Pampoennek road project
Road design that takes nature into account
The Pampoennek Road project, which is located in one of the mountainous Magaliesberg nature reserves in Hartbeespoort, has shown that infrastructure development can help sustain the environment rather than damage it. Zutari was appointed in 2008 to conduct a geotechnical investigation to determine the approximate volume of suitable material in the dyke of the cutting. A slope stability analysis was also conducted to calculate the stability of the cutting and to determine the settlement of the roadbed sections where engineered fills were required on the northern and southern sides of the cutting.
The geotechnical investigation found that due to the in-situ soil conditions, the restraints imposed by the width of the road reserve, and an existing Eskom powerline, near-vertical retaining walls would be required in the cutting. It determined that soil-retaining mechanisms, such as permanent soil nailing with shotcrete, were the solutions best suited to supporting the environmental effects and ensuring slope stability in the cutting.
The potentially unstable slopes of the cutting were mitigated by constructing a benched retaining wall at the eastern embankment that peaks at heights of 4 m and 7 m for the upper and lower walls, respectively, as well as constructing a retaining wall at the western embankment and a continuous piled wall to ensure that no settlement occurs at the Eskom pylon located at the top of the western cutting. The continuous piled wall is 30 m long and consists of 1.05 m diameter piles varying in length from 15 m to 19 m. The piled wall was capped with a beam to ensure that the wall functions as a unit and smooths out the top of the wall. A drain was also implemented behind the capping beam to prevent run-off water behind the structure from overtopping the wall and subsequently staining the wall, and to collect and discharge the stormwater in a controlled manner.
The continuous piled wall and the retaining walls were anchored with a combination of 9 m- and 18 m-long titan anchors, as well as 8 m and 4 m galvanised soil nails. The combined exposed surface area of the retaining walls and the piled wall totalled 3 317 m².
In April 2017, the Pampoennek Road project was officially launched when the Aveng-Lubocon Joint Venture and Zutari’s supervision team established the site and commenced with construction. The project consists of a 7 km dual-carriageway road with an additional climbing lane on the approaches of the cutting through the Magaliesberg. The project has a total estimated fill of more than 1 Mm³ and a cutting through the Magaliesberg. The cutting caters for a total surfaced width of 33.2 m and has two 3.9 m concrete-lined drains. The cutting peaks at an excavation depth of 19.5 m and has a maximum clear opening 185 m wide over its length of 500 m. A total volumetric quantity in excess of 500,000 m³ was excavated, and a cut batter of approximately 50,000 m² was reinstated at a slope of 1:2.4 (vertical/horizontal) where applicable. The project also boasts a 76.2 m-long, 28.81 m-wide bridge carrying the route over the P123-1.
The initial surface finishes of the retaining walls and the continuous piled wall were exposed aggregate that would be easily identified as an artificial structure in the cutting. During construction, the Aveng-Lubocon Joint Venture proposed alternative finishes for consideration to soften the appearance of the artificial walls in the cutting. After several methods had been considered, it was found that a rock- scaping finish with rock art would blend into the Magaliesberg gorges, softening the appearance of the retaining walls in the cutting and increasing the overall aesthetics. In 2018 the rock-scaping and shotcrete work were submitted to the 14th Annual Shotcrete Project Awards held by the American Shotcrete Association and won the award in the category Outstanding International Project.
Digital tools
The project was a showcase for using digital tools during the design and construction phase, from 3D visualisation during design to regular drone surveys during construction.
A total volumetric quantity in excess of 500,000 m³ was excavated, and a cut batter of approximately 50,000 m² was reinstated at a slope of 1:2.4 (vertical/horizontal) where applicable.
Environmental challenges and solutions
A game underpass was designed to provide animals, including baboons, leopards and small antelope, with access from either side of the reserve.
An environmental footprint was determined because of the design proposed by Zutari’s transportation unit, and the project team ensured that all requirements were strictly adhered to during all phases of the project. Great care was taken to ensure that the fauna and flora were disturbed as little as possible and relocated throughout the construction process, and that, upon completion of the road, the environmental impact would be as small as possible.
Before major construction activities were permitted on site, a 2 m-high game-proof fence was erected on the road reserve to ensure that animals did not stray into the construction area and onto the road once completed. In addition, a search-and-rescue operation of indigenous plants was done before construction. A total of 3 556 plants were recovered from the project and temporarily relocated at a nursery close to the project. An additional 1 500 plants were acquired. This mixture included various species of tree, shrub, aloe, creeper and groundcover. The land- scaping in the cutting will use 3 930 of the plants and the remainder will be planted throughout other areas of the project. The rehabilitation of these plant species within the cutting’s construction footprint allows for quicker and more successful integration of the new road into the natural surroundings. An indigenous hydroseeding mixture, suitable for the site conditions, was also specified. This would ensure proper grass cover on erosion-prone areas such as the cut-and-fill batters.
When the design was done for the project it was identified that predominantly baboons, leopards and small antelope species inhabit the nature reserve, and that the construction of the road would divide the reserve into an eastern and a western enclosure, consequently restricting the animals’ access to either side of the road.
To mitigate the restricted access, a game underpass was designed to provide the animals with access from either side of the reserve. A location on the southern part of the cutting was identified as the most suitable area. This area is located at an existing watercourse situated approximately 12 m below the final road level. The game underpass consisted of a 2 m x 2 m x 88 m structure cast in situ, angled at 60° to the centre line of the road and following the natural watercourse and wildlife trails. At the beginning of the construction phase, however, interested parties from the Tshwane University of Technology (TUT) indicated that larger antelope species such as kudus had since migrated to the area.
It was evident that a 2 m x 2 m structure would be inadequate for these larger antelope species identified in the reserve. Another concern raised by the local stakeholders was the lack of natural light in the structure which would deter nonpredator species from entering the structure, as they would feel threatened by potential visual impairment. A minimum structure dimension of 4 m x 4 m was recommended by the TUT representatives.
After feedback from the interested parties, a decision was made to revise the design and to accommodate a larger clear opening. The alternatives considered were a 4 m x 4 m concrete structure cast in situ and a 6.5 m diameter corrugated steel structure. The corrugated steel structure was implemented as it was found to be a more cost-effective, less time-consuming alternative, and had the additional benefit of a larger clear opening.
Zutari is proud to have been part of a project that considered the environment by taking proactive steps and implementing alternatives that benefit the environment. This project has again proved that civil engineering can harmoniously integrate development and minimal environmental impact.
*The Aurecon Africa business has been officially renamed Zutari as at 21 July 2020. Zutari acquired Aurecon Middle East on 20 November 2020.
