Concrete structures such as buildings, bridges, roads, dams and tunnels are deteriorating. Cable tunnels are also deteriorating. For example, cracks and water leakages occur and these phenomena degrade the safety and serviceability of cable tunnel. If the deterioration is neglected, large-scale repair and reinforcement measures will probably be required, which will further increase the cost in the future. Therefore, it is highly recommended that a periodic inspection and timely maintenance be performed. Safety plans related to the maintenance of cable tunnels are discussed briefly in ITU-T Rec. L.11 (Joint use of tunnels by pipelines and telecommunication cables, and the standardization of underground duct plans). A model of a safety plan in the operational phase is presented in Tables A.1/L.11 and A.2/L.11, with an indication of possible preventive measures. These tables, however, do not describe defects that may occur frequently in reinforced concrete structures like cable tunnels, and the inspection procedures for maintenance. Therefore, recommendations concerning the maintenance of cable tunnels are needed.