Anisotropy evolution and irrecoverable deformation in triaxial stress probes

This paper presents the results and analysis of experimental investigations of compressible Chicago clays with regard to the evolution of stiffness anisotropy. The experimental program was conducted on high-quality block samples obtained from the excavation for the Block 37 project in Chicago. The specimens were consolidated to in situ stresses via a recompression technique and then were subjected to directional stress probes. On-specimen LVDTs and an internal load cell with high accuracy were used for stress-strain response of the specimen. The stiffness and stiffness anisotropy ratio at very small strains were obtained synchronously from bender element tests during the consolidation and stress probes. The structural change as anisotropy evolves within a specimen is discussed. The results of the experimental program showed that compressible Chicago clay is an initially cross-anisotropic material under the in situ stresses. This anisotropy changes at the onset of irrecoverable deformation at stresses defined by previously established Y ₂ yield surfaces.