Construction World December 2017

TUNNEY RIDGE EXT 12 ELANDSFONTEIN Variable geology, sloping land and an immense single-level platform presented an exceptional set of challenges in the construction of a warehouse and distribution centre for earth-moving-equipment giant, Komatsu, at Tunney Ridge Ext 12 in Elandsfontein, Germiston.

retaining wall was built at an angle of 75˚ using a minimum of 1 m geofabric and stabilised fill compacted at 150 mm layers. A more traditional geogrid installation of 50% to 60% wall height was applied. Undoubtedly an equally challenging aspect of this project was casting the 44 000 m² x 300 mm post-tensioned slab on a platform underlain by one third rock and two thirds compressible clay. To equalise the settlement variance between the two materials, 1 600 micro piles were installed in the clay section to reduce settlement. Varying in depth between 8 m-28 m and 141 mm in diameter, the piles mitigated most of the settlement.

Essential to the success of the project were two huge concrete retaining block walls, specified by the project developer, Investec Property, to secure a bulk-fill terrace which supports a large post-tensioned concrete surface bed for the warehouse and surrounds. The retaining walls were designed by Verdi Consulting Engineers (Verdicon) in collaboration with international consulting giant, Hatch. Local earthworks contractor, The lower wall, 450 m long and topping 13 m, was built to face off and secure the bulk-fill terrace above, maximising the space available for development. The upper wall, 436 m long and 15 m high, stabilises the embankment which rises above the building platform. Verdicon managing director, Trevor Green, said that besides creating additional usable space, the advantage of concrete block retaining walls is their modular Power Construction, was engaged for the civil work and Valcal International constructed the retaining walls.

structure which makes them sufficiently flexible to accommodate ground movement while retaining their structural integrity. “By contrast it takes only minimal movement for reinforced concrete or brick retaining walls to crack and they are typically several times more expensive. We specified Aveng Infraset’s Ridgebloks for the Tunney project primarily because they are solid, unlike most other blocks on the market which are hollow, and their interlocking design prevents them from sliding, a distinct advantage. “Power Construction battered the bulk earthworks platform at 45˚, while the lower wall was built at an angle of 70˚. During its construction, Valcal International benched the embankment to avoid the creation of a preferential failure plane." The cut wall section consists mostly of rock from several different geologies, including very hard rock quartzite and soft to medium hard rock greywacke. The upper

PROJECT INFORMATION

• Company entering: Aveng Infraset • Client: Investec • Start date: 2016 • End date: 2017 • Main contractor: Power Construction • Consulting engineer: Verdi Consulting Engineers and Hatch

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