Strain and pore pressure development on soft marine clay in triaxial tests with a large number of cycles

•A series of long-term cyclic (50,000 cycles) triaxial tests are carried out.•Long-term development of strain depends on the CSR values.•Empirical formula is established to predict the long-term permanent strain.•Relationship between the peak strain and pore water pressure is established.

Soft marine clays may be subjected to tens of thousands of cyclic applications of waves or traffic loads over a long period of time. Therefore, its cyclic deformation behavior is one of the major concerns of geotechnical engineers. In this study, a series of high cycle (50,000 cycles) triaxial tests have been carried out on soft marine clay with various stress levels and different confining pressures to investigate the development of strain and pore water pressure. Some useful conclusions are obtained. Firstly, the development of resilient and permanent strain depends on the cyclic stress ratio (CSR) values. When CSR is small, the resilient strain nearly keeps at a constant value after 1000 cycles and the permanent strain increases slowly and almost linearly with increasing CSR. When CSR is large, the resilient strain increases even after 50,000 cycles and the permanent strain increases rapidly and exponentially with increasing CSR. Secondly, log (εp/N) and log N exhibit a nearly linear relationship after a certain number of cycles which is called the reference number of cycles. An empirical formula is established to predict the long-term permanent strain by making use of this relationship. Thirdly, the peak axial strain increases exponentially with the decrease of the distance between the effective stress path and the critical state line. A formula is proposed to characterize the relationship between the peak axial strain and the peak pore water pressure after 1000 cycles.