Abstract
Major seismic events have shown that tunnels in cohesionless soils may suffer extensive seismic damage. Proper modelling can be of great importance for predicting and assessing their seismic performance. This paper investigates the effect of lining structural modelling on the seismic behaviour of horseshoe-shaped tunnels in sand, inspired from an actual Metro tunnel in Santiago, Chile. Three different approaches are comparatively assessed: elastic models consider sections that account for: (a) linear elastic lining assuming the geometric stiffness; (b) linear elastic lining matching the uncracked stiffness of reinforced concrete (RC); and (c) nonlinear RC section, accounting for stiffness degradation and ultimate capacity, based on moment-curvature relations. It is shown that lining structural modelling can have major implications on the predicted tunnel response, ranging from different values and distributions of the lining sectional forces, to differences in the predicted post-earthquake settlements, which can have implications on the seismic resilience of aboveground structures.
Highlights
Tunnels constitute critical underground infrastructure, vital for urban transportation and logistics, and for the economy of major urban conurbations
This paper examined the effect of the lining modelling on the seismic behaviour of horseshoe-shaped tunnels installed in sand or coarse-grained soil
Three different approaches were considered: (a) a Geometric Elastic Tunnel (GET) model that considers the geometric stiffness of the structural elements; (b) an Uncracked Elastic Tunnel (UET) that is linear elastic but considers the initial stiffness of the structural elements from their moment-curvature curves ( M ) to properly reflect the relative contributions of the concrete and steel reinforcement; and (c) a Nonlinear Tunnel (NT) that accounts for the stiffness degradation with curvature through direct input of the M curves for the lining
Summary
Tunnels constitute critical underground infrastructure, vital for urban transportation and logistics, and for the economy of major urban conurbations. Determination of their seismic response is challenging due to the large number of parameters affecting behaviour, including those associated with nonlinear soil response, soil–structure interface behaviour, and nonlinear structural response Their seismic performance is better than above-ground structures since inertia effects are not significant, with the main source of loading being of kinematic nature, stemming from the dynamic response of the surrounding soil, which can be carried efficiently by the tunnel acting as a pressure vessel ([1]-[6]). Aiming to bridge the apparent gap in the literature, this paper examines how the structural modelling approach used for the tunnel lining affects the predicted tunnel seismic response For this purpose, a non– circular (horseshoe shaped) tunnel in cohesionless soil, inspired from an actual sprayed-concrete tunnel in Santiago de Chile, is used as an illustrative example. The results reveal the importance of proper modelling of the tunnel lining, offering insights that can be useful for re-interpretation of previous numerical and physical model simulations where the GET idealisation has been employed
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