Structural design model for tunnels in soft soils: From construction stages to the long-term

In bored tunnel design, most recent structural design models for tunnel linings concentrate on the behaviour of the tunnel lining in the long-term. The load on the tunnel lining in these models is derived from the original soil stresses, often simplified for a single homogeneous layer. Field observations show that higher loads may occur in the initial hours after the assembly, that might effect the tunnel lining and that soil layers with different stiffnesses may have a negative impact on the internal forces of the tunnel lining. This paper proposes a new model for these early construction stages and also includes a more accurate model which explicitly models the impact of multilayered soils. The change of internal forces in the tunnel lining from the initial construction time to the long-term is investigated with this model. Validations with field observations and other analysis results at time of construction and the long-term confirm that the new structural analysis models can accurately predict internal forces in the tunnel lining. The analysis results also show that internal forces in the tunnel lining have an increasing trend in time and become stable in the long-term and accord with field observations.