加勁擋土結構物光纖安全監測研發與應用

Abstract

加勁擋土結構物光纖安全監測研發與應用 土壤是一種具有壓縮強度與剪力阻抗，但是缺乏抗張強度的材料，所以若是能於土壤中放入高張 力強度的加勁材料，藉由土壤的自重與加勁材所提供的阻抗，使之成為一個具有優越力學性質的複合 材料，這即是所謂的加勁擋土結構物。加勁擋土結構物因為其具有造價較低廉、能配合植生美化、耐 久且能夠允許較大不均勻沉陷之優點，已大量使用於坡地擋土、路堤及水土保持等工程。加勁擋土結 構物的破壞可歸納為自然因素與人為因素二方面。自然因素包括降雨與地震，台灣地區因雨量豐沛且 分佈不均，使得土壤受沖刷、侵蝕與土壤內孔隙水壓上升等因素，導致土壤剪力強度降低而發生破壞。 因地震而產生之結構破壞主要集中於921 集集地震所導致者，相較於降雨所引發之破壞發生率低。人 為因素包括規畫分析設計不當、使用材料錯誤、施工程序與使用維護不當等。台灣地區現有數百座加 勁擋土結構物，但至今還未有一可長久且穩定的量測與安全監測方法。光纖光柵（Fiber Bragg Grating, FBG）柔軟細小，有不怕雷擊、不受電磁波干擾沒有受潮短路問題以及同一條光纖上可以安裝多個FBG 等優點，本計畫將使用光纖光柵做為感測元件，將光纖光柵與加勁材結合再一起成為光纖光柵加勁材 應變計，並將光纖光柵加勁材應變計與主持人過去所研發的光纖光柵水壓計、光纖光柵測傾儀一起於 現場進行測試安裝且進行即時監測，本計畫可以提昇現有加勁擋土結構物量測與安全監測的技術且量 測到的數據可提供未來加勁擋土結構物設計與分析之參考，相同的技術也可應用於水庫壩體、庫區或 道路邊坡、橋樑與河堤等安全監測上。

Development and application of optical fiber sensors for reinforced earth retaining structure safety monitoring Soil can resist compressive and shear stress, but lacks capability in withstanding tensile stress. A superior composite referred to as the reinforced earth is formed by embedding a reinforcing material with high tensile strength in soil, because of the combined effects of soil weight and tensile resistance offered by the reinforcing material. The reinforced earth is relatively low cost, can be beatified with vegetation, durable and capable of withstanding large differential settlement. It has been applied extensively in slope stabilization, embankment and soil conservation related projects. Generally, the failure of reinforced earth structure can be induced by natural and man-made causes. The natural causes can include rainfall and earthquake. The rainfall in Taiwan is heavy but non-uniformly distributed throughout the year. The high intensity rainfall often causes corrosion, surface erosion and development of excessive pore water pressure that weakens the soil and result in ground failure. The earthquake induced failures are mostly related to the Chi Chi earthquake, and significantly less frequent than rainfall related ground failures. Man-made causes can include inadequate design, false selection of materials, improper construction procedure and poor maintenance. Hundreds of reinforced earth structures have been built in Taiwan. Yet, there is still a lack of long-term, reliable means to monitor the safety of these structures. Optical fiber Bragg Grating, FBG has the advantages of being minute, immune to lightning, electromagnetic interference and short circuit, and capable of connecting multiple FBG’s using a single optical fiber. This project intends to use FBG as the main sensing unit, combine the FBG with reinforcing material and form an integrated strain transducer. These strain transducers along with the FBG ground displacement and pore pressure sensors developed earlier by the principle investigator, will be installed at a test embankment in the field for real-time monitoring. This research project can enhance our capabilities in monitoring the performance and safety of reinforced earth structures. Results from the study can be used as a reference for future reinforced earth structural designs. The same techniques can also be used for safety monitoring for reservoir dams, embankments, highway slopes and river levees.