Spatial Variability of London Clay Using CPT and SPT Data

London Clay has been the subject of intensive investigations, but further research is required to characterize the spatial variability in greater detail. This study focuses on establishing a measure of the spatial variability using the Scale of Fluctuation (SoF), a key input into random field modelling of geotechnical problems. At two sites in Central London, the SoF is calculated using cone penetration tests (CPT) and standard penetration tests (SPT), both driven perpendicular to the lithostratigraphic sequence. The vertical interval (spacing) of CPT data is 0.02 m. The spacing of SPT data is ≥ 1.5 m. The results show that the vertical SoF from CPT is 0.24 - 1.01 m with a mean of 0.48 m; the vertical SoF from SPT is 0.96 - 3.99 m with a mean of 2.26 m. The SoF from SPT is close to the SPT data spacing, therefore the accuracy of SoF from SPT is questionable. The results also suggest that the main drivers for spatial variability are likely attributed to sedimentary cycles acting over thousands of years. The results do not provide sufficient resolution to evidence any seasonal variations.

Keywords: London Clay, spatial variability, scale of fluctuation, ground investigation, cone penetration test (CPT)