تعيين پارامترهاي مدل رفتاري Cam-Clay در مدل‌سازي رفتار خاك ماسه يي در آزمايش سه محوري

Determination of Cam-Clay Constitutive Parameters in Numerical Modeling of Sandy Soil Behavior under Triaxial Testing

مدل‌سازي عددي رفتار خاك‌ها روشي جهت كاهش هزينه هاي آزمون‌هاي آزمايشگاهي مطرح است. با توجه به كاربرد زياد پارامترهاي مقاومتي حاصل از آزمايش سه محوري، نياز به مدل‌سازي عددي اين آزمايش و پيش بيني پارامترهاي مذكور احساس مي شود. در اين نوشتار، به پيش بيني رفتار خاك‌هاي ماسه ‌يي مخلوط با خاك ريزدانه تحت آزمايش سه-محوري تحكيم‌يافته- زهكشي‌نشده پرداخته شده است. خاك مورد مطالعه تركيبي از ماسه‌ي فيروزكوه با درصدهاي مختلف رس است. منحني تنش-كرنش خاك در اين آزمايش‌ها با استفاده از يك مدل اجزا محدود شبيه سازي شده است. با توجه به نتايج آزمايشگاهي، قسمت خطي نمودار تنش- كرنش مدل شده و پارامترهاي موردنياز از روش معكوس به‌دست آمده است. براساس نتايج شبيه سازي، پارامترهاي مقاومتي محاسبه شده و نمودارهاي تنش انحرافي- كرنش محوري، فشار آب حفره ‌يي-كرنش محوري و مسير تنش پيش بيني شده است. نتايج حاصل از مدل‌سازي هاي انجام‌شده با اين پارامترها نزديك به نتايج آزمايشگاهي هستند.

Numerical modeling of soil behavior is known as a new method for predicting soil sample behavior under each test, to reduce test costs used in the laboratory. Triaxial testing is one of the most common soil mechanics tests to determine the shear strength parameters of soil. Due to the excessive use of triaxial test results, numerical modeling is necessary to predict the behavior of soil under triaxial testing. This paper presents a numerical model to predict the behavior of clayey sands under consolidated-undrained triaxial testing. It is important to predict the relationship between stress and strain to describe soil behavior. The stress-strain curve of clayey sand soils during consolidated-undrained triaxial testing has been simulated using a finite element model, based on the cam-clay constitutive model. A series of triaxial compression tests was carried out on Firoozkooh sand with a different percentage of clay (0-15 percent) and different relative densities. These tests were carried out under two different confinement pressures (100, 400 kPa); low and high. For the modeling of these tests, a back analysis method is selected. In this method, the results of triaxial tests under high confinement pressures are used as the base data, and, based on simulation results, the strength parameters are determined using back analysis. The cam-clay constitutive model has several parameters to predict soil behavior. These parameters are predicted using the back analysis method and, so, soil behavior is predicted. After this step, triaxial tests under low confinement pressures are simulated with suggested parameters, and the results are compared with the same experimental results. If there is no good agreement between results, the cycle of modeling is restarted. Finally, the numerical results are compared with experimental results, which showed good agreement. Moreover, the effect of clay on the behavior of sand is also investigated and discussed. As a result of modeling, the graphs of q-? (deviator stress-axial strain), u-? (pore water pressure-axial strain) and q-p? (stress path) are obtained to predict the clayey sand behavior.