CSIC 10th Anniversary Event: Research Talk 'Closing the loop: Back analysis of sprayed concrete tunnel junctions'

Title: 'Closing the loop: Back analysis of sprayed concrete tunnel junctions' – Dr Nicky de Battista and Dr Alun Thomas 

Abstract: In ground-breaking work by CSIC in 2014, two junctions in a large Sprayed Concrete Lined (SCL) tunnel were instrumented and monitored with distributed fibre optic sensors (DFOS) to observe the changes in strain in the lining during the construction of cross-passages. This was carried out at the Crossrail Liverpool Street Station (Queen Elizabeth Line) in London. SCL tunnels are challenging to design, especially the junctions, because of the complex material behaviour of the sprayed concrete and the ground, the multi-stage construction sequence and the lack of instrumentation data from previous tunnels.

The SCL monitoring data are now being used to compare the measured behaviour with the design predictions. While the general mode of deformation matched expectations, the detailed pattern of strains differed. This may reflect the differences in construction sequence; nonlinear constitutive behaviour of the concrete may explain the more localised strain pattern. Converting strains into stresses will permit an assessment of the overall factor of safety – a vital task when tunnelling in sensitive urban environments. Sophisticated 3D numerical modelling has been undertaken using the FLAC3D software. Initial results indicate a good match with some of the measured data. We are now exploring ways in which the analyses used for designing such tunnels can be improved. This work is being led by Dr Alun Thomas, who is an established authority in sprayed concrete design and a member of the original tunnel design team, and is currently a secondee at CSIC.

In this presentation, we will give an overview of the instrumentation and moitoring project carried out in 2014, and describe how the data are being used in combination with finite element modelling to gain a better understanding of SCL behaviour at tunnel junctions.

Event Code: CSIC 2406

Please contact Jemma Andrews (csic-admin@eng.cam.ac.uk) quoting the event code to register to attend this event. 

We hope you will join us to celebrate 10 years of CSIC at this special online event organised to mark the occasion.