2,400 meters from the peak of Jinping Mountain lies the China Jinping Underground Laboratory, the deepest underground laboratory in the world with horizontal access. Located in Sichuan, China, this exquisite laboratory is surrounded by thick rock cover that prevents cosmic rays from reaching the lab and allows the lab to be capable of new research particle detection and physics research. It also allows research of the elusive substance, Dark Matter, estimated to account for about 85% of all matter in the universe. Due to its unique location of being within a mountain, it uses an intricate tunnel system to maximize its use of space and allow the user to safely conduct groundbreaking research without outside interference.
Project name: China Jinping Underground Laboratory
Owner: Yalong River Hydropower Development Company
Operating Agency: Tsinghua University
Completion Year: Excavation finished in 2010, second phase completed in 2017
Project Location: Jinping Mountain, Sichuan, China
Area: Provides 200,000-300,000 m^3 of usable space
The purpose of the China Jinping Underground Laboratory (CJPL) is to have a site suitable for low background neutrino and supernova relic neutrino physics research. Physicists from Tsinghua University determined that this type of research would best be conducted in a deep underground lab because it constrains cosmic rays from space and radiation that would tamper their research above ground. Within the depths of this lab, multiple experiments are operating. Some include the China Dark Matter Experiment (CDEX), a germanium dark matter detector that conducts research on a matter that would typically not be detected by observing electromagnetic radiation. Dark matter research is an essential activity in underground laboratories worldwide due to its difficulties gathering information and conducting experiments without outside variables. Another important experiment that would not be possible above ground is the Jinping Neutrino Experiment, a study that collects precise measurements of solar and geoneutrinos, which is only possible due to the advantage of its unique location far away from nuclear reactors and having the lowest flux of reactor neutrinos of any underground lab. Furthermore, The laboratory’s room design and horizontal access are essential to projects that need easy access between the interior of the mountain and the exterior. Such is the case with DIANA, a nuclear astrophysics facility that is built and tested on the surface but can be disassembled and transported to a permanent underground location. With multiple projects going on inside and the exterior of the tunnels, the Jinping Underground Laboratory aims to be the largest deep-scale laboratory, welcoming scientists from across the globe to expand their knowledge.
Beginning in August 2008, the China Jinping Underground Laboratory was excavated from the Jinping II Hydroelectric Dam Power project that had previously occupied Jinping Mountain. From its predecessor, the laboratory inherited several large tunnels throughout Jinping Mountain, constructed using tunnel boring machines (TBM) and later drill and blast techniques (D&B). These tunnels allow vehicular transportation, water supplies, water drainage, as well as usable space. There are four immense 16.7 km headrace tunnels that carry water east, two 17.5 km tunnels that allow vehicles to pass, and one water drainage tunnel. The laboratory was developed on the southernmost of the seven parallel tunnels. Surrounding Jinping Mountain lies the U-turn shaped Yalong River. The tunnels from the laboratory were excavated to connect the two hydropower houses constructed on opposing sides of the mountain to capitalize on the different river water levels over the length of the tunnels and convert that to electric power. Due to its surrounding features as well as the preexisting structure of the hydroelectric dam project, the underground laboratory is a self-sustaining engineering and architectural feat that uses hydropower from the nearby river. With no shortage of water, the high-powered equipment being used for experiments has an excellent cooling system.
While the laboratory’s location within the major hydroelectric facility had multiple benefits, researchers expanded and reconstructed the laboratory further to suit their purposes. First of all, the overall expansion provided an additional 96,000 m^3 of laboratory space. The increased space created interconnecting access tunnels for large experimental halls, and two pits for shielding tanks underneath the hall floor. Before the second phase of construction, there were issues with proper air ventilation throughout the tunnels, resulting in an accumulation of dust on equipment and radon gas. The expansion provided additional ventilation. There were also problems with the materials the dam was constructed from. The ordinary concrete used within the walls of the dam had naturally higher radioactivity than desirable for the underground laboratory, which defeated the purpose of using an underground lab. During the second phase of the reconstruction, the construction team used marble, which has an advantage for radiation shielding of low being in radionuclides to not disrupt the experiments. In addition to physics exploration projects, rock mechanics and geotechnical engineering studies are also present in the tunnels. When excavating and expanding the tunnels, micro-seismic and acoustic signals were used to determine damaged zones within the rocks that might cause problems with the infrastructure later on. There was also the hazard of stress release zones within the walls, which was reduced using the injection of fluids to reduce the effective stress. This technique is also used in mining operations and the petroleum industry where the user is put in a dangerous space that could collapse if the proper safety procedures are not followed along with frequent inspections.
The China Jinping Underground Laboratory is the deepest underground laboratory in the world with horizontal access. Deep within Jinping Mountain is a complex system of tunnels designed to optimize laboratory space, prevent above-ground disruptions to physics experiments, and welcome scientists from all over to utilize its technology and equipment. It is also an excellent example of a self-sustaining project, using its pre-existing hydroelectric dam power and the surrounding environment to optimize performance and power.
- “The Second-Phase Development of the China Jinping Underground Laboratory.” Science Direct, 13th International Conference on Topics in Astroparticle and Underground Physics, TAUP 2013, 2013, arxiv.org/ftp/arxiv/papers/1404/1404.2651.pdf.
- Wang, Zhe. China Jinping Underground Laboratory and Jinping Neutrino Experiment. 2016, indico.ihep.ac.cn//event/6156/session/8/contribution/22/material/slides/0.pdf.
- Li, Jianmin. The Recent Status and Prospect of China Jinping Underground Laboratory. www.taup-conference.to.infn.it/2015/day3/parallel/dma/3_li.pdf.
- “Jinping Neutrino Experiment.” Jinping Neutrino Experiment – Official Website, jinping.hep.tsinghua.edu.cn/.