ارزيابي عددي عوامل مؤثر بر جابه جايي و دوران لرزه اي ديوار حائل وزني در قياس با روش هاي تحليلي و تجربي

Investigation of factors effective on seismic deflection and rotation of gravity retaining wall compared to the empirical approach

سادگي در ساخت و سهولت اجرايي از مهمترين مزاياي كاربرد ديوارهاي حائل وزني است. يكي از موضوعات مهم در طراحي ديوارهاي حائل بر اساس عملكرد، تخمين جابه‌جايي، دوران و پيش‌بيني رفتار آن تحت بار زمين‌لرزه است. پيش‌بيني مقدار جابه‌جايي و دوران ايجادشده ناشي از زمين‌لرزه، يكي از پيچيده‌ترين مراحل طراحي لرزه‌اي ديوارهاي حائل وزني با مصالح بنايي در مهندسي ژئوتكنيك است. اين موضوع از پيچيدگي‌هاي خاصي برخوردار است و محققان با ارائه روش‌هاي مختلف تحليل پايداري، تغييرمكان و دوران ديوار حائل را ارزيابي مي‌كنند. هدف از اين تحقيق مقايسه نتايج حاصل از تحليل عددي با ديگر روش‌هاي تحليلي و تجربي استفاده شده مهندسان در طراحي بر اساس عملكرد ديوارهاي حائل وزني است. در اين تحقيق ديوار حائل وزني ذوزنقه‌اي شكل كه از مصالح بنايي ساخته شده است به روش عددي و با مدلسازي در نرم‌افزار آباكوس تحت تأثير نيروي زمين‌لرزه قرار گرفته و تأثير عوامل مختلف بررسي مي‌شود. ميزان و شدت تغييرمكان و جابه‌جايي ديوار ناشي از زمين‌لرزه در تراز بالادست و پايين‌دست امتداد قائم ديوار استخراج شده و متعاقب آن ميزان و نحوه دوران لرزه‌اي ديوار ارزيابي و تخمين زده مي‌‌شود. در ادامه نتايج اين بررسي با داده‌ها و روابط تجربي و تحليلي ديگر محققان مقايسه شده است. در اين بررسي پارامترهاي مختلف تحت زمين‌لرزه‌اي مشخص ارزيابي شده است كه شامل تأثير اصطكاك كف ديوار، مشخصات فيزيكي و مكانيكي خاكريز پشت ديوار و همچنين هندسه ديوار شامل قاعده كف و ارتفاع ديوار است؛ هرچند شدت و مدت زمين‌لرزه نيز بسيار تاثيرگذار است.

Retaining walls are designed to withstand lateral earth and water pressures, the effects of surcharge loads, and the self-weight of the wall and, in special cases, earthquake loads in accordance with the general principles specified in this section. Retaining walls are constructed for a certain service life based on consideration of the potential long-term effects of material deterioration on each of the material components comprising the wall. Permanent retaining walls are designed for a minimum service life of 50 years. Temporary retaining walls should be designed for a minimum service life of 5 years. Gravity retaining walls rely on their self-weight to resist lateral earth pressures. Analysis of the seismic behavior of gravity retaining walls during earthquake loading is a quite complex task. Seismic wall movements can occur as sliding or rotational displacements. In some cases, only one of these displacements can be dominant and for some of them, both sliding and rotation can occur. Foundation soil deformability, backfill, wall stiffness, and input record motion as the main variables used in the analysis of walls are subjected to a strong earthquake. The analysis of the seismic stability of walls retaining backfill soil is based on the following assumptions: (1) the wall–soil system is long enough for ignoring the end effects (plane strain condition); (2) the soil is homogeneous, dry, and cohesion-less; (3) the retaining wall is subjected only to horizontal displacements; (4) the seismic action is uniform horizontally distributed in the whole mass of the system; and (5) the failure wedge is a plain. Furthermore, the upper bound limit analysis is based on the assumption that soil will be deformed according to the associated flow rule and the convexity of the soil yield condition. In the following analysis, we assumed that these conditions are met. For many decades, the seismic analysis of retaining walls has been based on the simple extension of Coulomb’s limit equilibrium analysis, which has become widely known as the Mononobe-Okabe method. The method modified and simplified by Seed and Whitman has prevailed mainly because of its simplicity and the familiarity of engineers with the Coulomb method. Designing walls for stability against earthquake risks in seismic zones is done through the analysis of the seismic behavior of the soil-structure system. The methods established using newmark sliding block procedure are based on forces (pseudo-static and pseudo-dynamic) and allowable displacements. These methods are frequently used in the seismic design. Dynamic analysis of retaining walls can also be done by finite-element methods. ABAQUS is among the computer programs that suite for finite-element analysis. In this study, a series of finite elements were carried out in ABAQUS in order to find out typical wall movements including rotation and lateral top and base displacements. This research presents that many variables such as maximum acceleration, properties of foundation and backfill soils, and characteristics of the wall affect the seismic behavior. Design charts were derived from the numerical analyses to predict both lateral displacements at base and top. The proposed charts consider the most relevant factors in the system response. The result obtained can be used to develop an optimum design procedure for gravity retaining walls.