Characterization of the masonry lining of an underground structure by geoendoscopy

Abstract Maintenance and sustainability of underground structures are the major tasks for infrastructure owners. To carry out these tasks, managers need to qualify the actual state of these facilities. There are very few operational methods to describe separately each component of an underground structure (structure lining, contact interface and surrounding soil). Therefore, most usual diagnosis methods are qualitative and focus the surveying operations on the tunnel intrados. In consequence, they collect limited quality information for maintenance decision. This article focuses on a new methodology for diagnosis of the lining status of an underground structure in order to obtain a mechanical characterization of materials. The methodology is based on an analysis of low diameter drillings on tunnel lining using geoendoscopy and automatic image recording. Then an automatic image processing, is applied on the recorded images in order to locate discontinuities and evaluate the tunnel lining condition. A definition of lining layers were adopted thanks to discontinuities rate criteria. In parallel, a comparative study of the mechanical parameters of old masonry materials by laboratory test cores’ samples was carried out Finally, based on the result of the geoendoscopy analysis and on the laboratory study the methodology establishes a link between the local state of the lining and the mechanical parameters of materials. The application of this methodology to carry out an evaluation of masonry lining of the Paris Metro System shows that the proposed method and tools are particularly well adapted to obtain masonry lining characterization at the local scale. It has been possible to identify each discontinuity leading to a grade of masonry alteration. Using this information it was possible to define a simplified model of lining by sectioning the masonry thickness on three homogenized layers with different mechanical properties.