Abstract: The behaviors of strength and deformation of natural soils differ from that of remolded and unstructured soils due to structural property. The effective consolidation stress method for the undrained shear strength evaluation of remolded and unstructured soils is reviewed and the corresponding equations are derived. The equations of the method for the undrained shear strength evaluation of structured clays are hereafter established in terms of the strength envelopes simulated by two segment lines with different slopes (tangents of internal friction angles) and intercepts (cohesions). The component of effective stress in the equation of effective consolidation stress method should be multiplied by a revised coefficient of 0.8 for the effective stress range less than the yielding stress. The undrained shear strengths of structured soils can be then determined if the consolidation stresses prior to shearing would be known. The applicability of the effective consolidation stress method is validated using the isotropically consolidated triaxial test results of soft structured Lianyungang clay. The undrained shear strengths estimated by the effective consolidation stress method are in good agreement with the laboratory results. Furthermore, the structure-induced yielding stress predicted by the effective consolidation stress method has a certain but negligible deviation from that fitted by the laboratory data.

Key words: structured clays, undrained shear strength, effective consolidation stress method, internal friction angle, cohesion, strength envelope