INFRASTRUCTURE NEWS
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UGANDA Refurbishment of Nalubaale Dam GIBB was awarded the contract to design and oversee the construction of Nalubaale Dam. Located 3 km downstream from the source of the Nile River in Jinja, Uganda, the Nalubaale hydropower station’s first turbine unit was commissioned in 1954. Cracks were first noticed in the powerhouse structure in 1964. These were caused by an alkaliaggregate reaction (AAR). Cracks had also developed in the main dam wall and leakages from the reser voir were obser ved against the downstream face. All repair attempts before 2020 had a limited ser vice life as long as the concrete kept on swelling due to AAR. Louiza van Vuuren, civil engineer, GIBB, says Eskom Uganda decided to implement a new grouting programme to improve the structural and functional integrity of the dam structure. The grouting approach used by GIBB was based on the GIN (grouting intensity number) method. The acceptable pressures and volumes of grout injected were derived from stability calculations to avoid hydro-jacking of the dam’s concrete during grouting. “The specifications stipulated that the pressures used for grout
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injection should be controlled with a pressure transducer, which is fitted to a grout pump equipped with an automatic data acquisition system capable of measuring, displaying, and recording data in real time,” explains Van Vuuren. In December 2020, the contractor star ted the drilling and grouting works on a trial section of the dam. This was done to confirm or modify the grouting method (boundar y cur ve, boreholes spacing, stop criteria), the grout mix design and grouting materials, as well as the equipment such as pumps, mixers, sensors and automated control devices, among others. Primar y holes were inspected with a borehole-imaging device to establish typical crack elevations, directions and widths, and to inspect the mass concrete condition. This led to the detection of large cracks of up to 17 mm wide. Crest levelling sur veys of the concrete blocks were also conducted to detect any evidence of hydro-jacking. Due to the grout trial section taking longer than originally anticipated, the project experienced a slow star t, compelling the contractor to increase the number of employees on-site – as well as drilling equipment – to catch up with the planned schedule.
NAMIBIA Shell hits oil and gas in offshore well Shell has made a significant oil and gas discover y at an offshore well in Namibia, which could spark a wave of investment. Namibia is not a fossil fuel producer, although nor thern neighbour Angola is a major oil and gas producer. The discover y at the Graff-1 well, which Shell star ted drilling last month, has so far shown at least two reser voirs containing what one of the sources described as a “significant amount of oil and gas”. The drilling results have shown one layer of hydrocarbons at least 60 m deep, holding an estimated 250 to 300 million barrels of oil and gas equivalent. Developing new oil and gas fields in a countr y with no existing energy infrastructure and regulation, similar to what has happened in Guyana on the other side of the Atlantic in recent years, is timely and costly. Namibia has sought to develop oil and gas fields for decades with no success. But, in recent years, interests in its offshore prospects have attracted many foreign companies, including Exxon Mobil and TotalEnergies following discoveries in neighbouring South Africa as well as Brazil and Guyana, which share geological similarities.
