Construction World June 2017

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CONSTRUCTION WORLD JUNE 2017 30
PROJECT PROFILE: ROADS AND BRIDGES
The project which started in March 2016 is on track and scheduled
for completion in the first quarter of 2019. Significantly this project,
an initiative of the South African National Roads Agency SOC
Limited (SANRAL), is currently one of the largest road infrastructure
developments underway in the country.
Scope
It includes the construction of a new two-lane northbound
carriageway, rehabilitation of the existing southbound carriageway
and a large number of structures including bridges, overpasses,
culverts and drainage.
Bulk earthworks will amount to 800 000 m3, with layerworks
requiring 400 000 m3 of material and some 220 000 t of asphalt.
The total concrete volume is 37 000 m³, of which the ancillary works
will use over 16 000 m3 of concrete.
Contracts manager at Murray & Roberts Infrastructure, Jonathan
Pearce says the project features the full array of civil engineering
activities and includes the construction of 21 major culvert/under
pass extensions and 11 bridges.
The construction of two major river bridges on the northbound
carriageway is on the critical path and work on both has begun.
Preserving the environment
Pearce explains that all the requisite environmental assessments
have been conducted, and construction work is being done in
accordance with these. This is in line with Murray & Roberts
Infrastructure’s solid commitment to preserving the environment
for future generations and ensuring minimum harm to the areas in
which construction is taking place.
The water use licence dictates stringent measures as to how the
rivers may be worked in as well as restrictions to limit the footprint
in and around these areas. In addition, there are strict rehabilitation
programmes in place for after contract completion.
Bridge construction underway
The larger river bridge being constructed is over the Mhlatuze River
which has its source over 100 km away. The river catchment area
supports agricultural and industrial activities before it forms an
estuary as it flows into the deep water port of Richards Bay.
The Mhlatuze Bridge will be 240 metre long and have a total of
70 900 mm diameter bored piles with oscillated liners below seven
piers, some to a depth of 65 metres to reach competent founding
material and ensure adequate load bearing capacity for the final
structure. The bridge construction consists of eight deck spans com-
prising a total of 48 30 metre long post tensioned beams. Each span
has six 1,83 metre high beams which are cast elsewhere on the site.
“Complex geological conditions encountered in this area, with stiff
clay that has similar properties to soft rock found at around
35 metres, has caused delays in completing the piling activity”,
Pearce says.
The stiff clay creates a syringe-like effect on the piling casings
causing complications when liner extraction takes place. “While
delays have put pressure on the construction, we are adapting our
construction schedule to ensure that we meet the deadline and
SANRAL expectations,” he says.
The second major bridge under construction is over the Mlalazi
River and has its own set of challenges, largely emanating from the
inclement weather experienced during February and March this year.
Being so far up the KZN north coast, the tail end of cyclones in the
Madagascan channel normally hit the region bringing heavy rainfall
and major flooding. This was, indeed, the case with cyclone Dineo in
February with rainfall reaching more than 300 mm in 72 hours.
The Mlalazi River is tidal and although the bridge is situated
some 12 km from the ocean, the water level between tides can
rise and fall by up to a metre. Geo-synthetic sand bags have been
used to create working platforms to provide an adequate water
channel with minimum environmental impact while providing safe
working conditions.
The specialised sand bags provide an effective seal between the
water and the construction works, preventing any seepage, such as
unnatural siltation, from the construction site into the river channel.
The Mlalazi Bridge will have a final span of 120 metres with three
piers and two abutments. Ten piles per pier, to a depth of 25 metres
each, will support two of the piers and one abutment. A total of 28
post-tensioned precast beams will be placed on top of the piers
and abutments
“Apart from the John Ross interchange bridge, yet to be
constructed, and the extension to existing overpasses currently
being built in-situ, precast beams will be used. This has allowed the
construction process to be sped up and has negated the need for
extensive scaffolding and formwork along this busy national route,”
Pearce says.
The precast yard is situated in a location that allows the beams
to be easily transported to where required for installation. “Access to
the structural and ancillary works was given special attention as the
bulk of the works could not be accessed from the N2 highway. This
necessitated optimisation of vehicle usage and haulage routes to
remain as productive and cost effective as possible.”
As on all Murray & Roberts Infrastructure sites, safety is a
major focus and on-going safety training ensures that workers
comprehend potential risks associated with construction activities
and how to work towards a Zero Harm goal. On this particular
construction programme, special attention has been placed on
working at height given the number of high structures being built.
“Another mitigating step to ensure optimum safety of workers
on the highway during construction activities was the building of
scaffold towers to enable workers to cross the N2 to the side where
work needs to be done,” Pearce concludes.
Murray & Roberts Infrastructure is a division of Murray & Roberts
Construction which has been purchased by a consortium led by
the Southern Palace Group of Companies, creating the first major
black-owned infrastructure and building construction business in
South Africa.
FIRST BRIDGES ON N2
contract in KZN under construction
By offering an alternative construction methodology,
Murray & Roberts Infrastructure reduced the
proposed construction programme from 40 months
to 37 months on the contract to construct 33 km of
dual carriageway on the N2 between the Mtunzini
Toll Plaza and Empangeni interchange on the
KwaZulu-Natal North coast.
CONSTRUCTION ORLD JUNE 2017