بررسي رفتار حالت بحراني ماسه‌هاي رس‌دار تحت بارگذاري استاتيكي و سيكليك

Investigating the Critical State Behavior of Clayey Sand under Static and Cyclic Loading

رفتار حالت پايدار ماسه هاي حاوي ريزدانه‌ي خميري با استفاده از آزمايش‌هاي سه محوري سيكليك و استاتيك بررسي شده است. نتايج آزمايش‌ها نشان داده است كه افزايش چگالي در درصد هاي كم ريزدانه منجر به افزايش قابل ملاحظه در مقدار مقاومت حالت پايدار خواهد شد، در حالي كه با افزايش درصد ريزدانه، تاثير تراكم در مقاومت در كرنش‌هاي زياد تقريباً نامحسوس خواهد شد. همچنين با افزايش ريزدانه‌ي خميري، ناپايداري تركيبات افزايش مي‌يابد و اين روند بعد از رسيدن به يك حد آستانه معكوس مي شود. حد آستانه مستقل از نوع بارگذاري است و براي آزمايش‌هاي سيكليك و استاتيكي تقريباً يكسان است. مقايسه‌ي نتايج مربوط به چند نوع ريزدانه با حالت‌هاي خميري مختلف و در شرايط يكسان، نشان داده است كه در زير حد آستانه، افزايش حالت خميري تركيب منجر به ناپايداري بيشتر آن خواهد شد، ضمن آنكه با افزايش درصد ريزدانه‌ي خميري، تاثير حالت خميري آن در نتايج بيشتر خواهد شد.

Observation of such phenomena as liquefaction and flow 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 fines, 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 flow 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 fine content, more density will result in a significant increase in steady state strength, while, at high fine content, the effect of density on the steady state strength would be insignificant. Also, increasing fine 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 different plasticity fines under similar conditions shows that increasing plasticity leads to more instability under the threshold value, while the effect of plasticity will be more significant with an increase in fine 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.