In-situ testing key to firm foundations

Haberfield designed the footing system for Nakheel's kilometre-high tower which is currently on hold.

One geotechnical and environmental expert has urged others in the field to commit to more in-situ testing rather than allowing all tests to take place in the lab.

Dr Chris Haberfield, principal at Golder Associates – the firm charged with designing the foundations and footing system for Nakheel’s shelved kilometre-high tower – made the appeal while speaking at the Piling & Deep Foundations Middle East Summit, being held in Dubai.

“Originally, the location for the tower was near the Palm Jebel Ali; however, that changed to a second site near Ibn Battuta,” explained Haberfield, whose firm not only needed to examine the geotechnical effects of a two-million-tonne dead load, but also needed to overcome the challenges caused by significant bearing pressures coupled with soft rock.

”Geologically, the sites were very similar, so we were able to use the information we had from site one and improve our data for the second site.

“We used triple tube coring, as this provides a continuous long length, rather than the broken samples you receive from double tube.”

The samples were then wrapped, packaged and sent for testing in laboratories in Dubai, Australia and the UK.

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However, the team also made significant breakthroughs in on-site testing, explained Haberfield, with elastic stiffness, bond yield strength, displacement and variability yield tested in-situ.

“We developed a scratch hardness test that could be done straight away on-site.”

The results helped Golder, along with contractors such as WSP and Fugro ME, formulate a foundation and piling approach to anchor the world’s tallest and biggest tower – with a 100m diameter.

And, added Haberfield, while Dubai has a simple geology, there are differentials that need to be considered for such a project.

“Surface sand goes down to about six metres; variable cemented sand runs from six metres to 20 metres; while calcareous mudstone takes us down to a depth of around 77 metres. Mudstone with gypsum then goes down to around 200 metres and beyond that lies very big, strong gypsum layers of between three and five metres thickness.

“In this region, there’s a high stiffness and elasticity prior to the breaking of the cementitious bonds but, after that, it compresses easily. You have to make sure you don’t break the bonds.” 

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