World's longest transoceanic bridge

As one of the fastest growing countries, China has attracted the world's attention for its phenomenal rate of economic development and modernization efforts. Infrastructure projects especially in the areas of transportation, telecommunications, water conservation, energy and environmental protection are a national priority.

The Zhejiang Province, located on the eastern coast of China is the site of RMB $US1.7 billion construction project -- The Hangzhou Bay Transoceanic Bridge.

The contractor, China Railway Bridge Bureau Group, is using Trimble 5700 GPS systems, Trimble DiNi 12 digital levels and Trimble Geomatics Office software.

According to the China Railway Bridge Bureau Company, the Trimble equipment helps improve efficiency and reduce costs; provides high accuracy and very close tolerances; is easy to operate and rugged enough to use in any harsh environment.

While conventional optical systems could be used for control near the coast as well as to position piles at a distance, the project requires precise positioning for the 9-25km bridge span off the coast.

Conventional survey systems would either reduce the accuracy or require extra control stations, which would demand more work as well as increase the potential for error accumulation.

By using the Trimble 5700 RTK GPS systems with a reference station for differential corrections, accuracy is improved at greater distances enhancing the contractor's productivity.

To date, approximately 50 Trimble 5700 RTK systems have been set up at sites where the bridge will span the Bay of Hangzhou. Three Trimble 5700 CORS GPS systems are used as reference stations to broadcast the differential corrections required for precise measurements of the project.

Additional 5700 systems are located on barges in order to provide millimeter accuracy for the real-time positioning of piles and pre-fabricated sections of the bridge; this is accomplished by moving sections of the bridge on barges for precision placement using GPS for position and orientation.

The Trimble 5700 RTK systems are also used for measuring the coastal topographic details as well as hydrographic surveys of the seabed. Using Trimble equipment across the entire construction site enables all surveying, mapping and construction activities to share a common geodetic reference system.

Since the China Railway Bridge Co has been using Trimble equipment, the construction project has progressed quickly, with significant improvement in the offshore positioning accuracy and complete positioning process.

With the GPS reference stations covering the entire construction area, overall project accuracy is enhanced and working efficiency is improved.

When completed in 2008, the Hangzhou Bay Transoceanic Bridge will significantly shorten land distance between Shanghai and Ningbo by over 120km and is expected to promote economic development in the province.

The bridge will span across the Hangzhou Bay on the East China Sea, crossing the Qiantang River at the Yangtze River Delta. The Delta area is said to be one of the world's most complicated sea environments, with one of the three highest tides on Earth, typhoons and challenging soil contents.

With an overall length of 36km, the six-lane bridge includes 32km over the sea. The main span of the new bridge uses the 'stayed-cable' design. When completed, it is estimated that the bridge will carry 45,000 cars a day in its first year of operation.