Some of the country's civil engineers have been exposed for shoddy work on high walls built on the side of zig-zagging roads and rivers.

The shoddy workmanship was uncovered on 18 walls across three provinces - Gauteng, KwaZulu-Natal and Eastern Cape - according to Stellenbosch University academic Loren Agostini, who conducted the investigation.

Of the 18 walls that failed, 12 collapsed and six were "excessively" deformed.

Known in engineering parlance as concrete retaining blocks, the walls are designed to allow drainage of flowing water.

"The failures usually occurred less than one year after completion of construction," said the Engineering Council of South Africa (Ecsa) in a new notice to registered engineers.

"In recent years, there has been an increase in the number of failures of concrete block retaining walls to the extent that Ecsa's investigating committee has identified these walls as problem structures," it said.

Ecsa said roughly a quarter of the walls failed due to shoddy construction, but 75% collapsed owing to poor design. This meant most of the walls "would have failed even if correctly constructed".

"Other issues attributable to the designer include inadequate construction monitoring and poor standard of the construction drawings."

Ecsa said standard procedures were barely applied during construction. "All too often, any material available on site is used as backfill without due regard to its drainage characteristics, strength ."

But no specific engineer or group has been taken to task for the identified shoddy work.

Said Agostini: "In the same way as it is difficult to assess the proximate cause of failure, so too is it difficult to assign responsibility for the failure to a particular party. In many cases, more than one party contributed to the failure."

Ecsa urged engineers not to take up jobs that they are not competent in.

"Before accepting an appointment for the design of a wall, make certain that you understand how these walls operate and the basic soil mechanics principles involved."

And when doing the job, engineers should "ensure that the site conditions are adequately investigated prior to design and are verified by inspections during construction".

"The designer should carry out sufficient inspections during construction to ensure that the design assumptions are met and that the completed structure fulfils the design intent."