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Reconstruction of Section 3 N7 Highway


Our Role

SMEC undertook the geotechnical engineering investigations, design and construction monitoring of the reconstruction of section 3, N7 Highway.

Project Overview

SMEC South Africa successfully delivered a project which saw the upgrading and improvement of a 27.7km section of the N7, the National Highway which runs between the Western Cape and Namibia. Section 3 runs between the Citrusdal and Cederberg Intersections.

The existing road, which consisted of a surfaced width of 6.6m with narrow gravel shoulders, was upgraded to SANRAL’s standard cross-section of 12.4m surfaced width. The standard of the vertical alignment was improved by constructing 650 000m³ fills using material obtained from cuttings.

A hard rock quarry was opened and operated to produce approximately 175 000m³ of crushed materials for use in the pavement layers, for stone in concrete as well as for use in stone pitching to erosion protection works.

The reconstruction of a road following essentially the same horizontal alignment but with major vertical improvements resulted in significant differences in levels between the old road and the new. It provided unique challenges in meeting conflicting demands for traffic accommodation, keeping hauling distances to the minimum, and ensuring that available cut materials were put to best use as dictated by its engineering properties.

The available width of the road over a 4km section was restricted by the Olifants River on the right and the mountainside on the left. The geology consists of sandstone dipping towards the road with varying strike, mostly perpendicular to the road. The sandstone formation included inter-bedded clay layers which caused a number of slope failures in places during construction, and which were stabilised using rock bolts and mesh.

Location:
South Africa
Technical Area:
Transport
Client:
South African National Roads Agency SOC Ltd. (SANRAL)


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