One-way cyclic deformation behavior of natural soft clay under continuous principal stress rotation

The design of traffic infrastructure foundations formations has traditionally been empirically rather than analytically based, and for the advanced methods currently in use, input parameters are typically determined from cyclic triaxial testing. In actual engineering, the stresses acting on soil elements induced by passing wheels are not as simple as cyclic triaxial loading. Due to real traffic loads involve the change of the principal stress direction in the ground, cyclic loading induced by traffic loading are typically one-way cyclic loading involved continuous principal stress rotation. Testing in a hollow cylinder apparatus (HCA) can impose the rotations in principal stress direction likely to be experienced by a soil element in the field, and may therefore be preferable to triaxial testing. The soil mechanics problem is one of understanding how soils respond to cyclic loading and applying this knowledge to foundation design. Non-linear stress-strain characteristics are a particular feature of the problem and have to be catered for design and evaluation. In this paper, a series of normally consolidated undrained HCA tests are performed to investigate the one-way cyclic deformation behavior of natural soft clay from Wenzhou, China. The principal stress axis continuously rotates while holding the deviator stress at a constant level. The tests results show that, the pore pressure, stress-strain hysteretic loop, dynamic modulus of the tested samples are significantly dependent on cyclic stress ratios and initial effective confining pressures. The value of degradation index becomes larger as the cyclic stress ratio and initial effective confining pressure increase. The threshold limit of the tested clay samples in terms of cyclic stress ratio can be considered as 0.255.