Modeling the degradation of old subway galleries using a continuum approach

• Underground structures are affected by time-dependent degradation of their tunnel lining.
• A numerical procedure is used to model long-term mechanical behavior of degraded tunnels.
• A strain softening model is used to consider the decrease in material cohesion.
• The numerical model shows how strain and stress evolve over time.

The underground transit system of the Paris metro was built in the early 20th century. Many tunnels and galleries of this underground system were constructed with old masonry whose properties have changed with time and increasing use, and its strength may have deteriorated under the impact of several weathering factors. Therefore, research has been initiated to diagnose structural deterioration of the tunnels and galleries used by the Paris metro system. This paper outlines the current state of the metro galleries in which cracks have developed in the tunnel lining caused by degradation of the abutment materials. The initial state of the stresses applied to the structure immediately after the construction is also analyzed through a double comparison (analytical–numerical and numerical 2D–3D). Then the damage of the galleries is modeled by taking into account the effect of the tunnel linings’ reduced strength. By means of an equivalent homogeneous model and a strain-softening approach, deformations associated with crack appearance can be located. The numerical results show that the state of different components of the underground structure during the lifetime of the galleries can be assessed.