Fiber optic instrumentation of concrete foundations

Fiber optic instrumentation of concrete foundations allowing the support of new generation electrical pillars.

Presentation of the Eiffage-RTE project

Client: Eiffage

Location: Between Avelin and Gavrelle, North of France

Objectives and stakes of the project:

As part of the reconstruction of the 400,000-volt line between Avelin and Gavrelle, Cementys instrumented the concrete foundations of the electrical pillars. To date, 4 of the 9 pillars have been instrumented.

Cementys concrete RTE Eiffage auscultation fibre optique pylones massifs béton

Cementys’ solutions :

In order to carry this out, our engineers have placed fiber optic sensors on the massif’s reinforcement level, on which the electrical pillars will be placed. The fiber is embedded into the concrete and allows to measure the temperature within a few hours. The goal when monitoring the massif is to avoid any risk of concrete cracks.

This requires continuous monitoring of the concrete temperature immediately after concreting the slabs. Raman effect allows to carry out this monitoring with the different optical loops present in the massif. If the concrete exceeds a certain temperature, the risk of cracking will be higher and the integrity of the structure would be at risk. Therefore, we can understand the interest in this type of monitoring. We can visualize the structure’s evolution over time but also prevent issues by observing the massif as soon as the concrete is set.

 

The second set of fiber optic loops is also placed in the concrete blocks in order to monitor the deformations in the long run thanks to the Brillouin effect.

Cementys’ solution is a fibrooptical monitoring, a method that is very suitable for this type of structure.

Installation of the optical fibers :

First of all, here is a plan corresponding to the different positions of the optical fibers.

We see here the presence of 3 different optical loops, the green one allows to monitor the upper part of the sole. The loop shown in blue corresponds to the lower part of the sole. And the red fiber passes inside the barrel to observe the central part of the massif.

Let us now observe a view from above to see the distribution of these fibers. Here is the representative diagram :

Projet RTE Eifage Cementys

The entire massif is equipped with our optical fibers, both along the entire perimeter and in height.

First results obtained :

Now it is interesting to analyze the results of temperature measurements inside massifs.

For greater clarity, we have drawn 3D curves to visualize temperature evolutions over time along the length of the fiber.

We can clearly see in this figure the moments where the concrete’s temperature is higher (red parts) and out of the concrete which corresponds to the blue parts.