تعیین عملکرد رفتار دینامیکی دیوارهای خاکی میخ گذاری شده تحت بارگذاری‌های لرزه‌ای بر اساس تغییر مکان

با توجه به گسترش روزافزون بهره‌وری از فضاهای زیرسطحی، نیاز بشر به پایدارسازی در زمان حفر و گودبرداری بیش ‌از پیش قوت ‌می‌گیرد. پایدارسازی و بررسی این روش در حالت دینامیکی به دلیل بهره‌مندی در سازه‌ها‌ی دائمی نظیر پایداری شیب کناره راه از اهمیت بالایی برخوردار است. یکی از روش‌های پایدارسازی دیواره‌های گود استفاده از روش میخ‌گذاری ‌است. لذا در این مقاله رفتار پایدارسازی‌ دیوارهای میخ‌گذاری شده دائمی تحت بار دینامیکی مورد بحث و بررسی قرار گرفته است. به کمک ابزارگذاری‌ها‌ی صورت گرفته در گود هتل نرگس شماره 2 و مدل‌سازی آن با استفاده از نرم‌افزار flac صحت این نرم‌افزار مورد تایید قرار گرفت. سپس با در نظر گرفتن 15 نگاشت و ساختگاه‌های نوع 1، 2 و 3 بر اساس آیین‌نامه 2800، بارهای هارمونیک معادل محاسبه شده و تحلیل‌های دینامیکی برای چهار بار هارمونیک معادل، سه ساختگاه و سه ارتفاع مختلف 3، 6 و 9 متر و در دو زاویه مختلف میخ‌گذاری انجام شد. برای این منظور با در نظر گرفتن تغییر شکل لبه بالایی دیواره به‌عنوان معیار مقایسه بین تحلیل‌ها، مقادیر تغییر مکان در 72 حالت مختلف مشخص شد. بررسی نتایج تحلیل‌های فوق نشان داد که، با کاهش مشخصه‌های مقاومتی ساختگاه (از نوع 1 به 3) جابه‌جایی افقی لبه گود و پوسته نما افزایش یافته و با کاهش زاویه میخ‌ها جابه‌جایی افقی لبه گود و پوسته نما کاهش می‌یابد.

Determination of the Dynamic Behavior of Soil Nailed Walls Basedon Displacement

Demand for highrise buildings and shopping malls has increased in recent years. For this reason, these buildings have a variety of basements. Due to insufficient land, some parts of these structures are being built underground. Stabilizing vertical cuts by emerging methods provides a new way for the construction industry. In addition, the demand for stabilizing vertical cuts on highways and railways against dynamic forces has been raised. There are various methods for stabilizing underground cuts. Soil nailing is one of the most common methods for stabilizing cut slopes in building industry. In this method, the soil is strengthened by placing the steel rods into the drilled holes on the wall and the ground. It is worth mentioning that, this method could be used for underground construction. Whereas soil nailing wall system needs less space in comparison with other retaining wall systems, in urban areas especially where walls cuts are surrounded by structures is more applicable. Observations of the performance of soil nails walls in recent earthquakes indicate that their destruction by deep excavations rarely occurs. Literature review on the soil nail walls shows that the mechanism of reinforcement and design of the soil nail walls is without considering of seismic loading. However, few studies have been performed on the seismic behavior of these walls. In this paper, the dynamic behavior of the steel soil nail walls has been investigated numerically. In order to validate twodimensional, nonlinear finite difference model created by FLAC software, obtained results from the instrumental excavation wall (Hotel Narges No.2) were used. In this study, a numerical parametric study was performed to investigate the factors affecting the behavior of the soil nail wall system. This parametric study has the effect of wall height (3, 6 and 9 m), nail angle (10 and 15 degrees), soil properties (type 1 to 3 based on Iranian code of practice for seismic resistant design of building (2800)) and seismic loading characteristics such as magnitude, frequency of the maximum acceleration of the earth’s surface were examined. In addition, four equivalent harmonic loads instead of 15 time history are used. After analyzing 72 different models, it was concluded that by decreasing the soil shear strength (types 1 to 3), the displacement of the upper edge of the wall would increase sharply, with the decrease of the nail angle (from 15 to 10) horizontal displacement of the upper edge wall reduced. By decreasing the angle of the nails (from 15 to 10), the force of the nails is increased. Increasing the height of the wall increases the horizontal displacement of the upper edge of the wall. Also by changing the type of harmonic loading type 1 to type 4, the behavior of the soil nail wall varies with soil type changes, which can be attributed to the effect of soil damping and soil type on the different seismic behavior of the nailed structures. The calculated dynamic analysis results show that the data are scattered under four different harmonic loads. Therefore, the seismic performance of the soil nail structures depends on the geometry parameters and the selection of the main mapping parameters including mold period, acceleration, and mapping duration is very important and requires sufficient accuracy. The dominant mode of deformation of the soil nail wall for four harmonic loads, and for all heights is around the intersection point of the wall and cavity.