不同加勁措施對於加勁路堤與基礎系統作為跨逆斷層減災工法之研究

Abstract

地震災害是臺灣常見災害之一，斷層錯動引致的地表變形破壞，對於眾多地表結構物造成嚴重損毀。1999年集集地震，車籠埔斷層帶鄰近地表與結構物，產生嚴重破裂及倒塌。儘管國內建築技術規則中訂定，鄰近活動斷層兩側不得進行建築開發，但有些線型公共工程，像是高速公路、隧道、橋樑等，無法避開通過斷層帶，本研究參考國道四號臺中環線豐原至潭子段，以加勁擋土牆作為公路路堤，跨越車籠埔斷層，並透過加勁路堤與基礎系統進行整體性考量評估，致力於減緩斷層錯動引致之災害。 本研究採用1/15物理縮尺模型試驗，探討加勁路堤與基礎系統抗逆斷層之效能。研究旨在藉由不同加勁措施評估加勁路堤與基礎系統之減災功效，同時比較傳統剛性RC路堤與柔性路堤抗逆斷層之表現。其中，加勁措施包括基礎型式、路堤型式、路堤加勁材鋪設長度與加勁層垂直間距。首先探討加勁路堤與基礎系統受逆斷層作用下，其減緩牆面前傾位移之效果，並評估路堤牆頂變形、斷層剪裂帶發展、力學機制與現象，最終提出加勁路堤與基礎系統抗逆斷層之最佳建議。 考量各項加勁措施的改善效果，鋪設蜂巢格網基礎與施作加勁路堤取代傳統剛性RC路堤的效果最佳，得以提升整體系統穩定性，分別減少約8.5-10%與7.5-9%的最大正規化牆面前傾位移；增長路堤加勁材鋪設長度依然有效，能減少約5%。蜂巢格網基礎提供土壤圍束力，增加土壤剪力強度。與平面加勁材不同，屬於三維加勁結構，本身具有彎矩勁度，能有效阻擋與消散斷層剪裂帶之發展。加勁路堤作為柔性結構，可以消散斷層剪裂帶，並且容許剪裂帶引致之地表差異沉陷。然而，縮短加勁層垂直間距，由於近牆頂的加勁材上方垂直覆土減少，導致近牆頂牆面前傾位移較大，導致效果並不顯著。因此本研究提出三項具有減災效益之加勁改善措施，分別是鋪設蜂巢格網、施作加勁路堤取代傳統剛性RC路堤與增長路堤加勁材鋪設長度。 研究結果顯示採用加勁路堤(加勁材鋪設長度增長)與蜂巢格網基礎系統最為有效，相較於傳統剛性RC路堤與未加勁基礎，能大幅減緩接近七成之最大正規化路堤牆面前傾位移，有效地降低逆斷層錯動引致之災害。亦即當未來地震來襲，採用本研究提出之加勁路堤與基礎系統得以於災害中倖免，儘管破壞可於災後迅速搶修恢復交通運輸之功能。

Earthquake disasters are one of the most common hazards in Taiwan. Surface deformations caused by fault movements lead to significant damage to numerous surface structures. During the 1999 Chi-Chi earthquake, severe ruptures and collapses occurred in the surface and structures near the Chelungpu fault. Despite regulations in Taiwan prohibiting construction near active fault zones, some linear public infrastructure, such as highways, tunnels, and bridges, cannot avoid crossing fault line. This study references the National Highway No. 4, using a geosynthetic-reinforced soil (GRS) wall as a highway embankment crossing the Chelungpu Fault. It evaluates the comprehensive performance of the GRS embankment and foundation systems in mitigating fault-induced hazards. This research conducts a series of scaled model experiments to explore the effectiveness of GRS embankment and foundation systems across reverse faults. The research aims to assess the disaster mitigation efficiency through various reinforcing measures, comparing the performance of rigid and flexible embankments. The reinforcing measures include foundation types, embankment types, the length of the reinforcement, and the vertical spacing of the reinforcement layers. Firstly, the study examines the effectiveness of GRS embankment and foundation systems in reducing normalized facing displacement subject to reverse fault. It evaluates the top deformation of the embankment, fault shear rupture development, mechanical mechanisms, and phenomena, ultimately proposing the best recommendations for GRS embankment and foundation systems against reverse faults. Considering the improvement effects of various reinforcing measures, the use of geocell foundation and the construction of a GRS embankment instead of a traditional RC embankment have the best results. These measures can enhance the overall system stability, reducing the maximum normalized facing displacement by approximately 8.5-10.0% and 7.5-9.0%, respectively. Extending the length of the reinforcement in the embankment remains effective, reducing displacement by about 5%. Geocells provide soil confinement, increasing soil shear strength. Unlike planar reinforcement materials, the Geocell foundation is a three-dimensional reinforcement structure with bending stiffness. The development of shear rupture is mostly intercepted by the Geocell. The GRS embankment, being a flexible structure, can diffuse fault shear rupture and accommodate differential settlements induced by shear rupture. However, reducing the vertical spacing of the reinforcement layers results in increased facing displacement of the wall near the top due to the decreased vertical overburden on the reinforcement material above. Hence, this effect is not significant. Therefore, this study proposes three reinforcing improvement measures: utilizing Geocell foundation, constructing GRS embankments instead of traditional RC embankments, and extending the length of the reinforcement layers in the embankment. The research results indicate that the use of GRS embankment with long reinforcement and Geocell foundation system is most effective. Compared to traditional RC embankment and unreinforced foundation system, they significantly reduce maximum normalized facing displacement by up to reduction of 70%, effectively mitigating disasters caused by reverse fault movements. Thus, during future earthquakes, utilizing the GRS embankment and foundation systems proposed in this study can help prevent disasters, allowing for rapid post-disaster repair and restoration of transportation functions.