Construction World January 2016

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CONSTRUCTION WORLD JANUARY 2016
ROADS AND BRIDGES
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Consultation with Kaytech’s Christiaan
van Wyk significantly cut the costs on a
huge road upgrade project in Pretoria
East. Traffic congestion on Simon
Vermooten Road, an important arterial
route from Mamelodi and the eastern
suburbs to the N4 Highway, had reached
critical proportions.
REINFORCING Simon Vermooten Road
A decision by the City of Tshwane Municipality to double the
size of the road included adding an extra lane to the bridge at
the intersection of the N4. The multi-million rand contract was
awarded to construction group, Liviero Civils with Aurecon as
consulting engineers.
The previous construction of the road embankment was found to
consist of a G9 fill material whose high Plasticity Index (PI) explained the
evidence of cracking in the layerworks. Having first considered the use
of lime to reduce the PI of the fill material, engineers decided to contact
Kaytech for possibly a better solution.
Wouter van Zyl of Kaytech suggested the use of its unique RockGrid
PC, the first composite reinforcing geotextile to bemanufactured in South
Africa. Wherever soft soils with low bearing capacity are encountered,
RockGrid PC will provide the most economical and time-saving solution.
It consists of a nonwoven layer in conjunction with high tenacity, bi-axi-
ally orientated, multifilament polyester yarns, the combination of which
guarantees the unique characteristics of the product. The high tensile
modulus of RockGrid PC provides excellent reinforcement characteristics
and minimum creep deformation compared to polyethylene or polypro-
pylene grids or woven fabrics.
By mid 2014, 4 000 m2 of RockGrid PC 100/100 had been installed
along one section of the route, thereby providing a robust reinforcement
layer upon which the new road could be constructed. Graded material
was imported for construction of the layerworks above.
The high tensile modulus of RockGrid PC provides excellent rein-
forcement with minimal deformation, while its nonwoven component
provides high resistance to installation stresses. Only RockGrid PC
provides sufficient drainage capacity to drastically reduce flow paths in
the reinforced soil. Due to this water transmissivity, RockGrid PC facili-
tates the reduction of pore water pressure and improves shear charac-
teristics, thereby increasing stability.
This installation of RockGrid PC covered only a section of the full
project which has been subjected to numerous delays including heavy
rains and the subsequent decision to incorporate Tshwane’s Bus Rapid
Transport (BRT) system. This necessitated the redrawing of plans to
include future BRT stations on the median of the road as well as another
extra lane on the bridge to accommodate the BRT system.
Kaytech will continue supplying its RockGrid PC which, compared to
the use of lime, has already saved a considerable amount of time and
money. Once completed, the upgrade to Simon Vermooten Road will
greatly reduce travelling time for the thousands of commuters working
in the city.
RockGrid PC was chosen over lime to mitigate the embankment's high PI.
Base layerworks being constructed over the reinforcing RockGrid PC layer. Additional lanes were created on Simon Vermoten Road.