Soft clay on seabed posed biggest challenge for engineers

The complex geology of the Pearl River estuary in South China was a driving force behind the technological innovation that makes the Hong Kong-Zhuhai-Macao Bridge stand out from similar projects around the world, according to civil engineers.

They point to the estuary's variable soil conditions, with thick layers of soft alluvial clay that subject its undersea tunnel section, at a depth of about 50 meters, to high hydraulic pressure, and say the entire 55-kilometer structure may be the most complex and challenging sea crossing ever built - in addition to being the world's longest.

Hans de Wit, managing director of Tunnel Engineering Consultants, a leading tunnel construction company based in the Netherlands, said complicated infrastructure projects like the bridge typically stimulate innovation.

De Wit, who has nearly 30 years of experience in immersed tunnel projects, was the lead consultant for the design and construction of the HZMB's island and tunnel project.

The size of the bridge project and its immense budget allowed for study and innovation, he said. "Additionally, these large infrastructure projects very often contain technical challenges beyond the current state of the art. This is also the case with the HZMB."