Kaytech’s RockGrid PC was installed at Mponeng Mine when high tensile geogrids were required for reinforcement of a newly constructed concrete retaining wall.
Mponeng Mine, formerly Western Deep Levels South Shaft, situated in Carletonville, Gauteng, is one of the richest gold mines in the world and so deep that a trip from the surface down to the bottom (reaching 3 400m) takes over an hour. Kaytech’s RockGrid PC was installed at Mponeng Mine when high tensile geogrids were required for reinforcement of a newly constructed concrete retaining wall.
As a result of ongoing expansion at the mine, Anglo Gold Ashanti realised that new cooling towers had become a necessity. Due to insufficient surface area being available for the proposed towers, the existing stone-pitched embankments were demolished and steepened by constructing a new concrete block retaining wall. A larger platform area above the wall provided much-needed construction space.
The heavy point loads in close proximity to the top of the wall led the main contractor, JJG Construction, to specify Kaytech’s RockGrid PC 200/200 as reinforcement in the backfill of the five-metre high, 140m-long wall, built at an angle of 75o.
RockGrid PC is the first composite reinforcing geotextile to be manufactured in South Africa. It offers the reinforcement characteristics of stiff geogrids and wovens and in conjunction with its non-woven geotextile fleece component, provides high resistance to installation stresses and optimum hydraulic characteristics, one of the special features of this unique product.
RockGrid PC provides sufficient in-plane drainage capacity, enabling it to drastically reduce pore pressure in the reinforced soil, thereby improving shear strength characteristics and increasing overall stability of the structure. Even moist, cohesive soils can be utilised as a fill in steep retaining structures as the consolidation process is accelerated. This makes soil exchange and the import of expensive fill material unnecessary, saving both time and money.
The retaining wall at Mponeng Mine consisted of 13 500 Enviro wall blocks which were installed with a closed-face configuration by the subcontractor, Engineered Interlock Solutions. A G5 material was used as backfill and compacted to 95% Mod AASHTO. RockGrid PC 200/200, which has a biaxial ultimate tensile strength of 200kN/m, was then installed at every third row of blocks, with a tieback length of 3,5 metres.
The highly robust RockGrid PC 200/200 was extended through to the front face to ensure maximum connection strength with the block. The exposed grid was then trimmed and burnt off by means of a blowtorch.
To further reduce any possibility of pore pressure build-up behind the wall, a blanket drain was constructed at the base of the wall, with the tieback length of the geo-synthetic reinforcement determining the width and length of the drain.
The drain consisted of a bottom layer of bidim A3, followed by a 100mm thick layer of 19mm stone, which was then covered by a second layer of bidim A3. Bidim A3 has a high transmissivity (in-plane) as well as permittivity (through-flow) drainage capacity. To complete the drain, 75mm slotted pipe outlets were installed from the drain through the wall face at two metre centres.
In 1971 Kaytech began supplying the civil engineering industry with its non-woven continuous filament needle-punched polyester bidim geotextile. This unique product is manufactured according to internationally renowned technology. The bidim content in this project equates to 4 666 recycled two-litre cool drink bottles.
This important slope reinforcement project took three months to complete, during which time 4 500m2 of RockGrid PC 200/200 and 1 400m2 of bidim A3 had been installed. Overall, the results of the project at Mponeng were highly satisfactory and due to the performance and extreme durability of Kaytech’s geotextiles, Anglo Gold Ashanti is assured of a long-lasting retaining wall at one of their deepest and most lucrative mines.
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