The following Thesis focusses on the definition of the technical specifications of a diagnostic platform based on Ground Penetrating Radar (alternatively known as georadar or GPR) methodology to be integrated within a Tunnel Boring Machine (TBM) to determine the distribution of the injected backfill grouting behind shield tunnel concrete lining and recognise potential unevenly filled areas occurring beyond them. Within this context, the primary objective of the study is the definition of the optimal GPR system configuration, in terms of antenna polarisation and operating frequency, so that the tunnel stratigraphy can be properly delineated and the thickness variations accurately identified. In particular, the Rocchetta Tunnel (Benevento, IT) stratigraphy consists of a concrete segment characterised by a double-matted steel rebar cage and a variable grid array, while the filling material is a two-component grout or pea gravel, within which the system is expected to be able to determine the eventual presence of a cavity. The first phase of the work included an extensive experimental campaign aimed at verifying which antenna frequency and polarisation could achieve the required penetration and resolution performance in such an unfavourable propagation environment. To replicate the expected tunnel conditions, a number of GPR profiles have been collected on an equivalent pre-cast concrete segment supported by a wooden frame structure specifically designed to elevate the segment from the ground, and create two sealed compartments that simulate the presence of a void, either water-filled or air-filled, within the grout layer. The obtained GPR profiles have provided the basis for determining the optimal GPR system design and for assessing potential limitations of its application. Following this activity, the survey setting has been numerically modelled through a finite difference time domain software (gprMax), from which it was possible not only to validate the obtained GPR profiles and to aid their interpretation, but also to examine whether the considered configuration will continue to be as effective as it has been in this specific situation even in case of changing grouting conditions. Therefore, an additional modelling activity has been carried out simulating a different grout moisture content, so that the suggested system design can be evaluated from a more general perspective, at the same time refining its definition.
Il seguente elaborato si concentra sulla definizione delle specifiche tecniche di un sistema di diagnostica basato sulla metodologia Ground Penetrating Radar (noto come georadar o GPR) da integrare all’interno di una Tunnel Boring Machine (TBM) per determinare la distribuzione del grouting di riempimento iniettato dietro il rivestimento in calcestruzzo del tunnel e per riconoscere potenziali aree riempite non uniformemente che prendono forma dietro i conci. In questo contesto, l'obiettivo primario dello studio è la definizione della configurazione ottimale del sistema GPR, in termini di polarizzazione dell'antenna e frequenza operativa, con la quale si possa definire adeguatamente la stratigrafia del tunnel e identificare con precisione le variazioni di spessore. In particolare, la Galleria Rocchetta (Benevento, IT) è costituita da un strato di calcestruzzo all’interno del quale è presente un doppio strato di armatura con inter-distanza tra i ferri variabile, mentre il materiale di riempimento è un grouting bicomponente o pea gravel, all'interno del quale è previsto che il sistema possa determinare l'eventuale presenza di una cavità. La prima fase del lavoro comprende un'ampia campagna sperimentale volta a verificare quale frequenza e polarizzazione dell'antenna possa ottenere le prestazioni di penetrazione e risoluzione richieste in un ambiente di propagazione così sfavorevole. Per replicare le condizioni previste nel tunnel, sono stati raccolti una serie di profili GPR su una piastra di calcestruzzo prefabbricato che replica un concio prefabbricato, supportato da una struttura a telaio in legno appositamente progettato per sollevare il segmento da terra e creare due compartimenti sigillati che simulano la presenza di vuoti, riempiti d'acqua o d'aria, all'interno dello strato di grouting. I profili GPR ottenuti hanno fornito la base per determinare la progettazione ottimale del sistema GPR e per valutare i potenziali limiti della sua applicazione. A seguito di questa attività, l’indagine è stata modellata numericamente attraverso un software nel dominio del tempo alle differenze finite (gprMax), dal quale è stato possibile non solo validare i profili GPR ottenuti e aiutarne l'interpretazione, ma anche esaminare se la configurazione considerata continuerà ad essere efficace come lo è stata in questa specifica situazione anche in caso di mutevoli condizioni di riempimento dell’intercapedine. È stata quindi svolta un'ulteriore attività di modellazione simulando un diverso contenuto di acqua nel grouting, in modo da poter valutare il progetto del sistema suggerito da una prospettiva più generale, affinando nel contempo la sua definizione.
Diagnostica georadar per la verifica della posa di grouting in galleria
Galli, Roberto
2019/2020
Abstract
The following Thesis focusses on the definition of the technical specifications of a diagnostic platform based on Ground Penetrating Radar (alternatively known as georadar or GPR) methodology to be integrated within a Tunnel Boring Machine (TBM) to determine the distribution of the injected backfill grouting behind shield tunnel concrete lining and recognise potential unevenly filled areas occurring beyond them. Within this context, the primary objective of the study is the definition of the optimal GPR system configuration, in terms of antenna polarisation and operating frequency, so that the tunnel stratigraphy can be properly delineated and the thickness variations accurately identified. In particular, the Rocchetta Tunnel (Benevento, IT) stratigraphy consists of a concrete segment characterised by a double-matted steel rebar cage and a variable grid array, while the filling material is a two-component grout or pea gravel, within which the system is expected to be able to determine the eventual presence of a cavity. The first phase of the work included an extensive experimental campaign aimed at verifying which antenna frequency and polarisation could achieve the required penetration and resolution performance in such an unfavourable propagation environment. To replicate the expected tunnel conditions, a number of GPR profiles have been collected on an equivalent pre-cast concrete segment supported by a wooden frame structure specifically designed to elevate the segment from the ground, and create two sealed compartments that simulate the presence of a void, either water-filled or air-filled, within the grout layer. The obtained GPR profiles have provided the basis for determining the optimal GPR system design and for assessing potential limitations of its application. Following this activity, the survey setting has been numerically modelled through a finite difference time domain software (gprMax), from which it was possible not only to validate the obtained GPR profiles and to aid their interpretation, but also to examine whether the considered configuration will continue to be as effective as it has been in this specific situation even in case of changing grouting conditions. Therefore, an additional modelling activity has been carried out simulating a different grout moisture content, so that the suggested system design can be evaluated from a more general perspective, at the same time refining its definition.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/173504