The Roads Authority of Namibia appointed VKE Namibia as consulting engineers to design and oversee the construction of the Windhoek – Okahandja Freeway upgrade project, which comprises the reconstruction of the old B1 Windhoek – Okahandja road as a new dual carriageway. The current construction phase, Section 4a Extension (originally termed Phase 4b), undertaken by CMC/Otesa Civil Engineering (Pty) Ltd Joint Venture (CMC/Otesa), aims to complete the portion of the road between the Omakunde Interchange (km 27.6) and the Okahandja Interchange (km 48.4).
At approximately km 28.2 along the new Windhoek – Okahandja freeway, to the south of the Osona Military Base and near the Omakunde Interchange, the (new) road alignment veers to the west of the alignment of the existing road and thus crosses NamWater’s Von Bach – Windhoek Pipeline. This pipeline is a vital supply link, transferring most of Windhoek’s water from NamWater’s Von Bach Water Treatment Plant to the capital city. Due to the alignment of the road, the new freeway crosses NamWater’s pipeline at an oblique angle, such that the pipeline needs to be realigned through a new culvert constructed underneath the new freeway to shorten the length of the pipeline underneath the new road embankment and to facilitate easier access to the pipeline for inspection, maintenance and possibly also repairs.
VKE approached LCE for assistance with the specialist pipeline design, which was carried out by LCE, together with specialised input from Prof. S. Van Vuuren and Prof. S. Jacobsz of Pretoria University. This project consists of the construction of approximately 380 m of 1,100 mm diameter Class 25 GRP pipe, buried, and approximately 60 m of 1,100 mm diameter steel pipes in un underground culvert, but in an “above ground” configuration on pedestals, as well as connecting steel specials, the construction of pedestals, thrust blocks, appurtenances, ancillary works and the connections to the existing NamWater pipeline. The two connections to the existing pipeline need to be constructed with specially made steel pipes with spigot and socket ends to fit into the corresponding socket and spigot ends of the existing 1,100 mm pre-stressed concrete pipe which is some 46 years old. These connections need to be constructed with great care and to very tight tolerances. A multi-step construction process has been laid out to first install new straight steel spool pieces into the existing pipeline across each of the two connection points, to allow flow to be reinstated whilst two thrust blocks are constructed; the first on one of the new steel pipes installed into the existing pipeline and the second on a new length of steel pipe installed nearby at a 45-degree angle to the existing pipeline. After these concrete thrust blocks have cured, the central spool piece installed in the existing pipeline needs to be removed and replaced with a bend and short distance piece to connect to the nearby pipe installed at a 45-degree angle. This requires the installation of pipework and the construction of thrust blocks to very exacting tolerances.
LCE has conducted the designs with specialised input from others, oversaw the tendering of the pipeline supply and the pipeline construction works as two separate contracts and is busy conducting the construction supervision and contract administration associated with these works.
Location: Between Windhoek and Okahandja
Completion: Before the end of 2022