To monitor deformation in a road tunnel in service, periodical inspections are performed and countermeasures are taken as needed. Cracking of the permanent lining and heaving of the road surface often occur, however, so it is difficult to assess the development of such deformation features from data acquired during the construction and service stages. In this paper, the deformation mechanism and the effect of countermeasures are discussed based on the results of in situ measurements over a six-year period and of numerical analysis. The relationship between tunnel deformation and the occurrence of defects is examined using boring data. The mechanism of tunnel deformation when the characteristics of the ground indicates a swelling condition, and the relationship between the load acting on tunnel lining and the behaviour of countermeasures are also mentioned.