Retrofit of Fibre Optics for Permanent Monitoring of Leakage and Detection of Internal Erosion

The experience of the last 20 years has shown the great advantage of the use of fibre optics for the efficient monitoring of dams. More than 100 large dams have been equipped during construction or major refurbishment. But old existing dams have been excluded until now from the use of this valuable technique.

In 2014 GTC developed a new fibre optic cable with optimized fibres which could be inserted into small diameter tubes. The fibres in these cables form an internal loop, allowing light to travel in both directions in the same cable. The well-established GTC's temperature sounding method is used to install high grade steel probes into the earth fill dam along its axis, and down into the foundation if required. The new cables are inserted and connecting cables form a “light pass” from one end of the dam to the other. Thereby a two-dimensional view of the temperature distribution within the dam is obtained which can be monitored remotely and in real time.

In 2015 three dams were equipped with this new technique, two in England and one in France; all three are monitored permanently. The cables have been installed to a maximum depth of 30 m and a crest length of 430 m. At one site the recorded data shows the successful sealing of a leak in the dam by a new slurry trench cut-off wall.

The new technique is described, the installation process is shown and results from permanent monitoring are demonstrated.