بررسي رفتار مخلوط خاك و خرده‏پلاستيك با استفاده از آزمايش‏هاي سه‏محوري و CBR

Experimental Study of the Triaxial behaviour and CBR Value of Plastic Waste-soil Mixture

در اين نوشتار، پتانسيل خرده‏هاي پلاستيك حاصل از بطري‏هاي پلاستيكي ضايعاتي جهت تسليح خاك و بهبود رفتار آن با انجام آزمايش‏هاي سه‏محوري و CBR بر روي ماسه‏ي تنها و ماسه‏ي مخلوط با خرده‏پلاستيك انجام شده ‏است. آزمايش‏هاي سه‏محوري بر روي خاك و خاك مخلوط با دو اندازه‏ي كوچك و بزرگ خرده‏پلاستيك و آزمايش‏هاي CBR بر روي نمونه‏هاي خاك تنها و مخلوط خاك و خرده‏پلاستيك با اندازه‏ي بزرگ صورت گرفته ‏است. نتايج حاصل از آزمايش‏هاي سه‏محوري نشان مي‏دهد كه افزودن خرده‏پلاستيك به خاك، موجب افزايش مقاومت نمونه‏ها شده ‏است. به عنوان مثال، در فشار همه ‏جانبه‏ي 50 كيلوپاسكال، تراز كرنش 6?، تسليح نمونه با 5/1? خرده‏پلاستيك موجب 25? افزايش در ميزان مقاومت شده است. اين افزايش در مقاومت، با افزايش اندازه و درصد خرده‏پلاستيك و هم‏چنين ميزان كرنش اعمال‌شده بر نمونه قابل ملاحظه‏ تر است. نتايج آزمايش‏هاي CBR نيز مبين كاهش نفوذ سنبه به داخل نمونه و افزايش در مقدار CBR با افزودن مقدار مناسب خرده‏پلاستيك به خاك شده ‏است.

Bottled water is the fastest growing beverage industry in the world, and recycling their plastic waste has become a major challenge worldwide. The present study provides an approach for using waste plastic strips as reinforcement material in soil backfill. The experimental tests investigate the behaviour of soil alone, and plastic waste-soil mixtures using static triaxial tests and CBR tests. The triaxial tests were carried out on the unreinforced soil samples and plastic-soil mixture samples at three confining pressures of 50, 100, and 150 kPa. The effect of small and large sizes of waste plastic was examined by three waste plastic strip contents of 0.5%, 1% and 1.5% (by total weight of the sample). The CBR tests were performed by standard CBR apparatus with a load rate of 1.27 mm/min on unreinforced and reinforced samples (i.e., waste plastic-soil mixture), with a large size of waste plastic particles, at four plastic contents of 0.5, 1, 1.5, and 2%. The results of the triaxial tests show that the strength of reinforced samples increases with increasing the size and percentage of plastic particles. For example, for the plastic content of 1.5%, at confining pressure of 50 kPa and strain level of 6%, a maximum improvement in the strength of the plastic-reinforced sample was obtained as 1.25 times the unreinforced sample. The results of CBR tests depict that the provision of waste plastic particles reduces the penetration of shaft into the sample and increases its CBR value. Overall, the results of CBR and triaxial tests demonstrate that the inclusion of waste plastic strips in soil with appropriate amounts improves the strength and deformation behavior of foundation beds substantially. The proposed technique can be used to advantage in bearing capacity improvement and settlement reduction in the design of shallow footings, embankments and road construction.