According to manuals on countermeasures against deformed tunnels, the cracks of secondary lining around the crown, are induced by uneven pressure and immersion of legs of supports. To investigate the cause of these cracks, questionnaires were gathered on the situation of the lining with cracks. Subsequently, it is found that the cracks tend to occur in sections near tunnel entrances employing no reinforcement, and constructed in cold season. A thermal stress analysis was also performed considering of support loads and measurement results on concrete stress. The result showed that it is possible for thermal stress and drying shrinkage to produce the cracks.
