كليدواژه :
ذرات چندگوشه , روش استوانه , روش اجزاي مجزا (DEM) , شبيه‌سازي عددي
چكيده فارسي :
در پژوهش حاضر، از روش اجزاي مجزا براي شبيه‌سازي دو بعدي رفتار زهكشي‌نشده در مصالح دانه‌اي چندگوشه استفاده شده است. براي شبيه‌سازي عددي رفتار زهكشي‌نشده از دو روش حجم ثابت و استوانه استفاده شده و نتايج حاصل از هر دو روش با يكديگر مقايسه گرديد. در روش استوانه فرض مي‌شود كه لوله‌اي ميان حفرات مجاور وجود دارد و امكان تبادل آب بين مراكز حفرات فراهم مي‌شود. در اين روش، قطر استوانه نماينده‌اي از نفوذپذيري خاك است. در روش حجم ثابت فرض مي‌شود كه حجم نمونه طي بارگذاري ثابت مي‌ماند. شبيه‌سازي به كمك هر دو روش براي نمونه‌هايي انجام شده است. اين نمونه‌ها تحت تنش همه‌جانبه 200 كيلوپاسكال قرار گرفته و پس از تحكيم همه‌جانبه، تحت بارگذاري انحرافي قرار گرفته است. نتايج نشان داد كه پاسخ‌هاي حاصل از روش استوانه انطباق خوبي با روش حجم ثابت دارد و با افزايش سختي آب، نتايج هر دو روش بهم نزديك‌تر مي‌شوند. رفتار زهكشي‌نشده برحسب مقاومت برشي و فشار آب حفره‌اي متوسط در نمونه ماسه‌اي در تنش‌هاي همه‌جانبه 800،400،200 و 1600 كيلوپاسكال به كمك روش استوانه مورد بررسي قرار گرفت. نتايج شبيه‌سازي انطباق خوبي با نتايج آزمايشگاهي دارد، بطوريكه در نمونه تحت تنش همه‌جانبه بيشتر، مقاومت برشي و فشار آب حفره‌اي متوسط مثبت بيشتري بوجود مي‌آيد، ولي با افزايش فشار همه‌جانبه، مقدار فشار آب حفره‌اي متوسط در نمونه كاهش مي‌يابد. در انتها گستردگي توزيع فشار آب حفره‌اي متوسط در نمونه در كرنش‌هاي 10 و 30 درصد به كمك روش استوانه نشان داده شد و تاثير تغييرات قطر استوانه در گستردگي توزيع فشار آب مورد بررسي قرار گرفت. بررسي گستردگي توزيع فشار آب حفره‌اي متوسط در كرنش‌هاي 10 و 30 درصد نشان داد كه فشار آب در مركز نمونه داراي كمترين مقدار است. همچنين با افزايش قطر استوانه، فشار آب در كل حفرات نمونه، بهم نزديك مي‌شود. در حاليكه هرچه قطر استوانه كمتر باشد، اختلاف فشار آب در حفرات نمونه بيشتر مي‌شود.
چكيده لاتين :
In the present study, discrete element method is used to simulate undrained two-dimensional behavior of polygonal particles in which, the cylinder method is used. By this method, pore pressure of the voids in a sample can be studied independently. In the cylinder method, it is assumed that there are channels among adjacent pores and the possibility of water exchange among the centers of the pores is provided. The pipes connect the adjacent pores center. Therefore, the pipe length is equal to the center distance of two adjacent pores. The diameter of all pipes is identical which represents the permeability of the soil. First, by using this method, the variations of average pore pressure versus deviatoric strain and pore pressure distribution contour in a sample with polygonal particles were compared with another study with elliptical particles that showed good conformity. The constant volume method was also used to simulate the undrained behavior of the sample and the results of both methods were compared. In the constant volume method, it is assumed that the sample volume stays constant during loading. The simulation was done for samples by two methods. These samples were subjected to confining pressure of 200 kPa and after consolidation, were loaded under deviatoric stress. The results showed that the output obtained by the cylinder method are in good agreement with the constant volume method and by increasing the stiffness of the water, the results of both methods containing the variations of the deviatoric stress and the pore pressure are closer to each other. In following, the undrained behavior was investigated by using cylinder method in terms of shear strength and pore water pressure in a sandy sample at the confining pressures of 200, 400, 800 and 1600 kPa. The Simulation results are in good agreement with laboratory results in such a way that more confining pressure, the shear strength and pore pressure are more positive, but by increasing confining pressure, the amount of pore pressure decreases in the specimen. The pore pressure distribution contour at the strains of 10% and 30% was presented by means of cylinder method and the effect of cylinder diameter changes on the pore pressure distribution contour was investigated. Investigating the pore pressure distribution contour at the strains of 10% and 30% showed that pore pressure in the sample center has the lowest value. The pore pressure in the sample pores closes by increasing the cylinder diameter, while the smaller the diameter of the cylinder, the greater the water pressure difference among the pores. At last, the effect of pore position on the pore pressure was studied. For this purpose, four positions were considered through the sample and the variations of the average pore pressure versus axial strain at three pipe diameters of 40,200 and 450 micrometers were investigated. The results showed that the pressure of the whole sample pores get closer by increasing the pipe diameter. As the pipe diameter decreased, the pressure difference between the sample pores gets higher and this difference will be greater in the larger strains.
