True Triaxial Tests on Cross-Anisotropic Deposits of Fine Nevada Sand

An experimental program was designed to study the effects of cross-anisotropy under three-dimensional conditions on fine Nevada sand using tall prismatic specimens. Eighteen drained tests were performed using a true triaxial apparatus. Specimens were created with both horizontal and vertical bedding planes by dry pluviation, then a freezing technique was used to solidify the specimens while they were mounted in the true triaxial apparatus. The specimens were then sheared at various b-values, where b=(sigma 2-sigma 3)/(sigma 1-sigma 3), in the three sectors of the octahedral plane. The stress-strain behavior and strength under various loading conditions on the octahedral plane are presented. Results show similar strength results in Sectors I and II. Effects of cross-anisotropy are shown when comparing the friction angles in Sectors I and II with those in Sector III. The strength is highest in Sector I, where the friction angle in triaxial compression (b=0.0, vertical specimen with horizontal bedding planes) is 5.3 degrees higher than the triaxial-compression friction angle in Sector II/III (b=0, horizontal specimen tested with the horizontal bedding planes in the vertical direction). In triaxial extension (b=1.0), the friction angle is 2.5 degrees higher in Sector I/II than that in Sector III. Shear band inclinations in these three sectors were essentially unaffected by the cross-anisotropy.