تعيين ضخامت بهينه ي لايه ي خاك درشت دانه ي محصوركننده ي ژيوگريد و مهار- شبكه (Grid-Anchor) در خاك چسبنده

Determination of the optimum thickness of granular soil surrounding the geogrid and Grid-Anchor in cohesive soil

در اجراي يك سازه ي خاك مسلح، براي بالابردن راندمان مسلح‌كننده ها، معمولاً از خاك‌هاي درشت دانه استفاده مي شود. خاك‌هاي درشت دانه به علت ويژگي هاي ذاتي كه دارند با چشمه هاي مسلح‌كننده بهتر درگير مي شوند، اما عموماً از محل قرضه به محل اجراي پروژه منتقل شده است و از اين جهت تهيه ي آنها پرهزينه است. به همين دليل در اين تحقيق سعي شده است كه فقط لايه‌يي از خاك درشت‌دانه در اطراف مسلح‌كننده استفاده شود وحجم باقيمانده با خاك محل يا خاك ريزدانه جايگزين شود. در اين نوشتار، نتايج آزمايش هاي بيرون كشش كه بر روي ژيوگريد معمولي و مسلح‌ كننده‌ي مهار- شبكه (Grid-Anchor) انجام شده اند، ارايه شده است و با مقايسه ي نتايج اين آزمايش ها، ضخامت تقريبي بهينه براي لايه-ي خاك درشت دانه ي اطراف مسلح‌كننده به دست آمده است. در نهايت، نتايج تحليل عددي، با استفاده از نرم افزار اجزا محدود Plaxis 3D Tunnel، از طريق مقايسه با نتايج تحليل آزمايشگاهي به تاييد رسيده اند.

In order to increase the efficiency of reinforcements in a reinforced soil structure, the granular soils are usually used. However, in the most situations, we have to transfer granular soils from the borrow area, usually far from the site of the soil structures. This will impose a considerable amount of money to the project. Therefore, in this research, just a layer of coarse-grained soil, surrounding the reinforcement layer is used and the remained volume was filled with the fine-grained soils or the soils that exist in the project site. This experimental study is performed for the selected thicknesses of coarse-grained soil surrounding the reinforcement. Furthermore, the numerical analysis for these pull-out tests was conducted using the finite element code, PLAXIS3D Tunnel. Finally, the experimental and numerical analysis results for the variety of coarse soil thicknesses were compared and the optimum thicknesses for coarse-grained soil are presented. According to the results, the pull-out resisting force increases with increasing the coarse layer thickness; in addition, the Grid-Anchor endures more pull-out resisting forces as compared with the usual geogrid. According to the experimental results, 10 centimeters coarse layer (i.e. the thickness of 5 centimeters for the top and the thickness of 5 centimeters for the bottom layer of the reinforcements) was found as optimum thickness of surrounding layer for the 5 kPa surcharge. Other findings of this research can be as follows: when the reinforcements begin to move against the soil surrounding them, the pull-out resisting force decreases due to the decrease in friction between the soil and the reinforcements. On the other hand, as the thickness of coarse layer around the reinforcements increases, a hardening state in the force-displacement curve of these reinforcements was observed. This situation is more visible for Grid-Anchor in comparison with the usual geogrid. Having compared the numerical and experimental results, there is a suitable conformance between them.