摘 要 目前加勁擋土牆的設計規範是以級配良好的顆粒性土壤作為回填材料，但施工現場常用現地的非顆粒性土壤或黏土回填。然而含水量對黏土的影響甚鉅，且過去曾有一些因含水量的提高而破壞的案例，因此針對含水量對以黏土做為背填土壤的加勁擋土牆之穩定性，有必要做進一步的研究。 本研究主要運用大地工程離心機進行實驗，以探討含水量對黏土加勁擋土牆穩定性的影響，及改變加勁間距對改善高含水量黏土加勁擋土牆穩定性的效果。 由研究結果可以得到下列結論。1.背填料若為黏土時，含水量的高低對加勁擋土牆的穩定性有極大的影響。2.減少加勁間距的確可以有效改善高含水量對於黏土加勁擋土牆穩定性的不良影響。3.以中大紅土為例，若使用的加勁間距為計算出來的0.35倍，則可以確保當含水量上升至43%時，加勁擋土牆依舊可以和按照規範設計的加勁擋土牆具有相同的變形量。4.加勁間距若小於規範設計出來的0.625倍，則加勁擋土牆的變形型態會由一般的前傾型，轉變成上凹肚凸型且可看出破壞的前兆，顯示使用較小的間距，會讓加勁擋土牆具有較好的韌性。 ABSTRACT The design and construction guidelines of mechanically stabilized earth wall (MSEW) require that the backfill of MSEW must be well-graded grained soil; however, on the construction sites, the cohesive soil or clay is frequently used to cut down the cost. There have been reports about the failures of MSEW with clayey soil as backfill due to the rise of its water content after heavy rainfall. As a result, it is imperative that the countermeasure must be developed to ensure the stability of MSEW with clayey backfill of high water content. A series of centrifuge model tests have been performed to study the influence of water content on the stability of MSEW with clayey backfill and the effectiveness of reducing the reinforcement spacing to maintain the stability of MSEW of high water content. From this study, the conclusions drawn are: (1) The degree of water content influences the stability of MSEW with clayey backfill very much; (2) Decreasing the reinforcement spacing can indeed improve the stability of MSEW of high water content; (3) For MSEW with clayey backfill of 43 % water content, reducing the reinforcement spacing by 65% of the original design spacing can lead to the same deformation characteristics of MSEW designed for normal conditions; (4) When the reinforcement spacing is smaller than 0.625 times of original design spacing, the deformation pattern for MSEW changes from small surface settlement with tilting wall face to large surface settlement with bulging wall face, indicating that the wall becomes more ductile before failure.