以實驗方法探討不飽和砂質土壤之液化行為研究

Abstract

不飽和土壤的課題存在於許多大地工程相關案例中，尤其是當案例場址發生在地下水位面附近時，不飽和土壤的問題應該被納入工程設計參考中。前人透過進行許多不飽和土壤試驗後發現，土壤在不飽和條件下有提升剪力強度及抗液化能力的效果，而隨著土壤飽和度下降，土壤強度逐漸提升。本研究以實驗方法進行土壤試體在不飽和狀態下受靜態及反覆循環載重後呈現的土壤行為。為了在實驗室中進行試驗，本研究發展了以三軸方法進行不飽和土壤試驗的實驗流程，而實驗流程可分為五個項目，其中包括了以濕霣降法進行土壤試體重模，及使用定流量泵以飽和度控制方法降低土壤試體飽和度；三軸底座經過改良可將高進氣陶板嵌入其中，以進行使用了軸平移技術的不飽和土壤三軸試驗。實驗結果顯示，土壤試體進行不排水靜態加載過程中，當剪切至大應變時，土壤試體表現出剪脹性；而從不排水的不飽和動態三軸試驗中發現，降低飽和度引致土壤試體抗液化潛能提升的效果並不明顯，此項發現與前人進行的研究比較後，歸結出以下幾兩點可能因素，其一為土壤顆粒大小的不同及試體到達目標飽和度階段採用的流程不同所致，研究成果在進行討論後統整出結論及研究建議，本研究的成果可成為後人進行不飽和土壤三軸試驗的參考。

Dynamic properties are often determined for sand at completely dry or completely saturated condition. Available correlation relationships for dynamic parameters and liquefaction potential are mainly applicable for saturated soils. The objective of this research is to perform extensive laboratory study (in terms of static triaxial tests, cyclic triaxial tests and flow pump tests) to determine the static and dynamic properties of unsaturated sand. The modified procedures for unsaturated sample preparation and conducting triaxial tests are developed, including the usage of wet pluviation for preparing remold specimens, usage of flow pump device for controlling the degree of saturation, modification of the pedestal in the triaxial apparatus for the fulfillment of the axis translation technique. The test results show that the unsaturated soil specimens exhibit dilative behavior under static loading with undrained condition at large axial strain. On the other hand, unlike the trend observed by other researchers, lowering the degree of saturation do not significantly increase the liquefaction resistance. This inconsistence may be due to the difference in the grain size of the specimens and the method to achieve the unsaturated state.