地工合成材加勁防砂壩之側向承載能力之數值研究

Numerical Evaluation of Lateral Bearing Capacity of Geosynthetic-Reinforced Earth Dam

謝嘉(Jia Hsieh)

指導教授 ： 陳榮河

國立臺灣大學/工學院/土木工程學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201701627

摘要

加勁擋土結構的設計可分為 Mechanically Stabilized Earth Wall (MSEW)與Geosynthetics Reinforced Soil Composite (GRSC) 的兩種設計理念。前者之設計理念是將加勁材視為背拉構件(tie-back wall)，後者則將加勁材與土壤視為複合材料進行設計。GRSW系統相較於MSEW系統，加勁材不需具有高強度，牆體的自立性較佳，有利於對抗牆面撞擊及牆基受淘刷。因此，本研究採用PLAXIS 3D數值軟體，研究以兩種地工合成材(地工格網與蜂巢格室)加勁兩種防砂壩(開口壩與梳子壩)在土石流衝擊力之作用下的壩體變形、加勁材受力狀況與壩體破壞模式。影響因子包含：(1)加勁材垂直間距與加勁範圍之影響；(2)壩基淘刷對側向承載能力之影響；(3)受巨礫撞擊時之影響等。
由研究結果發現，在變形方面，開口壩以凸出變型為主，梳子壩則是凸出變形加上壩柱推移。最大變形都約為壩高的2 %，而壩翼及壩基(跌水處)附近會發生土壤的擠壓破壞。在相同加勁材用量下之開口壩，受土石流衝擊時之側位移，以蜂巢格室開口壩(1.648 cm)明顯小於地工格網開口壩(4.821 cm)，蜂巢格室梳子壩(3.226 cm)則與地工格網梳子壩(3.365 cm)差別不大。改變地工格網垂直間距可知，間距縮小趨於GRSC時，抑制側向變形能力較佳。在淘刷方面，MSEW因淘刷導致側向極限承載力下降的幅度比GRSC大。在開口壩中，以地工格網加勁較蜂巢格室加勁者易受淘刷影響，梳子壩則相反。以蜂巢格室加勁之梳子壩受淘刷後承載力驟降(約40 %)，而地工格網加勁者下降則不明顯(小於10 %)。

關鍵字

地工合成材 ； 加勁 ； 防砂壩 ； 側向承載力 ； 數值分析

並列摘要

The design of geosynthetic-reinforced soil walls can be classified into two types according to the design concept: Mechanically Stabilized Earth Wall (MSEW) and Geosynthetics Reinforced Soil Wall (GRSW). The former is designed and constructed in the same manner as a tied-back wall; while the latter is treated and designed as a composite material. In this study, the finite element software, PLAXIS 3D, was used to analyze the behavior of two types of geosynthetic-reinforced earth dams (open-type and slit-type), which were reinforced with geogrids and geocells, respectively, and subjected to the impact force from debris flows. The influencing factors investigated were as follows: (1) the vertical spacing and zone of reinforcement; (2) scouring; (3) impact from boulders, etc.
The result of analysis indicated that deformation of both dam types bulged at their middle heights, with the maximum deformation about 2% of the dam height. Moreover, passive soil failure occurred within the two flanges and in the base of the structure. With the same amount of different reinforcements, the geocell open-type dam displaced less than the geogrid open-type dam, but the difference was not much for slit dams when they were subjected to quasi-static lateral pressures induced by debris flows. In addition, with reduced vertical spacing of geogrid layers, the dam tended to behave as a GRSW and had better resistance to lateral deformation. The effect of scouring in reducing ultimate lateral bearing capacity was more significant for MSEW than GRSW. For open-type dams, the effect of scouring was more serious for geogrid dam than geocell dam. However, the effect was reversed for slit dams. The lateral bearing capacity of geocell slit dam after scouring decreased significantly (about 40%); while that of geogrid dam is only less than 10%.

並列關鍵字

Geosynthetics ； Reinforcement ； Check Dam ； Lateral Bearing Capacity ； Numerical analysis

參考文獻

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