Deformation analyses and plastic zone expansion in the tunnel Isfahan Golab 2 rock mass by convergence-confinement and numerical methods

In this study, analytical Duncan-Fama (DFM) and numerical finite difference (FDM) methods based on convergence-confinement (CCM) procedure was used to deformation analyses, stress field and plastic zone expansion estimation for rock mass of tunnel Golab 2 which simulated by RocSupport and FLAC2D softwares. The CCM approach utilizes ground response curves (GRC), longitudinal deformation profile (LDP), and support characteristic curves (SCC) to evaluate tunnel wall displacements. The simulation is implemented for the most critical tunnel zones (zones 2 and 10 out of 15 zones) which generally consisting of shale with sandstone and siltstone geological units. These zones have variable features and highly tectonised. The geotechnical investigation results are shown that these zones (especially zone 10) have lowest strength mechanical parameters which main focus of this study is on these zones. Based on the analytical and numerical models were obtained for the 4 classes by CCM (GRC-SCC) curves for these intervals, it is found that these zones are under internal pressure about 7.56 and 4.18 MPa, respectively. Also, produce a plastic zone of about 2.85 and 2.88 meters. As results implementing maintenance structure with a permitted 10 mm displacement can reduce the plastic zone to 2.43 and 2.30 meters in the studied zones as well as provided structural stability in 15 mm. In conditional simulation, although the numerical method rather than analytical method is more falls and followed greater rigidity support system, but the CCM process is better suited to environmental conditions. On the other hand, by studying LDP-based behavioral diagrams, the estimated displacement is approximately the same for the short-term, mid-term, and long-term intervals. As evaluating the in-situ stress field for zones 2 and 10, it was found that the stress field variations in zone 10 was sudden but zone 2 was followed by continuous deformation changes.