Advertisement

Examples of landslides associated with the Natal Group and pietermaritzburg formation in the greater Durban area of Natal, South Africa

  • Bell F. G. 
  • Maud R. R. 
Article

Abstract

If the incidence of landslides in the greater Durban area is related to geological formation, then most landslides have been associated with the shales of the Pietermaritzburg Formation. However, in the last eight years, most landslides have been associated with the Natal Group Sandstone and occurred during the very heavy rains of September, 1987, and March, 1988. In fact, prior to 1987 the Natal Group Sandstone was considered relatively stable. On the other hand, many areas in the greater Durban area underlain by shale have long been regarded as unsuitable for development as they were considered potentially unstable. Two types of instability occur on these formations, that is, sliding blocks of rock along bedding planes, and sliding of the weathered and colluvial soil material on top of bedrock. Illustrations of both types of slides on both formations are presented.

Keywords

Sandstone Shale Pore Water Pressure Slip Surface Bedding Plane 

Exemples de glissements de terrain associés au “Groupe du Natal” et à la “formation de pietermaritzburg” dans la région du grand Durban, Natal, Afrique du Sud

Résumé

Si l'on veut relier les glissements de terrain du Grand Durban à une formation géologique, alors on peut dire que la plupart ont été associés aux schistes argileux de la Formation de Pietermaritzburg. Cependant, au cours des huit dernières années, la plupart des glissements ont été associés au grès du groupe du Natal et se sont produits au cours des très fortes pluies de Septembre 1987 et Mars 1988. En fait, avant 1987, ce grès était considéré comme relativement stable. D'autre part, de nombreuses zones du Grand Durban reposant sur des schistes argileux ont été longtemps considérés comme impropres au développement, en raison de leur instabilité potentielle. Deux types d'instabilité se produisent dans ces formations, le premier correspondant qu glissement de blocs rocheux le long de plans de stratification, le second au glissement des sols colluviaux et d'altération situés au sommet du substratum. Des exemples des deux types de glissements dans les deux formations sont présentés dans l'article.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. BELL F.G. (1994): Floods and landslides in Natal and notaly the greater Durban region, September 1987: a retrospective view. Bulletin Association Engineering Geologists, Vol. 31, pp. 59–74.Google Scholar
  2. KNIGHT K., EVERITT P.R. and SUGDEN M.B., 1977: Stability of shale slopes in the Natal Coastal Belt. Proceedings Fifth Southeast Asian Conference on Soil Engineering, Bangkok, pp. 201–212.Google Scholar
  3. MAUD R.R., 1988: The geotechnical effects of the recent Natal floods. In Proceedings Conference on Floods in Perspective, Council for Scientific and Industrial Research, Pretoria, Paper 3.3. 11 p.Google Scholar
  4. MAURENBRECHER P.M. and BOOTH A.R., 1975: Some slope stability problems in soils derived from the Ecca Shales of Natal, South Africa. Engineering Geology, Vol. 9, pp. 99–121.CrossRefGoogle Scholar
  5. OLIVIER M., BELL F.G. and JERMY C.A., 1994: The effect of rainfall on slope failure, with examples from the greater Durban area. Proceedings Seventh Congress International Association Engineering Geology, Lisbon, A.A. Balkema, Rotterdam, Vol. 3, pp. 1629–1636.Google Scholar
  6. PREMCHITT J., BRAND E.D. and PHILLIPSON H.B., 1986: Landslides caused by rapid groundwater changes. In Groundwater in Engineering Geology, Engineering Geology Special Publication No 3, CRIPPS J.C., BELL F.G. and CULSHAW M.G. (Eds.), The Geological Society, London, pp. 87–94.Google Scholar

Copyright information

© International Association of Engineering Geology 1996

Authors and Affiliations

  • Bell F. G. 
    • 1
  • Maud R. R. 
    • 2
  1. 1.Department of Geology and Applied GeologyUniversity of NatalDalbridgeSouth Africa
  2. 2.Drennan, Maud and PartnersDurbanSouth Africa

Personalised recommendations