Quantifying CPT cone factors in clays derived from weathered mudstone

Abstract

The empirical interpretation of cone penetration test (CPT) cone factors (Nk) can be subject to considerable variability for clays derived from weathered mudstones, leading to significant deviations in the estimation of undrained shear strength (Su). This paper presents a comparison of triaxial and CPT data from a site investigation in clays derived from weathered mudstones in central England. Corrected cone factors (Nkt,UU) were derived from a one-to-one comparison of 94 pairs of unconsolidated, undrained triaxial and CPT data from equivalent depths. The performance of the cone factors was evaluated using a training set (75 pairs) and a test set (19 pairs). A parametric study was used to explore the variability of Nkt,UU, quantified using the coefficient of variation (COVNkt,UU), for varied separation distance thresholds (Ds) between individual triaxial and CPT data. The absolute deviation between the laboratory shear strength (Su(Lab)) and that predicted from CPT profiles (Su(CPT)) was not sensitive to Nkt,UU values in the range 25 < Nkt,UU < 31. The parametric study showed that Ds could be increased from 50 to 250 m, to include more data pairs for estimates of Nkt,UU, without substantially increasing COVNkt,UU.

The cone penetration test (CPT) is an in situ test that produces continuous measurement profiles to assess and characterize subsurface conditions. Empirical relationships can be used to relate CPT measurements to the engineering properties of soils and weak or weathered rocks, and extensive research has focused on developing and calibrating such relationships (Mayne and Kemper 1988; Robertson

More information

Identifiers

ORCID for Kevin M. Briggs: orcid.org/0000-0003-1738-9692

ORCID for William Powrie: orcid.org/0000-0002-2271-0826

Catalogue record

Export record

Altmetrics