過去許多研究指出，基樁受拉拔時之樁身摩擦力約為受壓時的50%。顯示基樁之受力機制在受到承壓與拉拔荷載影響時有明顯差異。因此本研究欲進ㄧ步以離心機模型樁載重試驗探討在不同長徑比下，基樁受壓與受拉時承載力與摩擦力之差異，試驗首先進行不同長徑比之樁在乾砂中之極限承壓與拉拔承載力試驗，藉以討論基樁在達到極限破壞時承壓與拉拔行為之差異以及極限荷載的大小與長徑比之關係。爾後再以單一樁徑進行工作荷載下反覆壓、拉樁載重試驗，總計進行五次循環作用，探討工作荷載下壓樁與拉樁循環作用的軸力與摩擦力之變化。依據試驗所得結果在極限破壞的狀況下，拉拔與承壓之承載力百分比隨長徑比的減少由63 %降至38 %，摩擦力百分比則由85 %降至62 %，而反覆壓、拉樁載重試驗結果得到基樁拉拔與承壓百分比值約在52 %~46 %間，承壓的摩擦阻抗無論在極限破壞或是工作荷載下皆大於拉拔的摩擦阻抗。 This study conducted a series of centrifuge model test to discuss the mechanism of the pile subjected to compressive and tensile loadings, and three different slender ratios of piles with the same embedded length were designed in the test. During the test, the model pile was first driven into the dry sand at 1g condition, and then an artificial gravity of 80g was applied in the centrifuge to simulate a full-scale prototype situation. Subsequently, two kinds of loading conditions were performed - monotonic loading and cyclic loading, and the differences of ultimate capacity, skin friction and end-bearing between the pile subjected to compressive and tensile loadings could be observed by measuring the axial force along the pile. From the results, the smaller the slender ratio, the smaller the skin friction ratio of tension to compression, the quantity of which ranges between 85 to 62% at ultimate state of monotonic loading. In cyclic loading test, the skin friction ratio of tension to compression gradually decreased from 52% to 46%. Besides, the pile skin friction in compressive condition is always larger than the one in tensile condition.