When building the $1 billion Victorian Comprehensive Cancer Centre in the inner northern Melbourne suburb of Parkville in 2012, construction giant Grocon was carving out a rock wall 25 metres below ground on Elizabeth Street.
However, the excavation did not go as planned and part of the rock face allegedly become mobilised, cracking the pavement and the road near Melbourne University.
Images taken at the time by Grocon’s nemesis, the then Construction, Forestry, Mining and Energy Union (CFMEU), showed a crack in the centre of two lanes in the road.
Safety fears forced closure of the road for months. Last year, VicRoads filed a case against Grocon and its geotechnical engineer, Golder Associates, for $1 million in damages.
Whilst the case is ongoing, it highlights the importance of managing geotechnical risk during the building phase of major civil or commercial construction projects in an effective manner.
That raises questions about how risk should be managed and what can go wrong. To explore these issues, Sourceable spoke with two leading geotechnical engineers: Mark Ballard, geotechnical engineer at ICPS Australia, and Michael Morrison, director and principal geotechnical officer at Morrison Geotechnic.
According to Ballard, geotechnical risk needs to be carefully managed, especially as projects become larger and more complex.
When undertaking construction, he says several things can go wrong, including foundation failures, building movement, retaining wall and shoring failures, slope failure or land slips, surface and ground water issues, sub-surface conditions and materials not identified and inappropriate construction and shoring methodologies.
Further, the building methods which are appropriate vary according to the underlying ground conditions and the engineering properties of the ground. Where investigation of these is not adequate, he says risks that require mitigation may not be identified.
In many cases, he says, ICPS has been called in to provide expert advice in project disputes where structural or geotechnical failure had led to delays, cost overruns and litigation. In many of these cases, he said, either the recommendations of geotechnical engineers were not followed or the level of investigation conducted was inadequate.
Further, he says geotechnical issues – especially those which relate to surface of sub-soil water conditions – do not always become evident until after construction during a project’s life. This can lead to costly repairs and disputes about which party must pay.
According to Ballard, mistakes are common in several areas.
First, geotechnical investigations are often selected on the basis of price rather than quality. As a result, boreholes are often small and represent only a small proportion of the overall site area. As well, scopes of work for geotechnical engineering assessments are often inadequate.
In addition, the background and history of the site are often overlooked as a source of insights about the geotechnical risks which may be present.
Ballard says geotechnical engineers must be consulted throughout the project to identify potential changes that may impact either construction or post-completion maintenance.
More broadly, he says geotechnical engineering is undervalued and should be included within all multi-disciplinary teams.
Morrison, meanwhile, says strategies are needed chiefly in two areas.
First, he agrees that ongoing geotechnical support is needed throughout the construction process.
When assessing geotechnical risk during construction, Morrison says it must be remembered that ground conditions can vary according to specific positions on the site. This means it is possible that the soil at the point of the boreholes could be dry (and thus relatively strong), but the soil as little as 15 metres away could be damp and thus weaker. Likewise, ground conditions can vary by season. Thus any ground which is dry during a geotechnical investigation could be boggy and less trafficable when wetter seasonal conditions arrive.
When geotechnical engineers are involved during construction, Morrison says designs can be adjusted to accommodate these issues.
Next, the investigation must be thorough and not compromised by cost cutting.
On this point, Morrison gives the example of a new bridge being built over a gully which is supported by an abutment at each end and two piers along each side of the river bed. Where the project owner decided to save costs and have boreholes dug only at the point of each abutment, you would have no idea what conditions are likely to be like at the point where the piers are placed. This creates a risk that contractors could come on site and find conditions at the points where the piers intersect with the ground are different compared with what was envisaged and planned for. This can lead to delays and blowouts in construction costs.
Moreover, time must be taken to obtain a full laboratory report based on samples from the site. At times, Morrison says, geotechnical engineers can come under pressure to issue an opinion quickly. Where this happens, clients often choose to forego lab testing, which can take up to three or four weeks.
This, he says, is a mistake. Different soils, he says, may exhibit varying properties according to the context in which they are placed. Properties of a particular soil in one suburb may not necessarily resemble those of an identical soil in a neighbouring locality. Thus the only way to be confident about how a given soil is likely to behave on site is to have it tested.
Throughout Australia, potential hazards in relation to geotechnical matters must be carefully managed during construction.
Where sensible precautions are adopted, however, risks can be managed to an acceptable level.