The problem of constructing a 30 km highway in South Africa in an area of black and red clay having a high degree of potential expansiveness, has been overcome by irrigating the clay. The method is based on the theory that by increasing and maintaining the degree of saturation at 90 per cent, highway construction could proceed giving a road surface devoid of cracks and undulations caused by swelling of the clay. In order to maintain the saturation level a system of membrane seals and a double bitumen surface are used to make it virtually impossible for the saturated inner section to drain or evaporate. During construction a 150 MM gravel filter layer is compacted after irrigation of the subsoil through a system of pipes and sprinklers. After the saturation point has been obtained at a depth of 800 mm, the sprinklers are removed and the filter layer covered by A 300 MM compactive layer. The water is sealed in the clay by a tar membrane placed over each lane and then finished off by another 150 mm layer of fill and a final tar membrane. The roadway is then ready for normal fill. /TRRL/

  • Corporate Authors:

    Pithead Press Proprietary Limited

    4th Floor, Wynrop House, 91 Mooi Street
    Johannesburg,   South Africa 
  • Publication Date: 1975-11


  • English

Media Info

Subject/Index Terms

Filing Info

  • Accession Number: 00142763
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • Report/Paper Numbers: Analytic
  • Files: ITRD, TRIS
  • Created Date: Jul 19 1977 12:00AM