地工合成物包裹砂柱試體之尺寸效應探討

The size effect on Geosynthetic-Encapsulated Sand Column Specimens

魏照榮(Chao-Jung Wei)

指導教授 ： 吳朝賢

淡江大學/工學院/土木工程學系碩士班/碩士(2009年)

https://doi.org/10.6846/TKU.2009.00305

摘要

眾多土壤改良工法中，砂石樁改良法施工迅速，除了可傳遞荷重外，並能加速地盤排水及減少土壤沈陷，因此對砂石樁力學性質之研究為一重要且富價值之課題。打設於軟弱土層中之砂石樁，樁體上部結構易因側向束縛力不足而產生破壞，對砂石樁加勁可增加側向束縛應力並減少其破壞。由於試驗試體與現地砂石樁存在著尺寸效應，而尺寸效應對加勁效果有顯著之影響，故本研究主旨為探討其尺寸效應與加勁效果之關係。
試驗過程採用外包加勁，將加勁材縫製成圓管狀並包覆於砂柱試體外圍，進行實驗室靜態三軸試驗。模擬加勁砂石樁於土層中之應力－應變行為，探討地工合成材料以外包加勁砂石樁之效益，透過改變圍壓及試體尺寸來分析此複合結構之力學行為與尺寸關係。
經由改良之體積量測系統，量測加勁試體之體積變化，計算各軸向應變下加勁材之張應變。並以雙曲線模式模擬加勁材張力－應變關係，依此求取加勁材之張力，計算加勁材所提供之束縛應力，以分析加勁材對三種不同直徑試體所提供之加勁效果。
研究結果顯示：三軸試驗進行至軸向應變25%時，試體徑向應變尚未達加勁材最大張力所對應之應變，導致加勁試體軸差應力持續上昇並無尖峰值。而試體直徑越小，加勁後試體所發揮之視凝聚力越高，然而加勁材對試體發揮摩擦角並無明顯影響。

關鍵字

尺寸效應 ； 砂樁 ； 加勁 ； 地工合成材 ； 三軸試驗

並列摘要

Granular columns were introduced into engineering practice to improve bearing capacity and reduce settlement in a weak or soft soil. This method is considered one of the most versatile and cost effective techniques for improving in-situ ground conditions.
Most granular columns that fail from bulging near the top are due to insufficient lateral support.Skirting the granular column by wrapping a geosynthetic liner around the top section of the column and enveloping the granular column in a membrane were proposed to strengthen the column. When vertical and coincident lateral deformations of the granular column occur under a vertical load, the encapsulating geosynthetic generates additional confining stress to the column.
Because the mechanical behavior of the granular material is usually controlled by the lateral confining pressure, the improvement in bearing capability from the geosynthetic-encapsulated granular column depends upon the mobilization of lateral or confining stresses exerted by the geosynthetic. The reinforcing effect of the granular column thus depends on the size of the specimen and the filled granular material.
Transferred the radial strain rate of sand column to the tensile rate of geosynthetic.Hyperbolic model was used to simulate tensile stress-strain relation of the geosynthetics.
Results from three geotextiles encapsulating sand specimen of three diameter size show: (1) Geotextile encapsulating sand column enhances the axial strength; the reinforced specimen exhibited significant apparent cohesive strength. (2)The size effect clearly increase with lower confining pressure; The small-size samples show significantly higher stress ratio.

並列關鍵字

size effect ； granular column ； reinforced ； geosynthetic ； triaxial test

參考文獻

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