مطالعه آزمایشگاهی رفتار پی نواری لبه دار شده با ریزشمع بر روی ماسه به روش مدل سازی فیزیکی

نوع مقاله : پژوهشی اصیل (کامل)

نویسندگان
بهراد بختیاری 1
آرش رزم خواه 2
حسن قاسم زاده 3
فرج اله عسکری 4
1 دانشجوی دکتری گروه مهندسی ژئوتکنیک، دانشکده فنی، واحد تهران جنوب، دانشگاه آزاد اسلامی، تهران، ایران
2 استادیار گروه مهندسی ژئوتکنیک، دانشکده فنی، واحد تهران جنوب، دانشگاه آزاد اسلامی، تهران، ایران
3 دانشیار دانشکده مهندسی عمران دانشگاه صنعتی خواجه نصیرالدین طوسی تهران، خیابان میرداماد
4 استاد پژوهشکده مهندسی ژئوتکنیک، پژوهشگاه بین المللی زلزله شناسی و مهندسی زلزله
10.22034/24.6.23
چکیده
امروزه افزایش ظرفیت باربری و کاهش نشست در پی­ها بخصوص در پی ساختمان­های موجود، به یکی از موضوعات مهم در رشته مهندسی ژئوتکنیک تبدیل شده است. بطور کلی در مواجهه با خاک­های سست با قابلیت باربری کم با نشست‌ زیاد یکی از راه­های پیش روی مهندسان استفاده از المان­های باربر در خاک می­باشد. در این میان ریزشمع علاوه بر آنکه به عنوان یک المان باربر و مقاوم در برابر نشست عمل می‌کند، به دلیل تزریق دوغاب سیمان، سبب بهبود مشخصات مقاومتی خاک اطراف نیز می­گردد. در بسیاری از پروژه­ها، از ریزشمع­ها به عنوان عناصر سازه­ای استفاده می­شود. ریزشمع­ها در واقع شمع­های جانشینی کوچکی (معمولا با قطر کمتر از ۳۰۰ میلیمتر) هستند که غالباً با تقویت فولادی و تزریق دوغاب سیمان همراه می‌باشند. در این مطالعه با استــــفاده از مدل­سازی فیزیکی، به بررسی تاثیر استفاده از ریزشمع به منظور لبه­دار کردن پی مستقر بر بستر ماسه­ای پرداخته شد. برای این منظور در ابتدا اثر شرایط مرزی محفظه ماسه، بر نتایج مورد بررسی قرار گرفت. بررسی اثر فاصله پی از سطح تحتانی محفظه فولادی نسبت به عرض پی نشان داد که وقتی فاصله پی از سطح تحتانی محفظه کمتر از دو برابر عرض پی باشد، مرز پایین بر نتایج مدل­سازی فیزیکی تأثیر می­گذارد. ارزیابی مرزهای جانبی با در نظر گرفتن فاصله پی از دیواره محفظه نسبت به عرض پی نشان داد که اگر فاصله پی از جدار محفظه بیش از پنج برابر عرض پی باشد، مرز جانبی بر نتایج تأثیری نخواهد داشت. سپس تأثیرات پیکربندی­های مختلف ریزشمع در اطراف پی، از جمله طول ریزشمع و فاصله بین دو ریزشمع متوالی بر ظرفیت باربری و نشست مورد بررسی قرار گرفت. بررسی نتایج نشان داد که با افزایش طول ریزشمع و کاهش فاصله بین دو ریزشمع متوالی، ظرفیت باربری بهبود یافته است. استفاده از ریزشمع به عنوان لبه پی، ظرفیت باربری پی­های سطحی را بین 1.3 تا 2.95 برابر بهبود بخشید. مقایسه منحنی­‌های فشار- نشست نشان داد که، نسبت ظرفیت باربری بهینه در کمترین فاصله بین ریز شمع­های متوالی بدست آمد. علاوه بر این، ریزشمع به عنوان لبه پی، نشست پی نواری را بین 36 تا 82 درصد کاهش داد. همچنین پی نواری لبه­دار شده با ریزشمع، منجر به افزایش طول سطح گسیختگی گردیده و بسته به طول و فاصله ریزشمع­ها، مکانیسم گسیختگی را تغییر داد.

کلیدواژه‌ها

موضوعات

عنوان مقاله English

Determining of Sand behavior through model tests of Strip Footing with Micropile Skirts

نویسندگان English

Behrad Bakhtiari 1
Arash Razmkhah 2
Hassan Ghasemzadeh 3
Faradjollah Askari 4
1 Department of Civil Engineering, Faculty of Engineering, South Tehran Branch, Islamic Azad University, Ahang Bld., Abouzar Bld., Basij Highway, Tehran, Iran.
2 Department of Civil Engineering, Faculty of Engineering, Islamic Azad University, South of Tehran Branch, Ahang Bld., Abouzar Bld., Basij Highway, Tehran, Iran.
3 Faculty of Civil Engineering, K.N. Toosi University of Technology, Mirdamade Ave, Tehran, Iran.
4 Geotechnical Engineering Research Centre, International Institute of Earthquake Engineering and Seismology (IIEES), No. 21, Arghavan Street, North Dibajee, Farmanieh, Tehran, Iran.
چکیده English

Recently, the modification of bearing capacity and the reduction in settlement of existing foundations and buildings has become one of the important topics in the field of geotechnical engineering. Also, the foundation of the buildings on the problematic and flowing sand bed, especially in the coastal strips is inevitable. In general, when faced with problematic soils such as loose soils with low load-bearing capacity, high settlement, liquefaction, disturbed soils, etc., there are two ways for geotechnical engineers, one of which is to use bearing elements in the soil and the other is to improve and modify the physical-mechanical properties of the soil mass. In addition to acting as a bearing and settlement-resistant element, the micro pile also improves the bearing strength of the surrounding soil due to the injection of cement slurry. In many projects, micro piles are used as structural elements. In fact, micro piles are small replacement piles (usually less than 300 mm in diameter) that are often accompanied by steel reinforcement and cement grout injection. Micro piles can be designed and used at any angle and for different purposes, including bearing axial and lateral loads, replacing conventional piles, or as part of a soil-pile system, depending on the purpose of the design. In this study, by physical modeling, the effect of using micro piles on the edge the foundation on sand bed was investigated. For this purpose, the effect of the boundary conditions of the chamber was first investigated. The parameters included the width of the foundation (B), the distance of the foundation from the end surface of the tank (Z), the distance of the foundation from the right/left wall of the chamber (X, X'), unreinforced bearing capacity (Q0) and unreinforced sand settlement (S0). Also, the investigation of the effect of the distance of the foundation from the lower surface of the steel chamber to the width of the foundation (B) showed that when the distance of the foundation from the lower surface of the chamber was less than twice the width of the foundation, the lower boundary affected the results of physical modeling. The evaluation of the lateral boundaries given the distance of the foundation from the chamber wall (X) to the width of the foundation showed that for X/B≥5, the lateral boundary had no effect on the results. Influences of various micropile skirt configurations were investigated, including micropile length (L) and spacing between two consecutive micropiles (S) on bearing capacity-settlement. The micropile skirts improved the bearing capacity of shallow foundations, depending on the L/B ratio and spacing between micropiles depending on the S/D ratio. Analysis of the results indicated that improved bearing capacity upon increasing the length of micropile skirt and reducing the spacing between two consecutive micropiles. Comparison of the pressure-settlement curves showed that in constant micropile lengths, the optimum Bearing Capacity Ratio (BCR) was in S/D=2. Further, the skirt piles reduced the settlement of strip footing. The Micropile Skirted Strip Footing (MSSF) led to increased failure surface and, depending on the pile length and spacing micropiles, it changed the failure pattern of the soil.

 
 

کلیدواژه‌ها English

bearing capacity
Micropile
Physical Models
Failure mechanism
Confinement
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مهندسی عمران مدرس
دوره 24، شماره 6
آذر و دی 1403
صفحه 23-37