The effects of moisture changes in deep, active clay subgrades are reflected in the general deformation of roads which can develop and in the bumps which arise at pipe culverts in parts of South Africa. A deformation of 0.4 in. over 20 ft. is often found on sections of road about five years after new construction, and this constitutes an engineering problem if high standards are to be maintained for fast travel. The records of movement, obtained from several field sites during about seven years of precise level observations, are reviewed and the results are given of laboratory tests on a typical clay, residual from the weathering of Ecca Shale. The prediction of heave is mentioned and examples are given of the effects of change in the level of the water table, or of change in the thickness of cover. Remedial measures suggested for reducing the deformation include lime stabilization of the top layer of an active clay subgrade, additional cover thickness, and pre-wetting, not only of culvert sites, but also of the road formation by "fallowing" before construction in order to conserve moisture from rainfall. One of the most outstanding remaining problems appears to be the prediction of the rate of heave under various conditions, having in mind the diffusion of moisture through partially saturated and fissured material. /Author/

  • Corporate Authors:

    Commonwealth Scientific & Industrial Research Org

    314 Albert Street
    East Melbourne, Victoria,   Australia 
  • Authors:
    • Williams, AAB
  • Publication Date: 1965

Media Info

  • Features: Figures; References; Tables;
  • Pagination: p. 143-155

Subject/Index Terms

Filing Info

  • Accession Number: 00263863
  • Record Type: Publication
  • Report/Paper Numbers: TA7109 A82
  • Files: TRIS
  • Created Date: Jan 29 1975 12:00AM