The true triaxial strength anisotropy of sand

Sand exhibits transversely isotropic (TI) characteristics, with its strength properties influenced by the coupling effects of the intermediate principal stress ratio b and the orientation angle δ of the bedding plane (BP) relative to the major principal stress. To address this, a novel sample preparation method for true triaxial tests has been developed, allowing the BP to rotate around the major, intermediate and minor principal stress axes, enabling the measurement of the strength anisotropy across all sectors on the deviatoric plane. This method features a specially designed dry pluviation device followed by a freezing process to prepare TI specimens that preserve the designed fabric characteristics, ensuring the prepared TI specimens precisely match the specific loading conditions of the true triaxial equipment. In total, 52 drained true triaxial tests are conducted, covering the full range of b and δ values across all sectors of the deviatoric plane. In addition, test results and theoretical analyses based on the TI characteristic mobilised plane (TI-CMP) criterion are integrated to investigate the strength anisotropy. Comparisons reveal that the TI-CMP criterion effectively captures the strength anisotropy observed in a space defined by the peak friction angle ϕ versus b and δ.