This study is to evaluate the safety of a sea levee under earthquake condition. The evaluation is performed by both theoretical analysis and numerical simulation, besides a case in field is adopted to verified the analysis and simulation. Since a sea levee is subjected a combined forces and stresses, such as, wave force, earth pressure, self-weight, pore water pressure, and forces induced form earthquake, the theoretical analysis may obtain a closed-form solution, however, the complicated field condition may not be included in the analysis. A software with finite element method is used to simulate the complicated conditions. The revetment of a sea levee which found on a thick deposit with saturated loose sand may collapse or slide soil liquefaction as deposit subjected by earthquake force. The results also revealed that the hazards caused by a earthquake are not damage of the levee itself. Instead, the flood due to the collapse of the levee structure may induce the major disasters.
Since 1999 Chi-Chi Earthquake took place at the middle of Taiwan, the accompanied shallow seismic motions exerted a great impact on the riverbanks, sea levees, reservoirs, dams, weir, watercourses as well as farmland facilities and induced lots of serious damages. The failure modes include cracking, distortion, sliding, collapse, heaving, avalanche and especially the soil liquefaction. It was found that approximately 220m in accumulation of sea levees were damaged during this seismic excitation at the seafront of Chang-Hua County. Among those sea levees, some were damaged in collapse due to soil liquefaction, such as Han-Pao sea levee, Chang-Hua levee way, Chao- Yang-Cuo sea levee, Siasi-Chian sea levee, Shan-Keng sea levee and Siahai-Chian sea levee. It is revealed from the above field cases that the destructive power of the unexpected seismic loading was more intensive than the induced wave forces exerting on the rigid-type sea levee structures.
