ABSTRACT This paper conducts the behaviors of seabed sand under wave loading by experimental results in which a series of Chien's auto-triaxial testing system type (II). The tested sand was sampled at northeast coastal zone of Taiwan. According to the in-situ wave periods, the cyclic loading periods were adopted as 1, 5, 9 and 12 sec. The specimens prepared by moist tamping method under different relative densities and different effective confining pressures. A series of dynamic triaxial testing was performed to evaluate the mechanism of wave-induced seabed liquefaction. The liquefaction resistance of seabed sand would increase as wave period increased. Finally, combined with Near Shore Spectrum Wave Model, the experimental results and referred Ishihara & Yamazaki (1984), a new modified seabed liquefaction evaluation method was proposed.
INTRODUCTION Taiwan is located at the center of west Pacific that results 3 ~ 4 major typhoons hit Taiwan per year. Typhoon induced water waves propagating on the ocean create a cyclic pressure on the ocean-floor, which may be significant in shallow water and would cause severe damages in coastal zone. This in turn induces stress and pore pressure fields in fluid-filled porous seabed and the pore water pressure would accumulate increasingly until instability occurred such as erosion, liquefaction and shear failure in the seabed. According to the investigation by Chien (2001), erosive coast on sandy bed brought the coastline receded at northeast Taiwan that was showed in Fig. 1. Exploring the reasons of sandy shore eroded, wave-induced seabed liquefaction was introduced to explain this phenomenon. (Chillarige et al., 1997; Sumer et al., 1999; Sassa and Sekiguchi, 1999; Hsiao and Huang, 2000) Seabed liquefaction could cause sand drift, scour, undermining with incline, settlement and failure of the nearshore structures. Thus, the evaluation of seabed response under wave action is important for various offshore installations.