Deformation Characteristics and Noncoaxial Behavior of Fiber-Reinforced Soil under Pure Principal Stress Axis Rotation

Geomechanics tests and theories have confirmed that soil exhibits noncoaxial behavior under the rotation of principal stress. A series of hollow torsional shear tests were conducted in this study on fiber-reinforced soil using a hollow cylinder apparatus (GDS-SSHCA). Factors including deviatoric stress, q, the coefficient of intermediate principal stress, b, and fiber content, FC, potentially influencing the shear strain, volumetric strain, and noncoaxiality of fiber-reinforced aeolian soil were evaluated in the tests. The results revealed that both shear and volumetric strains of the fiber-reinforced aeolian soil samples increased as deviatoric stress and the coefficient of intermediate principal stress increased. However, the impact of fiber content initially decreased and then increased. Maximum shear strain and volume strain values were measured at 0.44% and 0.517%, respectively, with an optimum soil content of 3‰. During pure principal stress axis rotation, the fiber-reinforced aeolian soil exhibited noncoaxial characteristics and a fluctuating noncoaxial angle. The average noncoaxial angle decreased to a minimum of 23.59° as the deviatoric stress, the coefficient of intermediate principal stress, and the fiber content increased. Based on the range-analysis method, deviatoric stress was found to have the most pronounced effect on the average noncoaxial angle, followed by the coefficient of the intermediate principal stress and the fiber content. A shear strain prediction equation considering noncoaxiality under pure principal stress axis rotation was established and verified against previously published data. The equation's accuracy was further confirmed through comparison with monitoring data. These findings may serve as a valuable theoretical reference for preventing geological engineering disasters.