Construction World December 2015

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

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.

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

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CONSTRUCTION WORLD DECEMBER 2015