Coupled nonlinear site response analysis and porewater pressure generation for a long-span extradosed bridge project on liquefiable soil in Davao Region, Philippines

Abstract

The Philippines, being the archipelagic country that it is, has always understood the importance of inter-island transportation and, in a way, associated progress and development with it. Outside of the nation’s capital in Metro Manila, Davao Region is one of the strategic locations identified with the potential to thrive as a business center in Southern Philippines. In order to support and boost economic activity within the Davao Region, the Philippine government proposed the construction of a long-span extradosed bridge that connects two of the region’s major cities. This study presents the site characterization of the proposed bridge and the development of the site-specific ground motions. Situated on potentially liquefiable soil, this study implements an approach that couples porewater pressure generation with nonlinear site response analysis. The results show the expected period-dependent attenuation/amplification of the response spectra and reveal that, even at different hazard levels, the short- and intermediate-period spectral accelerations normalize to a certain intensity. The results are finally compared with the design spectra prescribed in the local design code as a way to demonstrate the effects of soil nonlinearity and liquefaction on the resulting ground motions. At the end of this paper, practical issues and key differences between this coupled approach and the conventional practice shall be highlighted.