Influence of Partial Consolidation during Cone Penetration on Estimated Soil Behavior Type and Pore Pressure Dissipation Measurements

Abstract

Estimation of soil behavior type from cone penetration testing, and the interpretation of dissipation tests, is complicated in in- termediate soil types, such as silty sands, sandy silts, etc., where partial consolidation occurs during penetration. This issue is investigated in this paper using results from cavity expansion and finite element analyses as well as field and centrifuge piezocone data. The implications for soil classification are examined using analytical expressions to explore the effect of normalized shear strength, rigidity index, and over- consolidation ratio relative to the influence of partial consolidation and viscous effects under fully undrained conditions. It is shown that partial drainage conditions can affect where data plots on soil behavior charts, thus complicating soil classification. The effect on dissipation tests following partial consolidation during cone penetration is shown to create errors in interpretation using experimental and numerical data. A new approach is developed based in part on manipulation of solutions for pore pressure dissipation (following undrained penetration) to account for these errors when interpreting dissipation tests. Errors can become significant during standard cone penetration testing when the t50 dissipation time is less than about 50 s. Guidelines, including equations and a chart, are presented for practical use. Finally, imple- mentation of this approach is demonstrated in a brief case study. DOI: 10.1061/(ASCE)GT.1943-5606.0000646. © 2012 American Society of Civil Engineers. CE Database subject headings: Soil consolidation; Cone penetration tests; Soil properties; Pore pressure; Sand (soil type); Silts. Author keywords: Cone penetration test; CPT; Cone penetrometer; Penetration rate; Consolidation; Dissipation test; Soil behavior type; Coefficient of consolidation; Intermediate soils.