Construction World April 2019

STABILITY FOR RANDBURG RENOVATION The Brightwater Commons shopping centre, situated in the centre of Randburg, is undergoing a major redevelopment by the Moolman Group and accordingly will be upgraded to a shopping mall.

W ith previous success using Kaytech’s quality geotextile products, it was no surprise that Remacon Consulting Engineers chose RockGrid PC, the first South African manufactured composite reinforcing geotextile, for a retaining wall project at the shopping mall. According to the developers, “the new mall will boast strong national brands and stores in response to an obvious gap in this densely populated market of 36 000 households surrounding the shopping mall. The mixed-use development improves

sustainability and is approximately 53 000 m² in total.” To provide extra shopping space, extensions on the previous parking area include retaining walls up to 13 metres in height to be constructed at a 60 o slope against weathered, residual granite cut face. Although the materials were generally high density, stiff, residual granites, engineers specified RockGrid PC 50/50 for reinforcement. The unique characteristics of RockGrid PC result from the combination of a nonwoven layer in conjunction with high tenacity, bi-axially orientated, multifilament polyester yarns. Compared to polyethylene or polypropylene grids or woven fabrics, the high tensile modulus of RockGrid PC provides excellent reinforcement properties with minimum creep deformation. Powergate Construction, a company specialising in block gravity retaining walls, commenced the project by creating a safe slope and allowing for a wedge of fill material between the retaining wall and the cut face. RockGrid PC 50/50 (20 000 m 2 ) was installed to reinforce the fill material, and was benched into the slope as work progressed. One of the special features of RockGrid PC is the nonwoven geotextile component which not only offers optimum hydraulic characteristics but high installation survivability. Due to its drainage capacity, RockGrid PC facilitates the reduction of pore water pressure and improves shear characteristics, thereby providing excellent stability. To mitigate sub-surface water seepage behind the wall structure, a collector base drain was constructed behind the wall. Kaytech’s WickDrain (100 mm wide) strips were then installed as seepage interceptors across the cut face at 45 degrees and 1,5 m intervals and tied into the base drain. WickDrain is a pre-manufactured composite vertical band drain system comprising a heavy duty, extruded HDPE geonet (100 mm flat cylinder) wrapped in a bidim filter geotextile. Manufactured from 100% recycled polyester processed from discarded cooldrink bottles, bidim is a continuous filament, nonwoven, needlepunched geotextile used worldwide. The needlepunching process provides several advantages including appreciable thickness, high porosity and a high drainage capacity in both the transverse and normal to the plane. Bidim provides the ideal interface for the creation of a reverse filter in the soil adjacent to the geotextile. A drainage channel was installed at the top of the retaining wall to drain off storm water. Once the installation was successfully complete, Kaytech representative, Winnie Botha proudly proclaimed, “These innovative geotextile products have demonstrated how the most cost effective option can also provide the most effective solution.” As the shopping centre extensions are taking place on the Republic Road side of the parking lot, the developers decided to rename the new 53 000 m 2 centre, ‘Ferndale on Republic’, and it is scheduled to open in September 2019. 

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CONSTRUCTION WORLD APRIL 2019