Reinforced Soil Retaining Walls for Infrastructure

This week’s episode of IAM News presented the case of the remarkable retaining wall incorporated into the structure of the Dubai-Fujairah Freeway in UAE. Let’s take a closer look at how reinforced soil retaining walls work, and their benefits to infrastructure assets.

Tensar, the designer and supplier of these mammoth walls, describes retaining walls as, ‘designed to restrain soil, or engineering fill, at an angle steeper than the material’s angle of repose – the steepest angle it can hold naturally without failing’.

One of the primary functions of reinforced soil retaining walls is to provide support to roads and railways where grade separation is needed at junctions, overpasses and to maintain a relatively flat traffic route through hilly terrain – as is the case in the Dubai-Fujairah Freeway example. They take up less space than embankments because they have vertical sides instead of the low-angle slopes of embankments.

The Dubai-Fujairah Freeway was constructed using mostly site-won fill, so very little fill material needed to be transported from off-site. The fill which was compacted in layers and reinforced with uniaxial geogrids. These geogrids are characterized by long, slim apertures and a monolithic structure that results from the manufacturing process of extruding, punching a drawing the polymer. An HDPE polymer is adopted for its high durability properties that give the wall a 120-year design life. The reinforcing function of the geogrids prevents shear failure through the reinforced soil mass that would otherwise occur in the vertical faces. There is also a mechanical connection between the geogrids and the wall facing blocks to prevent the blocks moving significantly and to maintain the walls’ impressive geometry. The geosynthetic reinforcements interlock with the fill particles, creating a composite material with enhanced shear strength. This adds to the reinforcing function and creates a very durable structure with minimal movements during service as demonstrated by the InSAR displacement data of this survey.

Another advantage of reinforced soil retaining walls and the mechanically stabilising effect of the geogrids is their ability to distribute loads efficiently. As a result, both lateral loads within the structure resulting from its retaining function as well as concentrated loads from heavy vehicles or construction plant are better distributed throughout the structure and to the supporting ground beneath. This minimizes the risk of localized settlements and uneven profiles developing in the infrastructure asset, thereby improving asset resilience. This reduces the frequency and cost of maintenance works. These benefits are in addition to the time, cost and carbon savings at the construction stage. According to Tensar, ‘load bearing reinforced soil walls can cut construction costs by up to 75% and halve build times compared with traditional solutions’.

IAM News brings you the very latest in infrastructure asset management every other Thursday. If you missed any episodes, you can watch them right here on our website!