J.L. Van Rooy

Affordable water resource development in the northern province, South Africa

Abstract An approach to groundwater exploration and utilisation is presented in an area that was traditionally regarded as having scarce groundwater resources. The area is situated in the Northern Province of South Africa and is known as the Nebo Plateau, which is formed by the Nebo Granite of the Lebowa Granite Suite, Bushveld Igneous Complex. Several historic tectonic events resulted in previously unutilised aquifers, of which the Spitskop Complex and geological lineaments associated with the Wonderkop Fault are examples. Both these areas show promising results, although high fluoride content in the groundwater may pose a problem. This can, however, be solved by treatment processes. The paper emphasises that the influence of the regional geology must be taken into account when exploring and developing groundwater in areas underlain by hard crystalline rocks.

Environmental geological aspects of the dolomites of South Africa

Abstract The dolomite rocks in South Africa coincide for the most part with the so-called Pretoria-Witwatersrand-Vereeniging complex which comprises the industrial heart of the country. Urban development will, therefore, also be concentrated in this area, with the inevitable establishment of townships on the dolomite. This development has great impact on the dolomitic environment and vice versa. The most important environmental aspects which influence Mans occupation of the dolomite environment include the formation of sinkholes and dolines (compaction subsidences) and also the potential pollution of the dolomite aquifers. These aquifers consist of weathered, blanketing materials overlying the bedrock with sometimes shallow water levels, high permeabilities, storativities and transmisivities. All these factors contribute to the excellent groundwater resource in the dolomite rocks as well as to their high pollution potential. The environmental hazards associated with development of dolomite land is discussed with reference to loss of life, financial implications and efforts to reduce the impact of development. The importance of pre-emptive and appropriate land management is stressed. A clear understanding of the dolomite environment is, therefore, essential.

The geology of the Lesotho Highlands Water Project with special reference to the durability of construction materials

Abstract The Lesotho Highlands Water Project is situated in the Kingdom of Lesotho and the adjoining north-easthern part of the Orange Free State Province of the RSA in an areaunderlain by Triassic and Jurassic basalts of the Lesotho Formation and Triassic sandstones and mudrocks of the Karoo Sequence. The Project will consist of a series of dams and tunnels to convey water from the Lesotho Highlands to the industrial centre of the Republic of South Africa. The geological setting of the project area and some engineering geological properties of the underlying stratigraphic horizons is discussed. The geotechnical properties of the different rock types are discussed with special reference to their use as concrete aggregate. The durability of basalt is primarily determined by the amount of secondary smectite clays present in the rock. These clays occur as discrete grains or as intergrowths with other secondary minerals disseminated throughout the rock. The clays originate from the deuteric alteration of primary glass, pyroxene, olivine and rarely plagioclase and also occur as infillings of amygdales. The durability of the sedimentary rocks is a function of their dimensional change with variability in moisture content and also the degree of cementation between grains.

The identification and treatment of poor durability Karoo dolerite base course aggregate - evidence from case studies (comment and response)

Table 1 (referencing COLTO 1998) of the above-mentioned technical paper incorrectly states that the PI shall be < 12 when the PI is determined on the -0.075 mm fraction because -0.425 mm fraction is non-plastic. COLTO requires that the PI of the -0.075 mm fraction shall not exceed 12 without any qualification. If the PI exceeds 12, the material shall be chemically modified. After chemical modification the PI of the -0.075 mm fraction shall not exceed 8. The Technical Committee involved in the COLTO 1998 edition based these criteria.

Behaviour of a Thin Compressible Clay Horizon Under Geogrid Reinforced Sand with a Wide Platform Load

Basal reinforcement, where high tensile strength geogrids are employed beneath structures, is becoming an increasingly accepted construction technique along the eastern coast of southern Africa. The presence of compressible, soft, thin and shallow clay horizons usually associated with complex estuarine or lagoonal deposits are a major consideration when using basal reinforcement as a founding technique. In order to define the deformation behaviour under a wide platform load, three centrifuge tests were undertaken. These tests compared the behaviour of the clay horizon in three scenarios, namely (1) without reinforcement, (2) with a single layer of reinforcement, and (3) with a double layer of reinforcement. It was found that the inclusion of geogrid reinforcement increased the vertical load-bearing capacity of the system and the inclusion of an additional geogrid layer further increases the load bearing capacity. Additionally, the inclusion of geogrid reinforcement also changed the deformation mechanisms of the materials. Without reinforcement, deformation is localised to the portion of clay directly beneath the applied load from the platform. Whilst the inclusion of geogrid reinforcement allows the applied load to be spread to the sand beyond the platform, which contributes to an increase in load-bearing capacity, it comes at the disadvantage of deforming a wider portion of the clay horizon.