Abstract

A system based on a PVC tube instrumented with optical fiber, connected to a Brillouin Optical Time Domain Reflectometer (BOTDR) apparatus, is proposed to monitor underground movement in tunnels from a long distance to the measured point. The tube sensors (TS) are attached to the rock mass at four points along the tube. It is expected that as the rock mass moves, the TS supports move relative to each other inducing axial strains along the TS that are recorded by the BOTDR. An iterative numerical algorithm (inverse model) is proposed to estimate the TS support displacements from the TS axial strains data using the linear theory of strength of materials. Experimental data are used to validate the estimated values of support displacements given by the proposed model and apply data field with success.