As is often the case, on Tuesday evening 12th May our Glenferrie Rotary Zoom Meeting proved that Club Members, more often than not, provide very different and interesting presentations.
Our own Peter Harries gave an interesting talk on how earth retaining walls work. We pass them daily without realising the technology behind them to keep them upright.  The construction technique used today goes back 3000 years when the ancient Babylonians built ziggurats using  papyrus reed in layers on structures still evident today.  Babylon is now part of modern day Iraq.
Contemporary walls are made of layered, mechanically-compacted free-draining aggregate, with layers separated by galvanised rods or polypropylene geogrids. The facing concrete blocks and panels that we see are really only facings to prevent erosion.
Peter showed a number of photos of walls he has been engaged on, including a wall making up part of the Tullamarine freeway, together with a couple of failure slides. The photo shows where a building site in progress was hit with a heavy downpour of rain, and the drainage was not yet completed…..the wall kept its integrity, and the bubble was unpicked and re-laid a testament to the layering, which held the wall.
Ian Salek
Meeting Chair
Peter Harries' presentation provided many insights into the success factors for retaining walls
The Ziggurats of Babylon. Techniques used 3000 years ago using straw are still in use today, using steel
Building a retaining wall for the Western Sydney Orbital, using techniques proven millenia ago in Babylon
The retaining wall for the Tullamarine Freeway. The technique explained by Peter enable the curving of the wall to allow for a sharp bend approaching the Bolte Bridge, an effect other building techniques were not able to achieve.
Inadequate building techniques can lead to eventual wall sag and collapse, as happened with this wall in the United States