Abstarct: Growth of urban population, increase in traffic jam and global warming emissions have led the transportation experts to design and construct large span tunnels in complex geotechnical conditions. In the meantime, the selection of tunnel excavation method on account of its effect on the tunnel stability on the one hand and the cost, allocation of the resources, and project scheduling on the other hand are of vital significance. Since large-span tunnels are excavated in several stages, the development of the knowledge in relation to the sequential excavation method, and evaluation of their stability are of vital significance. One of the most important issues in the excavation of tunnels with large sections is how to determine the excavation stages which has a huge effect on the construction costs of the project. In addition, evaluation of the stability of such tunnels during the excavation phase is considered as an important challenge in tunneling. Because it is known from the experiences of a number of unstable tunnels that changing the excavation method without changing the supporting system has led to its stability. This shows that the two matters of excavation method and stability are closely interrelated. Although within the last two decades efforts have been made to provide stability criteria taking into consideration the excavation method, three important constraints remain: (1) The criteria are mainly baxsed on the laboratory test results, and their application in the rock mass faces with questions. (2) The criteria presented are mainly stress-baxsed with complex behavioral assumptions (3) have been developed for rocks with specific mechanical behaviors. In this thesis, the critical strain and failure strain values of the samples have initially been determined by conducting uniaxial compression strength tests on different samples of rock and soil in different degrees of water content. Then, the Sakurai criterion was developed having had some modifications. Given that this criterion provides a high conservative margin in porous and weak rocks, the criterion of stability was developed baxsed on the failure strain. Two reasons including being baxsed on the intact rock data on the one hand, and the establishment of a relation between the rock mass strain and the geotechnical parameters on in-situ basis on the other, necessitated the establishment of another relation. In this regard, by use of the monitoring results of several tunnels in Iran, the relation between the failure strains of the rock mass and intact rock was determined, and then a relation was developed as the failure strain of the rock mass - strength factor. A multi-graph was also proposed for selection the sequential excavation method and then verified by various projects using two relations defined for the failure strain criterion in laboratory and in-situ conditions, and applying the concepts of the Yu and Chen model. The verification results indicate the high accuracy of the proposed model in determining the tunnel excavation method.