藉由本文中之分析,可瞭解外包加勁模式之效益,及對砂土材料強度參數之影響,提供設計加勁砂石樁時選材及加勁方式上之參考,並對後續試驗與理論研究上提供一概念性之建議。 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. 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 characteristics of the geosynthetic and the filled granular material. A numerical procedure to investigate the stress-strain relation of a reinforced column subjected to monotonically increasing confining pressure is therefore developed in this investigation. The theoretical analysis was validated through experimental triaxial compression tests on cylindrical specimen encapsulating with geotextile. Hyperbolic model was used to simulate tensile stress-strain relation of the geosynthetics. Results from three geotextiles encapsulating sand specimen of two relative densities show: (1) Geotextile encapsulating sand column enhances the axial strength; the reinforced specimen exhibited significant apparent cohesive strength. A remarkable increase in apparent cohesive is noted for geosynthetic with high stiffness. (2) The volumetric strain is not sensitive to the confining pressure; the magnitude of confining stress provided by the encapsulating geotextile varies slightly for different confining pressures. (3) Results obtained form the proposed theoretical analysis has good agreement with the experimental results.