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underground or underwater structures (underground tanks B65D88/76; hydraulic engineering, e.g. sealings or joints, E02B; underground garages E04H6/00; underground air-raid shelters E04H9/12; burial vaults E04H13/00); Retaining walls > Manhole shafts; Other inspection or access chambers; Accessories therefor (for underground tanks B65D90/10; for sewerage E03F5/02 )