TECHNICAL - Why Use an Engineer? Verwoed Rd, Lakeside:
The client had a house built on a steep site in Verwoed Rd, Lakeside. The site itself was retained by an existing retaining wall of approximately 4m in height that was not in a great condition. The client wanted the site to be further retained and requested that the existing wall be raised by another 4m. The client asked the housebuilder to quote on the job, and accepted the quote. The housebuilder was not a specialist retaining wall contractor and had no prior experience of retaining wall installations of this magnitude, nor did he recognise the potential instability of the existing wall. He did not think it was necessary or required to obtain an engineer's advice or plan for the wall.
The housebuilder ordered the GreenLock S12 retaining blocks from Cape Brick and proceeded with the installation. The wall was completed to the client's satisfaction and that was that... or not! A director of Cape Brick happened to drive past the site and recognising the GreenLock blocks, stopped for a closer inspection. At first glance the wall appeared to be well built.
However a closer inspection revealed several worrying aspects. A small shift in the existing wall had caused a line of shear cracking on the bend in the centre of the new wall. The first 5 courses of the new wall were filled with concrete. There was absolutely no drainage present anywhere in the wall. When the winter rains came there would be nowhere for the water to go and there were already signs of movement within the wall.
Although the sale had already been made and the installation had nothing to do with Cape Brick, the director saw it as his duty to inform the client and the builder that the wall was in danger of failure, both from a safety perspective and to prevent the inevitable bad publicity that results from such a failure. Both the builder and the client were on site and were told of the various concerns and were advised to rebuild the wall with drainage. The builder challenged the viewpoint of the Cape Brick director as being inaccurate and was supported by the client.
Ten days later the first major winter rains arrived in the Cape. Following on his curiosty, the director responsible for the earlier inspection made a turn past the site. What was seen confirmed his earlier fears, complete and catastrophic wall failure.
The failure exposed the corner foundations of the house, a four level structure. Thankfully there were no damges to either persons or property.
Following the failure, the owner called Cape Brick, and asked for a quotation for an engineered solution from a retaining wall specialist installer. It seems that some people have a need to learn the hard way. He refused the quote as being too expensive and the original builder rebuilt the wall, making many of the original mistakes again. Time will tell the result...
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