3D Monitoring in Tunnels, Ground-Support Interaction and its Implications with Emphasis on Tunnel T-74R of USBRL Project, India

Tunnel T-74R of USBRL Project is located at Jammu & Kashmir Himalaya, which is about 8.61 km long and is aligned almost South to North, traversing through the metamorphic rocks of the Ramsu Formation and Machal Formation. This tunnel lies in the Higher Himalayan tectonic belt, and is very close to Main Central Thrust or MCT. The design of the tunnel is based on NATM, which is an observational method of tunneling and deals with the fact that the surrounding ground becomes a load bearing structural component through activation of a ring-like body of supporting ground. Before excavation, the in-situ stresses were in equilibrium state, after excavation, the equilibrium state got disturbed. Therefore, initial primary support has been provided and continuous deformation monitoring by 3D monitoring points has been carried out. In this present study, the theoretical estimation of the deformation behavior of the implemented support system has also been done, which is then compared with the actual 3D monitoring data. The analytical model of the deformation involves the concepts of ground-support interaction. It has been observed that the actual deformations at different points are much higher than what has been estimated. This clearly indicates that the actual behavior of the rockmass might be different from what has been estimated by using geomechanical parameters of the rockmass. With 3D monitoring, proper ground assessment has been done in T74R and consequently the evaluation of design to tackle adversity has also been adopted. Therefore, 3D monitoring played a significant role on the evaluation of the actual behavior of the groundmass.