اندازه گیری میدانی و مطالعه تحلیلی تغییر بار میل مهار در گودبرداری با گذشت زمان

در سال‌های اخیر در شهر‌های بزرگ از جمله تهران تعداد زیادی گود وجود دارد که به دلیل مشکلاتی رها شدند. همچنین در برخی از گودبرداری لازم است تا برای طولانی مدت طراحی شوند ولی مبانی طراحی طولانی‌مدت در آن‌ها رعایت نشده است. پایدارسازی اغلب این گودها به وسیله میل‌مهارها یا انکرها انجام شده است. مشاهدات و اندازه‌گیری‌های طولانی مدت برخی از این گودها نشان می‌دهد که با گذشت زمان نیروی قفل‌شدگی میل‌مهارها کاهش می‌یابد و خطراتی را به دنبال دارد. مطالعه رفتار دراز مدت انکر در گودبرداری‌‌های مهار شده با انکر برای بررسی پایداری گودهایی که اجرای آنها طولانی می‌شود یا به مدت طولانی رها می‌شوند ضروری است. در این مطالعه از داده‌های میدانی در رابطه با رفتار بلند مدت یک گود در شهر تهران استفاده و مدلسازی عددی بر اساس این مطالعه موردی انجام شده است. راستی آزمایی و واسنجی مدل عددی بر اساس اندازه گیری‌‌های میدانی انجام شده است. همچنین در این مقاله سعی شده است بر اساس نتایج مدل عددی، رابطه‌ای برای پیش‌بینی بار انکر در طولانی مدت در خاک درشت دانه دارای چسبندگی پیشنهاد شود. در ادامه به مطالعه متغیرهای موثر بر رفتار طولانی مدت بار انکرهای تعبیه شده در گود پرداخته شده است. این متغیرها شامل مشخصات خاک، عمق گود و مقدار سربار همسایه گود است. نتایج این مقاله افزون بر ارائه رابطه برای پیش‌بینی بار انکر، شامل معرفی متغیرهای حاکم بر رفتار طولانی مدت است.

field measurement and analytical study of anchor load change in excavation over time

in many construction projects, it is necessary to excavate the land so that its walls are vertical or close to vertical. lateral pressure is exerted on these walls due to the movement of the soil behind it. in order to prevent the collapse of the walls of the excavated site and its possible consequences, temporary or permanent structures are implemented, which is called stabilization. excavations are secured for various reasons. they may be stabilized to protect personnel entering and working in the excavation or to protect buildings or municipal services adjacent to excavation. over the past years, there have been a large number of excavations in large cities, including tehran, which were abandoned due to some problems. furthermore, while some excavations need to be designed for a long time, long-term design basics are not observed during such processes. stabilization of most of these excavations has been done using anchors. in this method, after placing and implementing the anchors, they are prestressed by applying force. observations and long-term surveys of these excavations show that in some cases, locking force of anchors decreases, leading to dangers. therefore, it is very important to know the long-term behavior of anchors in excavations to investigate the stability of these excavations that are prolonged or abandoned for a long time. in this study, field data of the long-term behavior of a excavation in tehran is used and numerical modeling is done based on this case study. verification and calibration of the numerical model has been done based on field measurements. also in this article, relationships based on the results of the numerical model have been proposed to predict the anchor load in the long term in cohesive coarse-grained soil. the proposed relationships predict well the anchors load at one year after the end of excavation. these relationships are separated to three categories of five strands anchors, six strands anchors and six strands anchors with short length. in the following, the variables affecting the long-term behavior of the anchor loads embedded in the excavation have been studied. these variables include soil properties, depth of the excavation and neighbor surcharge of the excavation. the results of this article, in addition to presenting the relationship for anchor load prediction, include the introduction of variables that affecting long-term behavior. the parametric study shows that with the increase of the angle of internal friction or the increase of soil cohesion, the amount of anchors load decreases over the time. also, by increasing the depth of the excavation or increasing the neighbor surcharge of the excavation, the load of the anchors decreases less over time. of course, the impact of excavation depth occurs mostly in the lower anchors and does not affect the anchors of the first row and close to the ground. studies showed that anchors close to the earth surface have a greater rate of load reduction over time among anchors with the same length and number of strands. also, among the same anchors, anchors with shorter length experience more load reduction over time.