Construction World December 2015

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CONSTRUCTION WORLD DECEMBER 2015 2 15BEST
PROJECTS
Project information
• Company entering: SMEC South Africa
• Project start date: 2013
• Project end date: 2014
• Client: Western Cape Department of
Transport and Public Works
• Consulting engineer: SMEC South Africa
Emergency Repair and Stabilisation of Franschhoek Pass
Franschhoek Pass was the first profes-
sionally located, designed and
constructed stretch of highway
in South Africa. Completed in 1825,
the route traverses the Middagkransberg,
serving as a gateway to the Overberg, a vital
link between the communities of the Fran-
schhoek Valley and Villiersdorp.
During the latter half of 2013, unsea-
sonably high rainfall in the region lead to
several slope instability cases along the
route, resulting in the pass being closed on a
number of occasions. The majority of insta-
bilities occurred as rock falls and superficial
slidings.
SMEC South Africa was appointed by the
Western Cape Department of Transport and
Public Works, under an emergency works
appointment, to develop a timely solution
to the problem to ensure the pass could
remain open to traffic while not compro-
mising on safety. Furthermore, in keeping
with the heritage of the route and the
surrounding environment, aesthetically
pleasing and environmentally friendly solu-
tions were required.
Remediation measures comprised the
stabilisation of an embankment by means
of an anchored gabion wall, the stabilisa-
tion of a failed cutting by means of a soil
nail wall with subsoil drains, and reinstating
and improving sections of the route’s road
drainage, including dissipater structures,
culverts and debris barriers.
While mesh is less obtrusive than say
concrete, it simply would not support
and distribute the high loads anticipated
from the anchors stabilising the 10-m-deep
slip failure.
A key feature of the solution was to
significantly improve surface and under-
ground drainage. Sub-surface drainage
was collected by drilling 12-m-deep,
purpose-designed perforated-pipe-and-ge-
otextile drains at regular intervals and at
several different levels into the slope at an
inclined angle. The surface drainage was
improved by providing a cut off trench over
the top of the cut, and providing benches
to the slope with drainage channels on
each step to collect and rapidly discharge
the collected water, including that from
the subsurface drains which discharge into
these channels.
The above geo-structural compo-
nents were modelled in both structural
and geotechnical finite element software
to ensure the integrity of the system mate-
rials/products chosen and that these
effectively integrate with the overall
geotechnical solution.
The project demonstrates ingenuity and
quality in engineering design and imple-
mentation and did not detract from the
routes aesthetic value while at the same
time the safety and effectiveness of the pass
was not compromised. This and various
aspects of the project deem this project suit-
able for nomination.