Civil Engineering September 2022 | Vol 30 No 8

central highlands of Namibia, character- ised by rolling to hilly terrain. Traversing this terrain will include con- struction of an impressive 4.5 million m 3 of road embankment (fill) excavated from majority medium to hard mica schist, in addition to more than 500 000 m 3 of sandstone constructed layer-works and crushed-stone base course. The primary geometric design challenge hinged on the balancing of cuts and fills during the plan- ning of the earthwork and the positioning of interchanges that are not too far from the ideal connection points between existing roads and developments. The pavement design required careful consideration of material sources and availability. Road building materials in the Windhoek Basin are nearing depletion, and the source of large quantities of good quality layerwork materials is practically exhausted. The quartz pebbles, which served as the backbone source of G4 base material for road pavements over many years, are now contaminated with smaller mica and silt fractions and do not meet durability requirements for high pavement standards. For the freeway, sandstone will be crushed for a G3 sub- base. The method may seem laborious but has significant lifecycle benefit due to easier upgrade and rehabilitation in the future, when compared to cement stabilisation now. The base course layer has its own challenges with the nearest G1 phonolite source not producing sufficient fines and additional crushing and screening being required to obtain enough fines to meet specification. The base course will also be transported over long haul distances which will cause damage to the relatively marginal pavements en route as well as significantly affecting traffic through Windhoek. Hauling by train would be an advantage but has its own drawbacks with the availability of rail stock and locomotives. Double handling of materials may also cause segregation of the material to a point where additional effort may be required to re-mix the material to restore homogeneity. All these aspects require strict site supervision and quality control from the consultant as well as the contractor. The eastern-most section of the freeway, WHK-HKIA Phase 2B, runs through flat to hilly terrain and will include the final interchange link between Windhoek and Hosea Kutako International Airport before tapering to a single carriageway on TR6/1 towards Gobabis and Eastern Namibia. Construction commenced in September 2021. This last phase includes three inter- changes, of which the last one connecting the airport to the freeway is a trumpet- type interchange. Phase 2B requires five bridges in total of which three are post- tensioned twin spine bridges. CONCLUSION In an African country battling the odds of social injustice, economic difficulties and a global pandemic, any progress on major infrastructure is significant. Against all odds, Namibia has in recent years made substantial improvements in its road infrastructure and has continued to cement its place as the country with the best road network in Africa. This has been achieved through a decisive vision, excellent planning, and even better imple- mentation and quality control. Through tough financial drawbacks, the Namibian road network has continued to flourish, and the long-term investments promise to offer tremendous reward to the team that could foresee the relationship between equity and rideability.  Civil Engineering  September 2022 17