Arup Geotechnics has carried out two site investigations in London using geophysical wireline logging.
The work, at the Moorhouse construction project in the City of London and at King's Cross, used a tool that measures induced current and natural gamma. While the natural gamma log was not particularly useful in the London Clay, it has previously proved valuable in characterising the Lambeth Group strata beneath.
The sites are about 2.8km apart but the induction logs show close similarity in the pattern in the London Clay at both.
A higher overall conductivity of the two King's Cross logs is attributed to a higher water content than at Moorhouse where there is a thicker sequence of London Clay, while a low conductivity at 5-6m above the base corresponds to a sandier portion of the lower section of the London Clay.
The conductivity peak in the underlying Lambeth Group corresponds to the Woolwich Formation strata.
Many geotechnical plots for London Clay are compromised by the fact that they are not plotted to a geological datum but to a level datum.
Although the amount of Atterberg data was limited at Moorhouse, the induction log for the liquid limit data for the Millennium Bridge across the Thames at Bankside, where the base of the London Clay was known, shows good correlation, especially for the low conductivity point at 5-6m above the base.