INVESTIGATING THE CRITICAL STATE BEHAVIOR OF CLAYEY SAND UNDER STATIC AND CYCLIC LOADING

Observation of such phenomena as liquefaction and ow behavior generally occurring in loose and saturated sands have stimulated extensive investigation into sands and the parameters involved in their critical state behavior. Most studies conducted so far have mainly focused on clean sand or its mixtures containing non-plastic nes, with not much attention paid to the soil mechanics of the critical state of clayey sands. The reason for this neglect may be the misconception that plastic properties in clay prohibit ow behavior and liquefaction. However, the studies of the Northridge 1994, Kokaeli 1999, Chi Chi 1999, and Niigata 2004 earthquakes have indicated that notable settlements occur in soil containing considerable amounts of clay, resulting in great destruction. Researchers have emphasized that more detailed investigation is needed to determine the critical state behavior of clayey sands.
The critical state behavior of clayey sands has been investigated using cyclic and static triaxial tests. Based on the results, in low ne content, more density will result in a signicant increase in steady state strength, while, at high ne content, the eect of density on the steady state strength would be insignicant. Also, increasing ne content results in more instability, but the trend reverses after a threshold value. This threshold value is independent of cyclic or static loading.
Comparing the results of dierent plasticity nes under similar conditions shows that increasing plasticity leads to more instability under the threshold value, while the eect of plasticity will be more signicant with an increase in ne content Firooz-kooh crashed silica sand (sand 161) was used in the experiments due to its desirable properties. Specimens were prepared using the wet tamping method. Having obtained the appropriate blend, it was poured into a special mould and compacted in 6 layers to prepare specimens 50 mm in diameter and 100 mm in height.