|Abstract: ||摘要:台灣土地狹窄,人口稠密,資源有限,急需加速海 洋科技之發展,以拓展海洋空間之利用並積極開 發海洋資源,欲達此目標,就得有海洋結構物作為 開發基地.設計海洋結構物,例如防波堤等,需考慮防波堤趾 基礎之穩定,尤其是防波堤等海洋結構物受暴風 浪侵襲時之安全評估.奠基於砂質土壤之防波堤等海洋結構物之穩定性 ,必須考慮基礎土壤在暴風浪反覆作用下所導致 的反覆剪應力之作用,其孔隙水壓之增加潛能.若 暴風浪歷時長,而剪應力持續不斷反覆作用,終使 基礎土壤之孔隙水壓上升值累積致使土壤之有效 應力趨於零,而導致基礎土壤之液化.縱使基礎土 壤之孔隙水壓之增長沒有達致使土壤液化之程度 ,土壤之剪力強度也將因有效應力之減少而遞減, 也會造成防波堤之損害.這些都是防波堤設計時 必須考慮之問題.|
abstract:In designing a marine structure such as breakwater, the engineer must predict performance of the structure's foundation. In particular, he must predict stability of the foundation for the imposed environmental load. During storms, marine structures will be subjected to large force that are cyclic in nature, and the foundation soil will experience cyclic stresses. The cyclic shear stresses developed in the foundation soil under a marine structure as a result of a passing wave train may progressively build up pore water pressure in sandy soils. If the cyclic loading is maintained, such built-up pore water pressure may continue to grow up to a stage where it becomes equal to the vertical pressure, resulting in cyclic liquefaction and leading to possible instability. Even the generated pore pressure is small, both cyclic strains and residual or permanent strains may develop under cyclic loadings. Consequently, marine structures will be damaged. In this study, practical procedures, both laboratory cyclic test program and numerical liquefaction analysis, are developed to analyze the pore pressure response under a marine structure during a storm. Based on cyclic test results, a finite element computer program for the analysis of pore pressure generation and the consequent liquefaction is developed. Results show that the model developed is useful for foundation design of a marine structure.