چكيده فارسي :
در نوشتار حاضر، تاثير ريزشمع تزريقي در پتانسيل روانگرايي ماسه ي اشباع انزلي با چگالي نسبي 30٪ و 50٪ با استفاده از دستگاه ميزلرزه بررسي شده است. براي اين منظور، ريزشمع هايي با رعايت قوانين مقياس در 3 آرايش مختلف با قطر معادل 0٫9 سانتي متر و طول 23 سانتي متر تحت فشار 0٫1 بار در جعبه ي ميزلرزه ساخته شدند. نتايج به دست آمده، شان دهنده ي آثار چشم گير افزايش تعداد ريزشمع ها، چگالي نسبي خاك و سربار در بيشينه ي مقدار نسبت اضافه فشار آب حفره يي و تعداد سيكل هاي لازم براي رسيدن به آن هستند. مقايسه هاي انجام شده با روش هاي موجود ارزيابي پتانسيل روانگرايي بيانگر لزوم بازنگري روش هاي مذكور با درنظر گرفتن آثار كاهشي حاصل از اجراي ريزشمع در مناطق مستعد روانگرايي است. با توجه به نتايج به دست آمده، حدود بالا و پايين جديدي با توجه به شرايط آزمايش، جهت پيش بيني مقادير $r_{u}$ در ماسه ي خالص و مسلح شده با ريزشمع ارايه شده است.
چكيده لاتين :
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 water-cement 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 (ru) were decreased, and the required cycles for reaching the ru,max (Npeak) 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 grout-sand 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 Npeak. Based on the obtained results, the upper and lower bounds were proposed to predict the values of ru in pure and reinforced sand regarding the N/Npeak.
