The risk of ground failure during excavations on construction sites should be taken very seriously, says Brent Cock, engineering geologist at SRK Consulting, and engaging the right geotechnical expertise from the start of a project is extremely important.
Brent Cock, engineering geologist at SRK ConsultingWhile deep excavations – for high-rise buildings, for instance – require specialised geotechnical assessment and design to offset the risk of failure, there are also risks attached to relatively shallow excavations of just a few metres, he says.
“A cubic metre of soil might look innocuous, but it typically weighs more than a small car and can weigh almost two tonnes – so any scale of ground failure can cause considerable harm to anyone nearby. We know of fatalities in excavations as shallow as 1m,” he said. “Even if people are not harmed, such failures can lead to costly delays in the project timeline.”
Not only does an excavation wall collapse require immediate attention to allow construction to proceed, it may also hinder a range of subcontractor activities – who still need to be paid even if their equipment and personnel are standing idle. Often projects are conducted close to other structures, which may be damaged or threatened by a nearby ground failure.
Technical analysis of ground conditions
A fundamental starting point is a thorough technical analysis of ground conditions in the early stages of project planning. The Geotechnical Division of the South African Institute of Civil Engineering (SAICE) Code of Practice for Geotechnical Investigations provides excellent, industry-relevant guidelines on how to proceed with a geotechnical investigation for a wide range of infrastructure development projects.
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