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بررسی آزمایشگاهی اثر ریزشمع در پتانسیل روانگرایی ماسه ی اشباع انزلی
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نویسنده
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قربانی علی ,صمتی فومنی محمدعلی
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منبع
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مهندسي عمران شريف - 1399 - دوره : 36-2 - شماره : 1/2 - صفحه:15 -24
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چکیده
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در نوشتار حاضر، تاثیر ریزشمع تزریقی در پتانسیل روانگرایی ماسه‌ی اشباع انزلی با چگالی نسبی 30٪ و 50٪ با استفاده از دستگاه میزلرزه بررسی شده است. برای این منظور، ریزشمع‌هایی با رعایت قوانین مقیاس در 3 آرایش مختلف با قطر معادل 0٫9 سانتی‌متر و طول 23 سانتی‌متر تحت فشار 0٫1 بار در جعبه‌ی میزلرزه ساخته شدند. نتایج به‌دست آمده، شان‌دهنده‌ی آثار چشم‌گیر افزایش تعداد ریزشمع‌ها، چگالی نسبی خاک و سربار در بیشینه‌ی مقدار نسبت اضافه فشار آب حفره‌یی و تعداد سیکل‌های لازم برای رسیدن به آن هستند. مقایسه‌های انجام شده با روش‌های موجود ارزیابی پتانسیل روانگرایی بیانگر لزوم بازنگری روش‌های مذکور با درنظر گرفتن آثار کاهشی حاصل از اجرای ریزشمع در مناطق مستعد روانگرایی است. با توجه به نتایج به‌دست آمده، حدود بالا و پایین جدیدی با توجه به شرایط آزمایش، جهت پیش‌بینی مقادیر $r_{u}$ در ماسه‌ی خالص و مسلح شده با ریزشمع ارائه شده است.
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کلیدواژه
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ماسه‌ی انزلی، روانگرایی، میزلرزه، چگالی نسبی، ریزشمع تزریقی
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آدرس
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دانشگاه گیلان, دانشکده ی فنی و مهندسی, ایران, دانشگاه گیلان, دانشکده ی فنی و مهندسی, ایران
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پست الکترونیکی
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mohammadalisomti@yahoo.com
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THE EXPERIMENTAL STUDY OF THE MICROPILE EFFECT ON LIQUEFACTION POTENTIAL OF ANZALI SATURATED SAND
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Authors
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Ghorbani A. ,Somti foumani M.A.
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Abstract
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In this experimental research, the effect of the number of micropiles, the relative density of soil, and dry stone surcharge on the liquefaction potential of Anzali sand was studied by using shaking table apparatus with the rigid transparent container. The inner sides of the rigid transparent box, installed on the shaking table, were covered with the sheets of foams to reduce generation and reflection of body waves from the rigid sides. Two pore pressure transformers (PPT) were used to monitor the pore water pressure variations. For model preparation, the moist tamping method was used. The grouting operation for the construction of micropiles was performed using a grouting device under the injection pressure of 0.1 bar with a watercement ratio of 0.5. Three different arrangements of micropiles were used. The equivalent diameter and the length of micropiles were 0.9 and 23 cm, respectively. After 7 days of curing, the model was saturated from the bottom of the tank with a low hydraulic gradient. All models were shaken under a harmonic sinusoidal load with the frequency, the displacement amplitude, and the duration of 3Hz, 0.9 cm and 9.5 seconds, respectively. It was observed by increasing the relative density of the sand, due to reducing of void ratio, the values of excess pore water pressure ratio $(r_u)$ were decreased, and the required cycles for reaching the $r_{u,max}$ $(N_{peak})$ were increased. The obtained results showed that the liquefaction potential of saturated sand was significantly decreased by installing two and four micropiles into the soil model. On the other hand, one micropile had a negligible effect on reducing of the liquefaction potential. It can be explained by forming the groutsand zone around the micropiles and also the localized compaction in the soil after grouting, the rate of pore water pressure generation is limited. A dry stone surcharge with the stress of 1.2 kPa was placed on the surface of saturated sand, and due to the significant increase in effective stress, the liquefaction potential was reduced significantly, leading to the increase of $N_{peak}$. Based on the obtained results, the upper and lower bounds were proposed to predict the values of $r_u$ in pure and reinforced sand regarding the $N/N_{peak}$.
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Keywords
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