بررسی رفتار برشی و بیرون‌کشش استاتیکی ژئوکامپوزیت مدفون درخاک دو لایه

به منظور بررسی رفتار برشی و بیرون‌کشش ژئوکامپوزیت مدفون در خاک تک‌لایه و دولایه، مطالعه‌یی آزمایشگاهی به‌وسیله‌ی دستگاه برش مستقیم بزرگ‌مقیاس و بیرون‌کشش تحت تنش‌های قائم مختلف انجام گرفت. نتایج نشان داد تنش قائم، عامل موثری برای افزایش مقاومت برشی، مقاومت بیرون‌کشش و تغییر در نوع گسیختگی خاک ژئوکامپوزیت است و اثر چشم‌گیری بر جابه‌جایی در بیشینه‌ی مقاومت بیرون‌کشش دارد. در شرایط یکسان بارگذاری، قرارگیری ژئوکامپوزیت در سطح مشترک خاک دولایه باعث تغییر رفتار بیرون‌کشش نسبت به حالت تک‌لایه شده است. اندرکنش خاک ژئوکامپوزیت علاوه بر تنش قائم به نوع و اندازه‌ی ذرات خاک، تک‌لایه و دولایه بودن آن حساس است. میانگین ضرایب سطح تماس موثر محاسبه شده برای ماسه ژئوکامپوزیت 0/8 و برای شن ژئوکامپوزیت 0/91 است. قرارگیری ژئوکامپوزیت در مرز خاک دولایه باعث بهبود رفتار خاک نسبت به حالت تک‌لایه شده است؛ به‌طوری که میانگین ضریب اندرکنش بیرون‌کشش برای خاک دولایه (ماسه ژئوکامپوزیت شن) 0/51 و برای خاک ماسه‌یی و شنی به ترتیب 0/35 و 0/47 به دست آمده است.

Investigation of Shear and Static Pullout Behavior of Geocomposite Embedded in TwoLayers soil

Costeffectiveness, fast performance, and relatively long service life have made geosynthetics widely used in geotechnical structures such as road pavement, retaining walls, slope stabilization and foundations, bridge abutments, embankments or at the boundary between embankments and subgrade to be used. The soil geocomposite used in this research, which is made in Iran under the brand name of GC Soil 40/40, is a combination of geogrid and geotextile and is used in various projects such as embankment bed reinforcement and separation to implement embankment on fine and loose subgrade. In general, in the design of geosynthetics, including soil geocomposites, interaction mechanisms including slip and pullout as well as interaction coefficient between soil and geosynthetic should be considered. Accordingly, to evaluate the soilgeocomposite interaction, direct shear and pullout tests were performed in onelayer soil (sandgeocomposite and gravelgeocomposite) and twolayers soil (sandgeocompositegravel) under different vertical stresses. The results of direct shear tests showed that reinforcing the soil with geocomposite reduced the angle of friction and increased soil adhesion. Despite the increase in shear stress and pullout resistance with increasing vertical stress, the interaction coefficients decrease with an increase in the vertical stress. This issue can be related to the nonlinear behavior of pullout force and soilgeocomposite shear stress with vertical stress. Vertical stress is an effective factor to increase the pullout resistance and type of mode geocomposite rupture and also has a significant effect on the displacement at the maximum pullout resistance. The results showed that under the same loading conditions, the placement of the geocomposite on the common surface of the two layers soil changes the pullout behavior compared to the onelayer soil. In general, it can be stated that the soilgeocomposite interaction, in addition to vertical stress, is sensitive to the type and size of soil particles, one and twolayers of soil. For sandgeocomposite and gravelgeocomposite interfaces, the average coefficients of interaction(𝑐𝑖 ) for direct shear are 0.8 and 0.91, respectively. Also, the average pullout interaction coefficients(𝑓𝑏) for sandy and gravel soils reinforced with geocomposite (onelayer) are 0.35 and 0.47, respectively, and this coefficient is obtained as the average of 0.51 for sandgeocompositegravel (twolayer).