تأثیر چرخه های تر و خشک شدگی بر رفتار تورمی-انقباضی خاک های متورم شونده بهسازی شده با نانوسیلس، الیاف پلی پروپیلن و سرباره EAF

نوع مقاله : پژوهشی اصیل (کامل)

نویسندگان
سجاد شاهسونی 1
امیر حسین وکیلی 2
مهدی مخبری 3
1 دانشجوی دکتری ژئوتکنیک، دانشکده مهندسی عمران، استهبان
2 موسسه آموزش عالی زند شیراز، شیراز
3 دانشکده مهندسی عمران، استهبان
چکیده
خاکهای متورم شونده جزء خاکهای مسئله داری هستند که در سراسر جهان پراکنده شده اند. تغییرات رطوبت در این نوع خاکها موجب تغییر حجم شدید و باعث آسیب و خرابی سازه های واقع بر روی آن می شود. خاکهای رسی متورم شونده در چرخه های تر و خشک شدن متوالی، رفتار تورمی-انقباضی از خود بروز می دهند. در این پژوهش رفتار تورمی-انقباضی یک نوع بنتونیت طبیعی با درصد تورم بسیار زیاد و نمونه تثبیت و تسلیح شده با افزودنیهای نانوسیلیس، الیاف پلی پروپیلن و سرباره کوره آهن با نام EAF بررسی و سعی گردید کارایی و دوام این مواد در مواجهه با چرخه های تر و خشک شدگی متوالی مورد ارزیابی جامع قرار گیرد. به منظور مطالعه این نوع رفتار، ابتدا تورم اولیه ی خاک بنتونیت و تأثیر افزودنیها بر تورم آن در دستگاه اودئومتراستاندارد بررسی گردید. مطابق نتایج، فرایند همزمان تثبیت و تسلیح دنبال شده در این تحقیق، سبب کاهش 85 درصدی تورم نسبت به نمونه اولیه با درصد تورم 26/75% گردید. پس از آن، تأثیر چرخه های تر و خشک شدگی بر روی رفتار تورمی-انقباضی خاک مبنا و نمونه بهینه تثبیت و تسلیح شده در دستگاه اودئومتر اصلاح شده مورد بررسی قرار گرفت. ثبت تغییر شکل محوری خاک و همچنین تغییرات درصد رطوبت، نسبت تخلخل و درصد اشباع آن حین چرخه های تورم و انقباض نشان داد که چرخه های تر و خشک شدگی موجب کاهش پتانسیل تورم در نمونه های تثبیت و تسلیح شده و نمونه مبناء گردید. همچنین بررسی تغییرات نسبت تخلخل در مقابل درصد رطوبت خاک اولیه حین چرخه های تر و خشک شدگی نشان داد که منحنی تغییرات، یک منحنی s شکل بوده وبیشترین نسبت تخلخل و تغییر شکل بین درصد رطوبت معادل درجه اشباع 50تا 90درصد رخ می دهد. در حالی که برای نمونه تثبیت و تسلیح شده منحنی تغییرات به صورت s خوابیده بود که عمده تغییرات در درصد رطوبت معادل درجه اشباع 70تا 90درصد اتفاق افتاد که نشان می دهد در نمونه های تثبیت و تسلیح شده از تاثیر منفی رطوبت بر تغییر حجم کاسته شده و میزان تورم و انقباض در تعداد سیکل های کمتری به حالت تعادل می رسد. نتایج حاصله در کنار آنالیزهای به دست آمده از آزمایش های SEM و XRD ثابت کردند که افزودنی های استفاده شده در این پژوهش نه تنها پتانسیل تورم را به صورت چشمگیر کاهش دادند، بلکه ضمن کاهش رفتار تورمی-انقباضی دارای دوام مناسب در چرخه های تر و خشک شدگی متوالی نیز بودند.

کلیدواژه‌ها

موضوعات

عنوان مقاله English

The effect of wetting and drying cycles on the swelling-shrinkage behavior of the expansive soils improved by nanosilica, polypropylene fibres and EAF slag

نویسندگان English

Sajad Shahsavani 1
Amir Hossein Vakili 2
Mehdi Mokhberi 3
1 PhD Candidate, Department of Civil Engineering, Estahban Branch, Islamic Azad University, Estahban, Iran.
2 Assistant Professor, Department of Civil Engineering, Faculty of Engineering, Zand Institute of Higher Education, Shiraz, Iran.
3 Assistant Professor, Department of Civil Engineering, Estahban Branch, Islamic Azad University, Estahban, Iran
چکیده English

The problematic expansive soils are spread in all parts of the world. The water content variations cause large soil volume changes and consequently, great losses on the infrastructure. The expansive clayey soils show swelling - shrinkage behaviour respectively in wetting and drying cycles. In this study, the swelling-shrinkage behaviour of a natural severely expansive bentonite was verified in its natural state and after being improved by nanosilica, polypropylene fibres, and the EAF slag. Firstly, the swelling potential of the natural soil was determined and then, different combinations of the stabilizers' effects on the swelling potential were assessed by means of oedometer tests under 1 kPa loading. The swelling potential of the untreated expansive clay sample was measured as 75.26%, thus the soil sample provided for the study was considered in the very high expansion category. The results indicated that the swelling potential of one-day cured samples by the addition of 0.5% of nanosilica decreased by 22.8%. The improvement by means of 0.5% of nanosilica and 0.6% of polypropylene fiber, and the optimum composition of 0.5% of nanosilica, 0.6% of polypropylene fibers, and 10% of EAF slag decreased the swelling potential by 70 and 85%, respectively. Afterwards, the wetting and drying cycles' effects on the swelling and shrinkage of the natural soil and that of the best identified combination of additives were verified by means of modified oedometer. The measurement of the axial deformation of soil, void ratio, and the saturation ratio during the swelling-shrinkage cycles indicated that the wetting and drying cycles caused the reduction of swelling potential of both untreated/natural and improved expansive soil samples. Additionally, the variation of void ratio versus soil water content during the wetting and drying cycles showed that the variation was an S-shape curve, which was almost a horizontal S shape for the improved soil. It was observed that the equilibrium occurred in lower number of wetting and drying cycles for the improved sample, compared to that of the natural soil. In addition, for the untreated samples, the highest void ratio variations occurred at saturation degree between 50 and 90%. However, for improved soil sample, the highest void ratio variations were recorded at saturation degree between 70 and 90%, reflecting the reduction of negative effects of water content variations on volume changes when the expansive soil samples were improved. Consequently, it was concluded that the additives used in the study not only decreased the swelling potential of expansive soil samples with very high expansion degree, but also decreased the swelling-shrinkage behaviour of the soil and increased the durability of the samples during wetting and drying cycles.

کلیدواژه‌ها English

Expansive soil
wetting and drying cycles
modified oedometer
soil improvement
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مهندسی عمران مدرس
دوره 21، شماره 3
خرداد و تیر 1400
صفحه 205-221