By Engineer Mike Clarke
The fastest road contract ever undertaken in Zimbabwe was completed at the end of November 2001.
The contract was worth US$19 million, was for the construction of a new high specification, 78 km long road linking Selous to Ngezi, and was carried out by several Zimbabwean companies working together as the Ngezi Road Joint Venture. It was completed two weeks ahead of schedule.
Here is the remarkable story.
Contractors did 1 km every 2.61 days. Peak equipment reached 591 units, and manpower was 1471 employees at the height of the project. Time taken to complete project; 200 days.
Ngezi Platinum mine is located about 150 km south-west of Harare. Australian company BHP had failed to mine the Hartley operation. Hartley was bought into production in 1997 at a cost of US$289 million but shut down within two years because the underground tunnels were unstable and many lives were lost.
Zimplats took over the Selous Metallurgical complex for a nominal sum. A local entrepreneur, Mr van der Spuy was aware that platinum could be mined on the surface, 70 km away from the Selous Complex. The ore had to be moved to the SMC complex at Selous and crushed there.
In early 2000, Zimplats announced the development of Ngezi Mine into a 2.2Mt/y open complex operation producing 208,000 ounces of ore per year from the platinum group metals plus nickel, copper and cobalt. This revived at least part of the original project. The ore body covered an area of 8 km north to south and 1 to 1.5 km west to east, and as mentioned outcrops at the surface about 70 km away from the main complex.
Initially the mine operated with caution and for a number of years operating an opencast mine but then because of environmental issues, the mine was forced to put the rock back into the pit. This operation turned out to be extremely expensive and so they decided with a lot of caution to go underground. The depth of ore was at a difficult depth but the mine managed using modified trucks and front-end loaders for its mining operations.
In June 2009, the total proven and probable reserves at Ngezi were estimated to be 217.4Mt which yielded 1.7g/t platinum, 1.32g/t palladium, 0.14g/t rhodium and 0.25 g/t gold plus nickel, copper and cobalt. In the year 2000, the economy of Zimbabwe was at its lowest but this did not deter the new owners to go to Absa bank in South Africa to borrow the money to construct the new highway from Ngezi to Selous which was 76 km long with three major bridges.
The owners then contacted the five biggest earthmoving contractors in South Africa asked a consortium of Zimbabwe contractors in the year 2000, if they would be interested at their own costs to build this highway. Up to that moment in time, the Zimbabwean authorities had always built structures using separate teams to supervise and construct their roads.
The Ministry agreed to combine the design and construction, provided that the public could also use the road and that it was built to the Ministry of roads specifications and obviously could carry 160-ton loads.
The crushed ore was carried to Selous in Australian-style road trains, each consisting of a Mack truck and three side-tipping trailers. In each train, (there were nine in all, one of which was one prime mover in reserve.)
They had a length of 42m, a width of 2.5m and a height of 3.5m. The payload was 90 tonnes. The trains were designed to run every 20 minutes night and day for at least five years, although there were plans to eventually build a concentrator at Ngezi, which would reduce the amount of material being transported to less than a hundred thousand tons per year.
Ngezi Road Joint Venture won the contract for the road in the face of stiff competition from several leading South African Road Contractors, Murray and Roberts, Stocks and Stocks, Group 5, Grinaker and LTA.
Zimplats’s main problem was to find the money from Absa Bank who promised the money if the investment ratio got to 16. In May 2001, the bank approved the loan and the contract was awarded on 14 May 2001 and had to be completed by 13th of December 2001. The success of the project hinged on the time it took to complete the road as borrowing the money was expensive.
The client actually insisted on penalties of $17,000 per day for not completing the road on time, but also fairly allowed that same amount of money for early completion.
The fairy tale was that the road was completed two weeks ahead of schedule. The client then narrowed the number of contractors to three South African and one Zimbabwean contractor. The contract was eventually awarded to the Zimbabwe contractor known as the Ngezi Road Joint Venture (NRJV).
The main South African contractor told the Project Director of the NRJV that it was an impossible task. It had never been done in South Africa and it would be certainly the fastest road ever constructed in Africa. A very difficult decision had to be made by Costain. The situation for the Zimbabweans was that either they invested or the local companies were going to go bankrupt.
Obviously, the design of the road had not been completed when the project was awarded. A very difficult design decision was the location of the bridge over the Mupfure River. If it followed the alignment of the old road, it would have been very difficult to negotiate the many twists in the road for the heavily burden trucks.
The Project Director, sitting in one of the initial meetings, looked at the new road which generally went in a North South direction, asked why it could not go in a due North-South to the mine. The design team used the excuse that servitude would be a problem.
The Project Director requested that the design team look at this aspect of the road. A week later, it was ascertained that there was no reason why the road could not go north south but the problem was that the abutments for the bridge would have to be built in water using caissons. This was a huge problem as the bridge could never be constructed on time, if the caissons had to be built.
The Project Director went on a field trip walking through long grass until the bridge site was reached. It was true that the river was very wide and there was lots of water.
“It was a very uncomfortable walk because there were many snakes…”
It did not make any sense that there should be so much water at that time of the year in the river, so a walk was undertaken downstream again through very long grass. It was a very uncomfortable walk because there were many snakes, but all of the sudden the river turned and there was a concrete dam which was used by a farmer as a mini hydroelectric scheme.
The Project Director had worked for the Ministry of Water Development before he became a contractor. He made communication with the district water bailiff and got permission to blast a V-section in the wall. The Project Director had not done any survey, so the final outcome of blasting the bridge was unknown.
On the day that the project was awarded, 14 May 2001, it was imperative to show the client that the contractor was capable of doing this project.
The Project Director and a friend from K.W. Blasting drilled holes into the weir. When it was all ready for blasting, the Project Director thought that it would be irresponsible of him not to check if there was insurance, in case the water caused devastation downstream. He phoned the Chairman and asked that since the project had been awarded, did the NRJV have the requisite insurance in place in case of damage.
“Keep blasting the weir, and you will no longer be Project Director”
The Chairman was completely puzzled because the Project Director had done all of the work without telling any other members of the consortium. He had no option to blast because all of the blasting components were in place.
The Project Director was told in no uncertain terms that if he continued to blast the weir, he would no longer be Project Director.
Some very quick decisions had to be made and it was decided that unless the NRJV showed the client that it was determined to complete the project on time; the project was not going to succeed. This action also caused the other NRJV members to realise that there was no comfort zone. This also showed the Ngezi Mine that we were very serious about our commitment to complete the project in the requisite time. It was actually why the project was completed on-time.
The weir was blasted and when we walked upstream depressed, we found that the bridge site was completely clear of water and that construction could start that very day. We tried to phone the Chairman only to find that he was on his way to site. He was extremely surprised and aggravated but the onus was on him to start the construction of the bridge as soon as possible as this was most definitely the critical path of the project.
There were six spans – 18.6m per span – which required shuttering. It had an overall length of 124m. The deck consisted of post stressed beams, 1.2m deep and 690mm wide. The bridge was simply supported on elastomeric bearing pads. One abutment was supported on piles but the rest of the bridge was founded on rock. The use of post stressed beams was unheard of in Zimbabwe as a road bearing surface especially considering the mass of the loads that were going to travel over the bridge each day.
There was a company in Harare who was capable of making these beams. They like other construction companies in Zimbabwe had no work, so they were very happy to help. The pre-stressed beams were carried to site using a low bed and the concrete beams were put into position using trusses. It cut the construction time of the bridge by three months. It was surprising that the Ministry of Roads used this method of construction as it had never used this this method of construction in Zimbabwe especially considering the heavy loads that were going to use the bridge.
Njuzu: Muzvezve Bridge
This bridge had as many problems as the Mupfure Bridge, but completely different problems. The people that lived near the bridge were convinced that there were njuzus that would take people from the construction site.
I first visited the site with the Chairman who sat in the car for an hour while I made an inspection of the bridge site. It was a very difficult site because it was founded on Dolorite Boulders of varying sizes. It was important to pile on rocks that were able to withstand the loads of the road trains. It actually took as long to build this bridge as it did the large Mupfure Bridge. The length was 3 by 17.6m spans.
This was a relatively small bridge which was built to the Ministry of Roads standards. It was constructed using some of the team who were building the Muzvezve Bridge.
Some very large sized culverts were required for this project. In Zimbabwe, we had always used conventional concrete culverts but some of the catchments were so large that we would have been forced to construct more bridges. Instead we resorted to using custom made Armco culverts. One in particular has a very large catchment and was founded on poor materials.
When we thought that we had completed the road, we had some heavy rain which highlighted that we had underestimated the catchment of certain culverts as the rainwater crossed the road. This occurred at a number of culverts. The use of Armco Culverts although expensive, saves a great deal of time. Again, it was the first time that the Ministry of Roads had used this type of culvert.
Typically, the road had three courses; Base 1 consisted of a 120mm crushed stone, Base 2 was natural gravel cement stabilised and was 200mm thick and Bases 3 and 4 were conventional natural gravel-based courses.
Initially, it was found that the main contractors had very little road building expertise. This was foreseen and there was a special crew very experienced who had built many roads. Each week the road building crew would go to one of the contractors and show them the finer details of constructing roads.
The crew were definitely instrumental in making sure that the road was completed on time. The surface was a double seal chip and spray road. The tack coat consists of 19mm stone with RT55 road binder or MC 30. The seal coat was 7mm stone with a bitumen binder. Two Cat re-claimers were used to place the cement stabilised layer and played a major role in ensuring that pavement construction remained on schedule.
The re-claimers were able to mix the cement in the base material more effectively than conventional blade mixing. A saving in cement that was realised almost paid for one of the re-claimers on the project.
The road is still functional today and would be in better condition had the designers been aware that the road was also going to be used to carry cobalt by the locals. These miners did not adhere to the loading rules and many trucks were overloaded with cobalt ore. The road was vastly over-designed and is probably in excellent condition considering it has endured 20 years of life.
In order to keep to budget, there were changes that were made to the design, such as making the road 9m wide instead of 10m. This was accepted by the Ministry of Transport. Overall, the construction of the road in the time allowed represents a notable achievement and illustrates the ability and efficiency of the Zimbabwean road construction industry.
The road is still fully utilised today and is probably in the best condition of all the roads in Zimbabwe.