Construction World December 2016

Project information • Company entering: Maccaferri Africa • Client: Assamang • Start date: October 2015 • End date: December 2015 • Main contractor: Stefanutti Stocks • Project manager: DRA • Consulting engineer: DRA

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MECHANICALLY STABILISED EARTH WALL for Black Rock Mine expansion project The largest and richest Manganese deposit in the world sits in the Kalahari basin, approximately 80 km North-West of Kuruman, Northern Cape Province. Here, on a small hill called Black Rock, Assmang acquired an ore outcrop in 1940. Over the years this manganese ore mining operation expanded and today includes three underground mining complexes. The Black Rock Expansion Project was commissioned in 2014 to increase the output of the high-grade Manganese ore products and ensure the mine’s sustainable longevity. As part of the Black Rock Expansion Project the mine required four bridge abutments, each 7,5 m in height, to bring heavy trucks over the conveyor system to offload the manganese through the grizzly chutes below. Soil is strong in compression but weak in tension. By incorporating a tensile element such as a geosynthetic that is strong in tensile resistance within the soil mass, the soil is reinforced and able to sustain higher shear stress. Geosynthetic-reinforced soil systems can be adapted to a variety of site conditions. They are characterised by allowing one to work even with low quality backfill and are easy and fast to construct as they require no curing or lead time in the operation. The execution of the contract was awarded to the contractor Stefanutti Stocks Road & Earthworks in October 2015. Due to the time constraints Maccaferri SA t/a Maccaferri Africa was PILING AND BULK EARTHWORKS AND LATERAL SUPPORT to Kazerne Transit The Kazerne project is a Taxi Facility Development to improve the quality of life of commuters and streamline flow of traffic in the inner city of Johannesburg and strengthen the commuting connection with the rail service. The underdeveloped Kazerne Taxi facility close to Park Station provided an opportunity for such a facility. Studies have estimated that in 2014 the inner city had taxi facilities for 4 000 taxis; leaving approximately 1 800 taxis to rank and hold in the streets. This is one of the key reasons for traffic congestion in the inner city.

approached to propose an alternative solution for the insitu cast cantilever steel reinforced concrete wall originally specified. Four retaining walls, 7,5 m in height, were required by Black Rock Mine to accommodate tipper trucks dumping material onto conveyor belts for further transportation. Apart from the time and cost constraints, very high loadings and weak founding material had to be overcome in the proposal. After numerous solutions were discussed and considered in design related meetings between Maccaferri Africa, Stefanutti Stocks and DRA Mineral Resources, the Maccaferri MacRes ® T system, with Maccaferri’s Paraweb ® high strength geosynthetic reinforcement was chosen to satisfy all the requirements of the project. The complete package for the structure (design, mould hire, reinforcement, all accessories and project management assistance) were to the value in of R1-million. The two true bridge abutments (four walls which amounted to a face area of 850 m²) were constructed in less than three months as required in order for the client to commission the works in December 2015.

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residual andesite; followed by very soft rock to hard rock andesite. These ranged between 16 to 27 metres below the natural ground level, with the water table at eight metres. The Stefanutti Stocks Geotechnical design team carried out the analysis followed by the design of the most effective and suitable piling methodology for these soil conditions. Piles drilled under Polymer were identified as the preferred system, and were mainly used on the large diameter piles that were installed to depths of between 18 to 30 metres, to prevent side wall collapses. During the project a total of 440 piles were installed, including 242 Continuous flight auger (CFA) piles varying from 450 to 750 mm diameter, and installed up to 23 metres deep; and 133 Polymer-technology drilled piles varying from 750 to 1 500 mm diameter and installed up to 30 metres deep as well as 65 Auger cast-in-situ (ACIS) soldier piles varying from 600 to 750 mm diameter installed up to10 metres deep. Stefanutti Stocks Geotechnical’s environmental management system on site was designed, maintained and monitored in accordance with ISO 14001 specifications. These requirement was considered during risk evaluation for each unique operation and recorded as part of our aspect and impact registers.

During the early stage of the project, while installing the permanent lateral support, aggressive mine sands were encountered beneath Harrison Street on the north-eastern boundary of the site. This resulted in severe soil collapses during the drilling for the anchors as well as the perimeter piles; requiring a redesign for the anchors and piles in this section.

The perimeter piles were then installed closer together and permanent casings were used in the free- length of the anchors. During the structural piling the general soil profile encountered comprised

Project information • Company entering: Stefanutti Stocks Geotechnical • Client: Johannesburg Development Agency • Start date: 15 January 2015 • Project end date: 28 August 2015 • Main contractor: Stefanutti Stocks Geotechnical • Project manager: Badat Development • Quantity surveyor: Koor Dindar Mothei QS • Project value: R56 439 663

transported soils; a thick horizon of

Construction WORLD

DECEMBER • 2016