On August 15, at the construction site of the State Grid Xinyuan Hunan Pingjiang Pumped Storage Power Station, a rock tunnel boring machine (TBM) capable of continuous climbing at an ultra-large inclination of 50° and variable-diameter excavation from 6.5 to 8 meters successfully launched. This marks the start of construction of the first 700-meter-level head hydropower station diversion tunnel in Central China, and the project will fill a global gap in full-face mechanized construction of diversion tunnels for hydropower stations with ultra-high head and ultra-large-slope two-stage inclined shafts.

World's first variable-diameter inclined-shaft TBM launches

The project's tunneling equipment is named "Tianyue". With a total length of 87 meters and a total weight of about 900 tons, it was jointly developed by CRCHI, State Grid Xinyuan Hunan Pingjiang Pumped Storage Company, and Sinohydro Bureau 8. "Tianyue" pioneered launch without a guide platform and an upward climbing excavation method at a large inclination of 50 degrees, achieves diameter variation from 6.5 to 8 meters in the middle horizontal tunnel, and finally exits from the upper horizontal tunnel, enabling full-face continuous excavation and one-time completion of primary support for both horizontal and inclined sections of the two-stage diversion inclined shafts.

The Hunan Pingjiang Pumped Storage Power Station is located in Fushoushan Town, Pingjiang County, Yueyang, Hunan. At present, the project construction has entered the peak period of the main works, with comprehensive construction at 51 working faces including the upper reservoir, lower reservoir, underground powerhouse, and water diversion system. The project's horizontal tunnels, inclined shafts, vertical shafts, and large and small cross-sections all adopt full-face mechanized operation.

World's first variable-diameter inclined-shaft TBM rolls off the production line

It is reported that the project's diversion tunnel is a key part of the power station construction. The station has a rated head of 648 meters and a maximum lift of more than 700 meters. The height difference of the diversion inclined-shaft tunnel is 196 meters higher than Hunan's tallest building, the "Guojin Center", which is 452 meters tall. If the traditional pilot shaft plus drill-and-blast method were used, it would not be able to effectively cope with the complex ultra-large inclination environment and would face extremely high safety risks.

To accelerate the construction of pumped storage power stations and help achieve the "dual carbon" goals, the project vigorously advances the green and intelligent construction concept of "mechanization to reduce manpower, automation to replace manpower, and intelligentization to achieve unmanned operation", and actively explores the application of advanced construction methods and new equipment. By adopting variable-diameter TBM construction, the project has to a certain extent solved industry challenges such as high construction risk, great construction difficulty, and poor quality of formed sections in the construction of diversion inclined shafts for pumped storage power stations. It has a demonstrative effect on promoting the high-quality development of pumped storage power stations, breaking technical bottlenecks, and achieving independent and controllable technology.

Panoramic view of the workshop of the world's first variable-diameter inclined-shaft TBM

In response to the project's construction challenges, the "Tianyue" R&D team carried out five years of research and development, creatively proposed a large-slope composite anti-slip system, and for the first time overcame eight industry technical problems, including ultra-small vertical curve turning with a 50-meter radius, large-scale diameter variation of the large-cross-section cutterhead and shield body, launch without a guide platform, and continuous mucking under complex procedures. The team carried out 10 innovative tests including mucking, support, maintenance, and material transportation, enabling the equipment to efficiently achieve continuous excavation of horizontal tunnels and inclined shafts and greatly enhancing the equipment's applicability to complex underground cavern groups.

It is reported that the State Grid Xinyuan Hunan Pingjiang Pumped Storage Power Station is a major energy project of China's 14th Five-Year Plan, with a total investment of 8.8 billion yuan, a total installed capacity of 1.4 million kilowatts, a designed annual power generation of 1.009 billion kWh, and an annual pumping power consumption of 1.453 billion kWh. The station plans to put its first unit into operation for power generation by the end of 2025.