عنوان مقاله [English]
The steady state line or critical state line is one of the main factors used in critical state topics. It is used for investigating the variation of liquefaction potential, calculating state parameters and also determining the parameters affecting collapse or state boundary surface shapes. Sand skeleton void ratio, equivalent void ratio and the interaction of sand and fines are main subjects behind research into sand critical state behavior.Most studies conducted so far have mainly focused on clean sand or its mixtures containing non-plastic fines with not much attention paid to the soil mechanics of the critical state of clayey sands. The reason for this neglect might be the misconception that plastic properties in clay prohibit flow behaviour and liquefaction. However, the studies of Northridge 1994, Kokaeli 1999, Chi Chi 1999, and Niigata 2004 earthquakes have indicated that notable settlements occur in soils containing considerable amounts of clay, resulting in great destruction. Researchers have emphasized that more detailed investigation is needed to determine the critical state behaviour of clayey sands.Following, the possibility of presenting a unique frame work for interpretation of critical state clayey sand behavior is investigated, based on steady state lines and equivalent void ratio.Triaxial experiments are performed on the sand and its combination with 0 to 25 percent medium plasticity clay, resulting in a new relation used to calculate the b parameters. These are presented based on the fine and sand interaction concept and also steady state lines.The results have proved that by using the proposed relation, it will be possible to convert the different steady state line of sand, and its combination with clay, into one unique line. Also, it will be possible to attain the steady state lines of sand, and all its combinations with clay, based on only some tests performed on clean sand specimens. In order to generalize the proposed relation, it is verified using other available results.