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Measuring vertical strains and temperature with fiber optics in diaphragm walls.

The Geotechnics Division of the Flemish Government uses fiber optics in civil constructions to measure strains and temperature during construction. In the summer of 2016 the construction of a tunnel under an existing road started. In a first phase diaphragm walls were constructed. Those walls will keep the tunnel open during excavation and will function as the future walls of the tunnel. For safety reasons the deformation and stability of these walls are closely monitored. During construction of the diaphragm walls, fiber optics were attached to the reinforcement cage. The fiber optics runs on both sides along the complete depth of the wall. This emplacement allows to monitor the vertical strain and temperature changes during the different construction phases. An inclinometer tube is placed in the diaphragm wall in the vicinity of the fiber optics. This allows the researchers of the Geotechnics Division and the KU Leuven Technology Campus Ostend to closely monitor both the forces in the wall and the horizontal displacement of the wall. When these exceed the allowable limits, corrective actions can be undertaken. This paper presents both the practical aspects of installation and some preliminary results.