Fluctuating characteristics of excess pore water pressure in Nanjing fine sand under partially drained conditions

The fluctuating characteristics of excess pore water pressure (EPWP) are the basics to establish the transient EPWP model. A series of stress-controlled cyclic triaxial tests are carried out for saturated Nanjing fine sand with various fine contents of samples and loading frequencies. The loading frequencies are 0.5 Hz, 1.0 Hz and 5.0 Hz, and the fine content of samples are 0%, 5.0% and 13.5%. Based on quantitative analysis of the test results, it is found that: (1) When the cyclic load of 0.5 Hz frequency is applied on the samples with fine particles of 0% and permeability of 1.35×10-3 cm/s, the leading-phase angle between EPWP’s response and axial strain’s response is approaching 90 degrees, and the EPWP’s response is simultaneous with the axial strain-rate’s response; (2) With the increase of loading frequency or the decrease of permeability of samples, the leading-phase angle between EPWP’s response and axial strain’s response decreases, and that between EPWP and axial strain-rate increases. Based on the theory of saturated porous media, an EPWP equation for any drainage bound condition is established. The proposed equation can explain the phenomena of the EPWP’s response being simultaneous with the axial strain’s response in undrained condition, and also that of EPWP’s response leading axial strain’s response under partially drained conditions.