اثر تعداد سيكل و فشار آب حفره اي توليدي بر مدول هاي برشي خاكهاي شني

Effects of numbers of the cycles and excess pore pressure on shear modulus of gravelly soils

The change in stress-strain-strength properties namely dynamic properties of soil layers during cyclic loading may have a significant influence on stability of earth and rockfill dams, embankments, retaining structures, natural slopes, and site responses. Therefore, it is necessary to take into account the change in dynamic characteristics of natural soil layers to decrease the vulnerability. This paper, in addition to presents the results of shear modulus versus shear strain of gravelly materials, investigated the effects of number of cyclic loading in un-drained testing on shear modulus. The results show that, in gravelly materials, the fine content has high effect on shear modulus. Also, with increasing number of cyclic loading from 11 to 23, the excess pore pressure increases at strains higher than 0.01% and 0.03, for materials with <15% fine content and materials with >30% fine content, respectively; and as results, shear modulus decrease with number of cycles. The shear modulus reduction for materials with >30% fine content is less than that for materials with <15% fine content, due to less residual pore pressure generation with number of cycles. Also, at confining pressure more than 5 kg/cm2, the generated excess pore pressure with number of cyclic loading decreases and as the results, the reduction of shear modulus decreases. Moreover, results show that the reduction of sample volume due to opening the drainage valve at interval of cyclic loading is negligible. However, shear modulus must be measured at equivalent cycle to anticipated earthquake.