Tag Archives: Botes and Kennedy Manyano

DESIGN AND BUILD OF NEW 12,000m³ RESERVOIR FOR NAMWATER AT RUNDU, NAMIBIA

Work is progressing well on the new 12,000 m³ reservoir and associated pipework on Namibia’s northern-most border with Angola. Progress is over 60% and completion is expected to be well in advance of the contractual completion date of 12 April 2018.

The design and construction of the reservoir – awarded by the Namibia Water Corporation Ltd (NamWater) in October 2016 – is being conducted by a joint venture between B&K Civils and Windhoek-based Rock Leigh Investments.

The concrete reservoir situated near the Ndama Water Treatment Plant is being built to expand the water storage capacity in the Kavango-region. The current storage capacity at Rundu is insufficient to sustain the target area for the recommended 48 hour period. The new facility has been designed to cater for increased future water storage demands for this arid region.

According to B&K Civils’ project engineer, Antoni Botes, an interesting aspect of the project is that the reservoir foundation was constructed using the so-called RIC method or Rapid Impact Compaction.

“This methodology entails the use of a specially designed compaction unit fitted to the front of an excavator. It compacts the raft foundation at a grid spacing of 4.5 metres,” Botes explains. “The kinetic energy of this compaction technique is sufficient to densify the soil up to a depth of at least 5 metres and will provide the necessary bearing capacity to ensure the long term durability and stability of the reservoir.”

The remote location of the town – over 700 km north of the capital Windhoek and just south of the Cubango River – presents a logistical challenge for the consistent supply of the necessary high quality building materials used in the construction process.

“While this could be challenging for some contractors, our teams are well versed in operating in remote regions,” Botes says. “Streamlined logistics processes and careful planning ensures that all materials reach the project site on time. Adding to this are our stringent quality control procedures and the diligence applied by our quality control team, which will ensure the final product is of high quality and will meet the client’s specifications.”

Significantly since the Botes & Kennedy Group, which includes B&K Civils, began operations in 1980, the group has built more than 60 concrete water retaining structures in Namibia and South Africa.

“It is perhaps significant that our very first project was a water retaining structure; a 2,500 m³ reservoir with a 1,700 m³ pressure tower integrated into the reservoir,” says Botes. In the period since then, the company has undertaken numerous projects around Namibia, including a 20,000 m³ as well as a 16,000 m³ reservoir near Swakopmund.

“In all our work, we apply the highest standards of engineering quality and environmental protection, and this carries through to all phases of building and construction activities,” Botes says.

Panoramic view of the reservoir interior.

WIDENING OF BRIDGES AT HOPETOWN

Upington-based contractors Botes & Kennedy Manyano are progressing well with the widening of the 312 metre bridge on the N12 carriageway over the Orange River at Hopetown in the Northern Cape.

The substantial project is consuming 4,000 cubic metres of concrete and 500 tonnes of reinforcing steel, with about 28,000 bags of AfriSam High Strength Cement (CEM II A-M (L) 52.5N) being delivered from AfriSam’s Ulco factory near Barkley West.

AfriSam also designed a range of concrete mixes for the project to ensure optimal durability and certain workability requirements. This was done at its Centre of Product Excellence in Roodepoort which includes SANAS accredited laboratories.

The R88-million South African National Roads Agency SOC Ltd (SANRAL) project began in mid-2016 and is on track for completion by the end of February next year. It also includes a smaller bridge being widened a short distance to the north.

“This improvement will allow a widening of the road with a 2,5 metre shoulder on either side, as well as a dedicated asphalt surfaced pedestrian walkway along the eastern side, protected from the traffic by a concrete balustrade,” says Botes & Kennedy Manyano contract manager Deon Douglas.

The main bridge is a twelve span, simply supported structure constructed with precast pre-stressed I-beams. It comprises 11 concrete piers, each measuring some 12 metres in height, between a north and a south abutment. The road widening project requires new piers to be built alongside the existing ones and to similar dimensions.

The concrete mixes for the project included designs for 15 MPa, 30 MPa, 40 MPa and 50 MPa, according to Brendan Croney, technical consultant at AfriSam’s Centre of Product Excellence (CPE).

“Our concrete mix designs needed to meet SANRAL’s specification of a performance-based concrete, both in term of standard concretes and the ‘W’ concretes that must meet certain durability indices for oxygen permeability, sorptivity and chloride conductivity,” says Croney.

Almost 9,700 square metres of formwork was used in the construction of the 11 new piers, nine of which had been completed by August 2017.

The new abutments on the north and south banks of the river needed considerable earthworks to be done, according to Botes & Kennedy Manyano site agent Jeann van Tonder. At each abutment, 13 piles were drilled to an average depth of about 10 metres and socketed into bedrock.

“Before work could begin on the new piers, a causeway had to be constructed out into the river so that mass concrete bases could be poured, onto which a 1,7 metre deep concrete base could be constructed for each new pier,” says Van Tonder.

The piers were then cast in three lifts of 3,6 metres each and a final 1,5 metre lift. Concrete was poured from the causeway utilising a crane and concrete buckets.

The 12 spans for the new part of the bridge are created by 60 concrete I-beams, each measuring 26 metres long, with straight horizontal alignment and flat vertical alignment. The beams rest on elastomeric bearings on top of the piers. To complete the contract, the contractor will build a new road, laying down new sub base layers and a Cape Seal.

AfriSam also designed a range of concrete mixes for the project to ensure optimal durability and certain workability requirements at their Centre of Product Excellence, SANAS accredited laboratories based in Roodepoort.

CONCRETE REHABILITATION SUCCESS AT FINSCH BY BOTES & KENNEDY MANYANO

Botes & Kennedy Manyano offered Petra Diamonds a practical workable solution for the rehabilitation of three concrete silos at its Finsch Diamond Mine in the Northern Cape.

The design and construct project was aimed at restoring the structural integrity of the silos while addressing issues such as concrete and liner wear inside the structures.

Mantie du Toit, contracts manager at Botes & Kennedy Manyano, says that most importantly the solution provided an option whereby the concrete repair work would be done by taking one silo out of production at a time and recommissioning it before work would start on the next silo causing as little impact on the plant operation as possible.

Du Toit says that prior to the concrete repair work and construction taking place, Botes & Kennedy Manyano through the help of contracted consultants, was also responsible for the stability analysis of the structures. This formed part of the risk analysis phase of the project.

Construction work on this project started April 2016, and involved surface concrete repair work on the external faces of the three silos as well as on the internal faces. The spalled surfaces were repaired using various techniques depending on the severity of the damage.

Each silo has an external diameter (OD) of 13,4 metres and an internal diameter (ID) of 12,8 metres. The total height of the silo which includes a conical section at the bottom stands at 22,8 metres; the cylindrical storage section is 13 metres.

Access into the silos is restricted to entry from the top of the structure and the bottom outlet of the silo, and at the time of starting the repair work, each silo was filled to the top with kimberlite ore. The ore levels were discharged in a controlled way to a predetermine level in the silo to facilitate the concrete repair work. Use was made of a working platform lowered from the top entry giving access to the different levels going down at 2 metre increments. This was done by emptying the silos using the bottom draw point.

Outside access was facilitated through the use of scaffolding that was erected to the required height.

“During the project each of the silos was taken offline for a limited period of time, and this meant that the necessary resources had to be available to ensure optimum productivity was achieved, while still operating safely within the operational plant,” Du Toit says.

Mitigating the challenges faced by working at height required careful planning and stringent safety systems were implemented. All personnel received specific working at height training to ensure that all were competent and understood the working at height procedures. Du Toit says that the project safety statistics underpin the commitment show by the team.

Concrete repair generates a large amount of dust, and this was further aggravated by the work being done inside a silo. To mitigate this, ventilation ducting was installed to extract the dust and fumes, facilitating a much safer working environment for the personnel.

In addition to the concrete repair work on the inside of the silos, Botes & Kennedy Manyano was also tasked with increasing the wearability of these internal surfaces. This was achieved using a special epoxy product that will increase the abrasion resistance of the concrete surface

The scope of work also included the rehabilitation of the bottom cone section of each silo. Prior to this work beginning, custom carbon steel liner plates were manufactured and later installed to perform the function of protecting the concrete surfaces at the cone section. These also acted as an external shutter face to facilitate the casting of a concrete lining to strengthen the cone section of the silo. As the installation of the steel liner progressed upwards, the casting of the new 300 mm concrete lining followed the installation operation.

This was a labour intensive operation and to facilitate greater productivity in areas not subjected to interfacing with the mine, a bagged prepacked concrete mix was decided on. The bags were raised to the deck located at the top of the silo, where batching of the concrete was done in a portable concrete mixer. The concrete was then lowered from the deck level through a centre access, using a working platform with filled buckets of concrete placed on it, lowering it to the level of cast. The concrete was hand placed using the buckets and then densified. A retarder was used to lengthen the window of cast to prevent dry joints.

Attention to detail during planning as well as execution was essential to ensure that the safety of personnel was at not put at risk during this operation, and that the quality of the final product was not compromised. Some 64 m3 of concrete was used for the cone section of each silo.

A circular concrete beam was cast on the outside circumference of each silo to increase the strength and stability of the storage structure. This was done above the cone section of the silo.

Once all the concrete repair work had been completed, post tensioning was done on the outside of the structures. In total 58 strands, spaced vertically at predetermined intervals, were stressed. And this could only be done once all the repair work, both internal and external, had been completed.

Du Toit says that generally, concrete repair methods are application-specific and the solutions recommended and applied depend on the individual requirements. “We have the necessary technical expertise and experience to assess the best course of action in each circumstance and to develop a sustainable solution such as the one applied at Finsch to rectify any issues and maximise the useful life of the structure,” he concludes.

A top view from the roof inlet showing the liner plate stripping in progress in the cone section.