GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 3.2 ___ GNGTS 2023 Gpr Methodology For Testing Correct Construction Of A Tunnel: Verify The Concrete Cover Depth On The Precast Segments D. Di Massa, P. Luiso, L. Partipilo, D. Fiore Socotec Italia srl Introduction Checking the lining of a new built tunnel is a process of great importance and it is convenient to start this process before the works’ conclusion to be able to remedy the work progress in the least invasive way possible. Static testing is important to verify that all the works have been carried out in accordance with the contract and project scheme. Verifying the static conformity of the structural works guarantees the right safety level for the entire useful life of the building. In any case, static testing is an "obligatory step", without which the work cannot be delivered to the customer. At the same time, it is a guarantee for the client who can be sure of the work carried out by the construction company. The GPR methodology is often used to detect the presence of voids and cavities behind concrete tunnel linings (Harseno et al. 2022; Lalagüe et al., 2016 and references therein), the presence and shape of fractures and general defects (Li et al., 2021; Feng et al. 2018; Parkinson et al. 2008) and areas characterized by moisture (Garrido et al., 2020; Hugenschmidt et al., 2008; Koyan et al., 2018). More specifically, we show the importance of a correct use of GPR aimed to testing the correct implementation of a tunnel in North Italy (BZ). In general, tunnel construction is carried out using two types of methodologies: the traditional excavation and the mechanized using TBM (Tunnel Boring Machine). The choice of the advancement method depends on various factors such as the length of the excavated section, the type of rock and the construction times (Pizzarotti 2019). TBM excavates the rock, remove the excavated material and secure the excavation by laying prefabricated segments. The segments are a precast element in structural concrete with which rings are made for lining hydraulic, railway and road tunnels. In this work, we use the GPR method to check the concrete cover over rebars through a very detailed analysis. According to project scheme, the concrete cover over rebars has to be deeper than 35 mm from segments’ surface. The analysis is conducted over n°1060 precast segments through a series of steps described below.