The undrained behaviour of over-consolidated clay subjected to pure rotation of principal stress directions

Abstract

Foundation soil of offshore structures may be subjected to various non-proportional cyclic loadings, such as wave loading, tide loading and earthquake loading. The consolidation state may affect the undrained behaviour of clay under pure rotation of principal stress directions. A series of cyclic undrained torsional tests were performed on normally and over consolidated clay subjected to pure rotation of principal stress directions at constant deviatoric stress conditions. The effects of over consolidation ratio (OCR) on the excess pore water pressure, stress-strain loop, stiffness and non-coaxial behaviour of the clay were analyzed under different deviatoric stresses and intermediate principal stress coefficients (b values). The results indicate that owing to the pure principal stress rotation alone, strain and excess pore water pressure accumulated in samples and the accumulation is affected by OCRs, deviatoric stress amplitudes and b values. Negative excess pore water pressure and stress dilatancy can be observed in over consolidated clay. Compared with shear stiffness, the normal differential stiffness experiences greater degradation under the pure rotation of principal stress. The shear stiffness of over consolidated clay may show an increase with loading cycles, while the normal differential stiffness degrades at low deviatoric stress value. Over consolidated clay shows non-coaxial behaviour and the greater the OCR values or the smaller the deviatoric stress, the larger the non-coaxial angle. The effects of b values on the non-coaxial behaviour of over consolidated clay are also observed.

HIGHLIGHTS

• Over-consolidated clay subjected to pure rotation of principal stress.

• The effects of OCR, deviatoric stress and b value were analyzed.

• Negative EPWP and stress dilatancy were observed in over consolidated clay.

• The greater the OCR, the larger the non-coaxial angle.

Keywords:

• Over consolidated clay
• pure rotation of principal stress
• stress-strain loop
• excess pore water pressure
• non-coaxial behaviour

Disclosure statement

The authors declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.

Additional information

Funding

The project is funded by the National Natural Science Foundation of China (No.51968005), and Guangxi Natural Science Foundation (No. 2019GXNSFBA185038). The third author received PhD scholarship from the University of New South Wales.