ABSTRACT
The design and construction of railway tunnels in the Himalayan geology is always a challenging task as the cross-sections of the tunnels are larger, have long lengths, high overburden, and complex geology along the tunnel alignment. The design complexities increased manifold during the planning and design of tunnels as the track center between two tracks of a double-track railway tunnel needed to be increased from 5.9m to 25m in tunnel no 8 of the Rishikesh – Karanprayag railway line leading to a huge width clearance requirement. This paper illustrates the various options explored to finalize the tunnel layouts, cross-section requirements, and the design philosophy of temporary support systems adopted for the finalized layouts considering the three major objectives of high safety, less cost, and less excavation time. Due to the 3-dimensional nature of the problem, the study was made using 3D as well as 2D numerical approaches to understand the ground behavior and the support adequacy of the recommended design support system in line with the construction sequence.
