عنوان مقاله [English]
In this experimental research, the effect of the number of micropiles, relative density of soil and dry stone surcharge on liquefaction potential of Anzali sand was studied. The inner sides of the rigid transparent box, installed on shaking table, were covered with the sheets of foams to reduce of 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, moist tamping method was used.The grouting operation for construction of micropiles was performed using a grouting device under the injection pressure of 0.1 bar with the 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 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 show that liquefaction potential of saturated sand was significantly decreased by installing of two and four micropiles into the soil. On the other hand, one micropile had a negligible effect on reducing of 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 generation of pore water pressure is limited. A dry stone surcharge with a 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, leads 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.