Franki Defies Challenges to
Meet Tight Programme
An optimised design to match a taxing contract programme was instrumental in Franki Africa’s ability to
hand over the challenging foundations and lateral support work for the landmark 144 Oxford project on time
C
ontracted to provide geotechnical
services for the ground-breaking
144 Oxford project, Franki was
responsible for the design, supply and
installation of the earth retaining lateral
support system and the piled foundations.
The project scope included a five-level
basement to a maximum depth of 15m
below natural ground level with a total of
5,755m² of lateral support, as well as 235
no. foundation piles with column loads
varying between 3,800 and 15,000kN. calculations to conceptualise a workable
solution that would account for this
restriction,” explains Markides.
Changes in design were a constant
challenge and design development had
to conform to the engineer’s and client’s
specifications. In this regard, Franki relied
heavily on its uniquely integral in-house
design team to deal with the changes
as and when they occurred, as well as
providing cost-effective workable solutions
to the professional teams.
Contract Programme
According to Brett Markides, Senior
Design Engineer at Franki Africa, from the
onset, the contract programme proposed
by the client proved challenging. However,
the development was considered a key
project for Franki and an optimised design
to match the contract programme was
fundamental to winning the tender in such
a competitive market.
The west elevation of the development
incorporated a Gautrain servitude roughly
12m beyond the site boundary where no
structural elements of any lateral system
could be installed through. The solutions to
this problem were not immediately obvious
as the servitude posed a restriction on the
anchor lengths required for conventional
lateral support. “The design team at Franki
had to revert to first principles and hand Challenges in Lateral Support
The design of the lateral support system
on the North, East and South elevations
comprised soldier piles with a system of
active and passive support in the form
of anchors. On the west elevation, an
initial cut back and batter was proposed
to reduce the retained height of the wall,
effectively reducing the lateral forces and
mitigating the requirement for structural
elements extending into the Gautrain
Servitude. The west elevation comprised
soldier piles with a similar system of
alternative active and passive support.
Franki developed a FEM model in
Plaxis 2D, capable of staged construction
analysis and analysed all expected forces
in structural elements and factors of
safety at every stage. Verification of
stability and deflections in the temporary
50
and permanent state were analysed
and checked against the required
specifications. The resulting output
confirmed the expected modes of failure
at the factor of safety stages and the
model was deemed appropriate for the
design solution.
Verification of the design followed
an observational approach on site
through stringent monitoring to ensure
predicted vs actual deflections aligned
throughout construction.
Due to the innovative design process,
health and safety considerations were
incorporated by employing well understood
and recognised methodologies in Franki,
so that neither additional risk would be
placed onto the site teams nor would any
unfamiliar construction methodologies
be introduced.
Piling
The geotechnical information indicated
competent rock granite between 5m and
15m below bulk excavation level. Auger
cast in-situ piles socketed into competent
rock were chosen as the most economical
piling solution, and Franki optimised
the pile layout to accommodate higher
loads on fewer piles. This was made
possible with specialised cleaning tools
to effectively clean the pile bases through
mechanical action.
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