參數研究以現場實體尺寸為分析標的，分別探討邊界效應、砂石樁徑、加勁材勁度以及加載形式等，對外包加勁砂石樁承載行為的影響。數值分析結果剖析柱體變形、黏土側向壓力、加勁材徑向應變以及圍束應力等於受載過程中的變化。可知，砂石樁承載行為受邊界效應影響甚大，當邊界愈小，承載能力愈高，達20倍樁徑時已不受邊界的影響。另，樁徑愈小與加勁材勁度愈大，承載能力愈高。最後，承載能力也受加載形式不同而有所差異，當加載範圍愈大時，砂石樁受到垂直壓力也愈小。 Due to inadequate bearing capacity on soft clay often need to increase soil engineering properties through soil improvement. Granular columns are a common improvement technique for foundation embankments or structures on soft clay. This technique has been introduced into engineering practice to improve the bearing capacity, reduces the liquefaction potential of granular column foundations resting on the soft clay. However, granular columns may not be appropriate in very soft soils that do not provide enough lateral confinement to the columns. To increase the lateral confinement of the columns, and consequently their vertical capacity, encasing the columns with geosynthetics has been a successful solution in recent years. In this study, the finite difference software FLAC is used to complete the numerical analysis. This numerical study investigates the behavior of geosynthetic-encased sand columns installed in soft ground. Base on an elastic-plastic constitutive model used with the non-associated flow rule, the shearing-dilatancy behavior of granular materials is characterised through laboratory triaxial tests. The parameters of Modified Cam-clay model are extracted from the consolidation tests. By using the tensile force-strain relation obtained from wide-width test, the reinforcement properties are obtained. The shear stiffness of interface between sand and steel plate is obtained via direct shear tests. According to the boundary conditions of the laboratory model tests, establish a numerical model for encased granular columns in soft clay. The proposed numerical method is validated through laboratory model tests on un-reinforced and encased sand columns in soft clay. The clay boundary, column diameter, reinforcement stiffness and loading patterns influence encased column in soft clay response is also studied. Numerical results indicate the larger clay boundary the lower the bearing capacity of column. Up to 20 times the column diameter not effect the column bearing capacity. In addition, the larger column diameter or smaller the reinforcement stiffness result the lower the bearing capacity. Finally, the vertical pressure of column is smaller when the greater load range.
