Strain behaviour of sapric peat under long-term cyclic loading

Subgrade peaty soils under traffic infrastructures are often subjected to tens of thousands of cyclic loadings. The deformation behaviour of the subgrade depends on the peaty soils under such long-term cyclic traffic loadings. A series of monotonic triaxial and long-term cyclic (10 000 cycles) triaxial tests were conducted to investigate the development of undrained deformation behaviours and excess pore water pressures for the undisturbed sapric peats from Kunming City, China. The observed decrease in undrained shear strength with increasing organic content for these sapric peats is opposite to the effect on those fibric peats discussed in previous studies. The resilient strain, permanent strain and excess pore water pressure of the sapric peat samples were found to be significantly dependent on the cyclic stress ratio (CSR) and organic content. With an increase in the CSR and organic content, the resilient and permanent strains increased more significantly with the increasing number of cycles. Based on the experimental data, two empirical formulas were established to predict the long-term permanent strain and characterise the relationship between the peak axial strain and the peak excess pore water pressure of the Kunming sapric peat after 1000 cycles.