بررسي پارامترهاي تعيين‌كننده در افزايش ضخامت لايه هاي خاكريز مهندسي

Evaluation of Determinant Parameters for Thickening the Engineered Fills Layers

يكي از مهم ترين عوامل در بحث متراكم سازي خاكريزها، تعيين ضخامت لايه هاي خاكريزي است، كه با توجه به تاثير مستقيم در ميزان هزينه و زمان انجام پروژه، همواره مورد توجه كارشناسان امر بوده است. در اين نوشتار به منظور بررسي پارامترهاي موثر در ضخامت لايه هاي خاكريز مهندسي، از جمله شرايط بستر و انرژي غلتك، از مدل‌سازي عددي دو بُعدي در شرايط كرنش صفحه‌يي استفاده شده است. در اين راستا از 4 نوع غلتك چرخ فلزي، چرخ لاستيكي، پاچه بزي، و چرخ فلزي ارتعاشي جهت متراكم سازي تك‌لايه‌ي خاكريز به ضخامت هاي 15، 30، 45، و 60 سانتي متر استفاده شده است. طبق نتايج به‌دست‌آمده در صورت استفاده از بسترهاي تقويت‌شده به‌دليل سختي بالا و افزايش انرژي اعمالي غلتك، امكان افزايش ضخامت لايه‌هاي خاكريز به ميزان تقريبي 2 برابر ضخامت هاي 25-20 سانتي‌متر كنوني وجود دارد.

Roller Compaction is one of the most common methods for modifying soil behavior when constructing road embankments, railway tracks and earth dams. Using the compaction approach for achieving optimized engineered fill, the major factor is the thickening of soil lift, which is always considered by the relevant engineers. It leads to a reduction in project cost, timing, and energy. In this research, effective parameters regarding determination of the thickness of engineered embankments are explored, and then a 2D numerical modelling is carried out in order to evaluate the effect of these parameters on lift thickness. The modelling is based on some assumptions, e.g., the material of the embankment and subgrade have optimum moisture content and the underground water level is below the subgrade zone, so that no excess pore pressure is exerted on the model as the result of additional loading. The effects of subgrade conditions, roller energy, loading cycles and etc. were evaluated for a single layer embankment with four thicknesses of 15, 30, 45 and 60 cm. Four types of roller, steel wheel, pneumatic tyre, sheepsfoot and vibrator were modeled on the cross section of the road. Dynamic analysis was performed for the vibratory steel wheel rollers only, while static analysis was chosen for other cases due to the low roller speed. Results indicated that due to their special performance, if either sheepsfoot rollers with a high contact pressure, or vibratory rollers, while providing the suitable subgrade stiffness, were used, the thickness of the embankment lifts could be increased to approximately twice the common thicknesses of 20-25 cm, i.e., 40-50 cm. Case studies in which the maximum embankment lift was increased to 45 cm are also in agreement with the above mentioned results. According to the obtained results, increasing subgrade stiffness that causes limited lift displacement, allows for an increase in lift thickness. Increasing the applied energy can lead to an upgrade in the relative density of the embankment layer. This is due to the increase in the effective depth of stress. Therefore, a combination of treated subgrades, due to their higher stiffness, and an increase in roller energy, will allow for an increase in the thickness of the embankment lifts.