Possibilities of composite distributed fibre optic 3Dsensor on the example of footing pulled out from the ground: a case study

Distributed fibre optic sensing (DFOS) provides breakthrough possibilities in the field of structural health monitoring (SHM) in comparison to conventional spot measurements. It allows the measurements to be registered over the entire measuring length, not only in one point of the structure. That is why this technology is becoming more and more attractive for geotechnics and civil engineering applications, providing both technical and economic benefits. However, to utilize all advantages of distributed sensing it is necessary to apply appropriate sensors, which will be able to accurately reflect the real structural behaviour. This paper discusses in situ application of unique (patented) composite DFOS displacements sensors (3DSensors), which were embedded into the ground layers and compacted around the footing. The research was conducted to observe the potential slip plane generated during the vertical pulling of the footing out of the ground. Distributed measurements were performed to obtain vertical displacement profiles around the footing within the selected ground layers with a spatial resolution of 1 cm. Finally, special visualization of ground deformation in 3D space was performed to analyze in detail the physical changes between the footing and the surrounding ground. No other techniques are currently able to obtain such information, as their application inside the ground layers would disturb its behaviour. The operational rules of displacement DFOS sensor, way of installation, course of the study as well as the exemplary results are discussed hereafter.