Numerical Modelling of Double-O-Tube Tunnelling in Stiff Clays

A preliminary numerical investigation of the effects in terms of tunnelling-induced ground movements in short- and long-term due to the construction of a Double-O-Tube tunnel in London clay beneath Hyde Park is presented. The model is calibrated against oedometer and undrained triaxial tests on intact samples of London Clay using a kinematic hardening soil model (named M2-SKH). The adoption of this advanced constitutive model is justified through the simulation of some drained and undrained triaxial tests on normal-consolidated and over-consolidated samples. The results are compared to a recent analysis of the excavation of the new Crossrail twin tunnels, which provides excellent predictions of the measurements obtained with the available field monitoring data. The influence of the permeability of the lining significantly affects the short- and long-term predictions. The use of this technique not only allows a more efficient use of the underground space and a reduction in construction time, but also limits the negative effects due to the interaction between twin tunnels. The extension of the surface area affected by vertical settlements is very similar to that obtained by excavating the twin tunnels, but the values are slightly smaller. These encouraging results show that DOT shield tunnelling technology can be convenient compared to traditional techniques even when applied in stiff heavily overconsolidated clays.