Water, Sewage & Effluent July August 2018 | Page 20

Retains cell at design thickness
Even when care is taken, it is
inevitable that the cells will be stood
upon. The taut rigging bounces back
and so restores the cell to the original
design thickness. If the grout mix
had been a bit heavy and depressed
the cells, they slowly revert to
their original levels and it may be
necessary to top them up. The cells
therefore act as a template to ensure
that the flexible cast slab meets the
design thickness.
Working on the slopes
The rebar pegs must extend through
the bitumen layer so that the upper
Hyson Cells layer can be rigged
without needing to drive new pegs
through the bitumen and so threaten
its integrity.
These pegs were used as supports
for horizontal formers that allowed
the workers to walk without having
to stand on the empty cells. However,
it is important that these pegs do not
protrude above the final surface as
they could puncture vehicle tyres.
The workers wore safety
harnesses. The dry Waterblok can
be walked upon, so placing the final
layer of Hyson Cells without use of the
formers was not a problem with the
help of the harnesses.
In collaboration with Hyson
Cells’ experience and guidance,
Süllwald Bouers was rewarded
by a significant improvement in
production and lowered costs,
resulting in a high-quality job. u
Installation at Phalaborwa – speed of construction
Self-levelling slump used on floor: A slump of 100mm was used for the grout for the dam’s
floor. This was placed directly from the ready-mix truck. The discharge chutes were swung
from side to side to help distribute the fill over as wide an area as possible. The mix had
good flow characteristics because of the use of river sand, with no other aggregate, and
was largely self-levelling.
Installation speeds of 400m² per day were achieved on the floor of the dam.
Liner constructed concurrent with earthworks: As soon as the bottom of the dam had been
prepared, it was possible to commence constructing the waterproof liner on the floor
concurrent with the earthworks construction of the sidewalls.
The walls must be stable in their own right and in this case, Hyson Cells was not called
upon to achieve stabilisation, although the soil nailing of the liner to the underlying material
assisted in this regard. While the slopes are compacted to the engineer’s specification,
Hyson Cells is more forgiving on small displacements that may nevertheless occur.
List of professionals
Client Phalaborwa
Mining Company
Project Relocation of Raw
& Potable Water
Reservoirs
Consulting
engineers Knight Piesold
Main
contractor L A Crushers
Subcontractor Süllwald Bouers
for Hyson Cells
liner
18
Gravity-assisted flow of grout from head of slope: The ready-mix truck placed