Connecting e.g. telecommunications cable into inaccessible underground drainage line, involves using empty ducts pre-positioned along route to accommodate additional lines

摘要

At least one empty duct runs along, inside the drainage line. It is available, when required, to accommodate additional lines at any point along its length, and to carry them further. It includes openings enabling additional line(s) to enter or leave. After laying, the openings are re-sealed.