The machine excavated 14.12 meters per day, setting a new record compared to the average 11.6 meters of similar projects in China.

Experts investigated local conditions and realized building towers in the Yangtze River for overhead power lines would block shipping traffic in the river, and the foundations would need frequent maintenance.

All things considered, the tunnel was built so the power lines could be laid beneath the river, which has the advantages of lower construction and maintenance cost and avoids environmental destruction.

The transmission lines in the tunnel would be gas-insulated metal enclosed ones, bringing many benefits such as good transmission performance, outstanding safety, less space and lower maintenance cost compared to normal cable lines.

With an investment of 4.763 billion yuan ($696.8 million), the Suzhou-Nantong section is projected to be put into use in the next year.