Assessing the Performance of Masonry Railway Viaducts in the UK by Detecting Hidden Defects and Geometric Features =Structural Engineering

Masonry railway viaducts in the UK have at large exceeded the modern-day design life of 120 years, for which they were not designed for. More importantly, it must be highlighted that masonry arches were designed (largely) from empirical methods such as Molesworth's formula (small arches) and the 18th century revolutionary method developed by Perronet for multi-span structures (Robinson and Kapoor, 2009). As such, the verification of structural capability for modern day use is a major challenge, particularly considering the lack of as-built information for these structures, changes in loading, poor records of maintenance repairs and challenges with assessing the impact of various defects on structural performance.
The key to assessing the structural capability and residual life of masonry railway viaducts begins with verification of the geometric features and defects, including hidden defects. The collection of such data can be a timely process, with numerous access restrictions. This is exacerbated by the occupancy of arches within railway viaducts, which are known as 'tenanted arches'. Network Rail currently have 10425 tenanted arches across their portfolio, many of which include cladding panels, preventing direct visibility of the soffit and piers of arches. In order to view these defects, examiners must arrange access with tenants, remove cladding panels (usually fixed with anchors) then fix the panels back on. It is important to note that the arches were not designed for these cladding fixtures and loads, as well as lighting fixtures and other services suspended from the arch soffit. Many of these arches include shafts, which have been capped or plugged with concrete, which adds another complexity to the global behaviour of the structure.
In order to reduce the risk to the operational railway and to the tenants within these structures, there is a need to improve the methods to obtain asset condition data and model the structural behaviour more accurately with the data collected. Non-Destructive Testing (NDT) methods can aid this process and prevent the need to remove cladding panels and also to verify geometric features at track level, via the use of NDT tools on Unmanned Aerial Systems (UAS). This will provide additional benefits such as cost savings for maintenance, improved compliance with safety standards, better relationships with tenants and a more accurate understanding of the residual service life of the structures. The significance of this issue was highlighted when Network Rail released a challenge statement to the public to address the challenges they currently face.
The main aim of this study is to determine the viability of using NDT/NDE techniques on Masonry Railway Viaducts in the UK, and to utilise the data captured to improve the capability assessment of the viaducts. The focus of the study will be to capture hidden defects within tenanted arches, where the arch soffit is covered with cladding panels, as well as geometric features (distortions, voids, discontinuities, ring separation etc.) at track level, by deploying UAS equipped with various NDT/NDE equipment. Mohammed Al-SHarif am currently sitting on the Steering Panel for a CIRIA project, on behalf of Network Rail, to develop a best practice guidance document for NDE of Civil Structures. The outcome of this CIRIA project will support the PhD study and enable knowledge transfer between academia and industry.