本研究是引用台灣高鐵興建工程某一標分別施作單階段及多階段樁底灌漿的4支大口徑反循環基樁前期載重試驗結果，利用Fellenius（1980）建議的九種不同極限承載力判斷方法推估基樁的極限承載力，並應用應力-位移（t-z）曲線及q-z曲線分析模式，以研究基樁承受垂直載重後的應力傳遞行為及樁底土壤受力行為，評估不同樁底灌漿方法對基樁總承載力、摩擦力、點承力、土壤降伏應力位移與勁度等項目的改善程度，以判斷樁底灌漿對增加垂直承載力的成效。

　　研究結果，採用單階段樁底灌漿的基樁承載力僅為預估值一半，且發現由於基樁施工時間過久，使得皂土穩定液滲入樁周砂土層產生泥膜效應，造成摩擦力大幅降低，證明反循環基樁施工品質的不確定性，且顯示單階段樁底灌漿成效不彰。而經改採多階段樁底灌漿方法，發現基樁樁底承載力、樁周摩擦力明顯提高，沈陷量降低，樁尖阻抗發揮的比例提高，且由土層的t-z曲線及q-z曲線發現土壤勁度顯著提高，顯示多階段樁底灌漿除了增加基樁承載力，亦可增加基樁的經濟性。

　　本研究證明正確的樁底灌漿方法確實可有效改善基樁承載力，並增加基樁的經濟性，惟基樁長度、樁徑、灌漿壓力及灌漿量均對灌漿成效有相當程度的影響，如何建立其相互關係有待爾後進行更多的研究，進而建立國內樁底灌漿的設計準則及規範。

　　Four preliminary compression tests of bored piles with two different post-grouting methods of single-stage and multi-stage respectively in one project of Taiwan High Speed Rail are studied to explore the effectiveness of post grouting in this study. Nine methods recommended by Fellenius (1980) to determine the ultimate bearing capacity of four tested piles are applied. The t-z curve and q-z curve methods are also employed to study the loading distribution behavior and loading settlement behavior at pile tip under vertical loading so that the skin friction and end bearing can be otained and the effectiveness of post grouting can be understanded accordingly.

　　The bearing capacity, skin friction, end bearing, t-z curve, q-z curve and soil stiffness are discussed for single- and multi- stage of post grouting, rspectively. The following conclusions are made after thorough evaluation,
(1). The bearing capacity of pile applied single- stage post grouting is only half of prediction value. The caking effect caused by stabilizing agent in the shaft due to longer constrution period of pile significantly reduced the skin friction, especially for the cohesionless soil. The end bearing capacity is also lower than the expect value. The performance of this method is poor.
(2). The improved post grouting method, namely multi-stage grouting, is more significantly effective than single stage in the aspect of end bearing capacity, t-z curve, q-z curve and soil stiffness.
(3). The contribution proportion of end bearing under vertical loading is increased due to the improvement of q-z curve so that the design of pile can be proceeded economically.

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