The NeTTUN project: Design of a GPR antenna for a TBM

The NeTTUN (New Technologies for Tunnelling and Underground Works) Project involves a consortium of 23 industrial, research & development laboratories and small and medium enterprise organizations across 9 countries in Europe; the ultimate goal is to enable groundbreaking change in the construction and maintenance of tunnels. Most existing ground prediction methods require the stopping of excavation work for several hours, which relegates them to a once per week activity. This generally far exceeds the available nominal idle time required for the construction of a ring in a segmental lined tunnel. NeTTUN aims to develop a fully automated system, that when installed on a tunnel boring machine (TBM), provides identification of large obstacles that can obstruct digging (e.g. other tunnels, cavities, boulders, foundations, archaeological remains, etc.) as well as soil changes (e.g. from gravel to fractured rock). Current methods for predicting geological variations mainly exploit seismic sources and receivers, deployed during pauses in drilling. In contrast, NeTTUN proposes the combined use of a seismic system and a ground prediction radar. The design has to fulfil two conflicting requirements of a large inspection operating range (which requires low frequency sensors) and detection of rock fractures that can be just a few centimeters in length (requiring high frequency sensors), while also dealing with the main issue of the interaction between the metallic TBM cutter head and the sensors.