CMA MEMBERS DELIVER ON MASSIVE RETAINING WALL PROJECT:

The overall development has generated considerable interest among construction professionals and members of the public alike, owing primarily to some highly innovative architecture used in its design by Kim Fairbairn of Continuum Architects (Pty) Ltd.

Having been built on a site with a considerable and varied slope, it is a project which required extensive retaining wall support. A total of eight retaining walls were built, some of which reached heights of 7.5m. These cover an area of some 3 000m² and used close on 30 000 CRB in their construction.

CMA director, John Cairns, says CRB walls are more cost-effective than conventional reinforced concrete walls and are considerably more attractive, facilitating as they do varying shapes and contours as well as the growth of plants in the soil-filled blocks.

All the walls were built by Kalode Construction using INFRASET’s Terrace Blok retaining system, the one exception being an internal wall in Basement 3, which was built using Concor Technicrete’s Envirowall block system.

This wall comprised a geogrid reinforced fill structure built at 85º and the Envirowall block is best suited to this type of application.

The walls were built in two phases. Phase 1, which comprised the Basement 3 wall and a structured fill wall on the north side of the project for a fire escape, was designed by Johan Joubert of Foundation and Slope Stability Engineering, and Phase 2, which consisted of the remaining walls, was designed by Herman Pietersen of Herman Pietersen and Associates.

The fire escape wall on the north-west side of the development was one of the more challenging CRB projects. Seventy metres long and seven metres high, it was built at an angle of 70º. The fill in the wall was well compacted and reinforced with high strength polyester geogrids supplied by Kaytech . The fire escape itself sits directly on the structural fills and applies loadings on these fills of 150kPa.

On the south eastern and south western side of the building a sunken wall 6.5m high and 93m long was built at a slope of 70º.  A composite structure, it was constructed with a double skin up to a height of four metres and a standard geogrid reinforced fill was used above that to maintain the weight. 

Another wall section, the south-western pod, was built around a staircase.  It is also a composite structure in which cement stabilised soils and geogrids as well as plain geogrid reinforced fills and terraced stepbacks were used to accommodate the staircase landings and to break the stark lines of a high CRB wall situated in confined surroundings. It is 125m long, varies between three and eight metres in height, and has a 70º slope.

All structures were built with adequate subsoil drainage consisting of clean stone wrapped in  horizontally-laid Kaytape A2 . Wick drains 250mm wide were laid on the face of the exposed embankment and these act as sub-soil cut-off and collector drains.

A 140m x 7.5m high retaining wall section was built with INFRASET Terrace Bloks and is situated on the southern side of the FNB/Wesbank development.

This 90m x 6.5m high retaining wall is situated on the north-eastern side of the FNB/Wesbank development and was built with INFRASET Terrace Bloks.

This 70m x seven metre high retaining wall, built with INFRASET Terrace Bloks is situated on the northern side of the FNB/Wesbank development and supports a fire escape.

Some 14 000 Envirowall blocks, manufactured by Concor Technicrete, were used to build this 100m x 6.8m high retaining wall in Basement 3 of the FNB/Wesbank development. The basement houses fire fighting equipment.