Long stretches of black cotton soils had to be traversed on the sections which required widening and these posed special problems, particularly when such work was performed in the rainy season of 2010/2011[K1]
The demand for a ‘high specification highway’ between Ngezi Mine and Selous Metallurgical Complex (SMC) was driven by the fact that, on-site underground mining at the Zimplats’ Hartley Platinum Mine was no longer viable and thus was replaced by a new open-cast operation at Ngezi Mine, situated 78 km from Selous.
This in turn required a cost effective form of ore conveyance. After careful consideration of numerous options, it was determined that hauling the ore by road train would provide the most cost effective mode of delivery.
Known as the Platinum Highway, this road was then designed and built for Zimplats operations as well as public transport operations.
Being the biggest and fastest road construction contract ever undertaken in Zimbabwe, construction commenced on 14 May 2001 and was complete for hand over to the Ministry of Transport on 29 November 2001. With speed of construction taking priority, the contract was highly mechanised, with 575 pieces of equipment deployed at the peak of the project. The total labour force peaked at 1500.
Ten years after completion of the road
The road has relatively withstood the test of time 10 years after construction, considering its design life was 5 years. The road did however begin to exhibit signs of distress of varying nature in some of its sections. These distress problems are attributed to, extended design life of the road beyond 5 years, little or no maintenance of the road by the Department of Roads, overloading by private chrome ore haul trucks, block cracking of the cement stabilised natural gravel base 1 and rutting and crocodile cracking of the crushed stone base 1.
Zimplats Initiated Maintenance Programme
The road was handed over to the Department of Roads in 2001. However, on realising the constraints that the department was having in terms of resources to maintain the road, Zimplats appointed Brian Colquhoun, Hugh O’Donnell and Partners (BCHOD) in 2008 to carry out 13mm reseal work on sections of the road from 14.8 to 24km, 44.8 to 51.75km and from 66.6 to 69.6km.
Further maintenance work was deemed to be necessary and BCHOD, in consultation with Aurecon, implemented a more comprehensive maintenance programme in 2008.
Detailed pavement analysis was performed by Aurecon by means of the Falling Weight Deflectometer (FWD), test holes and detailed visual evaluation. Based on the findings of the detailed pavement analysis, a recommendation was made to Zimplats for the rehabilitation of certain sections of the road in a phased sequence of work over a number of years.
A project specific consortium (Ngezi 2010 Consortium), made up of three parties in; Bitcon, Tarcon (Contractors) and Sesanni Project Management, were awarded the Works Contract for “The Rehabilitation and Reseal of Road Sections between Ngezi and Selous” in August 2010.
Possession of site for works was effective from 2 November 2010, with contract duration of 9 months. The supervision of the Works Contract is performed jointly by BCHOD and Aurecon.
The rehabilitation work consisted of rehabilitation of approximately 10km of the existing road from 35 to 44.8km by reworking and stabilising the existing surface seal and 120mm thick crushed stone base 1 with addition of approximately 30mm of imported crushed stone aggregate, widening of the existing gravel shoulders to 2.5 meters, widening of existing drainage structures and construction of a new 40mm asphalt surface.
Also rehabilitation of approximately 7 km of existing road from 59 to 66.6km by widening the existing gravel shoulders to 2.5 meters, widening of existing drainage structures and construction of a new 40mm asphalt surfacing overlay, reseal of approximately 11 km of the existing road from 24 to 35km with 13mm pre coated aggregate, rejuvenation of approximately 7km of existing road from 52.55 to 59.0km and 69.6 to 70.4km by application of a fog spray. New road signs, were provided for along with installing subsoil drainage systems, erecting new guardrails, provision of road markings and upgrading of three intersections.
Due to the continued rapid deterioration of the road since the initial design and recommendations performed in 2008, it was deemed necessary once on site, for additional rehabilitation of certain road sections from 51.75 to 52.55km (Muzvezve River section) and 59 to 66km.
A further FWD and visual evaluation was performed by Aurecon in February 2011. Based on the findings of this analysis, a recommendation was made to Zimplats for the reworking and stabilising of the existing surface seal and base 1, prior to asphalt surfacing overlay, on the above mentioned sections.
The agreed scope of this work was to rework base of 40% of the southbound lane (unloaded lane) and 90% of the northbound lane (loaded lane). In addition a second base layer was constructed through the black cotton vlei from km 38.8 to 39.7km, in an attempt to reduce the negative action of expansive clay on the riding quality of the road over time.
The project was reasonably trouble free. However, problems and delays were inevitablyencountered. Delay in Environmental Management Authority approval, heavy rains in the 2010/2011 rainy season and the additional rehabilitation work required on certain sections mentioned above, resulted in an extension of time to 9 November 2011.
Other minor delays encountered included denied access to borrow pits by the local communities, reduced/erratic supply of bitumen from South Africa and frequent plant breakdowns of the Contractor’s plant and equipment. Long stretches of black cotton soils had to be traversed on the sections which required widening and these posed special problems, particularly when such work was performed in the rainy season of 2010/2011.
Despite these delays and problems the overall standard of work is good and assuming ongoing, albeit erratic supply of bitumen, the Contractor is expected to substantially complete the work by 9 November 2011.
Future Phased Rehabilitation Work
As part of ongoing maintenance plan of this road, the following rehabilitation work is recommended to be implemented in a phased approach, from 2012 onwards. This will be as follows:
Asphalt levelling layer and new 40mm asphalt surfacing overlay from 0 (Roundabout) to minus 2.5 (towards the SMC plant),
Reworking and stabilising the existing surface seal and base 1 with new 40mm asphalt surfacing from minus 2.5 to minus 5.0km (SMC Offloading Bay),
Widening the existing gravel shoulders to 2.5 meters, widening of existing drainage structures and construction of a new 40mm asphalt surfacing overlay from 0 to 8km,
Reworking and stabilising the existing surface seal and base 1 with new 40mm asphalt surfacing from 8 to 14.8km. Work to also include widening of the existing gravel shoulders to 2.5 meters and widening of existing drainage structures,
Reworking and stabilising the exiting seal and base 1 with new 40mm asphalt surfacing on the sections of fog spray rejuvenation performed in 2010 (52.55 to 59.0km and 69.6 to 70.4km). Work to also include widening of the existing gravel shoulders to 2.5 meters and widening of existing drainage structures and
Reworking and stabilising the existing seal and base 1 with 40mm asphalt overlay on certain sections of the 13mm reseal performed in 2008 (14.8 to 24km, & from 44.8 to 51.75km & from 66.6 to 69.6km). Work to also include the widening of existing gravel shoulders to 2.5 meters and widening of existing drainage structures.