In May 2017 Endecon Ubuntu Consulting Engineers contacted Kaytech for a solution on a differential settlement problem at a site in Centurion, Gauteng where a new branch of XtraSpace, a container storage facility, was to be constructed.
When Endecon engineers discovered dolomite pinnacles at a depth of 150 mm below the natural ground level, they realized that even once the Wad and weak soils were removed and replaced with higher quality fill material, differ-ential settlement might still occur. As a mineral composed of calcium magnesium carbonate, dolomite provides a higher load bearing capacity than fill material. Since the containers would easily span any voids and settlement, the main concern was to adequately reinforce the access roads between the rows of containers.
After a site inspection, a Kaytech representative consulted with Tensar, the manufacturers of TriAx geogrids. A de-cision was made to crush a portion of the dolomite rocks and mix this with the in-situ material to create a G6 aggregate that would be included in the Tensar analysis to create a specific design for this project.
The rigid polypropylene triangular geometry of this geogrid, a significantly different structure compared to bi-axial geogrids, provides numerous advantages, including near uniform radial stiffness through 360o, and greater reduction in aggregate layer thickness. This reduces the quantity of natural aggregates required as well as the volume of material to be excavated.
The design generated included compaction of the in-situ material to 100 mm above the top of the dolomite peaks to serve as a “cushion layer”, covering this by simply unrolling a layer of Tensar TriAx TX160 geogrid. Prior to surfacing, two 150 mm layers of the G6 material were installed above the geogrid.
The triangular structure of the geogrid, in conjunction with increased rib thickness and junction efficiency, provides significantly improved aggregate confinement and interaction, leading to improved structural performance of the me-chanically stabilised load-bearing sub-base. With tensile stiffness in three principal directions, this multi-directional product shows near isotropic properties.
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