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Impressive and environmentally sound bridge abutment solution in Johannesburg

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When a solution for a bridge abutment and retaining wall was needed at the William Nicol Northbound K46, we were able to help with the design.

In the heart of Fourways, we have built a bridge abutment and retaining wall that stands an impressive 11.8m high using our Terramesh™ System and Green Terramesh™, providing an environmentally sound and cost-effective solution compared to alternative methods like reinforced concrete or mass gravity walls.

WSP & Crossman and Pape approached us to assist in designing a solution to a bridge abutment and retaining wall that was needed at the William Nicol Northbound K46 off-ramp that leads to the Fourways Mall in Fourways, north of Johannesburg, South Africa.

The retaining wall is sloped at 70 degrees to tie in with the bridge deck and to provide an aesthetically pleasing finish.

Construction of the wall was awarded to MECSA, Mota-Engil Construction and Powergate Construction. We provided a design for a wall 222 m long with a total wall area of 1,696 m2. The most critical section of the wall is the bridge abutment that is 11.8 m high with a load of 150 kPa.

This section is reinforced at every 1,0 m vertical spacing with double-twisted, steel-wire mesh as the secondary reinforcement, then Paragrid 150 and Paragrid 100, a high tenacity low strain polymer-geogrid grid, as primary reinforcement.

The lower part of the wall is built using Terramesh, with Green Terramesh above. Green Terramesh allows for the 70-degree batter and adds an environmental feature allowing for greening to give a visually pleasing look.

Prior to starting construction, a detailed site investigation revealed a layer of alluvium material characterised by lower mechanical properties and high compressibility. To prevent settlement and cater for high bearing pressures this alluvium material was removed and replaced with a pioneer layer of clean rockfill, with a particle size between 200mm and 300mm. The pioneer layer thickness varies between 600mm and 900mm. Geotextile was placed over the rockfill and a 300mm layer of G7 was compacted to specifications.

The design of the wall was carried out by our Engineering Unit using MacStars W. MacStars is a software package used for the design of reinforced soil solutions. The software allows for complex modelling of the applied forces and considers the effects of any surrounding structures on the reinforced wall.

Next to the wall, a stormwater channel was planned to take water from the attenuation pond upstream of the site. Unmanaged water could have undermined the retaining wall and eroded the toe of the structure. This water channel was constructed along the retaining wall to direct water flow and to provide protection from erosion using gabions and reno mattress. To provide even more protection, shotcrete was applied to the wall face to prevent seepage within the wall.

Contact us to learn more on this project and our retaining walls solutions.

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