液化潛能指數P(下標 L)使用時可能產生之問題探究

Abstract

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.