Wiktionary
n. 1 One who works on the ground, as opposed to an aviator, etc. 2 Somebody employed to dig trenches, foundations, etc. in the ground.
Wikipedia
A groundworker is a British term for a subcontractor who is employed to prepare a home construction site for the shallow foundation of a new home.
Typically, the groundworker clears the site, lays a foundation, installs drainage and other pipework, and may build roads if necessary.
The groundworkers are usually the first and last trades performed on site. They will start the job putting in levels, digging the ground, excavating and concreting the foundations, and building the foundations until the floor is on and the work is up to the damp proof course (dpc).
They are also the team responsible for the drainage; connecting to the existing pipes installing in the new pipes.
At the end of a home build, groundworkers return to put in driveways and footpaths.
Groundworkers usually work on a labour, plant and material basis.