Evaluation of seismic parameters for an earthquake analysis

The Final Engineering Design for a cable-stayed 1347 m long bridge with 17 spans over the Cam river in Hai Phong, Vietnam, was made by a design team from the Finnish National Road Administration (Finnra) in 1997-1998. Subsoil on the site is composed of soft alluvial and flood plain deposits down to a depth of 30 metres, so that the only feasible foundations would be large diameter piles. One requirement for the bridge design was that an earthquake with a magnitude of M = 6.0, which may occur about 20 km from the bridge, should be taken into consideration. The special soil parameters needed for the earthquake analyses were the velocity of the shear wave, the dynamic shear modulus and the damping ratio. Because direct measurements on the site were not possible, seismic soil parameters for earthquake analyses were determined as based on laboratory tests on samples from the bridge site and on empirical correlations between geotechnical properties, SPT results and dynamic parameters. Laboratory tests performed in order to determine dynamic parameters were the resonant column test and the bender element test.