The Highways Department said a seawall of the Hong Kong-Zhuhai-Macau Bridge remains safe despite the gradual settlement of some support structures at the Hong Kong Boundary Crossing Facilities (HKBCF) of the project, hk01.com reports.
According to a local media report on Tuesday, the sinking was observed at two of the giant steel cylinders used in building a seawall at the HKBCF of the bridge, only about 10 meters away from a subsea tunnel that connects Tuen Mun and Chek Lap Kok, or the Northern Connection.
They have reportedly sunk by about 50 to 80 centimeters over the past year, compared with the department’s forecast of 1 cm per year on average, causing concern that they might one day lead to the collapse of the tunnel.
Responding to media inquiries about the matter, the department admitted the two cylinders have seen a settlement of about 130 to 170 mm respectively since 2017, adding that they are located on a marine mud layer rather than on an alluvium like the other 83 cylinders used for the structure.
But the department said the velocity and condition of their settlement were consistent with estimates by consulting engineers and independent experts.
Inspections conducted by consulting engineers responsible for reclamation work have shown that all the steel cylinders have no abnormal settlement, the department said, stressing that the situation would not affect the seawall’s structure and safety.
Cylinders used for similar purposes tend to sink at a faster pace during the construction period than after construction is completed, according to the department.
Based on the original design and an analysis of monitoring data, the two cylinders are expected to sink by about 2 meters in the 50 years after January 2017.
Raymond Chan Kin-sek, former head of the Geotechnical Engineering Office under the Civil Engineering and Development Department, said it is normal for such cylinders to sink, from an engineering point of view, and it is basically safe as long as the settlement is balanced.
Chan said the two cylinders in question sink faster than the others because they are shorter, adding that the situation will not pose any danger to the tunnel.
As to when the mega bridge will open to traffic, the department just said the governments of Guangdong province, Hong Kong and Macau will jointly seek Beijing’s approval of the opening date before an announcement is made.
The construction of the Northern Connection is expected to be completed as early as 2020, while the Southern Connection – the viaducts connecting HKBCF and North Lantau – is expected to be finished by the first half of 2019.
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