A Numerical Study on the Effect of Mechanical Precutting and Fiber Glass Bolts in Alborz Tunnel Passing Through Kandovan Fault

Summary: One of the most important problems during the tunnel construction in weak grounds with difficult condition is providing efficient support and prevent from failures and deformations in tunnel crown and face. In order to regulate the rigidity of the advance core and to thereby create the appropriate conditions for complete control of the deformation response of the grounds with poor mechanical ground and therefore, in the final analysis, for complete stabilization of the tunnel in the long and short term the use of pre-confinement methods is unavoidable. In this study the application of some pre-confinement methods for stabilizing the Alborz tunnel passing the Kandovan fault was investigated by means of numerical modeling. It was concluded that a combination of mechanical precutting and fiber glass face bolts could effectively improve the stability of the tunnel along the weak fault.
Ground improvement techniques in order to overcome difficulties of excavation of tunnels in the past decade has grown considerably and the use of them is consistent with development in technology. Increasing advances in electronics and mechanical engineering has led to the ability of excavate a tunnel under complicated Geological structure and to have confidence in a safe and affordable condition. In order to regulate the rigidity of the advance core and to thereby create the right conditions for complete control of the deformation response of the grounds with poor mechanical ground and therefore, in the final analysis, for complete stabilization of the tunnel in the long and short term the use of pre-confinement methods is unavoidable.
Methodology and Approaches: The finite difference based numerical modeling tool FLAC3𝐷 was used in this study to model the process of the Alborz tunnel passing through the Kandovan fault. Mechanical precutting as one of the effective pre-confinement methods is simulated in this study. Furthermore, the effect of fiber glass bolts on the tunnel stability has been investigated independently and in combination with mechanical precutting method.
Results and Based on the results of this study, the mechanical precutting in combination with fiber glass face bolts can successfully reduce the plastic zones around the tunnel and its face, resulting is a more stable ground for tunneling. Therefore the combination of precutting and fiber glass face bolts was recommended for pre-confinement of Alborz tunnel passing through the Kandovan fault.