Towards the non-destructive assessment of mechanical properties in roads and railways : new concepts and methodologies

Abstract

A proper maintenance of the transport infrastructure asset is a factor of paramount importance with dramatic macro-economic and safety implications. In this framework, the spreading of maintenance approaches based on the critical conditions of an infrastructure has determined a growing demand for nondestructive testing (NDT) methods for the non-intrusive assessment and the health monitoring of civil engineering infrastructures. Amongst the various NDTs available in the market, ground-penetrating radar (GPR) is a well-acknowledged electromagnetic tool capable to assess the geometric and physical properties of the subsurface. GPR systems equipped with air-coupled antennas and mounted on dedicated instrumented vehicles allow to investigate long distances with a very high productivity. This feature makes the system particularly suitable for transport asset monitoring purposes. This thesis focuses on the use of GPR and other NDTs for the assessment of the mechanical response of road pavements and track-beds for highway and railway engineering applications. In this regard, the main aim of the research is to provide new experimentalbased methodologies for the detection of decay areas within a transport infrastructure network. This is crucial to plan maintenance effectively and avoid potential growth of damage. In regard to the roads, a parametric model capable to assess the overall stiffness of flexible pavements is proposed. The model considers as input information the thickness of the base layer and the potential presence of clayey particles in the deeper layers. These information are assessed using GPR. The model is developed using ground-truth data collected by deflection-based NDT equipment for calibration purposes. With regard to the railways, a geometric and physical assessment of the ballast aggregates composing the railway track-bed is obtained by both time domain and frequency-based analyses of the data collected by air-launched GPR systems. The results achieved demonstrate the viability of the proposed methodologies for application purposes and inclusion in survey protocols as part of assessment programs for the maintenance of transport infrastructure assets.