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發生破壞，對砂石樁加勁可增加側向束縛應力並減少其破壞。本研究進行實驗室靜態三軸試驗以求得水平加勁砂石樁之應力－應變行為，且透過改變圍壓、加勁材種類、加勁材層數及試體尺寸等參數來分析此複合材料之力學行為。 將試體徑向應變率換算成加勁材之拉伸速率，並以此速率進行加勁材拉伸試驗。以線彈性－完全塑性模式模擬加勁材張力－伸張量之關係，依此求取加勁材之彈性模數。 試驗結果顯示：加勁試體之三軸試驗進行至軸向應變32%時，軸差應力仍持續上昇且未達尖峰值。加勁試體之視凝聚力與 角均隨著所施加之軸差應力而上升，加勁材勁度越高，加勁後試體所發揮之視凝聚力亦越高，加勁材勁度對試體 角並無明顯影響。 加勁材之間距比亦為影響加勁效果之ㄧ重要因素，間距比愈小，相同圍壓及軸向應變下對應之軸差應力值會越大；而體積應變值則會越小。由此可見，加勁材之層數越多，可增加試體之軸差應力，並減少其側向膨脹量。 由試驗結果亦可見，直徑較小之試體，對應之軸差應力較大，這可能是因為圍壓增加，且加勁材之間距縮小，導致砂土與加勁材間的互制效應減少所致。 在加勁試體之數值模擬上，試體軸差應力理論值與試驗值之平均誤差均在13.5%以下，而體積應變理論值與試驗值之平均誤差約為29.2%。 Most granular columns that fail from bulging near the top are due to insufficient lateral support. Laboratory triaxial compression tests were carried out in order to determine the stress-strain relation of sand columns. The mechanical behavior of the composite material was investigated through varying the number of geosynthetic layers, types of geosynthetic, different diameters of sample, and confining pressure. Transferred the radial strain rate of sand column to the tensile rate of geosynthetic. A linear relation was used between the tensile strain and tensile force of the geosynthetic. As observed from the the test result , the deviatoric stress varied for different types of geosynthetics used in different layers. The different in friction angle is marginal. But the c value is observed to be quite sensitive to the reinforcement types and layers of geosynthetic. Increase in stress for reinforced cand is more pronounced for greater number of geosynthetic layers. Nevertheness, the stress ratio decreases with an increase in confining pressure. The small-size samples show significantly higher stress ratio. The size effect clearly increase with higher number of geosynthetic layers and lower confining pressure. A numerical procedure to investigate the stress-strain relation of sand column. The theoretical analysis was validated through laboratory triaxial compression tests. The average error of deviatoric stress is less than 13.5%, for volumetric strain the average error is around 29.2%.