砂土中傾斜擴座地錨之錨碇行為

Chaoyang University of Technology Institutional Repository > 理工學院 > 營建工程系 > 博碩士論文 > Item 310901800/27991

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Title:	砂土中傾斜擴座地錨之錨碇行為 Anchorage Behaviour of Inclined Underreamed Anchors in Sand
Authors:	莊棓凱 Zhuang, Pou-Kai
Contributors:	營建工程系碩士班許世宗 Shih-Tsung Hsu
Keywords:	地錨 anchor
Date:	2003-12-31
Issue Date:	2016-01-23 14:16:56 (UTC+8)
Abstract:	摘要本文乃使用SHSE 模式(Strain Hardening-Softening and Volume ExpansionModel)配合FLAC3D 軟體進行傾斜擴座地錨於緊砂中之受力行為研究。由研究結果發現，在Dr=70%之砂土中，當地錨直徑D=0.076m、長徑比L/D=4.5、及覆土深徑比H/D=8 時，地錨之總拉力、面承力和摩擦力隨埋入深度之增加而增加，而總拉力和面承力亦隨傾斜角度之增加而減少，但傾角為o 20時，摩擦力最大。摩擦型地錨之最佳傾角為2 45 f - o 。發揮地錨尖峰拉拔力、尖峰摩擦力與尖峰面承力所需的位移量並非一致。地錨之摩擦力具有明顯之尖峰值與殘餘值，發揮尖峰摩擦力所需之位移量約為15%D達到殘餘摩擦力所需之位移量為50%D；面承力於埋入深徑比Z/D≧5之後，將無明顯之尖峰值，因此，面承力之臨界埋入深度Zcr=5D。經由定義地錨發揮降伏面承力Qqy所需之位移量Sq≒35%D。研究的結果亦顯示，地錨之面承力係數Nq隨埋入深度和傾斜角度的增加而減少。尖峰摩擦力之側土壓力係數Kf小於被動土壓力係數Kp，但大於靜止土壓力係數K0。地錨荷重傳遞曲線呈凹向上之方式由錨底向錨頂傳遞，埋入深徑比Z/D<10 之傾斜地錨，摩擦應力在錨頂會有應力集中現象，因此地錨之埋入深徑比不宜小於10D。從錨碇段周圍土壤之降伏過程可得知，錨底土壤會因解壓而先達到降伏，錨碇段上方土壤較下方之土壤先達降伏且降伏範圍較大。當地錨的埋入深度較淺時，面承前方土壤之降伏面將會觸及結構壁體。當地錨之覆土深徑比H/D≦8 時，其降伏範圍仍可能會發展至地表，因此傾斜地錨之覆土深度不宜小於8D。 ABSTRACTA constitutive model for sand named “SHSE” and FLAC3D software were used tostudy the anchorage behavior of inclined underreamed anchors in dense sand. Theanchor has a diameter D of 0.076mm, length-to-diameter ratio L/D of 4.5, andoverburden head of 8D, all anchors were placed in sand with Dr=70%.It was found that the total load, end resistance, and shaft friction were increased withincreasing embedded depth. Total load and end resistance were increased withdecreasing inclined angle, too. The maximum shaft friction occurs when theinclination angle “a ” equals to 20o, an inclination angle of 2 / 45 f - O may be theoptimum angle for a friction type anchor. Total load, end resistance, and shaft frictiondo not reach peak values at the same anchor displacement. Evident peak value andresidual value can be seen when anchors were pulled. An anchor displacement equalsto 15%D is need for the shaft friction reaches peak value. Shaft friction reachesresidual state at an anchor displacement of about 50%D. No peak value of endresistance can be found when free length of an anchor is greater than 5D and named adepth anchor herein. According to the definition of yielding end-resistance, theyielding end-resistance of deep anchor develops at an anchor displacement of about35%D.The end resistance coefficient Nq was decreased with increasing embedded depth andinclination angle of an anchor. The coefficient of lateral earth pressure Kf is less thancoefficient of passive earth pressure Kp, but is greater than coefficient of earthpressure at rest K0. A concave upward behavior can be seen from load transfer curve.Friction stress concentration on the upper fixed end results from an anchor of Z/D<10,hence do not place the free length of anchor in 10D. From the process of yielding soilsurround the fixed end can be found, soil surround bottom of an anchor reaches yieldfirst due to stress relaxation, the range of yielding soil above fixed length is largerthan the range of yielding soil below fixed length, the yielding range upon fixed endwill reaches structural wall if an anchor is placed in shorter free length. The yieldingrange will develop to ground surface when overburden depth of an anchor is less than8D, so do not placed those anchors in this area.
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