地震引致軟弱砂質地盤液化發生機率之評估

Evaluating Liquefaction Probability of Sandy Soil Due to Earthquake Shaking

軟弱砂質地盤在強烈地震時所產生的液化現象，極易損害都市地下維生管線及結構物，常造成嚴重的都市災害。本文乃利用地震能量消散理論及極限狀態觀念，提出一新的地震引致軟弱砂質地盤液化機率的評估方法，並以分層平均的概念，來計算土層之平均年液化機率(average annual liquefaction probability, AALP)。本文以1999年921地震時產生土層液化現象之彰化員林地區為研究案例，評估結果顯示區域內地面下第一層砂土層的AALP較第二層砂土層為高，符合一般淺層砂土具高液化潛能的概念，本文以第一層砂土層的AALP 代表整孔之AALP值，由所繪之區域內點位AALP等值圖，顯示員林地區在縣道148 以南及縣道137以西區域，其AALP值約0.01為最高，此結果與921地震時現地液化調查之液化區域相符，可推測其液化重現期約為100年。

In this paper, a new evaluation method of annual liquefaction probability was developed based on both seismic energy dissipation theory and limit state concept to change seismic loading in order to search for the liquefied and non-liquefied curve. Furthermore, a new approach was developed using the average annual liquefaction probability (AALP) of divided soil layer to represent the AALP of over hole. The case study evaluating the AALP is in Yunlin, where the soil liquefaction occurred in the Chi-Chi earthquake, 1999. The results show that the AALP of surface sand layer is more than the second sand layer ones, which conform to the general assumption. By mapping of AALP in Yunlin area, the results show that revealed the high AALP area is located between south of county road No. 148 and west of county road No. 137, where the AALP is approximately 0.01 indicating the cycle of liquefaction is about 100 years. The distribution characteristics of liquefaction average probability are also discussed in this paper.