Construction World December 2015

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Specialist Contractors or Suppliers

Kaytech SystemUsed in Major Ballito Road Upgrade

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Introduced into the South African market by Kaytech, the Tensar TW1 System was developed as an alternative to traditional retaining wall options and has been used extensively in Europe and elsewhere internationally. The system was recently used on a major road upgrade contract in Ballito, one of the first and largest local applications of the system to date. Project engineers, SMEC South Africa, were involved in the detailed design of the system and realised a number of cost benefits on the project by using the Tensar TW1 System. The scope of works entailed the widening of a two-lane, single carriageway to a three-lane, dual carriageway in Ballito,

into the existing fill was utilised. For the upper 3 m of the 11 m wall and for the 5 m high wall, Berea sand was used throughout. In utilising the new system a number of challenges were experienced during construction. These included: the setting of the base block, which is key to achieving the final face inclination of 86°, compac- tion criteria, stormwater control, and the use of labour inexperienced in building these walls. However, these problems were quickly resolved through close collab- oration between the contractor, consultant and supplier. From the Environmental Assessment it was noted that the removal of existing indigenous trees within the road reserve would result in a loss of biodiversity. This however was unavoidable due to the nature of development. Rehabilitation measures had to include replanting the same species of trees. Also during construction large amounts of soil disturbances are expected. Re-vegetation of all disturbed soil was insti- tuted immediately after construction. As another environmental advantage, the TensarTech TW1 system (MSEW) is ideal as an alternative to traditional retaining wall options as the geogrid and geotextiles used in its construction assist in reducing the project carbon footprint, and at the same time minimise the use of natural materials.

about 40 km north east of Durban. Due to the site’s undulating topography, earth-re- taining structures had to be built to bring the extra lanes to level. The lane widening had to be constructed within the road reserve to eliminate encroachment into existing devel- opments. To reach this objective, two near vertical, Mechanically Stabilised Earth (MSE) walls of 11 m and 5 m, covering a total length of over 400 m and 2 000 m 2 , were proposed. A key consideration in the design was to optimise the use of lower quality fill material, while simultaneously minimising the amount of lateral support required in cutting back and benching into the existing roadway; i.e. the back excavation slope. Limited space was available for the 11 m high wall, which restricted the length of the strips to 7 m. At the same time it would be beneficial to the project if Berea sands could be utilised. However, by using the lower quality fill, strip lengths would need to be increased, which implied either increased cut or the use of a near vertical back excava- tion slope requiring the use of shotcrete and ground anchors or nails. After a number of iterations, the final design for the 11 m high wall comprised the use of 7 m long strips, a granular backfill for most of the height and 1 m thick granular soil-raft foundation. No lateral support was thus required and conventional benching

Project information • Company entering: Kaytech • Project start date: June 2013 • Project end date: September 2014 • Client: Kwadukuza Municipality

• Project team: Kaytech, SMEC and Afriscan • Main contractor: Afriscan Construction • Project manager: SMEC South Africa • Project value: R8,5-million (walls and fills)

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