Maccaferri Africa works together with StefStocks and DRA Mineral Resources to develop a Macres T system for soil reinforcement.
The Assmang Manganese mine required a total of 4 retaining systems, approximately 7.5m high to accommodate tipper trucks, imposing up to 250kPa pressure in a vertical direction on the top slabs of the walls. The initial design was intended for a standard in-situ cast cantilever concrete wall, yet due to an increase in construction time and a cost reduction, StefStocks approached Maccaferri for an alternate solution.
The region where this solution was required faced a severe environmental complication: the soil in the area was made up of materials with elastic founding properties. The filling soil used for the wall was material coming from the mineral production that, being a manganese mine, had a grand unit weight of 28kN/m3, which added to the bearing capacity problem.
After design related meetings with StefStocks and DRA Mineral Resources, who were the project’s design engineers and managers, Maccaferri decided to devise a Macres T system, with high strength Geosynthetic reinforcement strips, to resolve the on-site problematic.
Two separate systems were constructed, each consisting of two facing walls. DRA designed a 1m concrete slab spanning from one wall to the other for the trucks to drive onto, tip through a grizzly onto a conveyor system below. The trucks now continue to drive in the same direction onto their next destination. This “actual abutment” design and the weak soils called for various soil tests to be done. The tests force Maccaferri to implement a backfill material, consisting of a blend of Manganese and Sand.
Moreover, a minor foundation improvement intervention called for the utilization of onsite material gained through excavation works below the foundation. These by-products were later used fro filling and compacting. Maccaferri future decided to increase the use of soil reinforcing lengths of Paraweb, thus spreading the loads over a larger area and make for a more stable solution.
In conclusion, the benefits and features of the project were ample and varied. Among other things:
- a high strength concrete mix was used so the panels could be stripped in within 24 hours,
- the walls element design of the wall was done by Maccaferri Technical Department using in-house MacRes software based on SANS 207:2006 coherent gravity method,
- construction drawings were supplied, comprising of plans, sections and elevations
- on site training (not full time) was supplied by Maccaferri, which ensured that the walls were constructed quickly and correctly.
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