High traffic volumes in Andries Pretorius Street, Mangaung, resulted in the rehabilitation of 2.2 km of road network, including intersections

Andries Pretorius Street is currently one of the main arterial streets in Mangaung, Bloemfontein. It provides access between the city centre and the N1, the north-western outskirts of Bloemfontein, Noordhoek residential area and the Hilton industrial area, andtraffic volumes are high on this four-lane street. The project includes the rehabilitation and upgrading of 2.2 km of the street, re-designing and construction of the traffic circle at the intersection with WillcocksStreet, as well as the upgrading of the Alexandra Avenue intersection. Various other intersectionswith turning lanes will also be upgraded.

Commissioned by the Mangaung Metropolitan Municipality and funded by the Urban Settlement Development Grant, the project mainly includes limited excavation of unsuitable pavement layers, in-situ reconstruction of the existing layers, construction of a new base layer, and asphalt surfacing. Concrete block pavingwill be constructed at the traffic circle. Ancillary works include stormwater kerb-inlets and pipes, concrete kerbing and channeling, road signs, the relocation of traffic signal lights and underground services.

Andries Pretorius Street background

Riding quality of the existing street is exceptionally poor due to pavement failures and numerous patches, making it clear that the pavement has reached the end of its design life. The rounded shape of the existing street creates an undesirable large cross slope on the outside lanes, which will also be improved with the upgrading of the street. The current geometrical layout of the traffic circle is not suitable for large trucks and high traffic volumes, and requires upgrading to facilitate smooth traffic flow during peak hours.

Traffic impact during construction

Construction commenced on 13 February 2012 and will continue for approximately 12 months. Although a concerted effort is being made by the contractor to keep traffic disruptions to a minimum, construction work has to be carried out on half of the street while traffic is accommodated on the other half. Two of the existing four lanes of the street will thus have to be closed for construction purposes. The remaining two lanes will be used to accommodate the traffic in both directions. Construction will be carried out in sections, meaning that only a portion of the road will be partially closed for traffic at any given time.

Challenges experienced

As with the most urban construction projects, the relocation of municipal and other services poses a major challenge. Numerous shallow copper pipe house connections need to be lowered before major construction of the layer works can commence. Other services include the relocation of optic fibre cables, a main water pipe and electrical high mast lights.

It is also interesting to note that the presence of a rock layer on one side of the road, approximately 200 mm below the existing surfacing, suggests that it could have been the foundation of an old tramline. The rock layer is being removed where it is too shallow and encroaches into the new in-situ reconstructed sub-base layer.

Materials used in the construction

The pavement design makes provision for the existing base and sub-base layers to be in situ reconstructed and stabilised with cement as the new sub-base. Where unsuitable in situ materials are encountered, these will be excavated and replaced with imported natural G5-G6 gravel material. A new base layer of imported G1 crushed stone will be constructed on the recycled sub-base. Continuously graded asphalt will be constructed as the final surfacing layer.

Concrete paving blocks, which have to comply with a high durability specification, will be installed at the traffic circle. Significant quantities of concrete are being used in the kerbing and stormwater channeling along the reconstructed street.