近幾年來,加勁擋土結構運用在國內各類型擋土牆及邊坡穩定工程相當廣泛,其優點不僅可降低支出成本、縮短施工期限且提升耐震性能,亦可降低二氧化碳排放量,兼具景觀綠美化與生態環境之諧和功能,達到永續發展之綠色概念。但因全球暖化、氣候異常之影響,頻頻發生極端暴雨,遂導致山坡地頻傳大規模的崩塌以及加勁擋土結構破壞等巨大災害。 本研究以STEDwin程式,針對降雨浸潤加勁擋土結構之穩定性影響進行分析,根據其分析結果加以剖析並提出改善對策。分析結果顯示,加勁擋土結構雖有助於提升邊坡之穩定性,但從圓弧滑動分析之結果顯示,加勁擋土結構之破壞滑動面皆為坡趾延伸至背填區位置(介面破壞)。相較於圓弧滑動分析以指定滑動介面分析於暴雨模式之結果顯示,坡角45°之加勁擋土結構,其安全係數減幅最大約為57%,坡角70°之加勁擋土結構,其安全係數減幅最大約為16%,坡角80°之加勁擋土結構則無明顯變化。說明分析者必須詳盡的搜尋整個加勁擋土結構範圍(上邊坡、下邊坡以及整體邊坡)之穩定性,不能僅以加勁擋土結構局部作為分析考量,容易誤判其穩定性提高破壞之風險性。 加勁擋土結構之破壞往往誘發於暴雨來臨時,其加勁擋土結構本身之排水性能不佳,且挖填介面往往形成一弱面,常導致加勁擋土結構之整體滑動破壞,而結構體本身依然完好無缺。因此,加勁擋土結構設計之重點在於提升加勁擋土結構之排水性能與地工格網之錨定力,降低介面破壞之發生率,提升加勁擋土結構之穩定性。
In recent years, reinforced soil structures have been widely applied to all types of retaining walls and slope stabilization construction in Taiwan. This structure reduces costs, shortens construction schedules, enhances seismic resistance, and reduces CO2 emissions. In addition, the adoption of this structure greens, beautifies, and harmonizes ecological environments, thus achieving the green concept of sustainable development. However, slopes have encountered frequent large-scale landslides and reinforced soil structures have been damaged because cloudbursts are triggered by global warming and abnormal climate changes. This study utilized STEDwin to analyze the effects of precipitation and saturation on the stability of reinforced soil structures. Analysis results were examined and improvements were suggested. According to the analysis results, although reinforced soil structures could increase slope stability, a circular sliding analysis showed that sliding surfaces that damaged the reinforced soil structure were caused by the toes of slopes that extended to backfilling areas (interfacial failure). Compared to circular sliding analysis results, the interfacial analysis on cloudburst models demonstrated that a reinforced soil structure with a 45° slope had a 57% reduction at maximum in factor of safety (FoS); a reinforced soil structure with a 70° slope had a 16% reduction at maximum in FoS; and no significant Fos change was observed for a reinforced soil structure with a 80° slope. In addition to partial analyses on reinforced soil structures, analyzers have to thoroughly investigate the stability of the entire reinforced soil structure (the upper slope, lower slope, and overall slope); otherwise stability may be miscalculated and increase risks of failure. Reinforced soil structure failure often occurs in the presence of cloudbursts. Because of poor drainage of the structure and the cut-and-fill interface as a plane of weakness, the overall structure may experience sliding failure without damaging the structure itself. Therefore, the design of the reinforced soil structure emphasize the enhancement of the drainage of reinforced soil structures and the anchoring force of geogrids. This enhancement will reduce the incidence of interfacial failure and increase the stability of reinforced soil structures.
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