沉箱式碼頭受震動力反應分析之研究

Seismic Analyses for Caisson-type Wharf Structures

李姿穎(Tzu-Ying Li)

指導教授 ： 陳正興

國立臺灣大學/工學院/土木工程學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.01598

摘要

臺灣港口眾多，台中港和蘇澳港分別於1986年與1999年分別遭受花蓮地震與集集地震之災害，造成兩者皆有受損。本研究利用之數值模擬程式為有限元素分析程式PLAXIS，進行有效應力動態分析。選取三個案例作分析，第一為921地震時因背填土液化造成沉箱式碼頭受震滑移破壞之臺中港1號至4A號碼頭、第二為花蓮地震時背填土未液化但仍造成碼頭滑移破壞之蘇澳港4號沉箱式碼頭，以及第三為921地震時未有明顯災情傳出之花蓮港19~21號碼頭。此三個代表性案例，針對沉箱式碼頭受震行為與沉箱背填區受震反應，以有限元素法程式PLAXIS進行有效應力動態數值模擬分析，並比較傳統簡易分析、滑動塊體分析、數值動力分析三種分析法之結果，並將分析結果，與現地勘災觀察量測、前人之物理模型試驗和前人之數值模擬結比對。
由數值分析結果顯示─臺中港1號和4A號沉箱式碼頭，在921受震時，遠離沉箱的背填土壤區所激發的超額孔隙水壓，較鄰近沉箱背填土壤所激發的超額孔隙水壓高，且鄰近沉箱的背填土壤區有效應力不為零，而是離沉箱較遠處的背填土壤區有效應力值較為接近零。因此臺中港1號和4A號沉箱式碼頭主要破壞機制為碼頭背填區土壤受震累積大量超額孔隙水壓，產生水平推力使碼頭有往海側移、沉陷或傾斜的破壞，沉箱位移趨勢與現地勘災報告大致是相符的。
由數值分析結果顯示─蘇澳港4號沉箱式碼頭，歷經1986年花蓮地震產生滑移，現地勘災發現，蘇澳港4號沉箱式碼頭背填土未發生液化，碼頭僅有輕微外移。而此次花蓮地震加速度振幅雖然比921集集地震較大，但經數值分析可知蘇澳港4號沉箱式碼頭，亦無液化發生，但仍有孔隙水壓的激發，且沉箱背填土區破壞沉陷趨勢，與現地勘災報告大致亦是相似的。
由數值分析結果顯示─花蓮港19~21號沉箱式碼頭，921受震數值分析結果，沉箱滑移量微乎其微，與921地震現地並無明顯破壞現象，結果亦相同。

關鍵字

沉箱式碼頭 ； PLAXIS動力分析 ； 超額孔隙水壓:有效應力

並列摘要

In 1986, Suao Harbor suffered disasters of Hualien earthquake which caused it damage ; in 1999, Taichung Harbor suffered disasters of 921 earthquake that caused it damage, too. The FEM program─PLAXIS is the main analysis tool in this study including effective stress dynamic analysis. This study chooses three representative cases: Taichung Harbor #1 and #4A gravity-type caisson wharf (liquefaction to silding failure), Suao Harbor #4 gravity-type caisson wharf (silding failure) and Hualien #19~21 gravity-type caisson wharf(no silding failure). For studying seismic behavior of gravity-type caisson wharf and backfilled zones, three cases use PLAXIS to proceed numerical analysis, and compare numerical results with field reports and numerical analyses by other researchers.
The numerical simulation results of this study show that the failure mechanism of both two cases─Taichung Harbor #1 and #4A caisson wharfs are due to the loss of shear strength of backfilled zones during earthquake. So backfilled zones produce large lateral force acting on the caisson, leading to its lateral sliding, rotation and settlement, the same as that found in literature. .The excess pore pressure at locations far away from the caisson rises up higher than that near the caisson when #1 and #4A caisson wharf suffered Chi-Chi earthquake. The effective stress of soil just behind the caisson does not reach zero during shaking, but further portion of the backfill reaches closer zero.
In 1986, during Hualien earthquake, there was sliding displacement in Suao Harbor #4 caisson wharf. Although the acceleration amplitude of Hualien earthquake was larger than 921 earthquake, the geological survey of the disaster found that # 4 caisson wharf was no liquefaction at backfilled zones, only a slight sliding displacement.Therefore, the result of the numerical analysis is similar to field reports.
In addition, Hualien Harbor #19~21 caisson wharf had no failure during 921 Chi-Chi earthquake, and the result of the numerical analysis shows that there is nearly no sliding displacement. So, this result is the same as field reports.

並列關鍵字

cassion ； PLAXIS ； excess pore pressure ； effective sterss

參考文獻

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