加勁纖維土壤為在土壤中添加人造或者天然纖維拌合，藉以提升土壤剪力強度及整體穩定性，可以應用在修復局部邊坡破壞，提升邊坡穩定性與坡面抗沖蝕性。本研究探討纖維與水泥對低滲透性土壤不排水剪力強度之影響。本研究以三軸無圍壓縮試驗求取粉土添加纖維與水泥後的無圍壓縮強度。此外，本研究亦利用電子顯微鏡觀察纖維、土壤與水泥顆粒的互制行為，進而驗證添加水泥對纖維握裹力的影響。本研究試驗變因包括纖維含量、纖維長度、水泥含量。試驗結果顯示，當加勁纖維含量提升，其無圍壓縮強度提升但勁度下降，試體破壞模式由原本脆性轉為韌性；而纖維長度提升對於強度影響較不明顯。此外，水泥的添加使強度以及勁度皆大幅提升，隨著纖維含量增加勁度逐漸下降，但仍大於純粉土之勁度。水泥加勁試體之破壞模式也隨纖維含量加，其破壞模式也由脆性轉為韌性。本研究探討添加水泥與纖維造成土壤強度提升增加之原因，研究發現除了纖維以及水泥自身對強度增加的貢獻外，添加水泥後，纖維將獲得額外握裹力造成更有效的土壤-纖維互制機制，故強度大幅提升。最後，在後續工程應用上，依據本研究結果，在加勁纖維土壤內添加微量之水泥能有效增加加勁纖維土壤的勁度與強度，進而提升整體地工構造物之穩定性。

Marginal soils (i.e., silt and clay) have not been a preferred option of a backfill material for reinforced soil structures due to its low shear strength and permeability. In this research, fiber-reinforced silt (FRS) and fiber-reinforced cemented silt (FCS) were studied as a measure of improving the stability of reinforced soil structures backfilled with marginal soil. A series of triaxial unconfined compression tests are perform to investigate the effect of adding polypropylene (PP) fibers and cement on the shear behavior and failure mode of silty soil subject to undrained loadings. The test variables considered in this study are fiber content (0, 1, 2, 3%), fiber length (6, 12, 19 mm) and cement content (0, 5%). The specimens were prepared at a maximum dry unit weight and optimum moisture content based on standard proctor compaction test results. For FCS specimens, the 7 day curing strength was obtained and compared in this study. The experimental results revealed that adding fiber and cement substantially increased the undrained shear strength and reduced the loss of post peak strength of the reinforced soil. The failure mode steadily transformed from brittle to ductile type as the fiber content increased. Test results also indicated that the modulus of FRS under working stress conditions (at 2% of axial strain) decreased as fiber content increased but increased as fiber length increased. Regardless of fiber content and length, the modulus of FRS is less than that of unreinforced silt, whereas the modulus of FCS is larger than that of unreinforced silt. The improvement of undrained shear strength as a result of cement-induced extra boning strength was determined by quantifying the strength increment between FRS and FCS specimens. The analytical results suggested that for reinforced specimens with 2 and 3% of fiber content the strength improvement from the contribution of cement-induced extra boning strength is larger than that from the contribution of fiber alone. This observation demonstrated the significance of adding cement as an adhesive to improve the bonding strength between fiber and soil matrix. As a result, higher fiber tensile strength could be mobilized and contributed to the increase of overall undrained shear strength of reinforced soil. Images acquired from scanning electron microscope (SEM) also provided clear visual evidences of soil-fiber interaction improved by adding cement.

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