Graduation of Simone de Roos

Crack Detection for Dikes using Distributed Temperature Sensing

• Professor of graduation: Prof. dr. ir. J. P. Aguilar-López

• Supervisor(s): Dr. L. A. Duarte Campos (TU Delft), Dr. ir. P. J. Vardon (TU Delft)
  
  The purpose of this research is to develop a desiccation crack detection method using distributed temperature sensing (DTS) data and, while doing this, to evaluate the output of an existing fiber optic sensor (FOS) cable on a cracked peat dike in Delft, The Netherlands. One-third of the Dutch dike system consists of peat dikes. Drought causes these dikes to crack and fail more easily. Visual dike inspections will therefore offer insufficient efficiency, especially considering the increasing climate changes of the future. Research has shown that a FOS cable can help measure soil thermal responses, but the question remains whether it is also suitable as a replacement for visual inspections of dikes. This study aims to answer this question by coupling a finite element method (FEM) model with measured DTS information. The measurement period was 20 summer days. The meteorological data was obtained via a weather station located in Rotterdam. The measured data consists of webcam images, thermal images, and temperature time series of a FOS cable. The FEM model, calibrated and validated with the measured data, helped to find the thermal response of the system in situations of which no data was available, for example various crack dimensions or cable positions. Crack detection via DTS turned out to be possible using a regression plot with the daily peak-to-peak amplitude of the air temperature on the one hand and the daily peak-to-peak amplitude of the cable on the other. With this plot a relation was found, making it possible to detect cracks using the differences in thermal response betweencracked and grass domains. However, due to a small data set and therefore a lack of knowledge on the most important conditions that influence the thermal response during winter, this method is only proven for sunny afternoons. On this basis, it is shown that the application of finding a relation between daily peak-to-peak amplitudes of air and cable temperature exists, but still more knowledge is required to further improve the method. Future studies have to map the thermal processes too, and check the model’s reliability with respect to reality even more. Additionally, larger and more varying data sets have to be used to make the method also robust for other situations.