Seismic site classification practice in Australia, China and India: suitability

Seismic site classifications are widely used to represent seismic site effects and estimate the hazard parameters at soil surface. Most countries including Australia, China and India follow seismic site classification system similar to that in International Building Code (IBC), which is based on 30 m average shear wave velocity (SWV), Standard Penetration Test (SPT) N values and undrained shear strength. The site classification system in IBC is developed based on the studies carried out in United States. The present paper presents the seismic site classification according to IBC considering 30 m average SWV and SPT N and compares with seismic site classification given in the seismic design codes of Australia, China and India. SWV and SPT N values have been collected from different part of Australia, China and India. These data were selected considering rock depth; the data are available for depth of few meters to about 180 m. This study shows that site classification based on 30 m depth gives stiffer site class and lower spectral acceleration coefficient for building design. New site classification based on average soil thickness, SWV and SPT N up to engineering rock has been proposed. The proposed site classification represents soil thickness and shear stiffness of site rather than adding the rock SWV and SPT N values, if the depth of soil is less than 30 m or omitting the same if the depth of engineering rock is greater than 30m.