan & \(9\times 700\) & \(388.5\times 28.5\times 76.4\) & Sandstone, Shale & II, III & 12.0–13.0 \\ Yangfanggou & \(4\times 375\) & \(228.5\times 27.0\times 75.6\) & Granodiorite & II, III & 12.6–13.0 \\ Jixi & \(6\times 300\) & \(210.0\times 26.0\times 53.4\) & Granite & II, III & 10.0–13.0 \\ Suofengying & \(3\times 200\) & \(135.5\times 24.0\times 58.3\) & Limestone & II, III & 12.9 \\ \hline \end{tabular}
\end{table} 
Table 1: Summary of fifty-one underground powerhouses in China [10; 40; 41; 42; 52; 53; 54; 55; 56; 57; 58; 59; 60; 61; 62; 63]. Figure 5: Distribution of underground powerhouses in China. Table 1 presents the engineering scale, size, lithology, rock classification and in situ stress level of underground powerhouses in detail. The surrounding rock condition is very complex where a variety of lithology and more than two classifications exist at hydropower stations. In situ stress level basically covers 0-40 MPa, which will lead to more complex construction issues. Since 1980s, the construction of underground powerhouses has been faced with complicated problems caused by high in situ stress in China. In addition, the high in situ stress gradually becomes the main factor affecting the excavation stability. Figure 6 shows the development history of numerous underground powerhouses in China.