half-built

From half- +‎ built.

half-built (not comparable)

1. Only partially built; not finished or completed.
   • 2012, Andrew Martin, Underground Overground: A passenger's history of the Tube, Profile Books, →ISBN, page 122:

     In 1901 the Great Northern cancelled its agreement with the backers of the Big Tube, by which time the latter was half-built, and its big tunnels looked like a grandiose folly, since it would now not be allowed running rights into Finsbury Park main-line station.

   • 2021 June 30, Tim Dunn, “How we made... Secrets of the London Underground”, in RAIL, number 934, page 49:

     North End station under Hampstead Heath was a half-built station that later became a Cold War bunker.

• half-finished