Abstract:
Large portions of the Transvaal Province, where urban development has taken place and which may be considered for future development, are underlain by dolomite of the Chuniespoort Group. In response to the sinkholes which formed in the Far West Rand during the early sixties. subject to regulation 24(b) of Ordinance 25 of 1965, all proposed new townships situated on or potentially affected by dolomite are geotechnically investigated before proclamation. Systematic geotechnical investigation of a proposed township site can only be conducted with a sound knowledge of karst formation. The aspects of importance to the engineering geologist are investigated and the relationship between the type of weathering and the various formations of the Chuniespoort Group are demonstrated. The study area considered is the area suggested for urban development in the Pretoria Witwatersrand- Vaal Triangle area underlain by dolomite south of Pretoria. A large variety of factors which play a part in the delineation of stable areas where the risk of sinkhole. formation is allowable, are covered. The techniques available, locally and overseas, for the geotechnical investigation of soluble rocks were researched and evaluated. Chert was found to be a major disturbing factor for most techniques applied overseas due to its random distribution in the residuum. Wad, the final residue of the solution of dolomite causes serious problems for the investigator. A variety of drilling techniques are evaluated and applications delineated. A standard technique for the description of pneumatic drill samples is given. Guidelines for the zoning of potential uses, based on the results of geotechnical investigations, of proposed sites for township development are given. In order to promote systematic investigation, the division into two stages of investigation, the reconnaissance and planning stages, is motivated. The investigation of foundation conditions for planning purposes is included in the latter. Building and repair techniques as applied to dolomitic areas are illustrated. Recommendations aimed at improvement of procedures and investigation methods are made.
