Applicability of the principle of superposition in estimating ground surface settlement of twin- and quadruple-tube tunnels

Prediction of tunneling-induced ground surface settlement is important to underground constructions in the densely populated city because excessive settlement could trigger potential damage to existing structures. This paper examined the interaction of multi-tube tunnels on ground surface settlement and the methods of prediction for the transverse ground surface settlement profile induced by the closure and grouting of tail void of shield machine of multi-tube tunnels in the CH221 Contract of the Taipei Rapid Transit System. The transverse ground surface settlements of a twin- and a quadruple-tube tunnels at two sections of this contract were back analyzed using the empirical equation that assumed the settlement profile over a tunnel to be a Gaussian distribution curve, and the finite element analysis. The applicability of the principle of superposition in the analysis and the characteristics of the ground surface settlement for a green-field land (previously undeveloped land) and a brown-field site (previously developed site) was also studied using the finite element analysis. The results showed that the ground surface settlement profile of multi-tube tunnel could be conveniently and reliably estimated using the empirical equation together with the principle of superposition. Extra effort required in the model set-up and result interpretation caused the numerical method to be outperformed by the empirical method.

► Surface settlement of twin- and quadruple-tube tunnels was modeled via Peck’s formula and finite element analysis (FEA).
► Applicability of principle of superposition has been validated; it can be applied to Peck’s formula but not the FEA.
► FEA overestimated field data – the more the existing tunnels the larger the simulated settlement it was.
► Because the model ground where the latter tunnel was to be constructed has already been subjected to some shear strain.