Novel fiber optic transducers embedded into concrete mass applied to the New Alto Ceira dam

Abstract

The New Alto Ceira Dam is a concrete arch dam, 41 m high and 133 m long at the crest, located in the middle region of Portugal. Its objective is the replacement of the existing dam located about 200 m upstream, which is highly deteriorated due to swelling phenomena. The dam is actually under construction and its monitoring safety plan is in accordance with the Portuguese Safety Regulations on Dams. The instrumentation embedded into the concrete is based on traditional electrical devices developed several decades ago and with proved durability characteristics. Considering the recent improvements in fiber optic based instruments for structural monitoring, benefiting of multiplexing technique, great reliability and accuracy, it was decided, in an experimental frame, to develop and to install in the New Alto Ceira Dam a set of fiber optic devices. Assuming the instruments embedded into the concrete mass as those exposed to the most aggressiveness of the construction methodologies, strain meters, thermometers and joint meters were selected to the development and implementation of fiber Bragg grating based transducers in order to appraise their performance, reliability, and installation requirements. After laboratory testing and validation, a limited number of these type of transducers were installed in the New Alto Ceira Dam. In this paper, the results from calibration tests are presented, and then a comparison of performance between new fiber optic sensors and the traditional electric sensors is made under controlled conditions, in laboratory. Some preliminary results of the experimental monitoring of the dam are also illustrated.