Undrained shear strengths of clay around an advancing cone
Strength anisotropy of clay is significantly associated with the orientation of principal strain. Mobilized undrained shear strength will vary with the orientation of the principal stresses because cone penetration imposes large rotations of the principal stresses in the surrounding soil. The objective of this paper is to investigate the undrained failure modes around an advancing cone. In this study, strain softening behavior is not considered. The strain field of the soil obtained using the strain path method shows that the principal strain conditions of the soil around an advancing cone can be simplified into the following zones: spherical expansion strain zone, plane strain shearing zone, cylindrical expansion shearing zone, cylindrical expansion zone, and transition zone. The mobilized undrained shear strength of clay in various strain states can be determined by employing the anisotropic strength criterion and the associated flow rule. The result shows that the ratio of the equivalent undrained strength mobilized in the vicinity of the cone tip over the undrained shear strength obtained from a Ko-consolidated undrained compression triaxial test is found to range from 0.88 to 1.07 when the strength anisotropy ratio ranges from 0.4 to 0.9.