On June 6, 2020, China Railway Group announced that the excavation of the foundation pit of the Longquan Inverted Siphon Receiving Well of the Central Railway of Yunnan, China Railway Fifth Bureau has been successfully completed, and the excavation depth is 77.3 meters. It is the deepest excavation in China. This project is a milestone in the construction of ultra-deep foundation pits in China and will lead the construction level of domestic deep well foundation pits to a new height.

The foundation pit of this project is a circular structure with a radius of 8.5 meters. The excavation depth is 77.3 meters. The enclosure structure uses a 1.5-meter-thick underground continuous wall curtain to stop the water. The ground connection wall is grooved to a depth of 96.6 meters. Beam. There is no relevant construction experience in China that can be used for reference. It has the characteristics of narrow construction site in the pit, limited operation space of mechanical equipment, many cross-operations, complex geological conditions, difficulty in earthmoving and difficulty in construction.

In order to ensure the excavation of the foundation pit of the receiving well, the project department has organized expert consultation meetings many times to organize the owners, supervision, design and site leaders to visit the site of Shanghai Shenjing Foundation Pit. After many studies and discussions, the construction method of ultra-deep foundation pits "overall operation, partial operation" was proposed to adapt to the characteristics of narrow foundation pits and tight construction period, which greatly reduced the time and cost of deep foundation pit operation. In order to ensure the safe and orderly construction, the project department has formulated a special construction plan and safety emergency plan, strengthened the construction site management, closely guarded all parts, strictly controlled the quality control, and guarded against potential safety hazards, ensuring the smooth excavation of ultra-deep foundation pits carry out.

The Yunnan-Central Yunnan Diversion Project passes through Lijiang, Dali, Chuxiong, Kunming, Yuxi, and Red Rivers, with a total length of 663.9 kilometers and a total construction period of 96 months. After the completion of the project, about 11 million people in central Yunnan directly benefited, improving the irrigation area of 636,000 acres, adding 672 million cubic meters of water to Dianchi Lake, Qilu Lake and Yilong Lake, creating about 3.4 million direct employment opportunities and creating a regional GDP 330 billion yuan.

Construction difficulty

The foundation pit of this project is the deepest foundation pit in China, and there is no relevant construction experience in China for reference.

Geological conditions are complex: there are unfavorable geological layers (silty soil layer, peat soil layer), and it is difficult to control the formation of grooves and the stability of groove walls.

High verticality requirements: The underground continuous wall is nearly 100 meters deep, which requires high verticality, and the error must be controlled at 1/630. In actual construction survey, the error is only 1/1300, and the error of the head and tail of the foundation pit does not exceed 10 cm.

Difficult earthwork transportation: The excavation depth of the foundation pit is up to 77.3 meters, and the lifting depth and stability standards of the lifting equipment are greatly improved, which makes the construction of the slag lifting difficult.

The construction site is narrow: there are harmful gases during the excavation of the foundation pit, which has high requirements for foundation pit ventilation and personnel protection monitoring.

The underground continuous wall is a circular structure with a radius of 10 meters, the depth of the groove is 96.6 meters, and the excavation depth of the foundation pit is 77.3 meters. These are rare in China. They are a milestone in the history of domestic water diversion projects and will lead domestic small radius deep well foundation pits. The construction level is moving towards new heights. There are fourteen continuous walls, which are divided into phase I and phase II trough construction. Among them, the reinforcement cage of phase I trough weighs 127.41 tons, and the concrete pouring volume is 950 cubic meters. The ultra-deep connecting wall brings a huge test to the verticality control of the groove. Only the verticality control is strictly in place to ensure the smooth installation of the steel cage in the next step, and the complex geological conditions make the overall construction difficult.

China Railway Group has overcome difficulties and created the deepest foundation pit record in China, which has laid a good foundation for the improvement of the domestic deep well foundation pit construction level. Do you really understand such a powerful central enterprise? Editor/Peng Xue