On March 10th, the first warehouse of the tunnel-spillway of Shuangjiangkou Hydropower Station’s flood discharge system, the world's largest cross-section spllway tunnel under construction by China Railway Construction Bridge Engineering Bureau Group Co., Ltd. (CRCC) was poured with impact-resistant and wear-resistant concrete, which marked the prelude to construction of lining of the tunnel-spillway.

Shuangjiangkou Hydropower Station is a national key energy development project in the 14th Five-Year Plan, which is also a national key clean energy project and a national key western development project. Its flood discharge system engineering mainly includes tunnel-spillway, lower level outlet, shaft-spillway and emptying tunnel, and its scale ranks among the top in the world. The main tunnel——tunnel-spillway is arranged on the right bank of the dam, with a total length of 1,818 meters and a maximum excavation section area of 516 square meters. The maximum single-hole flood discharge of the tunnel is 4138 cubic meters/second, and the maximum flow rate can reach 42 meters/second. In the extreme flood discharge state, the overall weight of the water passing the cavern will reach 886,000 tons.

Deformation monitoring of trolley during pouring

Facing the tough problems such as super-large cross section, super-high flow rate and super-strong impact, the project responded to the challenge with quality and fine products. At the beginning of the project construction, a special group for tackling key problems in science and technology was set up to carry out research, and more than 60 groups of concrete proportioning schemes were studied and tested. After thousands of groups of trial mixes, the optimal mix ratio data of impact-resistant and wear-resistant concrete with "flat and smooth, wear-resistant and crack-resistant" performance was determined. By introducing the first set of "ethylene glycol+water cooling" pre-cooled aggregate temperature control mixing system in China to control the temperature, adopting fine controlled ratio to reduce the hydration heat, and taking effective measures to strictly control the quality and safety, the technical problems have been successfully overcome; The internal intelligent water supply and intelligent surface maintenance greatly improve the smoothness of concrete surface. Nowadays, "mirror" is not only the standard configuration of the flood discharge system of Shuangjiangkou Hydropower Station, but also a synonym for high-quality construction of hydraulic tunnels.

Technicians measure the temperature on site

The lower level outlet has a "mirror" effect

After the completion of Shuangjiangkou Hydropower Station, the main stream of Dadu River can increase the dry period electricity by about 6.6 billion kWh per year, save about 2.96 million tons of standard coal and reduce carbon emissions by about 7.18 million tons, which will actively realize the overall goal of "promoting green development and harmonious coexistence between man and nature".