The power of roots and poor retaining walls

Here’s a garden retaining wall that garden wall we found on a single defect survey.  A retaining wall is intended to hold back ground on one side of it that is higher than the ground on the other, the load of that supported land can be considerable and retaining walls do need careful design and construction. In this case the garden wall was apparently a well-built retaining structure, but on further examination we found it wasn’t quite as good as it looked. It was in fact cracking and failing. Our close up photo reveals a large fracture and what can’t be seen is the tree on the land on top of this space behind the trellis.

What seems to have happened is that the retaining wall had been built without any reinforcement and of plain facing brickwork only– a bad start. There was an absence of any weep holes to allow water pressure behind to be relieved and then, as the tree had grown, the roots had pushed against the wall to create an effective ‘perfect storm’. The roots and the water pressure pushing against the wall and causing it to bulge outward.

Left unchecked we think the wall would have failed. What chance did the VW have of getting away unscathed? The wall needs to be taken down and properly rebuilt into a design suitable for the location and environment. This wall took less than 10 years to fail and the remedial cost will be well into four figures if not five!

Quite possibly, without the tree and for a lesser height, the selected solution may have sufficed, but for this height and with the conditions as they were, premature failure was inevitable! Always get a structure like this properly designed. It wall almost always need to have some degree of reinforced concrete within it and weep holes are essential to allow water pressure to be relieved.

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(Originally written by Steven Way, 3 April 2011)