| 摘要: | 近年來，隨著人口日益增加，都市化的活躍導致交通頻繁。透過窄加勁擋土牆(NGRS) ，可縮減現有擋土牆的體積，以便於在有限的空間內拓寬道路。根據美國聯邦公路總署的加勁擋土牆設計，加勁擋土牆的長寬比(L/H，牆寬 L 與牆高 H 之比)需小於0.7，需設置於既存穩固的牆前(或是有支撐的牆)。在牆頂的窄加勁擋土牆及既存擋土牆的交界處，常形成裂縫及溝槽，容易導致擋土牆破壞 (Yang et al. 2008b)。然而，目前仍未有對於避免既存擋土牆和窄加勁擋土牆之間的張力裂縫之形成的深入研究。本研究進行了一系列動態離心模型試驗，了解在基盤震動下，既存擋土牆與窄加勁擋土牆有無連結的動態反應。
本研究以17 cm高的NGRS牆模型，在60 g的離心力場中，模擬原型尺寸為10.2 m 高的 NGRS 牆，其長寬比為0.5，並使用聚酯材料和人造纖維布作為加勁材料，回填土為相對密度 70% 的矽砂。實驗結果顯示，NGRS牆與既存擋土牆若有連結，會使NGRS牆的正規化水平位移量 [(?x/H)/g] 從29.2%（未連接）減少到 5.1%（連接）；正規化沉陷量 [(?y/H)/g] 從 51.7%（未連接）下降到 12.8%（連接）。無連結的模型由於牆體變形導致不對稱加速度反應，牆頂向牆外加速度為向內加速度的 1.9 倍。由加速度反應結果得知，有連結牆受最大基盤加速度超過0.3 g的振動時，依然可有效的控制變形量，此外當振動的最大基盤加速度小於0.3 g時，有連結牆及無連結牆均可控制變形量。與Rankine主動土壓力的理論值相較之下，有連結的窄加勁擋土牆中，左牆（慣性力朝向牆內）的土壓力為理論值的3.23倍，右牆（慣性力朝向牆外）為1.79倍。在沒有連結的窄加勁擋土牆中，左牆為3.55倍，右牆為2.39倍。;Recently, increasing population and urbanization have led to increasing traffic demand. One solution to increase road capacity is to expand the existing roadways by constructing narrow geosynthetic-reinforced soil (NGRS) walls adjacent to previous stable walls. In the case where the space is limited, the construction of GRS walls has to be narrower than the conventional walls. The NGRS walls have an aspect ratio, L/H, (ratio of wall width, L, to wall height, H) less than 0.7 as suggested by FHWA Mechanically Stabilized Earth (MSE) wall design guidelines and placed in front of an existing stable wall (or shored wall). At the upper boundary zone between the reinforced soil and the stable wall, there easily forms a gap, crack, or even trench, triggering ultimate failure (Yang et al. 2008b). However, the interface connections to avoid tension cracks between the existing stable walls and NGRS walls are still not thoroughly investigated. Accordingly, series of dynamic centrifuge modeling tests are conducted to quantitatively investigate the dynamic response of NGRS walls with interface connection under base shaking excitation.
The wall model′s height was 17 cm and carried out under gravitational acceleration 60 g to simulate NGRS walls models with 10.2 m height in prototype scale. The wall models have 0.5 aspect ratio and use polyester and rayon geotextiles as the reinforcement material. The backfill material used in this study is silica sandy soil with 70% relative density. The results from this study indicated that interface connection has the most contribution to the deformation reduction. Connecting the reinforcement to the stable wall leads the independent normalized horizontal displacement [(?x/H)/g] decreases from 29.2% (unconnected) to be 5.1% (connected). The independent normalized settlement [(?y/H)/g] decreases from 51.7% (unconnected) to be 12.8% (connected). The narrow GRS wall without interface connection has a significant asymmetric acceleration response due to wall deformation. At the top walls, the outward acceleration response is about 1.9 times larger than the inward. Connecting the narrow GRS wall to the stable wall/slope can efficiently help control the wall deformation significantly in PBA > 0.3 g. Besides, the narrow GRS wall without interface connection still performs well in PBA < 0.3 g. Compared to Rankine′s active earth pressure, in the narrow GRS wall with interface connection to stable face, the left wall (inertia force moves to the inward of the wall) is 3.23 times larger and the right wall (inertia force moves to the outward of the wall) is 1.79 times larger. In the narrow GRS wall without interface connection, the left wall is 3.55 times larger and the right wall is 2.39 times larger. |
