The Civil Engineering Contractor June 2018 | Page 9

ON CONTRACTORS’ SITES
Erosion on West Coast held at bay
The massive
2.5km-long
retaining wall
installed by
Terraforce.
navigating and assessing of the steep, 15m-high, heavily
vegetated terrain with cranes and telescopic handlers. An
estimated 180 000 blocks, supplied by Van Dyk Stene,
Terraforce manufacturer on the West Coast — with 100m²
backfill sand per 1 200 blocks (100m 2 ) — were installed
using five TLB loaders, a 20 000-litre water truck, and 80
labourers, of which 90% were local, untrained labour but
who underwent on-site training. Also, under the auspices of
the Expanded Public Works Programme, 25 official learners
were given basic construction skills training over a period of
approximately three months.
On completion in March 2018, indigenous plants were
planted by a company specialising in establishing the
sensitive vegetation of the West Coast.
Located on the West Coast, Pepper Bay harbour area
has a massive retaining wall to stabilise existing eroded
embankments. Initiated by the Department of Public Works
as custodian of state land, this large retaining wall was built
in the interest of public safety.
The embankments consist of multiple layers of
sedimentation up to 21m in height and 2.5km in length,
where softer material has eroded, leaving harder layers of
overhanging and unstable rock. The Terraforce retaining
wall system was specified by Ulwazi Consulting Engineers,
as it offered practical, stable, and weather-resistant surface
protection.
Before block installation could begin, all vegetation and
loose material had to be removed to expose the underlying
rock face of the embankments. Says Adriano Guerrini of
Guerrini Marine Construction: “These were swept clean
and benched for slip prevention, so the extent of stabilising
could then be determined and the angle (generally between
60 and 70 degrees to the horizontal) of the final face slope
set out. Using Soilcrete (sand-cement mix) the rock face
was covered by backfilling in well-compacted layers, with
the depth of the backfilling monitored and minimised to
follow the natural contours of the exposed face. At the same
time, the block facings were built up and the blocks filled
with Soilcrete, stepping back towards the rock face where
appropriate, to minimise depth of backfill and reduce the
visual impact of a sheer wall. Finally, the tops of the step-
backs and the finished level are capped with a concrete slab.”
Some of the challenges encountered and successfully
managed during installation included the continual
The block facings were built up and the blocks filled with Soilcrete
and, where appropriate, to minimise the depth of backfill and
reduce the visual impact of a sheer wall, the blocks were stepped
back towards the rock face.
CEC June 2018 - 7