ABSTRACT:  Support system design has always been a critical engineering problem for large-scale tunnels excavated withinfault zones. In fault zones, it is possible to encounter face and ceiling stability problems encountered during thetunnel excavation in the short term and failures in the support systems due to squeezing in the long term. For thisreason, when designing support systems, short-term and long-term parameters should be considered. The mostimportant factors in selecting the support system to be installed are to describe the geological conditions well andthe correct selection of geotechnical design parameters. Therefore, the main purpose of this study is to investigate  the support design that considers the short- and long-term parameters for the Ankara-Istanbul High Speed TrainProject, T36 tunnel excavated within the fault zone. The total length of the T36 tunnel is 4100 m, and excavation andsupport works have been completed under a maximum overburden thickness of 180 m. In the fault zone transition,the supports were made under the overburden thickness of 115 m, and face stability problems were encountered inthe short term and squeezing problems in the tunnel in the long term. In this study, the causes of deformations in thetunnel affecting the tunnel in the short and long term are discussed and numerical analysis and support systems areexamined. Moreover, the criteria for fault zone crossings, which is one of the most important issues for tunneling,are discussed.