On the significance of stratigraphy in the prediction of the engineering behaviour of soils and rocks in Southern Africa

Abstract

The object of this thesis is to demonstrate that a knowledge of the stratigraphic unit occupying a site provides a basis for making broad generalisations regarding likely terrain and foundation conditions which may be used to advantage in designing a relevant site investigation programme. Stated simply: very different exploration programmes would be designed for a house on Oranqe Grove quartzite and a dam on Transvaal dolomite.

If climate as well as stratigraphy, is taken into account we may recognise a Regional Stratigraphic unit and achieve a higher level of generalisation which will lead to more accurate predictions being made regarding the likely engineering properties of the local rocks and soils. Subdivision of the regional stratigraphic unit into land patterns, and of land patterns into their constitutent land facets, represent yet further advances from lower to higher levels of generalisation. Apart from specific case histories, however, it is the regional stratigraphic unit that is adopted as the main level of discussion throughout most of the thesis.

The importance of the correct identification of the origin of each horizon of the soil profile during site investigation work is emphasised as this, too, may lead to meaningful predictions regarding the engineering behaviour of the soil. The significance of the pebble marker as an aid to the correct identification of soil origin is also emphasised. The introductory chapter concludes with a number of very broad generalisations about the typical forms of the soil profile in Southern Africa and the environmental factors responsible for their development.