CONCEPT OF FIBRE OPTICS GEOTECHNICAL DEFORMATION MONITORING AND IN-SITU DEPLOYMENT IN OPEN CAST MINE

The paper presents a concept of Fiber Bragg Grating sensors (FBG) and Brillouin Optical Time Domain Reflectometry (BOTDR) application for deformation monitoring on a side slope of an open cast mine. The fiber optics measurement techniques, instruments of our own construction and methods of instrumentations developed within two past research projects were used in-situ. Different means of geotechnical instrumentation for subsoil deformation monitoring were installed in a former opencast-mine in the Czech Republic in order to test our instrumentations and to gather information about the mine slope behavior. The first type is the sub-surface monitoring of the potentially unstable area and the second one is performed in boreholes to determine a slip surface location and to describe deformation development in time. The instrumentations were done both with fiber optics and geotechnical deformation measurement tools, so that the results can be cross-checked. FBG sub-surface extensometer for shallow slope movement monitoring, FBG borehole instrumentation with FBG chains in GFRP protective sleeve for axial deformation measurements and BOTDA borehole instrumentation for subsoil deformation measurement are described and discussed. Deployment and critical points of fiber optics deformation sensing as well as advantages and disadvantages are indicated and evaluated.