روشي براي بررسي رفتار لرزه‌اي ديواره‌هاي حفاظت‌شده گودبرداري‌هاي عميق با سيستم ديوار برلني1در آبرفت درشت‌دانه

Seismic Behavior of Soldier Pile Support Systems for Deep Excavations in Coarse Grain Alluvium

ديوارهاي برلني مهارشده با ميل مهار هاي جانبي در پروژه هاي زيادي مورد استفاده شده و به عنوان گزينه مناسبي در پايدارسازي ديواره-هاي گودبرداري‌هاي عميق مطرح شده است. با اين وجود، بيشتر پژوهش‌هاي انجام‌شده مربوط به حالت استاتيكي است كه تغيير مكان و گسيختگي ديوار در اثر افزايش ارتفاع آن را بررسي كرده است؛ اما رفتار لرزه اي اين نوع ديوارها به ندرت بررسي شده است. با توجه به افزايش استفاده از سيستم‌هاي ديوار برلني در مناطق لرزه خيز، بررسي رفتار لرزه اي اين سازه‌ها اهميت مي يابد. در اين پژوهش، به روشي براي بررسي رفتار لرزه اي ديوارهاي برلني در بخشي از آبرفت درشت دانه تهران پرداخته شده است. با توجه به آن‌كه بررسي پايداري لرزه اي شيرواني هاي خاكي نشان‌دهنده آن بوده است كه روش شبه‌استاتيكي، رويكردي مناسب و ساده براي معادل سازي تحليل هاي ديناميكي است؛ در اين پژوهش سعي شده است براي ديوارهاي برلني، روشي مشابه براي معادل‌سازي رفتار ديناميكي با در نظر گرفتن يك ضريب شبه‌استاتيكي برابر پيشنهاد شود. بنابراين سطوح گسيختگي محتمل در تحليل‌هاي ديناميكي و شبه‌استاتيكي با هم مقايسه شده و با در نظر گرفتن نيروهاي وارد بر ميل مهار ها (مهم‌ترين عامل پايداري گوه گسيختگي محتمل) به عنوان پايه‌ي مقايسه، ضريب شتاب افقي معادل زلزله براي مدل ارايه شده است.

Soldier pile consists of the passive reinforcement (i.e., no post-tensioning) of existing ground by installing closely spaced steel bars (i.e., nails), which are subsequently encased in grout and transfer the loads from steel piles to soil. As construction proceeds from the top to bottom, concrete is also applied on the excavation face to provide continuity. Soldier pile is typically used to stabilize excavations adjustment to the buildings to prevent surface movement and cracks in the buildings where top-to-bottom construction is advantageous compared to other retaining wall systems. For certain conditions, soldier pile offers a viable alternative from the viewpoint of technical feasibility, construction costs, and construction duration when compared to ground anchor walls, which is another popular top-to bottom retaining system. This paper addresses soil nails that are installed with a near horizontal orientation and are primarily subjected to tensile stresses together steel piles which act as cantilever beam with horizontal nails as supports. Soldier pile can be used for both temporary and permanent structures based on its service life or intended duration of use. Soldier pile is a form of ground retention used when ground conditions comprise of dense to moderately dense soils such as coarse grain alluviums. Soldier pile systems with lateral nails are used in many excavation projects. This method is one of the appropriate support systems in deep excavations. However, most of the researches have been focused on the effects of wall height on the stability of excavations in static conditions, but with increasing of the use of soldier pile systems in seismic regions, the dynamic stability of these structures cannot be ignored. According to increasing of the usage of the soldier pile systems in seismic active zones, it’s important to study the dynamic behavior of these structures. Hence, in this paper, the seismic behavior of soldier pile systems in Tehran coarse grain alluvium has been investigated. The methodology is based on pseudo-static approach to equalize the dynamic analysis. The numerical modelings have been done according to Finite Difference Method (FDM) to this equalization. Based on slope stability theory, it has been shown that the pseudo-static method is a suitable and simple approach to equalize dynamic behavior. Therefore, in this paper, a similar approach has been used to equalize dynamic behavior of soldier pile systems with considering a proposed pseudo-static coefficient. The failure surfaces in dynamic and pseudo-static analyses have been compared and based on the comparison of axial forces in the nails (as the most important factor of the stability), the equivalent horizontal acceleration coefficient for the model is proposed. The applied forces cause the reinforcement tension and the mobilized tension force can overcome the soil tension weakness. Thus, predicting mobilized forces in soldier pile nails during earthquake is very important. The effects of most important parameters such as wall height, nail arrangements and soil types through numerical modeling of the soldier piles under dynamic loading by using FLAC have been investigated.