The undersea tunnel section, a part of the extension project of the Hengqin Line, a light rapid transit route connecting China's Macao Special Administrative Region and the neighboring Hengqin island in Guangdong province, was completed on Friday, said its developers.

Jointly built by State-owned Namkwong Real Estate Co, China Civil Engineering Construction Corp (CCECC), China Railway Siyuan Survey and Design Group and China Railway 16th Bureau Group Corp, the completion of this project marks a breakthrough in Macao's first undersea tunnel project constructed by a tunnel boring machine, or TBM.

TBMs are used to excavate tunnels, subway tubes and sewer lines. In comparison with traditional tunnel-boring methods like rock drilling, blasting and hand mining in soil, the use of such equipment can minimize the impact on the surrounding ground and produce a smooth tunnel wall, helping certain tunnel projects run through unstable geological conditions.

The total length of this project is about 2.2 kilometers and the shield tunnel section accounts for 906 meters. With a diameter of 7.98 meters, the "Aoqin No 1" — a large shield tunneling machine manufactured by China Railway Construction Heavy Industry Corp in Changsha, Hunan province — was applied in this project. It is roughly 87 meters long and weighs around 600 metric tons, according to a statement released by CCECC, a subsidiary of Beijing-headquartered China Railway Construction Corp.

In addition to adopting the double-joint design for ultra-small turning radius, the giant machine is also equipped with a series of smart systems such as advanced geological detection, high-precision gas-liquid equilibrium and visualized soil bin monitoring, which helps ensure engineering security during construction.

Starting from the elevated station HE1, the line is located near the Lotus Bridge in Macao, which is connected to the Lotus Checkpoint Station, part of the Taipa Line. It runs along the Lotus Bridge and crosses the Shizimen Waterway before entering Hengqin island in Zhuhai, Guangdong province, through an underwater tunnel, and then arrives at the underground HE2 station located in front of Hengqin Port.

Experts said that the new line is expected to be a second option for passengers transiting Hengqin Port, a key comprehensive transportation hub for Zhuhai-Macao border-crossing.

Because the extension section of Hengqin Line is a major public service project for the 25th anniversary of Macao's return to the motherland in 2024, its upcoming operation will reinforce the regional cooperation within the Guangdong-Hong Kong-Macao Greater Bay Area (GBA), facilitating Macao to be included in the "one-hour living circle" in the GBA, said Feng Hao, a researcher at the National Development and Reform Commission's Institute of Comprehensive Transportation in Beijing.

Apart from enhancing connectivity between Zhuhai and Macao, it will increase passenger volume in the Guangdong-Macao In-Depth Cooperation Zone in Hengqin, he said.

The GBA has a complete supply chain in all aspects. It is supported by a number of international airports and major seaports in the world, two of the world's fastest-growing stock exchanges and an international financial center. Better transportation infrastructure development will certainly boost the region's competitiveness, said Lin Jiang, professor of economics at Sun Yat-sen University in Guangzhou.

"The GBA is also rich in tourism resources. This should be used to promote regional economic interaction, tourism investment and domestic consumption," he added.