TEMPERATURE MEASUREMENT IN A MASONRY DAM BY MEANS OF FIBREOPTICAL SENSORS

摘要

Gravity dams are stressed by two major loads. The first and most obvious type of load is water pressure according to the percentage of storage. The second type of load, which acts invisibly within the dam structure itself, causes deformations in almost the same quantity. Depending on the time of year, the temperature inside of the dam structure varies according to the water and air temperatures. This causes stress within the structure and deformation of the dam. Current equipment act as electronic temperature measuring instruments using temperature-dependent resistance which are placed in boreholes in the dam structure. These instruments allow temperature measurements in certain points. Opposite to conventional measuring techniques, fibre optic temperature measuring techniques using glass fibre cables enable localised measurements within a structure and at its surface along a line form. The measuring procedure is based on OTDR (optical time domain reflectometry), known from the optical communications technology.