
How high can you build with concrete retaining blocks? Concrete retaining blocks have been on the market for decades, but some people still think they cannot do the same job as poured concrete, especially for structures over 4m high.
However, when designed by experts in this complex field, these walls offer extensive flexibility at a range of heights and in varied soil conditions.
Karin Johns, director of marketing and business development at Terraforce, shares two projects where design engineers with the required expertise pushed beyond conventional boundaries.
Angled for success
At a property in Bishop’s Court, Cape Town, engineers at HKS Law Gibb designed a 7,5m high and 90m long Terraforce retaining wall.

A property in Bishop’s Court, Cape Town, boasts a 7,5m high and 90m long engineer-designed Terraforce retaining wall.
Angled at 65 degrees, it supports the fill section of the approximately 2 020m³ cut-and-fill earthworks that were undertaken to level the erf. Engineers specified L13 type blocks with in-situ concrete keys.
A 700×500 concrete foundation with lime-stabilised clay backfill was compacted to 90% AASHTO. Layers of Restrain 110, high-tensile geofabric securely anchored into the blocks with concrete, were specified at certain levels.

A halfmoon-shaped protrusion for the pool was constructed vertically on a reinforced concrete foundation and block infill in Bishop’s Court.
All necessary service pipes were installed simultaneously together with foundations and supporting columns for the swimming pool. A halfmoon-shaped protrusion for the pool was constructed vertically on a reinforced concrete (RC) foundation and RC block infill.
Driving new heights
A steep property calls for steep measures. Extensive earth works were needed to prepare this plot for a new house, and a driveway up to the level of the new garage also needed to be built.
Engineers designed RC retaining walls on both sides of the driveway. Above that level, Terraforce L11 retaining walls were used to a height of 9m, constructed on RC foundations that were in turn held in position with anchors through the foundation.
At predetermined positions, vertical RC columns were incorporated into the blocks, then linked to another horizontal RC beam approximately halfway up the wall height. This was tied back with soil nails up to 7m long into the benched embankment behind the walls.
In order to use the excavated decomposed granite material as backfill, it had to be reinforced with horizontal layers of restrain 50 geofabric placed at various levels in the backfill and locked into the L11 block-facing layer.
To improve service access, various terraces were specified between walls, with stairways connecting them. Planting was undertaken with hardy creepers and ground covers, including an irrigation system to ensure an even green cover in a short space of time.

A steep property calls for steep measures, especially when vehicle access proves to be difficult. This engineered wall made use of several strategies to reach its full height.
For more information, contact Terraforce:
Tel: +27 21 465 1907
Email: info@terraforce.com
Website: www.terraforce.com
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