Two dimensional analysis are carried out to provide new findings on the Twin Tunnel wall thickness optimization. It finds the wall thickness of tunnel openings which is prepared at varying width between twin tunnel in the modelling Phase-II software. The analysis is based on residual and peak parameters of rock mass properties. The overburden depth, extraction ratio and factor of safety are considered for model analysis. It focuses on Elasto-Plastic rock masses with non-linear failure criteria and non-associated flow laws. The rock properties are assigned in residual and peak values in Mohrs...