also: どうどう
noun
service tunnel; utility tunnel
Technical term for an underground tunnel housing utility lines such as cables, gas pipes, or water mains. Primarily used in civil engineering and infrastructure contexts.
この洞道には高圧ケーブルが敷設されている。
High-voltage cables are laid in this service tunnel.
ガス管を洞道内に収容する計画だ。
There is a plan to house gas pipes inside the utility tunnel.
共同溝 is a broader term for a common utility conduit that may house multiple utilities together, while 洞道 specifically refers to a tunnel-like structure for service lines.
Compound of 洞 (tunnel, cave) and 道 (path, road). The reading とうどう is the standard on'yomi combination; どうどう is a less common variant reading.