Challenges in design of a large tunnel in soft ground Kumar Rakesh UV Global Consult., Noida, India Online published on 14 April, 2023. Abstract Many hydroelectric, transportation, rail and metro rail projects are under construction in India. The underground structures for these projects especially tunnels and caverns are mostly constructed on/in rocks/soils. The-presence of joints, shear zones and shear seams significantly effect the rock/soil behaviour under loading and-unloading conditions. The shear zones and heavy seepage conditions pose challenging conditions for engineers-and shall be handled in systematic manner. The paper presents the analysis of a transport tunnel of more than 11.9 m diameter in a poor & challenging geological conditions (soft ground) for a project, located in Himalayan zone in Northern India. Since the area lies-in highly geologically disturbed zone with active faults/shear zones in the near vicinity, hence to decide upon the support system and to check its adequacy was real challenge. The soil cover is 35 m above the tunnel crown. The horizontal stress ratio of 0.54 is calculated using Jacky’s formula. The stress conditions were anisotropic. The stress-deformation analysis has been carried out using RS 2 software using Mohr Coulomb model. The excavation has been simulated in three stages for the tunnel i.e. heading, benching and invert excavation. The analysis has been carried out, to decide upon the optimal support system for the tunnel. Based on the stress-deformation analysis and analyzing the stress behavior, deformation characteristics and-plastic zones around the tunnel, the optimal support system is decided and implemented at site. The support-measures in terms of shotcrete with wiremesh/SFRS, lattice girders and grouting are adopted. Top Keywords Tunnelling, Soft ground, FEM, Stress-Deformation. Top |