EFFECT OF VERTICAL ACCELERATION ON SITE LIQUEFACTION IN PULSE GROUND MOTION
GAO Guangyun1,2, LI Yongjia1,2, DONG Wenkui3
1. Department of Geotechnical Engineering, Tongji University, Shanghai 200092;
2. Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Tongji University, Shanghai 200092;
3. Department of Civil and Environmental Engineering, University of Technology Sydney, NSW Australia 2007
This paper is based on the boundary surface plastic constitutive model developed with finite element platform OpenSees. It established a dynamic simple shear test model and a three-dimensional finite element model of saturated sand. The target was to explore the effect of vertical component of pulse-like ground motion on the site liquefaction. Therefore, 10 sets of seismic waves with pulse-like characteristics were selected from the Chi-Chi earthquake in Taiwan as inputting load. The simulated vertical displacement, cyclic stress ratio(CSR),pore pressure ratio and equivalent cycle number of the soil column were compared and analyzed under the ground motion with or without the vertical component. Hence the differences clearly defined the effect of vertical acceleration of pulse-like ground motion on the liquefaction of sand. The results show that the vertical acceleration component of tri-directional pulse-like seismic wave has little influence on the final site settlement but significantly increased the duration. As the CSR of soil column is less affected by vertical ground motion, the tri-directional ground motion can be simplified as horizontal bidirectional ground motion when analyzing the shearing properties of the site. The divergence of pore pressure ratio caused by the tri-directional pulse-like seismic wave is larger, and meanwhile, it spends more time to dissipate the pore pressure. Besides, tri-directional pulse-like seismic waves generate a larger equivalent cycle number and increase the duration of ground motion. As a result, the vertical acceleration have more tendency to induce site liquefaction.