Linear Trendlines to Assess Soil Classification from Cone Penetration Test Data: Fid-Bau Portal

Linear Trendlines to Assess Soil Classification from Cone Penetration Test Data

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

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, $Q_{t} - F_{r}$ , 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 $Q_{t}$ against $f_{s} / σ_{v o}^{'}$ , where $f_{s} / σ_{v o}^{'}$ is sleeve friction normalized by effective vertical stress. In $Q_{t} - f_{s} / σ_{v o}^{'}$ space, CPT/CPTu data for a given soil yields a linear relationship with a slope designated $Δ_{Q}$ . The linear $Q_{t} - f_{s} / σ_{v o}^{'}$ relationships from many variably overconsolidated soils converge to a common origin that is offset from zero. When plotted in $Q_{t} - F_{r}$ space, the linear $Δ_{Q}$ relationships become hyperbolas, similar to the Schneider hyperbolas, but the position of the individual hyperbolas in $Q_{t} - F_{r}$ space are defined by the offset origin location. The $Δ_{Q}$ index provides a numerical value that can be linked to soil index and engineering properties. Using $Δ_{Q}$ values computed for uniform-texture, variably overconsolidated soils, and empirical correlations between $Δ_{Q}$ and soil index properties, a CPT/CPTu assessment chart is presented to improve soil classification and the generalized $Q_{t} - F_{r}$ framework.