Construction World December 2016

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Specialist Contractors or Suppliers

TERRACED RETAINING WALL GARDEN FOR GROVE MALL

The reason why concrete block retaining walls are used so widely is that they offer much more than the stabilisation of earthen embankments. They also give full reign to the creative talents of landscape architects and retaining wall builders. The Grove Mall, an upmarket shopping precinct developed by Resilient Africa and situated off Lynwood Road in eastern Pretoria, illustrates this point in spectacular fashion. Its 420 m long multi- faceted retaining wall structure on its southern and western boundaries has transformed a six metre high erosion-prone earthen embankment into a terraced wall garden, comprising three, and in one section four, layers of retaining walls interspersed and overhung with abundant plant and flower life. Despite their eye-catching attributes, public safety rather than aesthetics was the prime motivator for shoring the embankment with terraced walls which were designed, built and engineered by Engineered Interlock Solutions to provide many years of trouble- free service. According to Engineered Interlock Solutions, owner, Manie Troskie, before the retaining wall option was considered, gabions were the front-running reinforcement solution. Actual construction was complicated because it commenced while the centre was fully functional. “This meant we had to work in a public space and this restricted our available working area. In addition, a section of the parking basement adjacent to the embankment had to be used for temporary storage of the excavated soil. Moreover, although the soil was sufficiently stable for backfill purposes, there was so much water in one section of the embankment that it ran continuously, and we had to pay particular attention to drainage,” said Troskie. The walls were completed at the end of 2014 and took six months to build. The bulk of the structure comprised three walls, apart from the south western corner where a fourth wall was added. Detailed logistical planning was required to counter the restricted working space and a ramp, which provided access to the upper wall sections, had to be built. Besides excavating and

stockpiling the soil, an existing precast concrete drainage channel, which ran along the bottom of the embankment, had to be temporarily filled in to provide adequate and unimpeded access for building the lower wall. Provisional alternative drainage was installed in this section during construction. Dust was another problem during construction and the on-site water was used to damp down the soil. To ensure that the walls were structurally sound and well drained, Engineered Interlock Solutions was obliged to use low-fines concrete as the backfill material for the first wall. This wall varied in height between one and three metres and in one three metre section the wall was built around a substantial quantity of rock. The upper walls ran between one and two metres in height.

Project information • Company entering: Aveng Infraset • Client: Resilient Properties • Start date June 2014 • End date: December 2015 • Main contractor: Engineered Interlock Solutions • Consulting engineer: Axiom Consulting Engineers • Retaining wall consulting engineer: TMV Consulting & Design • Quantity surveyor: BJV Quantity Surveyors • Contract value: R2,5-million

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THE PROVISION OF SAFETY FACILITIES on N2 Section 7 near George

The R61-million project, initiated by the South African National Roads Agency (SANRAL), comprises approximately 8 km walkways, fencing, retaining walls, a pedestrian bridge crossing the railway line, CCTV and lighting along the N2 between the Pacaltsdorp Intersection and the George Mall. Quite a few fatal accidents were reported on this section of the N2, that runs through a densely populated area, making it crucial

to install fenced pathways to ensure the safety of pedestrians on their way to work, school or shopping. The appointed engineers, SMEC SA, were tasked with designing a safe pedestrian pathway along the highway. With the hilly typography of the region, it was necessary to make use of retaining walls for the cut and fill slope parallel to the highway, to facilitate a stable foundation for the 2 m wide footpath. Some 8 500 m 2 walls were built to hold

Project information • Company entering: Mobicast • Start date: September 2015 • End date: October 2016 • Main contractor: Civils 2000 • Architect: SMEC SA • Quantity surveyor: Civils 2000

the paved route, using roughly 90 000 L11 Terraforce retaining blocks with integrated geotextile reinforcement fabric to counter any horizontal and vertical loads. All walls were also placed on a concrete base and each block was reinforced with vertical rebar and a 5% cement mortar mix. A Kayteck filter system was added to accommodate the wet ground conditions typical to this area.

Says Chris van Zyl, owner, Mobicast: “Terraforce is a cost effective alternative to other products. The ease of use together with the special reinforcement makes it superior to other earth retaining solutions. The completed structure is functional and adds aesthetic value to the area. Landscaping will still take by place, by the main contractor, Civils 2000”.

Construction WORLD

DECEMBER • 2016