Cyclic strengths for high density soils related to pore water pressure

In studies of soil mechanics, a common approach has been to consider a state of 100% pore water pressure build-up or, alternatively, the development of 5% double-amplitude cyclic strain as a yardstick for identifying a state of cyclic instability. For clayey soils or sandy soils with a considerable amount of fines, the excess pore water pressure during cyclic loading does not reach the case of 100% of the confining stress. For such soils, the cyclic strength is recognized when a certain level of double-amplitude cyclic strain is developed after a certain number of cycles, without taking into consideration the level of excess pore water pressure induced during cyclic loading. Therefore, these soils undergo high levels of effective stress loss on their way to cyclic failure. In this paper, an approach is proposed for determining cyclic strength in relation to the level of the excess pore water pressure or the loss of mean effective stress. This results in a greater decrease in cyclic strength than that determined by the known method. Therefore, additional safety factors are introduced to ensure that both the loss in effective stress and the induced cyclic strains do not exceed certain limits during cyclic loading.