Technical Studies


Development and Testing of a Distributive Ground Subsidence

Optical fiber sensors have the advantages of being small, light-weight, immune to short circuit or electromagnetic interference, durable, good for long distance data transmission (over 10km) and multiple sensors can be connected on a single optical fiber. This project intends to make use of these advantages, develop an optical fiber Bragg grating (FBG) extensometer that is capable of monitoring ground subsidence. When coupled with FBG piezometers, the integrated sensor system can be deployed to monitor pore-water and ground subsidence profile simultaneously, in a single borehole. An observation well has been established at Guon-Fu elementary school, in Hu-Wei Township of Yun-Lin County, where the developed sensor system was installed and soil samples taken for physical property tests. The field installation was completed in the end of April, 2012. The FBG sensor readings have been taken on a monthly basis. A continuous 24 hour reading sequence was taken for the analysis of daily variations of pore-water pressure and ground subsidence profiles. This report describes the development of FBG sensor systems, procedure for field sensor installation according to experiences gained in this project, and discusses the effectiveness of the integrated FBG sensor system.