Influence of short-distance multi-line overlapped shield tunnelling on deformation of existing tunnels

Considering the complicated project of four-line overlapped tunnels in Shanghai metro construction, in which Metro Line 11 below-shield and above-shield crosses the existing Metro Line 4 successively, numerical modelling and in-situ monitoring are employed to study the influence of shield tunnelling on the deformation of the existing tunnels. According to the distribution law of earth pressure around the existing tunnels, the shield operation parameters are set to change with the advance of the EPB shield machine. Particular attention is paid to the effect of the chamber earth pressure and grouting pressure on the deformation of the existing tunnels during the below-shield tunnelling as well as the loading scope and its value during the above-shield tunnelling. The results show that the settlement of the existing tunnels stays at the same level as the chamber earth pressure ratio increases, while it increases with the decrease of the grouting pressure ratio. Construction measures, which follow the principle of synchronous loading in the new tunnel mainly and loading in the existing tunnel secondarily, should be taken to control the heave and partial uplift of the existing tunnels during the above-shield tunnelling.