China Jinping Underground Laboratory

The China Jinping Underground Laboratory (Chinese: 中国锦屏地下实验室; pinyin: Zhōngguó jǐn píng dìxià shíyàn shì) is a deep underground laboratory in the Jinping Mountains of Sichuan, China. The cosmic ray rate in the laboratory is under 0.2 muons/m²/day, placing the lab at a depth of 6720 m.w.e.^: 2 and making it the best-shielded underground laboratory in the world.^: 17 The actual depth of the laboratory is 2,400 m (7,900 ft), yet there is horizontal access so equipment may be brought in by truck.

Although the marble through which the tunnels are dug is considered "hard rock", at the great depth it presents greater geotechnical engineering challenges^{: 16–27 : 16–19} than the even harder igneous rocks in which other deep laboratories are constructed.^: 13–14 The 10 MPa (1500 psi; 99 atm) water pressure in the rock is also inconvenient. But marble has the advantage for radiation shielding of being low in radionuclides, such as ⁴⁰K, ²²⁶Ra, ²³²Th,^: 17 and ²³⁸U.^: 16 This in turn leads to low levels of radon (²²²Rn) in the atmosphere.^: 5

The laboratory is in Liangshan in southern Sichuan, about 500 km (310 mi) southwest of Chengdu.^: 3 The closest major airport is Xichang Qingshan Airport, 120 km (75 mi) away by road.^: 5