Underground facilities such as tunnels, maintenance holes and handholes are deteriorating continuously as time go by. For example, cracks and water leakages occur and these phenomena degrade the safety and serviceability of the underground facilities. If the deterioration is neglected, large-scale repair and reinforcement measures may be required, which will further increase the cost in the future. Therefore, it is highly recommended that periodic inspection and timely maintenance are performed. Safety management of telecommunication infrastructure facilities is generally described in ITU-T Recommendation L.330, but the detailed technologies and countermeasures for each facility are left for other Recommendations. This Recommendation describes the inspection procedures, technologies and countermeasures for maintenance of underground facilities defined in L.330.