Many operational tunnels worldwide experience progressive deformation due to hydraulic drainage failure, structural deterioration, ground rheological behaviour, and other factors. This study presents a three-dimensional finite element analysis of an ageing horseshoe-shaped tunnel at CERN (European Organization for Nuclear Research), excavated in molasse rock, to investigate the effects of tunnel lining hydraulic and mechanical deterioration, marl swelling, ground layering, and ground permeability anisotropy. Hydraulic deterioration, caused by drainage clogging, is modelled by reducing lining permeability, while mechanical deterioration is represented by decreasing the lining stiffness. Model validation is conducted by comparing simulated results with geodetic and distributed fibre optic sensing (DFOS) data at a representative tunnel section. Parametric studies are then performed to assess the effects of ground layering and permeability anisotropy. Results show that: (1) hydraulic deterioration leads to vertical elongation, mechanical deterioration to tunnel contraction, and their combination to more severe deformation; (2) marl swelling is the dominant mechanism, with deterioration effects being secondary; (3) inclined tunnel alignment through stratified ground induces varying deformation modes due to geological heterogeneity; and (4) permeability anisotropy accelerates groundwater pressure buildup, amplifying vertical elongation. These findings highlight the complex interplay of deterioration and geological factors in ageing tunnels and demonstrate the need for 3D hydromechanical modelling to support long-term performance assessment and maintenance.
Xiao et al. (Sun,) studied this question.