現今加勁擋土牆設計規範多以滲透性高之顆粒性砂土級配料作為回填材料，但實際上卻常用現地的非顆粒性土壤回填，這樣的背填材料對牆體的穩定性影響甚鉅。過去案例中不乏因連日豪雨致使回填材料含水量上升，造成土壤不排水剪力強度迅速減低，側向土壓力增加而破壞的案例。 因此本研究乃利用地工離心模型試驗探討改變加勁材的配置方式，探討在高含水量下以中大紅土為背填材料之加勁擋土牆穩定性的改良效果。研究結果顯示：1.藉著本研究所提出之改善率等高線圖可得到在高含水量粘土加勁擋土牆之加勁材的最佳配置方式。2.加勁間距減小為0.067H、加勁長度增長為0.85H時，可獲得最大改善量為90%。3.當加勁間距為0.1H時，牆面變形行為肚凸狀；加勁間距為0.067H時，牆面變形行為前傾狀。4.牆體的破壞面不會穿過牆趾，而外部不穩定破壞面是在牆趾上方約0.133H處開始大約沿夾角θ=tan-1(0.43H/L)向上發展；內部不穩定破壞面是在牆趾上方約0.133H處開始大約沿夾角45°向上發展。 Mechanically Stabilized Earth Wall (MSEW) is required to use the high quality granular soil as reinforced backfill materials. In practice, however, the in-situ clayey soil is usually used instead to cut down the cost, which obviously violates the design assumptions. Nevertheless, the clayey soil backfill may block the draining path, leading to increase in water content and lateral earth pressure during heavy rainfall. There were many cases of failure of MSEW with clayey soil backfill caused by cloudburst in Taiwan. Sixteen centrifuge modeling tests were performed to investigate the effectiveness of different combinations of reinforcement length and spacing in improving the stability of MSEW with clayey soil backfill at high water content (41%). Based on the test results, a contour plot is proposed which can be used to determine the different combinations of reinforcement length and spacing for a given amount of improvement ratio of deformation. From the test results of this study, the maximum improvement ratio is 90% with 0.067H reinforcement spacing and 0.85H reinforcement length. The deformation types of wall facing are bulging and tilting with 0.1H and 0.067H reinforcement spacing, respectively. The failure surface for external instability starts at 0.133H above the toe of the wall and extends along the angle of tan-1(0.43H/L) until it intersects with reinforcement end and then extend upward; the failure surface for internal instability also starts at 0.133H above the toe of the wall, but extends along an angle of 45° until it intersects the horizontal line at a height of 0.5H and then extends upward, lying within the reinforced zone.