The prediction of settlements above tunnels in soft ground is of major importance for both existing surface and subsurface structures. The settlement above single tunnel constructions can be predicted with acceptable accuracy using relatively simple empirical techniques based on the Gaussian curve equation. However, it has been shown by various authors that the settlement trough observed above a second tunnel construction in close proximity to the first tunnel is not well predicted by these techniques. The maximum settlement above the second tunnel is offset towards the first tunnel and the side of the trough closest to the first tunnel exhibits greater relative movements than those on the side of the trough furthest from the first tunnel. This paper outlines research being conducted by the authors to improve empirical predictions by using key findings from simple 2D finite element analyses. A method is proposed that allows the settlements above twin tunnels to be predicted. The method incorporates the fact that the maximum relative increase in settlement occurs above the centreline of the first tunnel driven in twin side by side tunnel problems.
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