The behaviour of existing cast iron tunnels subjected to ground movements induced by new tunnelling works, is a much discussed topic. In many cases, new tunnels in highly populated urban cities like London will need to be constructed underneath a dense network of existing tunnels to avoid them. The construction of new tunnels, however, inevitably results in ground deformations that are transmitted to adjacent existing structures. The response of existing cast iron tunnels to tunnelling-induced deformation is not well understood and practicing engineers are faced with significant uncertainties about their response. This paper presents a case study in which multiple monitoring technologies have been deployed in a section at an existing cast iron tunnel in London underneath which a new, much larger tunnel is being constructed. The new tunnel is being excavated parallel with, and directly below the existing tunnel for a length of approximately 100 m. Instrumentation technologies deployed in a 40 m long section within the 100 m zone include analogue linear displacement transducers, fibre optics, digital tilt sensors, Video Extensometry and Digital Image Correlation, laser scanning and photogrammetry. The multi-technology deployments in this case study are presented in a unified dashboard system specifically developed for this project and provide an ideal scenario to investigate the detailed cast iron tunnel response using independent data sets. They also provide an exceptional opportunity, within the dashboard system, to use these data sets to understand the capabilities of the associated technologies when compared and contrasted against each other. The dashboard system can provide practicing engineers with the ability to understand tunnels' response accurately and rapidly and hence potentially provide significant time and cost savings for complex infrastructure projects. 293Tunneling and Underground Construction GSP 242

A new photogrammetric system has been developed to monitor tunnel deformations with high precision. The system fundamentally applies digital image correlation techniques to process images. It is digital in nature and is compatible with the industry's vision of moving towards the smart and digital monitoring of existing assets. It has been installed successfully within the London Underground railway and a number of other tunnels to demonstrate the potential of remote deformation monitoring of such assets using off-the-shelf cameras. The system is able to measure deformations with precisions higher than 0·1 mm, enabling the monitoring of sensitive deformations such as imposed curvatures. This paper highlights the application of photogrammetric systems in monitoring the deformation and condition of assets in real time and highlights the advantages that such systems bring. A case study has been chosen to demonstrate these. The case study is the monitoring of an escalator barrel in Moorgate station in London that was influenced by a sprayed-concrete-lining excavation directly underneath for the new Elizabeth line.

Displacements imposed upon existing cast-iron tunnel linings attributed to new underground construction often cause changes in their alignment. The rate of change in alignment, or curvature, is a key parameter in assessing the impact of displacement. Owing to the installation limitations and the precision deficiency of conventional monitoring systems, measuring such curvature deformations, especially locally, has been a challenging task. In this paper, the curvature measurement data of the following two case studies are presented: (a) Crossrail's Liverpool Street station construction affecting the Northern Line (NL) tunnels, and (b) the Bond Street station upgrade project affecting the Royal Mail tunnel (RMT). Both new tunnels ran perpendicular to the existing cast-iron tunnels. They experienced substantial longitudinal curvatures, but the damage was limited. The NL tunnels were monitored using conventional electrolevel-beams for minimum chord lengths of 5 m, while the curvature of the RMT was monitored for chords as short as 2 m using a new photogrammetric monitoring system, called Sattar image tracking. The new system offers a high-precision measurement enabling such lengths of local measurements. This paper describes how curvatures are measured and proposes methods that need to be followed to evaluate the accuracy of curvature measurements.

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