Concrete Manufacturers Association (CMA) members were involved in every step of a concrete-retaining block (CRB) wall project at the new Middelburg Mall to ensure that best-practice standards were followed.
The Middelburg Mall is an ultra-modern regional shopping centre in Mpumalanga, which is due for completion in April 2012. Several retaining walls were erected and completed in August 2011. Silvio Ferraris, CEO of CRB manufacturer and CMA member ReMaCon, designed the walls as gravity-retaining walls. CMA contractor member Friction Retaining Structures, who worked as a sub-contractor for the earthworks contractor, Protech Khuthele, built the walls against cut faces.
“The CRB wall design complied with all CMA and SANS 207 requirements,” said Hamish Laing, director of the CMA. “CMA members’ involvement in the design, construction and CRB production aspects of the project resulted in a well-built retaining-wall system which will provide many years of maintenance-free support.”
All the walls were built at an angle of 70̊. The main wall is 433 linear metres long and four metres high in places. The remaining walls have a combined length of 270 linear metres and are all less than three metres high.
The design accommodates the groundwater below foundation level and the placement of electrical transformers above one of the walls. Standard drainage at the base of the walls was used to deal with the former. The drainage system was assembled using geopipes or perforated pipes covered with 19mm of aggregate and encased in a Bidim A4 fabric.
Kaytech supplied the rock PC 50/50 geotextile reinforcement that was used to anchor the wall below the transformers. According to Laing, the gravity-wall, as opposed to a geotextile-reinforced design, was necessitated owing to the cut-faced embankments.
“Apart from the area immediately below the transformers, limited space precluded the use of geotextile reinforcement. Instead multi-layered skins were used to create the required additional mass and depth at the base of the walls. G7 minimum classification soil was used for the backfill areas and was tested using the Dynamic Cone Penetometer (DCP) method,” he said.
CMA members supplied all the blocks used in the project. Envirowall blocks, manufactured by Technicrete and placed in a semi-closed-face configuration, were used for the front facing, whereas Remblock 30s and Terraforce L11 blocks, manufactured by ReMaCon, were used for the more economical open spacing layout on the unseen second section of the double-skin design.