APPLICATION OF FIBRE-OPTICS SYSTEMS IN EMBANKMENT DAMS FOR TEMPERATURE, STRAIN AND PRESSURE MEASUREMENTS - SOME COMPARISONS AND EXPERIENCES

摘要

The rapid development of fibre-optic systems within the last decade has further increased its applicability for dam monitoring. The number of parameters that can be measured has increased, as well as the monitoring performance. A first test installation for temperature measurements was made at the Loevoen embankment dam. Two optical fibres were installed for research purposes in the dam for a Distributed Temperature Sensor (DTS) system. Measurements were made between 11 November 1998 and 15 February 1999 within a research project. Three monitoring sections were also established for long term monitoring of pressure and temperature. The result between the two temperature monitoring systems could then be compared. The DTS measurements were successful but not as accurate as expected. The relative accuracy was excellent (below 0.2°C) but the absolute temperature was 2.5°C higher than real temperatures, measured by the temperature sensors in the piezometers. However, the results provide valuable information about the seepage in the repaired part of the dam and adjacent part of the old dam. The development of fiber-optic system for other parameters such as strain and pressure is promising. The installation made in summer 1999 at Saedva will be used to test strain measurements. A system for pressure measurements in embankment dams is not yet installed. Combined information from conventional pressure and temperature sensors has, however, been valuable, because it provides a better understanding of the seepage in the dam or in the foundation. A distributed fiber optic system that can measure pressure, strain and temperature, seems therefore to be appropriate for general monitoring problems in embankment dams. Some systems are already available and future developments will further improve accuracy and, hopefully, also decrease the cost of the systems.