|M.Sc Student||Dromy Idan|
|Subject||Monitoring Tunneling Induced Ground Displacements Using|
Distributed Fiber-Optic Sensing
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Assaf Klar|
|Professor Raphael Linker|
|Full Thesis text - in Hebrew|
Determination and monitoring of tunneling induced ground displacement is an important component in tunneling design and construction. Since many design processes are based on greenfield input, it is of interest to monitor these displacements in the field to ensure that the tunnel excavation process lies within the design bounds. In recent years several interesting technologies for distributed strain measurement along fiber optics have been developed, namely the Brillouin Optical Time Domain Reflectometry (or Analysis) and the Rayleigh backscatter wavelength interferometry (OBR). The current work focuses on empirical 2D and 3D ground displacement models, with the aim of evaluating their input parameters using fiber optics field measurements. It is suggested that by monitoring a horizontally laid optical fiber, at a shallow depth above the tunnel, significant information could be derived through an appropriate 2D and 3D optimization and signal analysis. The approach is demonstrated through four field investigations:  excavation of a 3 m diameter tunnel by TBM at depth of 18 m.  excavation of a 1 m diameter tunnel by pipe-jacking at depth of 6 m.  excavation of a 1 m diameter tunnel by pipe-jacking at depth of 10 m.  excavation of a 1 m diameter tunnel by pipe-jacking at depth of 15 m. It was found that reliable and meaningful signals could be obtained by the approach, even with imperfect fiber installation and exposure to environmental disturbances (e.g. rain, vehicle movement, etc). Comparison between the different technologies (at two field investigations) demonstrated an excellent agreement, and proved that both technologies could be used in the above approach. An interesting observation, supported by the analytical models, is that non-perpendicular alignment of the fiber relatively to the tunnel line, results in a shift in the peak strain location. It was demonstrated that the rate of change in peak strain location, with tunnel advancement, can be used to obtain the trough length, without the need for complete evaluation of all other model parameters.