Sonering van 'n dolomietgebied suid van Pretoria met behulp van 'n meervoudige-faktor klassifikasiestelsel

Abstract

One of the requirements for establishing a township on dolomitic rocks in the Transvaal is the submission of a geological report on the township. The aim of the geological investigation is to delineate areas of low risk for the formation of sinkholes and subsidences where township development is permissible. Presently there is no standard procedure for such an investigation. Five classification systems could be found in the literature. A new classification system is proposed, which is based on data obtained from present investigation techniques, namely pneumatic percussion drilling, test pits, gravity surveys, thermal infrared line scanning, damage and surface instability history of a site. This new classification system was developed on an area to the south of Pretoria which is underlain by dolomitic rocks of the Lyttelton and Eccles Formations of the Chuniespoort Group with overlying shale outliers and aeolian soils. The area is representative of most conditions encountered in dolomitic areas. All the classification systems were applied in the same area and the results were compared on the basis of the sinkhole history of the area. Not one of the classification systems is totally successful. A reason for this could be the complex distribution of different materials and the unpredictable behaviour of the dolomitic residuum when it becomes saturated. Two classification systems, system E and the proposed MF-system, give the best results. The MF-classification system, proposed by the writer, could possibly, after additional modification, be used as a standard for the classification of dolomitic areas for township development.