Back-analysis of sprayed concrete lined (SCL) tunnel junctions at Liverpool Street Crossrail station

Sprayed concrete linings (SCL) offer a versatile method of tunnel construction, particularly in regard to forming junctions since the lining acts as a shell structure which can redistribute the stresses around the opening efficiently. This process is easy to understand conceptually but it is much more difficult to illustrate in calculations. Conventional calculation methods make a number of far-reaching simplifications such as the assumption of linear elastic behaviour in the lining. This often leads to overly conservative designs and a residual concern over the loads in the lining. This study compares detailed measurements of strains recorded by distributed fibre optic sensors at a pair of junctions on the Crossrail project in London with a sophisticated numerical model of these tunnels. Having demonstrated that the results of the numerical model are broadly consistent with this unique set of field data, a variety of influences on the model have been examined. This includes the excavation sequence, the constitutive model for the lining and adjacent structures. The results indicate significant scope for the improvement of SCL junction design. Future papers will present the more results from other parts of this study along with their implications for the design of tunnel junctions.