كليدواژه :
روش اجزاي مجزا , محتواي درشت‌دانه , محتواي ريزدانه , ضريب مشاركت , حالت حد بحراني
چكيده فارسي :
در مهندسي ژئوتكنيك، قبلا تصور مي شد كه با افزايش سهم فاز ريزدانه غيرخميري به فاز درشت دانه باعث افزايش مقاومت برشي خاك و كاهش نسبت تخلخل كلي خاك مي‌گردد، درصورتي كه طبق نتايج آزمايشگاهي چنين نيست. در اين مقاله با استفاده از روش اجزاي مجزا، چندين نمونه خاك با مخلوط كردن دو نوع خاك مختلف با فاز درشت دانه و ريزدانه تهيه شده و بصورت دوبعدي تحت بارگذاري دومحوري قرار گرفتند. دانه‌هاي مورد استفاده بصورت دايروي در نظر گرفته شدند. بارگذاري نمونه ها تا رسيدن به حالت حد بحراني ادامه يافت. بر طبق نتايج بدست آمده، پارامترهاي مربوط به مشاركت سهم بخش هاي درشت دانه و ريزدانه بدست آمدند. بدين منظور، از شاخص‌هاي تماسي جايگزيني به نام نسبت تخلخل معادل محتواي درشت دانه و معادل محتواي ريزدانه استفاده شدند. بررسي نتايج شبيه سازي ها نشان از انطباق خوب با نتايج آزمايشگاهي موجود در ادبيات فني دارد. محتواي ريزدانه آستانه براي مجموعه نمونه ها، كه بيانگر نقش غالب يكي از دو فاز درشت دانه و ريزدانه است، بدست آمد. شبيه سازي ها در فضاي دوبعدي نشان داد كه مي توان براي خاك‌هاي با درصدهاي وزني مختلف فاز درشت و ريز، به حالت حد بحراني منحصر به خود رسيد. اگر از تعريف نسبت تخلخل هاي معادل فاز درشت و ريز استفاده شود، مي‌توان به يك خط بحراني واحد براي مجموعه اي از خاك ها با درصدهاي وزني مختلف فاز درشت و ريز رسيد. همچنين، در اين مقاله، روند تغييرات پارامترهاي سهم مشاركت دو فاز درشت و ريز بر حسب درصد ريزدانه بدست آمد.
چكيده لاتين :
It is believed that the addition of fine-grained soil to a base coarse-grained soil would result in shear strength increment due to filling up the voids among coarse-grained content and reducing global void ratio. However, this belief was against the following experiments. Instead of the definition of classical void ratio, two variables referred to as equivalent inter-granular and inter-fine void ratios, have been proposed to resolve this problem. Using these variables can help how a binary soil behaves. In this paper, by using the discrete element method, several binary soil samples were created by mixing two coarse and fine-grained soils. The two fine and coarse-grained soils have different gradations. The soil samples were prepared by considering zero, 10, 30, 40, 70, 100 percent fines content. Simulations were performed in two-dimension in which, the particles were circular. After each soil sample preparation, it was consolidated under isotropic confining pressure followed by biaxial compression loading. Each sample was tested under three different confining pressures. The biaxial loading condition was continued until the samples reached the critical state. This is the case where there is no variation in the deviatoric stress as well as the volume change along with the increase in the axial strain. Based on the simulated results, the required parameters to estimate the portion of the role of coarse and fine-grained parts in the global soil behavior were obtained. Comparison of the results of this study with those of experiments showed good agreements. The threshold fines content after which, the mechanical behavior of the binary soils is governed by fine grains, was assessed. It was shown that for the two-dimensional samples, the critical state can be obtained and the critical state line (CSL) can be constituted in the q-p’-e space. It was also seen that for the two groups of samples where either of coarse or fine-grained content are dominant, a unique critical state line can be obtained if the inter-granular and inter-fine void ratios are used instead of the global void ratio. The influence factors were back-calculated and the values were justified in comparison with the experiments.
