本研究針對黏土中外包加勁懸浮砂柱進行數值模擬，探討懸浮砂柱在不同強度黏土中的適用性，並探討不同參數條件下，懸浮砂柱之力學機制。文獻研究著重於黏土中端點支撐於堅硬底盤之外包加勁砂柱行為，本研究探討砂柱懸浮於不同強度之黏土中的行為，藉以評估外包加勁砂柱在適當的膨脹與沉陷發展下，是否依舊可以有效提升其承載力。 分析結果得知，砂柱樁徑介於0.5 ~ 1.5 m及加勁材勁度介於100 ~ 5000 kN/m之條件下，適合使用懸浮砂柱之黏土剪力強度約20~35 kPa。樁長較短時承載力-沉陷量曲線有一轉折現象，本研究藉由樁底週圍黏土降伏區域、樁頂傳遞到樁底的應力、及樁頂沉陷量與樁底沉陷量之關係了解其力學行為，探討轉折現象成因，並定義不再隨樁長增加提升承載力之長度為臨界長度；大於臨界長度之樁其承載力與樁底沉陷量都有趨於定值之現象。以勁度1000 kN/m之加勁材外包樁徑1 m之砂柱，在本研究所討論的五種黏土中，臨界長度皆為6 m。 This paper studies numerical modeling of geosynthetic-encapsulated floating sand column. It discusses the applicability of floating sand column in different shear strength clay. Moreover, the mechanical mechanism of floating sand column under different parameters is investigated. Most studies of the literature focus on the behavior of geosynthetic-encapsulated sand columns embedded in clay with end supported by a hard stratum. This paper studies the behavior of floating sand column embedded in different shear-strength clay, which is used to evaluate the effectiveness of geosynthetic-encapsulated sand columns under appropriate development of sand column expansion and subsidence. The analysis shows that for a sand column with diameter ranging between 0.5~1.5m wrapped by a geosynthetic having stiffness ranging between 100 ~ 5000 kN/m, the floating sand columns are suitable to be placed in clay with shear strength ranging between 20 ~ 35 kPa. Critical length of an encased floating sand column is defined as the length that bearing capacity of the column is no longer increases with the increase of column length. As for a 1 meter diameter sand column wrapped with geosynthetic of 1000 kN/m stiffness, the critical length is 6 m for column embedded in every four clay types adopted in this study.
