Linear trendlines to assess soil classification from cone penetration test data

Steven R. Saye, Jorge Santos, Scott M. Olson, Ryan D. Leigh

Research output: Contribution to journalArticlepeer-review


The data format developed by Robertson and his coworkers to assess soil behavior type with cone penetration test data using a series of concentric circles can provide an unreliable assessment in overconsolidated soils.With increasing overconsolidation, the normalized net-tip stress-normalized friction ratio, Qt-Fr, data for uniform-texture, but variably overconsolidated soils follow the shape of a hyperbola as shown by the generalized soil behavior type chart developed by Schneider and his coworkers. To improve soil classification from cone penetration test/piezocone penetration test (CPT/CPTu) data, a method is proposed that plots Qt against fs/σ ' νο, where fs/σ ' νο is sleeve friction normalized by effective vertical stress. In Qt-fs/σ ' νο space, CPT/CPTu data for a given soil yields a linear relationship with a slope designated δQ. The linear Qt-fs/σ ' νο relationships from many variably overconsolidated soils converge to a common origin that is offset from zero. When plotted in Qt-Fr space, the linear δQ relationships become hyperbolas, similar to the Schneider hyperbolas, but the position of the individual hyperbolas in Qt-Fr space are defined by the offset origin location. The δQ index provides a numerical value that can be linked to soil index and engineering properties. Using δQ values computed for uniform-texture, variably overconsolidated soils, and empirical correlations between δQ and soil index properties, a CPT/CPTu assessment chart is presented to improve soil classification and the generalized Qt-Fr framework.

Original languageEnglish (US)
Article number04017060
JournalJournal of Geotechnical and Geoenvironmental Engineering
Issue number9
StatePublished - Sep 1 2017


  • Cone penetration test
  • Insitu testing
  • Piezocone
  • Site characterization
  • Soil behavior type
  • Soil classification

ASJC Scopus subject areas

  • Geotechnical Engineering and Engineering Geology
  • Environmental Science(all)


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