The shaft (1) forms part of a drainage system and may be set in a roadway. The larger diameter portion of the shaft consists of interlocking rings (3) with the lowermost ring supported by a deep foundation (2). The top end of the larger diameter portion is closed by a structural lid (4) with a thickened rim (10) which rests on a foundation surrounding the top ring of the lower part. There is a tapered hole in the lid on which rings (5) forming a smaller diameter upper shaft are placed. A sealing lid is placed on the top ring of this upper shaft.
