基樁在承壓與受拉拔時，因受力機制的不同，使得兩者的行為有所差異，過去有許多學者指出，基樁受拉拔時之樁身摩擦力約為受壓時的50%。因此本研究以模型樁載重試驗探討基樁受壓與受拉時承載力與摩擦力之差異，在乾砂與飽和砂中進行反覆壓、拉樁與反覆拉、壓樁載重試驗，總計進行五次反覆作用，以探討壓樁與拉樁的承載力與摩擦力之變化，最後將壓樁與拉樁之承載力與位移以及摩擦力與位移關係繪製成正規化曲線，得到抗拉與抗壓之承載力與摩擦力的比值，比較基樁抗壓與抗拉阻抗之差異。本模型試驗結果顯示，抗拉與抗壓之承載力和摩擦力的比值會隨樁頭位移增加而趨於變小。在福隆乾砂試體中極限抗拉承載力約為極限抗壓承載力的15%，飽和福隆砂試體中，極限抗拉承載力則約為極限抗壓承載力的23%。就摩擦力而言，樁體受拉時，摩擦力分佈會隨深度往下而增加；受壓時，摩擦力分佈則是中間段大兩端小之現象。在乾砂與飽和砂中，拉樁摩擦力約為壓樁的22%及30%，顯示抗壓之摩擦力大於抗拉之摩擦力。 This paper presents the results of model test for tensile and compressive bearing behavior of pile in sands. A model pile was statically pushed into a dry sand or a saturated sand, then, there are two kinds of pile load tests were performed. One is the pile was loaded first in compression and then loaded in tension, and then the compression-tension load cycle was repeated five times. The other case is the pile was loaded first in tension and then loaded in compression, and then the tension-compression load cycle was repeated five times. The measured end-bearing capacity and skin friction of the piles in tension and compression were then compared. The tension-compression capacity and friction of the pile varies with the pile head displacement. The larger the displacement, the smaller the ratio. It is found that the friction increases from the top to the bottom for tensile pile, however, the frictions at the top and bottom are smaller than the friction at the middle part for compressive pile.
