ارزيابي استاتيكي و چند‌مرحله‌يي مقاومت بيرون كشش ژئوسل ها در خاك هاي دانه يي

Evaluation of the static and multistage geocell pullout behavior in coarse grained soil

به منظور بررسي رفتار بيرون‌كششي استاتيكي و چندمرحله‌يي ژئوسل‌ها در خاك‌هاي دانه‌يي، يك مطالعه‌ي آزمايشگاهي به وسيله‌ي دستگاه بيرون‌كشش زرگ‌مقياس انجام شده است. آزمايش‌هاي بيرون‌كششيِ سرعت ثابت و چندمرحله‌يي به ترتيب براي بررسي رفتار استاتيكي، تناوبي و پساتناوبي ژئوسل مدفون در خاك‌هاي دانه‌يي ترتيب داده شده است. مقاومت بيرون‌كشش نهايي به‌دست آمده از آزمايش بيرون‌كشش، شامل: مؤلفه‌هاي متفاوتي است كه هر يك از آن‌ها توسط يك روش تئوري محاسبه شده است. درنهايت مشاهده شد كه رفتار بار بيرون‌كشش ـ جابه‌جايي ژئوسل‌ها به صورت سخت‌شونده بوده است كه مقدار آن وابسته به مؤلفه‌ي مقاومت پاسيو و اصطكاكي بسيج شده است. همچنين مقاومت بيرون‌كشش نهايي پساسيكلي به‌دليل شكسته يا ضعيف شدن برخي از قفل و بست‌ها بين دانه‌هاي مصالح پُركننده و خاك اطراف در هنگام حركت رفت و برگشتي فاز سيكلي، كمتر از مقاومت نهايي استاتيكي بوده است.

Geocell mattresses are one type of three-dimensional honeycomb soil reinforcements that is manufactured from polyethylene sheets using ultrasonically welded joints. This type of geosynthetics is commonly used to stabilize geotechnical problems in which the pullout failure is likely to occur. The present study has been conducted to evaluate the pullout behavior of a geocell by considering the effect of soil grain size. A series of 18 monotonic and 24 multistage geocell pullout tests were performed in sandy and gravely soil. The obtained geocell pullout loads were divided into two components: passive and frictional resistance. A previously made theoretical approach was used to measure the mobilized frictional and passive resistance components to evaluate the contribution of each mechanism. The results obtained from monotonic geocell pullout tests showed that the geocells exhibited hardening pullout behavior and the pullout failure occurred when the geocell material did not have any more pullout capacity to resist external load. Increases in the geocell height and soil grain size had significant effects on the passive component and it was seen that the contribution of geocell height developed passive resistance higher than the soil grain size. Furthermore, the multistage test results indicated that for removal of the geocell, the ultimate post-cyclic pullout load was less than the monotonic pullout load. This was the result of a reciprocating motion from loading caused by the interlock between the geocell infill soil and the surrounding material, which weakened and broke during the cyclic phase. As the coarseness of the soil increased, the interfacial strength increased. The theoretical approach did not single out the passive component between monotonic and multistage tests and the obtained passive resistance values were the same in these calculations. However, the cyclic loading could affect this component. Also, the soil particle size had a significant effect on the cumulative displacement during the cyclic phase.