- 期刊
液化潛能指數P(下標 L)使用時可能產生之問題探究
A Study on Doubts May Occur in Using Liquefaction Potential Index, P(subscript L)
摘要
日本學者Iwasaki於1982年提出之液化潛能指數(Liquefaction Potential Index，PL)為目前廣泛使用於將一工址各深度土壤發生液化危險程度量化成土壤能發生液化潛能之方法，其計算方法為以積分將土壤液化危險程度（1-安全係數）函數與深度加權函數乘積展開，理論上能充分展現計算深度範圍內之液化發生潛能。若此方法中之土壤液化危險程度函數能以CPT結果計算之，將較能符合連續積分的計算精神；然而目前工程界較廣泛使用之試驗仍為SPT，則因其為不連續採樣而使土壤液化危險程度函數呈不連續，故計算之積分式則需要依照SPT打擊位置進行深度範圍區隔後，再以積分展開式將結果疊加。此一方式應用在SPT打擊位置深度分佈均勻之工址並無疑慮；然而若應用在SPT打擊位置分佈不連續之工址則可能產生高估液化潛能指數之計算結果，而誤判該工址之發生液化潛能。本文發現，在某些情況下，深度分佈不連續的SPT結果計算出之安全係數將導致PL越過臨界門檻值（5或15）而造成嚴重誤判。
並列摘要
A widely used method for estimating soil liquefaction occurrence probability called Liquefaction Potential Index, P(subscript L), was proposed by Iwasaki ill 1982. The index is a computation adopted for quantifying the occurrence potential of soil liquefaction and its calculation is in form of integration by multiplying the dangerous function (1-safety factor) and depth weighting function. Theoretically, the computation can adequately express the potential of soil liquefaction among the calculating depths. If the dangerous function is calculated by CPT logs, the integration should be more suitable for continuity. However, at present SPT logs are much generally used in engineering. Thus the dangerous function calculated by SPT logs becomes discontinuous, the integration has to be spread up by divided zones with SPT performed depth first, and then summed each part of integration. If the performed depths distribution of SPT is uniform, the calculation should be correct or the calculation result will be higher, therefore the potential of liquefaction will be highly estimated. A serious misjudgment will be made and lead FL surpasses the threshold values (5 or 15) 0n some cases if the depths distribution of SPT is discontinuous.