Composite geogrid used to reinforce a retaining wall at the new Watercrest Mall.
The new multi-level Watercrest Mall in Waterfall near Hillcrest in KwaZulu-Natal is being built on a site with very steep slopes that necessitates the construction of safe, durable, flexible retaining structures, the costs of which can be debilitating in terms of materials and construction time.
To address this challenge, MCJ Engineers decided to use Kaytech’s unique RockGrid PC for the project. It is the first composite reinforcing geogrid to be manufactured in South Africa.
RockGrid PC offers the reinforcement characteristics of geogrids and woven geotextiles in conjunction with the favourable hydraulic qualities of nonwoven geotextiles. Its polyester, nonwoven geotextile fleece component protects the high tenacity polyester reinforcement elements during the critical installation phase, thereby ensuring a safer optimum performance.
The difference between RockGrid PC and conventional biaxial geogrids is that the geotextile fleece component wicks away moisture from the fill material, both during and after installation. This assists in drainage of the fill material during compaction so that higher, more stable fill-compaction rates can be attained. RockGrid PC provides sufficient drainage capacity to drastically reduce the flow paths in the reinforced soil. Due to this water transmissivity, RockGrid PC facilitates the reduction of pore water pressure should there be any groundwater ingress. This improves shear characteristics, which in turn increases stability.
The near vertical, 140-metre long concrete retaining block wall at the Watercrest Mall site comprises three sections: a 60m long section that ranges from 10m to 12m high, a 45m long by 12m high section, and a third 35m long x 15m in height section. The sub-contractor, Advanced Retaining & Paving Systems, installed RockGrid PC 100/100 at every third layer of retaining blocks. This grade of RockGrid generates a biaxial ultimate tensile strength of 100kN/m at 10% strain.
Kaytech’s technical sales engineer, Paul Lombard, was regularly on site to assist Advanced Retaining & Paving Systems with the installation.
Due for completion in October 2014, construction of this mall is taking place simultaneously with large-scale earthworks and the demolition of the existing multi-level shopping centre. Constricted spaces, in which the many contractors were forced to work, as well as time-constraints, made for an interesting and challenging project. However, the quick and simple installation of 15 000m2 of RockGrid PC, which does not require highly skilled or experienced labour, ultimately saved the developer both time and material costs.
The result was a neat and highly durable retaining wall that happens to be the highest RockGrid PC-reinforced concrete retaining block wall in KwaZulu-Natal, and possibly also the highest geosynthetic reinforced concrete retaining block wall in the province.
Tel: 031 717 2300
The challenge – solved:
• Very steep slopes necessitated retaining structures.
• A 140m x 15m concrete retaining block wall (three sections).
• RockGrid PC 100/100 installed at every third layer.
• Wicks away moisture from the fill material.
• Biaxial ultimate tensile strength of 100kN/m at 10% strain.