Performance of systematic fully grouted rockbolts and shotcreted layer in circular tunnel under the hydrostatic conditions using 3D finite difference approach

Fully grouted rockbolts with or without shotcrete layer are widely used in practice. Thus, studying their roles in decreasing induced tunnel strains is an important issue. In 2D analytical methods, a unit length of the tunnel along its longitudinal axis is considered. Therefore, the influence radius of a bolt, as well as the non-uniform strains in the longitudinal axis cannot be highlighted. FLAC3D software was used to determine these parameters. After verifying the conducted finite difference program, a parametric study was performed to study the rockbolts and the shotcrete layer roles on controlling the induced tunnel strains. The results indicate that in the very severe squeezing rock mass conditions, the ratio of the strains in the middle between two bolts to that of in the rockbolt head is slightly high. Also, the influence radius of a bolt is almost the same for the cases conducted in this research.