Multi-Suite Monitoring of an Existing Cast Iron Tunnel Subjected to Tunnelling-induced Ground Movements

Abstract

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

Mechanical deformation mechanism and verification of sections at junctions of light and dark tunnel in a mountain area

“…With the improvement in environmental awareness, environmental problems associated with highway construction have attracted increasing attention. One such problem is the slope near highway tunnels [1][2][3]. With the traditional method, we often need to anchor the slope when we excavate it, but that would destroy the vegetation near the portal, the surrounding environment and the landscape.…”

“…Thus, the physical and mechanical parameters of the rock are unstable. (3) The construction process for the junction of light and dark tunnels includes many procedures, which creates a complex force transmission process. Then, due to insufficient systematic research on this structure, a modest lack of attention to the project may lead to a large deformation and even cracks [12].…”

Construction Technique of Long-Span Shallow-Buried Tunnel Considering the Optimal Sequence of Pilot-Tunnel Excavation

“…Due to the poor geological condition like fragile surrounding rock, the abundance of surface and ground water, the construction difficulty, and the high possibility of collapse, urban longspan tunnels are usually constructed by shallow subsurface excavation method [2], which includes the underground pilot-tunnel excavation and the supporting system and lining construction [3]. Aiming to the long-span shallow-buried tunnel, the main construction methods could be sorted as center diaphragm method (CDM), cross diaphragm method (CRDM), double side drift method (DSDM), and threebench method (TBM) [4][5][6].…”

The monitoring of an existing cast iron tunnel with distributed fibre optic sensing (DFOS)

“…The bolted rings could either respond as an intact and continuous unit where the bending mode deformation would be dominant or the segmental rings could behave discontinuously such that each ring displaces or shears vertically in relation to each other in the shearing mode deformation [1] as shown in Fig. 2.…”

“…With this in mind, several state-of-the-art instrumentation systems such as DFOS, wireless displacement and tilt sensors and photogrammetry were deployed [1]. This paper will only focus on the DFOS system although some monitoring results from the other instrumentation systems will be included for comparison.…”