樁基礎在承壓與受拉時，因為受力機制的不同，使得彼此的行為也有所不同，這樣的行為差異在樁身摩擦力上最常被討論。由前人的研究結果顯示，許多學者指出基樁承壓與抗拉之樁身摩擦力，均有明顯的差異。其中，Tomlinson（1977）指出砂質土層中，基樁受拉拔時的樁身摩擦力約為受壓時的50％。由Mansur & Hunter（1970）於美國Arkansas River的研究計畫中指出打入式基樁承受拉拔力時，其樁身摩擦力約為受壓時的65％。茶古文雄（1994）整理日本地區的現地樁載重試驗的結果，指出基樁受拉時的樁身摩擦力約為受壓時的80％。為了瞭解基樁抗壓與抗拉承載力之差異，本研究利用直接剪力試驗儀進行一系列的樁-土界面試驗，藉以模擬樁身與樁周土壤間之摩擦行為。緊接著，再利用模型基樁載重試驗來進一步探討基樁承壓與受拉時承載力之差異。由試驗結果顯示，不論是直剪界面試驗或模型樁試驗，對於基樁承壓與受拉時之摩擦力，其差 異並非十分顯著。 The objective of this study is to investigate the difference of shaft frictions between tensile and compressive piles, by comparing the results of direct shear and model pile test. Previous results indicate that the shaft frictions of tension and compressive piles are different. For examples, Tomlinson (1977) proposed that the ratio of tensile and compressive shaft capacities is 50% for piles driven into sand. The American Arkansas River project report, as pointed out by Mansur & Hunter (1970) showed that the ratio of tensile and compressive shaft capacities is about 65% for driven piles. Based on the results of in-situ pile load test in Japan, Fumio Sako (1994) presented that the ratio of tensile and compressive shaft capacities is about 80%. In order to understand the difference of shaft frictions of tensile and compressive piles, this study performed pile-soil interface test by direct shear test first, for simulating interface frictions in different directions between shaft and the soil around the pile, theu, carried out same use model pile tests to investigate the difference of shaft frictions of tensile and compressive piles. Based on the test results, it seems that shaft frictions of tensile and compressive piles are of little.
