Hangzhou Bay Bridge, China

CONSTRUCTION CHALLENGES

One major challenge faced by the project was the eruption of natural gas in a shallow layer along the bridge line. A special study was conducted and exploration was performed to investigate the distribution of the gas and the property of the soil during and after releasing the gas. The gas was released before pile driving to avoid any disturbance to the soil, collapsing of ground or eruption and flaming of gas.

Mostly, construction activity will be performed on land and then the prefabricated components will be transported to the site for erection and final installation. For shipping and erecting the girders in sea, giant floating cranes with accurate anchoring devices and launching gantries are being used.

Construction on mudflats near the south shore, in an alternating wet and dry tidal area, presented serious technical problems. A temporary 10km trestle has been erected for pile driving and pier construction. Girders weighing 1,430t will be erected from the top, starting from the land end and launching towards the sea. Each previously erected span will serve as the deck for transportation and erection of the next girders as the launching gantry moves forward.

Also, severe marine conditions caused difficulties in anchoring barges and construction vessels. Under turbulent tidal flow and typhoon influences, water flow currents are in the range of 2m/s to 3.32m/s at the Hangzhou Bay Bridge sites. The floating cranes can safely transport the 2,000t girder from the shore to the site and then anchor stably to erect and install the precast concrete box girder.

BRIDGE LAYOUT AND STRUCTURE

The Hangzhou Bay Bridge consists of nine sections. The first is the bank lead road to the north approach.

The north approach rests on low piers with post-tension concrete box-girder spans spanning pre-stressed continuous concrete box-girders and drill-shaft pile

The north approach leads to the north navigable bridge; a cable-stayed bridge with twin diamond-shaped towers, double cable and steel box-girders. The main span of the north approach is 448m. Including side spans, the total length is 908m.

The north high piers have continuous, 70m, post-tensioned, concrete box-girder spans with a total length of 1,470m.

The middle bridge approach is laid on low piers with 70m, post-tension, concrete box-girder spans with a total length of 9,380m.

The south navigable bridge is a cable-stayed bridge with an A-shaped single tower, double-cable and steel box-girders. The main span is 318m, and the total length including side spans is 578m.

The south high piers have continuous 70m, post-tension, concrete box-girder spans with a total length of 1,400m.

The eighth section measures to a total of 19,373m, and is composed of three sections:

·6,020m in-water section with 70m girders and steel piles ·10,100m mud-flat section with 50m girders and drill-shafts ·3,253m land section with 30m to 80m girders and drill shaft foundations The ninth section is Bank Lead Road at the south approach.

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