بررسي رفتار پي واقع بر لايه هاي مخلوط خاك و خرده لاستيك دانه ‌يي: مطالعه‌ي آزمايشگاهي روي مدل‌هاي كوچك‌مقياس و بزرگ‌مقياس

Investigation into Footing Behaviour of Layered Granulated Rubber-soil Mixture: Experimental Study on Small and Large Models

در اين نوشتار با انجام مطالعات آزمايشگاهي بر روي دو مدل پي دايره ‌يي به قطرهاي 3/11 و 30 سانتي متر واقع بر بستر غيرمسلح و مسلح با 1، 2، و 3 لايه‌ي مخلوط خاك- خرده‌لاستيك دانه ‌يي، رفتار بار- نشست پي بررسي شده است. نتايج آزمايش‌ها نشان مي‏دهد كه ضخامت بهينه‌ي مخلوط خاك- خرده لاستيك صرف‌نظر از مقياس آزمايش ها (اندازه‌ي مدل پي)، جهت دست‌يابي به بيشينه‌ي باربري و كمينه‌ي نشست در حدود 4/0 قطر مدل پي است. همچنين استفاده از دو لايه‌ي مخلوط با فاصله‌ي بهينه‌ي معادل 2/0 قطر مدل پي از يكديگر به جاي استفاده از يك لايه‌ي مخلوط با ضخامتي معادل مجموع ضخامت دو لايه مي‏تواند موجب بهبود بيشتر رفتار بستر شود. با افزايش تعداد لايه‌هاي مخلوط خاك- خرده‌لاستيك، نرخ افزايش در بهبود باربري بستر كاهش مي‌يابد، به‌طوري ‌كه با افزايش لايه‌ها به بيش از 3 لايه‌ و خارج‌شدن آن‌ها از حوزه‌ي تاثير تنش وارد بر پي، انتظار بهبود بيشتر در رفتار بستر وجود ندارد.

This paper describes the reinforcing effects of multiple layers of a rubber–soil mixture in sand, using small scale and large scale static plate loading tests, respectively, at diameters of 113 mm and 300 mm. The small scale test and large scale plate load tests were conducted in a testing tank measuring 800×800×800 mm, and in an outdoor test pit dug in natural ground measuring 2000×2000 mm in plane and 700 mm in depth, respectively. According to previous studies of Moghaddas Tafreshi et al. [12], the optimum embedded depth of the first layer of the rubber-soil mixture was found to be approximately 0.2 times the footing diameter, and the optimum percentage of rubber replacement was found to be around 8% the weight of the soil mixture. The thickness of the rubber-soil mixture, hrs, in terms of hrs/D (D: the loading surface diameter), the vertical spacing of the rubber-soil mixture layers, h, in terms of h/D, and multiple layers of rubber-soil mixture (N) in the foundation bed were the main parameters affecting the bearing capacity and settlement of the foundation bed. The optimum thickness of the rubber-soil mixture and the optimum vertical spacing of the rubber-soil mixture layers were 0.4 and 0.2 times the loading plate diameter (i.e., hrs/D=0.4) and h/D=0.2). Results show that reinforcement efficiency decreases as the number of rubber-soil mixture layers increases. For example, in the small scale loading plate at a settlement ratio of 4%, the bearing capacity was obtained at about 89, 102, 110 and 112 kPa for the unreinforced and reinforced beds with one, two and three layers of rubber-soil mixture, respectively. Furthermore, the reinforced bed with two layers of the rubber-soil mixture with optimum thickness located at optimum vertical spacing, shows more efficiency than one layer of the rubber-soil mixture in increasing the bearing pressure of the foundation bed, whereas the total thickness of the mixture is the same.