Analysis of a simple displacement sensor based on BOTDR optical fiber

A monitoring system based on a PVC tube instrumented with optical fiber connected to a Brillouin Optical Time Domain Reflectometer (BOTDR) apparatus is studied to estimate slope movement. A series of displacement tests were performed on 4 and 5m long PVC tubes with 40 and 25 mm diameter using optical fiber along their external surfaces. The PVC tubes are subjected to controlled displacements on 4 contact points of the PVC to replicate the possible response of soil mass during slope failure or displacement. The response of this system is described through measurements of axial displacements on the PVC tube using BOTDR optical fiber, strain gages and theoretical estimates based on strength of materials formulae. The experimental findings indicate that the use of optical fiber is adequate to obtain the axial deformation of the tube and to estimate the displacements at the contact points (back-analysis).