الفهرس 
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Abstract
Many high-rise structures are being constructed and constructed at the present time, and these structures are subjected to very high lateral loads, which result in torque and tensile forces in the foundations. Therefore, the foundations of these structures need to use piles with a wider base in order to resist the high uplift forces and torques generated on these foundations. At the present time, there are also many water facilities that are subjected to very high uplift forces on the foundations, so it is preferable to use the foundations with a wider end in order to resist very high tensile forces and water lifting forces. Although many researches are available to estimate the uplift capacity of single piles, only a few researches deal with the group action of the enlarged base piles that are constructed in transition depth. So, this research effort is presented to study the group effect of enlarged base piles installed in sand with small spacing under tension loading. The aim of this research is to study the uplift capacity of enlarged base piles in dry sand. Laboratory studies have been done on this type of piles with changing the diameter of the pile base (Db), the angle of inclination of the base of the pile (θ), the embedment length inside the soil (L) and different relative density of sand (Dr= 30%, 50% and 80%) and compared the results with the normal piles without base. in addition to using these piles in the form of groups and calculating the efficiency of the pile group based on changing the spacing between piles relative to the diameter of base (Sp/Db)), different number of piles in the group (N) and different relative density of sand (Dr= 30%, 50% and 80%). The results showed that in the case of increasing the diameter of the pile base, the pile’s uplift capability increases with the increase in the length of the embedded part and the decrease in the value of the angle of inclination of the base. It is concluded that, using the base at the end of the normal piles has led to increase in the uplift capacity of the piles when compared to the other systems which used in improving uplift capacity.