Behaviour of cast-iron bolted tunnels and their modelling

The behaviour of cast-iron bolted tunnels in London underground railway network was investigated using the 3-D finite element (FE) method. A series of numerical simulations on a cast-iron segmental ring were conducted and its performance was compared against the analytical assessment used by London Underground Limited (LUL). Unlike the 2D plane model used in the LUL standard, the proposed FE model considered the 3D lining structural features (i.e. the geometry of the tunnel segment and the bolted joint) in a detailed manner. The behaviour of a cast-iron tunnel primarily goes through three stages: tunnel construction, soil loading and structural deterioration. At each stage, the influences on the tunnel behaviour such as external loading, soil-tunnel interaction were examined. Considering that, the proposed model thus resulted in more realistically structural performance in agreement with the field measurements.