Constitutive Models and Determining Methods Effects on Application of Convergence–Confinement Method in Underground Excavation

Stress reduction factor (λ) is an important component in the two-dimensional (2D) analysis of tunnel using convergence–confinement method (CCM). So far, however, there has been little discussion about effective parameters on λ. The aim of this study was to evaluate what the effect of constitutive model and determining method of λ is on CCM application in circular tunnel in shallow depth. For this purpose, at first, a series of parametric studies were carried out in different circular tunnel radius and depth. Parameters calibration of each constitutive model was carried out by triaxial simulation using finite difference method (FLAC). The results showed significant impact of constitutive model on λ in tunnel walls. The effects of constitutive model on λ were reduced by increasing depth, radius and distance from tunnel face. Then a comparison of the 2D analysis using CCM to in situ monitoring data of Lyon–Vaise tunnel was carried out. To this aim, two different constitutive models (CJS2 and Mohr–Coulomb) and various determining method of λ (direct and indirect method) were used. The results represented that λ obtained via indirect method cause more precise results. CJS2 constitutive model enable the convergence–confinement method to more accurate prediction of tunnel behavior than Mohr–Coulomb.