Tunneling in weak ground has been one of the challenges of engineering technology. Try and error was given valuable information to technicians. Generally temporary support and passing through dangerous and difficult zones is major purpose in designing and building structures in unstable conditions. Koohrang tunnel 3 in the area of Zar'ab fault has been a good example for testing engineering skills and available technology. Weak and faulty ground with high amount of overburden and tunnel existing under high pressure of water makes a condition that necessity of research study is clear before performing project. In this thesis has been tried by using new advances in computer science and recent softwares, to model Zar'ab fault and check efficiency of artificial ground freezing method that is comparatively new and less known. Simiulation of frosty ground condition require recognition of frozen soil and rock and changes during freezing. There are good laboratory facilities in some developed countries for sampling and exraction of geomechanical properties. By recording information in laboratory , weak and strongly unstable zone simulated in numerical model and step by step excavation accomplished. As for high overburden, ground improvement by freezing around of tunnel is not efficient and safe solely by merging steel liner and ground stabilization before excavation by this method, finally can reach to an specific state, in the beginning freezing pipes has been located around tunnel profile and after reching specified temperature by cooling, tunnel digging started in certain advance. There are a lot of variants in simulation of condition of ground and material that need sensitivity analysis and choosing optimum values for realization of conjugate influence. Compared variants were temperature of frozen material, resistance of steel liner, length of freezing pipes, length of support rings , excavation advances and support order that is a exploitation subject. The final state that is result of this analyses suggests -5 c? for freezing temperature, 12 meters for pipes length and support in advance of 1 meter in first 11 meters of tunnel, by purpose of reducing expenses and boosting progress. Specifications of steel liner that appliqued have been attached.