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DECEMBER • 2016
Construction
WORLD
46
THE PROVISION OF SAFETY FACILITIES
on N2 Section 7 near George
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
Specialist Contractors or Suppliers
B
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
TERRACED RETAINING WALL GARDEN FOR GROVE MALL
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: Mobicast
• Start date: September 2015
• End date: October 2016
• Main contractor: Civils 2000
• Architect: SMEC SA
• Quantity surveyor: Civils 2000
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
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”.