Interpretation of piezocone penetration and dissipation tests in sensitive Leda clay at Gloucester test site

• Published in: Canadian geotechnical journal 2018-12, Vol.55 (12), p.1781-1794
• Main Authors: Agaiby, Shehab S, Mayne, Paul W
• Format: Article
• Language: English
• Subjects: argiles; argiles sensibles; Cavity expansion; Clay; clays; Compression; Compression index; Compressive strength; cone penetrometer; Consolidation; contraintes d’élasticité; Dynamic testing (Engineering); Effective stress; essais in situ; Field tests; Friction; Hydrostatic pressure; in situ testing; Leda; Mathematical analysis; Mechanical properties; Membrane permeability; Methods; Overconsolidation; overconsolidation ratio; Parameter sensitivity; Parameters; Penetration; Permeability; piezocone; piézocône; Pore water; Pore water pressure; preconsolidation; Profiles; préconsolidation; pénétromètre à cône; Quick clays; rapport de surconsolidation; Rigidity; sensitive clays; Shear modulus; Shear strength; Soil; Soil mechanics; Soil permeability; Soil sampling; Strain; Stress-strain curves; Testing; Tests; Triaxial compression tests; Volumetric strain; Water; Water pressure; Yield stress; yield stresses
• ISSN: 0008-3674; 1208-6010
• DOI: 10.1139/cgj-2017-0388

A modified piezocone penetration test (CPTu) analytical solution based on spherical cavity expansion and critical state soil mechanics (SCE–CSSM) is employed for assessing yield stress, undrained shear strength, and flow parameters in sensitive Leda clay at the Gloucester test site. For sensitive and structured clays, the formulation relies on the mobilized effective stress friction angle ( ) defined at two parts of the stress–strain curve: (i) peak stress ( ) and (ii) maximum obliquity ( ). Input parameters for assessing the overconsolidation ratio ( , where is preconsolidation stress and is current effective vertical stress) from CPTu results include: undrained rigidity index (I R = G/s u , where G is shear modulus and s u is undrained shear strength), plastic volumetric strain potential (Λ = 1 – (C s /C c ), where C s is swelling index and C c is virgin compression index), and effective friction angles ( and ). A direct CPTu means of assessing the undrained rigidity index in a reliable manner is also developed that gives the N kt cone factor and matches profiles of undrained shear strength from triaxial compression tests (s uTC ). The modified solution is also implemented on two additional sites: a sensitive-quick clay in Norway and structured varved clay from New England. Interpretations of the coefficient of consolidation and permeability from pore-water pressure dissipation tests at Gloucester are evaluated using the SCE–CSSM formulation and shown to be comparable with independent laboratory and field tests.