近年來國內建築工程已有相當多之案例，採用矩形壁樁承載上部結構荷重，且數量有逐漸增加之趨勢，過去對矩形壁樁之相關研究較少，目前工程實務上仍多直接採用圓形基樁之承載力公式來估算壁樁極限承載力。然而國內矩形壁樁主要使用MHL工法施做，除斷面形狀外，所使用之施工機具及方式亦與傳統圓樁不同，直接採用圓形基樁之經驗來評估壁樁極限承載力是否合適，宜進一步深入探討。 本研究利用樁徑D=20mm之圓型模型基樁，進行離心機模型試驗，並進一步與三種不同長寬比之矩形模型壁樁，比較其在原型尺寸下之行為，三種矩型樁之長寬比分別為1：l、1：2及1：4，其四組不同基樁其樁底截面積相等，以此來控制樁底發展區之範圍，比較之間的最終樁身平均摩擦應力與位移曲線t-z曲線之間之差異，並繪製樁頂荷載與位移曲線(P-S curve)圖，進一步比較圓樁以及壁樁於離心模擬下之成果，最後運用染色砂層進一步觀察樁體底部所發展的塑性區為何種形狀。 本研究發現：1. 在相同荷重下，各基樁的阻抗能力L/B=2壁樁>L/B=1壁樁>L/B=4壁樁>圓樁。2. L/B=4壁樁摩擦應力發揮至一定量，摩擦應力會變小後繼續發揮作用，行為有點像突破靜摩擦力，轉換成動摩擦力的現象發生。3. 圓樁樁身摩擦力與樁底承載力約呈現4:6之比例；而壁樁均在較小載重時，樁身摩擦力有較大的發揮，最後較大荷重時，大部分由樁底承載力支撐其荷重，比例約為1:3。4. 圓樁的樁底有較明顯及完整的發展區，其立體形狀約呈現橢圓球形狀，長側影響範圍總長度約為5倍樁徑，短側影響範圍總長度約3倍樁徑。5. 各組壁樁試驗之剖面結果較無明顯發展區發生。 ;Diaphragm wall construction equipment and technologies develop with time. The barrettes are frequently used for supporting high rise buildings to replace pile foundations in recent years. There are more and more cases that barrette replaces the big diameter cast-in-place pile. The barrette shape and construction methods are different from those adopted for cast-in-place piles. The understandings of vertical loading behavior and mechanism of deformation are required. In this research, a instrumented circular pile with diameter (D) of 20 mm and three instrumented barrettes with different length-width ratios (L/B=1:1, 2:1, 4:1) but the circular pile and barrettes have the same area of cross section to perform a series of the pile load centrifuge model test. Test results give the following conclusion. 1. The bearing capability of barrette with L/B=2 is better than that of L/B=1 barrette, and the bearing capacity of L/B=1 barrette is better than L/B=4 bearing capability, and the bearing capability of L/B=4 barrette is better than circle pile bearing capability. 2. The unit frictions on the barrette of L/B=4 start to grow until reaching one of limit loading. This phenomenon seem from the static friction force changing to kinetic friction force. 3. The ratio of circular pile skin friction and the end bearing on the circular pile are 4:6. The ratio of barrette skin friction and the end bearing are 1:3. 4. The developed plastic zone of circular pile is bigger than those developed on the barrette. 5. The circular pile plastic zone are 5 times pile diameter in long side of rigid box and three times pile diameter in short side of rigid box.
