【Haichuan Explores the World】Storing liquid gases in underground caverns – did you know about this?

The LPG cavern storage facility at Wanhua’s Yantai Industrial Park is located in the Lingang Chemical Industry Park within the Yantai Economic and Technological Development Zone in Shandong Province. It was funded by Shandong Yantai Wanhua Chemical Group Co., Ltd., with construction carried out by China Railway Tunnel Group. Construction began on July 23, 2011; the cavern was sealed off on August 7, 2014; gas storage started on March 5, 2015, and the facility was fully operational by August 18, 2015. It is the fifth LPG underground cavern storage facility in China, following those in Shantou, Ningbo, Zhuhai, and Huangdao. It is also China’s first gas storage facility that was designed and constructed entirely independently, and at that time it was the largest LPG underground cavern storage facility in the world. This project uses an underground sealed cavern for storage, with a total storage capacity of 1 million cubic meters, a depth of 170 meters, and a total excavation volume of 1.46 million cubic meters. The engineering design includes 3 main caverns with a gas storage capacity of 1 million cubic meters. It is primarily composed of traffic passages, butane water curtains, LPG water curtains, propane water curtains, the butane main cavern, the LPG main cavern, the propane main cavern, as well as butane shafts, LPG shafts, propane shafts, and ventilation shafts. Among them, the LPG main tunnel vault is one of the three underground main vaults, with a clear height of 26 meters and a clear width of 18 meters. Its excavation cross-sectional area is 399.5 square meters. It consists of 3 parallel main tunnels and 4 connecting adits, with a total length of 1,080 meters and a total excavation volume of 288,300 cubic meters, which is equivalent to the excavation work for 3 kilometers of a standard double-track railway tunnel.

Water-sealed underground vault? Is it similar to submarines, with the inlets and outlets underwater, using water as a sealing mechanism?

Hehe, you don’t even know about it; it seems that not many people are aware of this. It’s a relatively new method of storage that emerged alongside large-scale propane dehydrogenation facilities

Shock-absorbing blasting for tunnels with extremely large cross-sections, groundwater level control, and ventilation during construction are all key aspects and challenges in the construction of underground caverns sealed by groundwater. The water curtain system is crucial to the technology of underground LPG caverns sealed by groundwater. The water curtain technology system involves driving nearly 100 meters of steel pipes at intervals of 10 meters above the main tunnel vault and on its left and right sides deep into the ground strata; after connecting these pipes with expansion plugs, water is injected to create a water curtain that maintains a natural groundwater level, thereby using water to seal off gaps and pores in the rock layers. During construction, it is necessary to monitor and maintain the groundwater level and pore pressure; if the groundwater level drops to a critical level (the warning threshold for groundwater levels), the entire gas storage facility will become useless. This technology has long been monopolized by a few developed countries abroad. The constructor, China Railway Tunnel Group, has prioritized the use of advanced technologies and equipment such as large-scale mechanized systems, fully hydraulic tunnel drills, in-hole imaging devices, and inclination measuring instruments, thereby gradually mastering the core aspect of this project: water curtain technology. During the construction of the water curtain tunnel, the contractor conducted a thorough study of the geological conditions of the tunnel site. Based on repeated trials, they adopted a method of short excavation steps and mild blasting, adjusting the blasting parameters according to the characteristics of different rock formations. This approach effectively prevented excessive vibration caused by blasting from leading to increased cracks in the rock formations and significant loss of groundwater, thus ensuring the overall quality of the water curtain system. Furthermore, the water curtain efficiency test is an important task for monitoring the success or failure of the water curtain system. To ensure the success of this test, a plan was established to conduct the horizontal water curtain efficiency test first and then the vertical one. Activities such as collecting and transmitting data on water leakage in each main tunnel reservoir, as well as monitoring the water supply for the water curtain, were carried out. Based on the test results, additional holes were added to the water curtain system to ensure its effective operation.

The project features a complex structure with variable tunnel cross-sections; shafts, traffic tunnels, water curtain tunnels, and gas storage chambers intersect with each other. Moreover, the timeline is tight, and tunnel excavation is severely constrained by groundwater exploration and grouting processes. It is therefore particularly important to make effective use of available resources, organize construction in a rational manner, ensure efficient utilization of all resources, and maintain order at the site. Based on the characteristics of the project, the contractor identified the sequence of \"open trench → traffic roadway → propane water curtain roadway → propane water curtain boreholes → main propane tunnel reservoir → sealing of the main propane tunnel\" as the key construction sequence. During construction, on-site organization and resource allocation are carried out in close accordance with the key task sequence, with secondary tasks progressing in coordination. Based on the overall project deadline, annual, monthly, and weekly plans are developed, with detailed specifications for the workload to be completed each day. Furthermore, the construction party places great emphasis on safe production, fully implementing advanced HSE management concepts. By drawing on the company’s experience in safety management, it enhances on-site safety controls with the goal of creating a \"safe construction site.\" It strictly enforces safety production responsibilities, provides thorough training, ensures adequate investment in safety measures, and promotes standardization in safety protection, site organization, and safety management procedures. As a result of these safety measures, no safety-related incidents occurred during the construction process.

On July 17, 2013, the \"High-Level Seminar on Key Technologies for Constructing Groundwater-Sealed Energy Caverns\", jointly organized by the Chinese Academy of Engineering and China Railway Tunnel Group, was held at this project. Academicians and experts gave full affirmation and recognition to the achievements made in the Yantai LPG project as well as to the research results regarding the technologies for building underground energy caverns. The total storage capacity of this project ranks first in the world, and the capacity of each individual storage facility is also the highest in the world. One single facility is capable of storing three different types of gases at the same time, and it is quite rare to find chemical processing units built densely on the ground level of such underground facilities, both domestically and internationally. This project represents an important milestone in China’s ability to construct such facilities independently.