headwall

English

Etymology

From head +‎ wall.

Noun

headwall (plural headwalls)

1. (geography) The highest cliff of a glacial cirque.
2. (geology) The steep cliff at the back of a cirque.
3. (civil engineering) A retaining wall at the outlet of a drain, culvert or tunnel.
   • 1950 September, “Central London Railway Jubilee”, in Railway Magazine, page 622:

     The platforms of all stations from Shepherds Bush to Liverpool Street have been lengthened from 325 ft. to 427 ft. between tunnel headwalls, to take longer trains.

   • 2020 August 12, “Network News: HS2 tunnel portal readied for TBMs”, in Rail, page 10:

     HS2 Ltd has built a 17-metre-high headwall and reinforced the ground at what will become the south portal of the ten-mile Chiltern Tunnel, as part of preparations for the arrival next year of tunnel boring machines (TBMs).

References

• “headwall”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022.