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CONSTRUCTION WORLD
MAY
2015
PROJECT PROFILE
The project entails the replace-
ment of the original NAS using
concrete pipes with a Calcium
Aluminous Cement (CAC) sacrifi-
cial layer, including construction of the asso-
ciated manholes. The total length of the NAS
Phase II is approximately 5,2 km. The three
pipe sizes used for the NAS are 1 650 mm,
1 500 mm and 1 350 mm nominal diameter
respectively. The pipes are 2,44 m in length.
The depth of installation of the NAS
Phase II typically varies between 4 m and
7 m and in terms of bedding preparation,
trenches are dug up to a depth of 8 m. Having
to deal with a water table as high as 500 mm
above ground, adds to the complexity of
the contract.
In addition to the construction of the
new outfall sewer, manholes are constructed
at approximately 90 m intervals, and also at
changes to the vertical and horizontal align-
ment of the sewer, to allow for chambers
(with benching) constructed to terminate
below ground level with access chimneys
constructed to ground level making use of
precast concrete manhole rings.
Construction of the sewer at major road
and railway crossings are carried out by
means of pipe jacking. Two of the pipe jacks
cross some of Metrorail’s main railway lines
and no disruption to commuter services
were allowed while these sections of the
construction were done. Strapping and
extra support structures had to be designed
and installed to prevent any subsidence
of the rail tracks and measures were put in
place to monitor this in conjunction with
the fluctuating water table levels which
had to be maintained. A total of eight
pipe jacks were done during this contract
with the pipe diameter at these sections
varying from 1 470 mm to 1 680 mm and
the length of the jacks varying from
22 m to 84 m. Horizontal directional drilling
technology was also implemented at one
crossing which consisted of a 630 mm diam-
eter HDPE pipe 60 m long.
A section of the existing NAS, a 762 mm
diameter concrete pipe with an approximate
length of 1,2 km will be rehabilitated using
‘cured in place pipe’ (CIPP) technology. This
rehabilitation work comprises cleaning the
sewer, isolating the sewer and over-pumping
the existing wastewater, CCTV inspections
and the installation of the new pipe liner.
Curing of the resins is achieved with the
recycling of heated water.
Construction innovation
technology
CSV Construction has specifically invested
in technologically advanced shoring equip-
ment for this contract which includes
two High Frequency Excavator Mounted
Vibrating Sheetpile Hammers fitted to 30 ton
Hydraulic Excavators and it also imported
a PTC high frequency Excavator Mounted
vibrating pile driver.
The steel sheetpiles that were imported
from Asia are of the Nippon Type FSP IV
Sheetpiles and the ones being used on this
specific project are 7,5 m long. These sheet-
piles are interlocking resulting in a solid
wall capable of deflection and providing a
very effective water cut-off which is much
needed with the ground water level being
generally 1,5 m below NGL but in places as
high as 500 mm above NGL. Sheetpiles are
driven so that the bottom tips (toes) of the
piles are 1,5 m below the trench floor level.
This is to provide adequate toe stability
to the system. Specially designed braces are
used to brace the upper part of the shoring
system, spanning the width of the trench
between the sheetpiles.
CSV also acquired two Japanese manu-
factured Giken Silent Piling machines for
this project. These machines are used to
install Nippon Type FSP IV Sheetpiles, the
same as for the vibrating hammers, but can
also be used for other types of sheet pile
installations. The silent piler makes use of
a press-in method to install piles. The silent
piling technology is applied where the 7 m
deep trenching is carried out as close as
1,5 m from existing sensitive high voltage
cables that could not be exposed to any
vibrations or movement.
Corporate social investment
Although this project mostly involves special-
ised work and is more machine orientated,
10% of CSV’s labour is sourced from the local
ward council’s job-seekers database.
Local businesses and service providers
such as fuel stations, hardware stores,
plant-hire companies, construction supply
companies and other local companies are
well supported due to the close proximity
of industrial areas to the project and we
are also saving on fuel cost by doing local
business. With the employment of about
130 workers on the project the local take
aways and grocery stores also benefit a lot
from this project due to its close proximity
to their business.
A section of the project traverses the
grounds of a technical college with whom
CSV has built up a very good relation-
ship. The company is currently setting up
interviews with civil/building technology
students from this college for employment
as site foremen and supervisors. The aim is
to employ 10 students from this college.
CONSTRUCTION
of the
NORTHERN AREAS SEWER
The Northern Areas Sewer
(NAS) is a major collector
sewer currently serving an
area of approximately
4 100 ha of the northern
suburbs of Cape Town. The
total future catchment area
to be serviced by the
NAS is approximately
4 600 ha of the bigger
Cape Town metropole.
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Main components of the silent piler.