Spatial characterization of joint planes and stability analysis of tunnel blocks

• Digital photogrammetry technique was adopted to reproduce deterministic joints.
• Monte-Carlo simulation of stochastic joints was carried out.
• The stability of rock blocks were analyzed based on limit equilibrium theory.
• The stability of tunnel structure was evaluated in terms of the factor of safety.
• The failure process display can be animated by GeoSMA-3D.

It has been gaining credence over the past several decades that the spatial characteristics of rock joints exert detrimental effect on the stability of tunnel structures. The deterministic joint spatial distribution around the tunnel was defined by digital photogrammetry technique, which statistically provides the basis for performing Monte-Carlo simulation of stochastic joints that are hidden inside the surrounding rock. The blocks generated by the intersection between structural planes and excavation surfaces were analyzed based on the block theory and limit equilibrium. The keyblocks were identified and the corresponding factors of safety were determined. All these analysis procedures were codified into the computer program GeoSMA-3D (Geotechnical Structure and Model Analysis). The developed software satisfied the fast analysis requirements of joint plane simulation, spatial block modelling, keyblock identification and failure process illustration. The case study was performed with reference to Dabeigou Tunnel on Duolun Second-class Highway in Duolun Town, Nei Mongol, China. Failure process illustration would be useful to facilitate the practical engineers to understand the basic mechanism and select the strengthening strategies.