Failed Concrete Block Retaining Wall

Failed Concrete Block Retaining Wall - Written by De Vries Cronje
Erf 8307 Brackenridge, Plettenberg Bay, South Africa

After the heavy rains we had during the period 13-15 July 2012 another concrete block wall collapsed due to bad workmanship and inadequate design.

This retaining wall was also build by Mr Chris Viljoen from the company Vilco Retaining Walls. The choice of block was the GreenLock R12 (specifcations).

During inspection I found that the blocks forming part of the collapsed section of wall were not cracked or broken in any way. I have found that uncompacted clay was used for backfill and that there was no drainage installed whatsoever. The wall was also build on an eighty degree setback which is far to steep. The acceptable norm is seventy degrees.

Since 2008 we had very low rainfall and this is the first year since then, that we are receiving our normal average winter rainfall figures. Because of the fact that no drainage was provided behind this wall the embankment got saturated in time and with the additional load on the wall the pressure reached a point where it had to find a place to release.

This failure would not have occurred if the block manufacturer's installation guidelines was followed. If  the setback was on 70 degrees, a subsoil drain was installed and well compacted free draining backfill used, this would never have happened. The property is furthermore located at the bottom of a steep landscape and storm water management is therefore of the utmost importance. Needless to say no attention was given in this regard.