在直埋光缆施工中,有时光缆需从铁路、公路乡间大道等下方通过,目前,一般采用顶管(钢管)或预埋钢管(或硬塑管),在钢管(或硬塑管)内穿入塑料子管以保护光缆。子管数量一般为3根(3色),备用1根或2根,以便日后施工及维护用。在实际施工中选择什么规格(内径)的钢管(或硬塑管)才合适呢?也就是说钢管(硬塑管)与子管两者管径之间比例如何?如钢管(硬 In the construction of buried optical cable, sometimes the optical cable needs to pass below the railway, highway country road, etc. At present, generally, pipe jacking (steel pipe) or embedded steel pipe (or hard plastic pipe) Plastic tube to protect the cable. The number of sub-pipe is generally 3 (3 colors), spare 1 or 2 for future construction and maintenance purposes. What kind of pipe (or plastic pipe) to choose in actual construction is suitable? That is, the ratio between the pipe (hard plastic pipe) and the sub-pipe diameter, such as steel pipe