Civil Engineering January/February 2021 | Vol 29 No 1

Civil Engineering January/February 2021 35 The Gauteng Department of Roads and Transport runs an ongoing programme to maintain and upgrade its network of primary, secondary, and tertiary roads totalling thousands of kilometres. A substantial portion of this network consists of roads that have exceeded their design load capacity, many of which were constructed to outdated road standards with respect to width, intersections, drainage, signage, and general safety features. As an integral part of the maintenance programme, a 13.2 km portion of the P175/1 (commonly known as the Potchefstroom road from Vanderbijlpark) was rehabilitated in 2019/20. The road forms a vital link be- tween the industrial, commercial, mining, and agricultural districts of Emfuleni and Potchefstroom/Klerksdorp. As is usual on these types of roads, the material in the road layers had degener- ated significantly over time. The base layer also invariably consisted of natural gravel material. SCOPE OF THE PROJECT The contract was broken into three phases, with phases one and three constructed simultaneously to limit the length of phases to approximately 4 km. Construction was executed on half-widths with stop/go control points at the phase extremities controlling traffic. The contract specification called for the removal of the base, sub-base, and selected subgrade layers to either stockpile or spoil, depending on the quality of the material. This was to be followed by compaction of the roadbed layer, and then the selected layer from stockpile. The sub-base layer material had to be imported from commercial sources and chemically stabilised to achieve a C3 con- sistency. The base course layer was a G1 from commercial sources followed by a 40 mm continuously graded asphalt layer. BENEFITS TO THE COMMUNITY Two wards in the Emfuleni Metropolitan District were identified as beneficiaries of the project, which made provision for substantial work packages to be offered to the local community. A community liaison officer (CLO) was appointed, and all local labour, sup- pliers and sub-contractors were appointed through the CLO and with the assistance of two local ward councillors. The supply of fuel, plant, and materials was also sourced through the local community. Apart from the direct financial benefit to the community, the road upgrade has improved access to markets, aided public transport, and benefitted the local agri- cultural and industrial industries. INNOVATIVE TECHNOLOGIES Impact compaction was used to great effect in the construction of the layer- works on the project. The high energy levels allow for the creation of a strength- balanced subgrade profile to a depth of more than 2 m. The strength-balanced subgrade significantly reduces the risk of internal shear, particularly as there are no horizontal interfaces between layers, and improves the structural number of the subgrade profile. Differential strain was also reduced, which in turn slows down Innovative rehabilitation of the P175/1 Rienk van der Leij Managing Director Intelligent Compaction Solutions vanderleij.rienk@gmail.com Livelethu Dlamini Engineer Celankobe Engineering & Architectural Consultants livelethu@celankobe.co.za When the P175/1 between Potchefstroom and Vanderbijlpark needed to be rehabilitated, an innovative impact compaction method was employed that has the potential to realise significant economic savings in road construction. Local sub-contractors busy laying stormwater pipes Three-sided impact compactor in action