It is a project of superlatives: a tunnel borer over 12 meters in diameter cuts its way down to a depth of more than 74 meters beneath the Yangtze River with ground conditions characterized by high water permeability, high compactness and high quartz content. Maximum external pressure: 9.8 bar. And as if that were not enough in the way of challenges – methane deposits.

Ready to go in the launch shaft in just 45 days

"We've built a lot of tunnels already, but this one sets standards in many ways," says Chen Peng, Project Manager at China Railway 14th Bureau Group Co., Ltd. It was all the more important that everything ran like clockwork from the first day: in just seven and a half months the team of experts from Herrenknecht and 14th Bureau Group Co., Ltd designed and built a machine that met the complex requirements of this job. After being transported from Herrenknecht's subsidiary in Nansha, Guangzhou, to the launch shaft in Changshu, it took only 45 days for the machine to be fully assembled. In order to achieve this, some of the components were transported in large, preassembled parts. On July 15, 2017, the tunnel boring machine began its almost 5.5 kilometer long mission under the Yangtze, Asia's largest river.

The TBM was designed and built in record time, thanks to perfect teamwork between Herrenknecht and our people.

Chen Peng, Project Manager, China Railway 14th Bureau Group Co., Ltd.

Renewable energy for China’s east coast

The Sutong GIL Cable Tunnel is part of the Huainan-Nanjing-Shanghai UHV AC project, which aims to further expand the share of renewable energy in China. The problem: large amounts of green power are produced in huge hydropower plants in the mountainous west of the country. The electricity, however, is needed mainly in the metropolises on the east coast. The solution: "Gas Insulated Transmission Lines" (GIL), i.e. pipes filled with sulfur hexafluoride, in which a voltage of 1,000 kilovolts can be transmitted with minimum transmission losses. That is more than any other power line can handle. "We are building this tunnel primarily for the GIL network," says Chen Peng. "But it also has room for additional lines." The upper part of the tunnel contains six GIL pipes. In the lower part there are two 500 kilovolt lines and a maintenance corridor.

With premium technology and teamwork to a successful breakthrough 

With the Herrenknecht TBM perfectly adapted to conditions underground, the customer's jobsite teams delivered excellent advance rates: they achieved top performances of up to 30 meters per day and up to 150 meters per week. Key design features of the 140 meter long and 2,404-tonne machine include a 10 bar pressure rating, cutterhead main arms accessible under atmospheric pressure for safe and quick cutting tool changes and a sophisticated methane gas detection and warning system. On August 21, 2018, the miners completed the drive with a successful breakthrough in the target shaft.

The realization of the Sutong GIL Cable Tunnel benefits the entire region. Transport, in particular shipping, at this wide part of the Yangtze River remains unimpaired. Installation of the cables above ground with several towers in the river would have severely restricted it. The commissioning of the new cable tunnel is also an important step toward reducing pollution and plays an essential part in ensuring the supply of electricity in eastern China. Lining and assembly of the Sutong GIL Cable Tunnel are due for completion by the end of 2019.