Prediction of plastic zone size around circular tunnels in non-hydrostatic stress field

This paper discusses the calculation of plastic zone properties around circular tunnels to rock-masses that satisfy the Hoek–Brown failure criterion in non-hydrostatic condition, and reviews the calculation of plastic zone and displacement, and the basis of the convergence–confinement method in hydrostatic condition. A two-dimensional numerical simulation model was developed to gain understanding of the plastic zone shape. Plastic zone radius in any angles around the tunnel is analyzed and measured, using different values of overburden (four states) and stress ratio (nine states). Plastic zone radius equations were obtained from fitting curve to data which are dependent on the values of stress ratio, angle and plastic zone radius in hydrostatic condition. Finally validation of this equation indicate that results predict the real plastic zone radius appropriately.