加勁擋土結構物除了能夠承受垂直的荷載之外，近年來也逐漸被用來抵抗側向自然破壞力，如洪水、海嘯、土石流及雪崩等。加勁擋土結構之外部穩定性分析如一般常規重力式擋土結構物的穩定性檢核，視加勁區域為剛體，然而這與柔性的加勁擋土牆性質不符，因此本研究以PLAXIS 有限元素法數值軟體進行分析，目的為探討加勁擋土壁壘(GRS barriers)受側向力後的力學機制與破壞模式，再以參數分析的方式找出影響GRS壁壘側向承載力的關鍵因子。研究結果發現牆體受側向力之後，其牆內應力也呈現撓曲應力的增減方式，牆體的背力側發展出一般擋土牆受到垂直力後牆面向外變形所引起的主動破壞，而牆體受力側產生界面滑動破壞。參數分析研究結果發現，對於GRS壁壘側向承載力的關鍵影響因子為寬高比(L/H)，且寬高比的變化會使得破壞模式也不同，寬高比為L/H=0.5~1之間，其破壞模式控制再牆體之主動與界面破壞，而寬高比為L/H=1~3之間控制在底部滑動破壞，而寬高比大於3之後，其破壞控制在擋土牆之被動破壞。

Geosynthetic-reinforced soil (GRS) structures are often used to carry vertical surcharges. Recently, GRS structures have been applied as barriers to resist lateral force from natural disasters such as flood, tsunami, rock fall, debris flow, and avalanche. In design guideline, the stability of such structures is often evaluated by conducting the conventional external stability analyses assuming the reinforced soil mass as a rigid body. However, the assumption of rigid body contradicts with the flexible nature of reinforced soil. In this study, finite element (FE) models of back-to-back GRS walls were developed to investigate the failure mode and lateral bearing capacity of GRS barriers subjected to lateral loadings. The FE result showed GRS barriers generated bending deformation when subjected to lateral force. As a result, the vertical stress at the side of wall subjected to lateral force decreased due to the bending deformation induced tension stress. On the other hand, the vertical stress at the opposite side increased because of the bending deformation induced compression stress. The failure mode depended on the aspect ratio of GRS barriers L/H (ratio of wall width to wall height). When 0.5 < L/H < 1, the GRS barriers subjected to lateral loading failed internally. Due to the development of bending stress, the GRS barriers failed due to the internal sliding along the soil-reinforcement interface at the side subjected to the lateral force and meanwhile the active failure of reinforced soil wedge at the opposite side. When 1.0 < L/H < 3.0, sliding failure at the bottom of GRS barriers occurred. When L/H > 3.0, the passive soil failure occurred within GRS barriers at the side subjected to the lateral force. The parametric study results indicated the major factor to affect the ultimate lateral bearing capacity was the aspect ratio of GRS barriers. As L/H increases, the lateral bearing capacity of GRS structures increased from approximately twice of active lateral earth pressure at L/H = 0.5 to the passive lateral earth pressure at L/H = 3.0.

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