Project cracks geological puzzle

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.