JG Afrika’s Coastal Park: Material’s Recovery Facility (MRF) project won two awards at Construction World’s 2020 Best Project Awards.
Richard Emery, a JG Afrika Executive Associate and Integrated Waste Management Specialist, accepted the awards on behalf of the firm at an awards ceremony that was hosted at the Thunder Walker in the Johannesburg central-business district on 4 November 2020.
The project won in both the Consulting Engineers category and against stiff competition, including impressive renewable energy projects, in the AfriSam Innovation Award for Sustainable Construction category.
Undertaken on behalf of the City of Johannesburg, Coastal Park MRF is the first to be located on an existing operational landfill site.
The facility was constructed on 65 000m2 of land that was underlain by a 5m- to 6m-thick municipal solid waste deposit and covered by about a 325 000 m3 rubble stockpile.
A major challenge was engineering the building platform, as well as supporting the foundation loads of the structures over a waste body.
The geotechnical engineers immediately ruled out the use of a stiffened waste body to support the foundation loads of the structures. This is considering the differential settlement risk, as well as the inconsistent nature of the material.
Any conventional foundations would, therefore, need to be founded on the underlying unconsolidated aeolian and beach sand deposits. This was an unacceptable solution, considering that they were located under the water table and trenching 5m through municipal solid waste material posed occupational health and safety risks.
It was, therefore, decided to support the building structure using single 600mm diameter piles in each footing position, as part of a piled foundation solution.
Dynamic compaction ground improvement techniques were used to support heavy vehicle traffic, ancillary structures and services.
JG Afrika prepared a performance specification for the dynamic compaction, which entailed achieving a 150kPa bearing capacity across the entire site, with a stiffness modulus of at least 35MPa.
Considering the variability of the waste, it was also necessary to include 500mm engineered fill caps over the compacted waste with the earthworks design. The caps ranged from G7 to G5 in quality and comprises of a high strength geogrid to help distribute loading across the platform and mitigate any differential settlements experienced. This was then followed by the construction of the road or platform sub-base and base course.
The builder’s rubble was processed into an engineered fill product and used in the layer and bulk earthworks, as well as for in the capping of the existing landfill embankments.
This approach provided significant savings in transporting the material to a different site and in the procurement of material from traditional commercial sources for use in the earthworks – even after considering the cost of overseeing the quality of material that was produced from the stockpile by the contractor.
An innovative gas vent system was also designed to ensure that landfill gas does not build up and pose a risk to the Coastal Park Integrated Waste Management Facility and its operations. It incorporates drilling relief wells across the site, allowing a preferential path for gas release. The wells are linked by a collection pipe just beneath the surface of the dynamically compacted waste, which leads to a typical “whirly bird” extraction fan. This ensures a negative pressure to draw the gas to the surface and vent it to the atmosphere. There is also an option to extend this to the gas collection system, should the gas yield be strong enough to warrant this.
This project has again demonstrated JG Afrika’s ability to work with government to find innovative solutions to solve South Africa’s unique socio-economic-challenges.