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New CPT technique aims to cure problem of cyclic loading in chalk

Geotechnical Specialist Lankelma has trialled a new CPT technique in north Kent, as part of a research project aiming to improve the design of piles subjected to cyclic loading in chalk – such as those supporting wind turbines.

“Cyclic loading can have a significant detrimental effect on pile capacity,” explained Andrea Diambra of the University of Bristol. He is leading the research team which includes Lankelma and WindSupport.

“Offshore structures are subjected to cyclic loading from wind and wave action, so this already forms a key part of pile design in these environments. However, while the phenomenon is relatively well understood in sands and clays, little is known about how pile capacity degrades in soft rocks, such as chalk.”

Lankelma managing director Eric Zon said: “We modified the piezocone (CPTU) set-up to allow small cyclic motions of the cone and measured the progressive degradation of sleeve friction and changes in pore water pressure. In effect, the CPT acted like a miniature driven pile.”

Results suggest CPTU has the potential to increase understanding of the underlying mechanisms of cyclic loading and help pile design in chalk – but more research is needed, Zon said.

“Lankelma’s involvement and skills were fundamental in exploring the idea of performing cyclic CPTUs in chalk,” Diambra added.

“The high quality of the data obtained was guaranteed by Lankelma’s great reliability and experience.

“The cyclic technique appears to have promising potential for all soil types and I really look forward to exploring further developments together.”

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