On the importance of dissipation effects in evaluating pore pressure changes due to cyclic loading

One of the aspects of cyclic loading which is of primary importance in engineering design is the progressive build-up of pore water pressures which accompanies the progressive sequence of shear stress reversals in the loading process. This is true whether the loading occurs as a random series of stress applications over a relatively short period of time (say 10 to 90 seconds) as in earthquake problems or as a more uniform series of applications over a much longer period of time (say 2 to 24 hours) as in wave induced pressures on off-shore structures. Of particular significance is the fact that when a saturated sand is subjected to a series of cyclically reversing stress or strain applications, the pore pressures build up progressively regardless of whether the sand is dilative or compressive under monotonically increasing stresses. Thus even sands which develop a reduction in pore pressures when subjected to monotonic loading will develop increases in pore water pressure when subjected to cyclic stress applications.