Evaluation and analysis methods for key elements affecting tunnel behavior : spatial variability, shotcrete bonding state, pre-reinforcement

Abstract

The stability of a tunnel is affected by principal elements such as inherently heterogeneous ground, primary, and auxiliary supports, and seepage forces induced by groundwater. The effects of such principal elements are more significant as the tunnel scale increases. Thus, effective evaluation and analysis methods of these influential factors are required for reliable design, safe construction, and effective operation of tunnels. This dissertation focuses on the evaluation and analysis methods of the principal elements that affect tunnel behavior. The spatial variability of tunnel design parameters, such as geotechnical and structural properties, has a large effect on the behavior of tunnels both during and after construction, including long-term response. Interestingly, the uncertainty and spatial variation of design parameters increases with the scale of the tunnel. In order to design large, and structurally stable, tunnels, the design framework must include a quantitative investigation of design parameter variation. Literature surveys on statistical characteristics of rock have been carried out and the impacts of inherent spatial variability of geoproperties represented by COV (coefficient of variance) and correlation length on tunnels were analyzed using Monte Carlo simulation with finite difference modeling. A truncated non-Gaussian random field function is developed to aid in the simulation of the logical and effective correlated random field. Simulated random field elements are explicit in the numerical models. Strength parameters in Mohr-Coulomb and Hoek-Brown models and stiffness parameters (i.e., elastic modulus) are considered as random variables. Numerical results, normalized by deterministic cases, indicate that the tunnel excavation induced deformation increases with the variation and correlation lengths of geotechnical design parameters. Effects of heterogeneous elastic moduli on the variation of the elastic-plastic interface and the failure me...