Seismic Site Amplification Maps and Design Spectra for Reclamation Islands in Hong Kong Considering Spatial Variation of Site Conditions

In alignment with the 2030+ vision for Hong Kong, the development of artificial islands through reclamation around Kau Yi Chau, Peng Chau, and Sunshine Island aims to create approximately one thousand hectares of land. Given Hong Kong's moderate earthquake risk, the absence of a seismic design code and limited guidelines, it is greatly needed to conduct comprehensive seismic hazard assessments of these new development areas.
This study investigates seismic site amplification at the new proposed artificial island at the reclamation site in Hong Kong considering spatial variation of subsurface conditions. Data from over 100 boreholes facilitated the characterization of subsurface soil layers, with dynamic properties derived from laboratory and field tests, which account for confining pressures in granular soils and plasticity indices in cohesive soils. The representative boreholes were selected for one-dimensional site response analyses utilizing nonlinear method.
The analyses incorporated eleven earthquake records as outcrop motions, matching the rock Uniform Hazard Spectrum (UHS) of 2% probability of exceedance over 50 years, representing the Maximum Considered Earthquakes (MCE) level. The influence of the spatial variation of the marine deposit layer and the depth of rockhead on seismic site amplification were assessed for ground conditions before and after the reclamation process.
Site amplification maps of peak ground acceleration (PGA) have been created for before and after reclamation cases and comparison of surface spectral accelerations with design spectra from Hong Kong was conducted. Findings indicate that variations in the soil profiles significantly affect spectral accelerations and site periods, necessitating the development of new design response spectrum models for these specific locations. Finally, based on all these site-specific analyses, new design spectral acceleration curves for MCE level are proposed for these reclamation islands.

Keywords: Site conditions spatial variation, Marine deposit, Site response analysis, Site amplifications maps, Design spectral acceleration.