Development and Applications of a Pore Water Pressure Profile Monitoring Technology
|關鍵字:||光纖光柵;光纖光柵水壓計;孔隙水壓分佈;橋墩基礎沖刷;邊坡崩塌;應力路徑;Fiber Bragg grating;FBG piezometer;pore water pressure profile;bridge foundation scouring;landslide;stress path|
From soil mechanics point of view, under a constant total stress, the increase of pore water pressure causes reduction in effective stress and eventually soil failure. Practical problems that relate to this soil mechanics phenomenon can include rainfall induced landslides and bridge foundation scouring. The currently available technologies in field water level or pressure monitoring are difficult to apply for real-time automated measurements. Hence, even though theoretically, pore water pressure measurement can be an important parameter of a warning system in case of a potential landslide or bridge foundation scouring, it is rarely used in practice due to these deficiencies. Taking advantage of the optical fiber Bragg grating (FBG), this research developed the technology to install FBG piezometer array in the field for pore water pressure profile momnitoring. To verify its practicality, the author installed an FBG piezometer array as part of slope stability monitoring at Five Turn Point of Alishan. In this case, piezometers were spaced at 5m intervals in a single 60m borehole. Using similar techniques, FBG piezometer arrays were installed at three bridge sites along Tachia River. These installations included Pier 27 of Taiwan Highway 1 bridge, pier P27L (P30R) of National Highway No. 3 bridge and pier P5 of Tungshih bridge. Laboratory bridge model scouring tests were carried concurrent with the field installation to establish correlations between dynamic pore water pressure and scouring depth. The author developed a stress based warning method to predict the occurrence of a slope failure or bridge foundation scouring, based on real-time pore water pressure profile measurements from the field and the concept of stress path. The thesis describes the technology of FBG piezometer array, its development and cases of field applications in slope stability and bridge foundation scouring monitoring.
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