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CONSTRUCTION WORLD
AUGUST
2016
PRECAST
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 trou-
ble-free service.
Reasons for the choice
According to Engineered Interlock Solutions,
owner, Manie Troskie, before the retaining
wall option was considered, gabions were the
front-running reinforcement solution.
“We were approached by Axiom
Consulting Engineers to provide an alter-
native terraced concrete block retaining
wall design using a cut-and fill construction
technique. We submitted our design, which
was based on Aveng Infraset’s very attractive
and natural looking split-face retaining block,
the Infrablok™ 350, to BJV Quantity Surveyors.
“This solution not only proved less expen-
sive to build than the gabion-based alterna-
tive, but offered the opportunity of creating a
wall garden. Over 46 000 block were supplied
by Aveng Infraset to cover a total wall-face
area of 2 570 m².
“We incorporated terracing for two
reasons. It was a far more attractive option
than a single wall and it provided the parking
basement with more natural light. The
individual walls were built in S shapes with
varying wall heights to lend further aesthetic
appeal,” said Troskie.
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 embank-
ment 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 contin-
uously, and we had to pay particular attention
to drainage” said Troskie.
The project
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 exca-
vating 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 and the on-site
water was used to damp down the soil.
In order to ensure that the walls were
structurally sound and well drained, Engi-
neered 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.
All the walls were built with concrete
foundations and the excavated soil was used
as backfill material for the upper terraces. All
the walls were built at an angle of 80˚ with
Maccaferri WG4 geosynthetic reinforcement.
In addition, a layer of bidem was installed
under the second to last layer of blocks on all
the walls for erosion protection.
Drainage was a very important facet of
the project, given the large volume of water
on site. Sub-soil pipes were placed at the
bottom of the cut face and outlet pipes were
run from the cut faces to the bottom of the
completes retail centre
TERRACED RETAINING WALL
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 lower wall under construction at The Grove.