Experimental Investigation of Load- Displacement Behavior of Enlarged Base Piles under Oblique Tension Loadings in Sandy Soil

One of the most used deep foundations are piles. The piles are tall members that are used to transfer the foundation loads from the weak layers of the soil to the ground at a deeper and stronger layers. In some structures, the piles may be exposed to uplift forces, including those subjected to extreme overturning moment, such as power towers or docks. During numerical modeling in relation to vertical pile under axial load, it was observed that the axial load bearing capacity of the pile was reduced at the presence of lateral loading (Abdel-Rahman and Achmus, 2006). For the pile under load, the ultimate vertical load ratio (p < sub>u) to the lateral loading (p < sub>L) was greater than 1, with a maximum resistance to load times, when the load angle was 30 degrees. The ratio p < sub>u/p < sub>L was between 0.18 and 0.72, and for the angle of 60 degrees, p < sub>u/p < sub>L less than 0.18 ratio, the ratio value is maximized at 90 degrees (Chattopadhyay and Pise, 1986). Baki et al. (2013) reported that the optimal load bearing of the piles under tensile loading is achieved in rough piles in anchored sand. By changing the angle of application of the tensile loading from zero to 60 degrees relative to the vertical, the pile frictional resistance only turns to the side resistance with the lateral side of the earth, and both components contribute to the final capacity. The study of piles behavior under oblique tension loadings showed that tensile loads are depending on the buried length ratio (L/d), the ratio of the enlarged base diameter to the pile diameter (B/d), the loading angle (α) and the relative density of the soil around the pile (Dr). The ultimate resistance of pile increases with increasing the ratios of (L/d), (B/d) and soil density. The analysis of the results showed that the critical angle (αcr) which the pile reaches its maximum tensile strength depends on the ratio (L/d), (B/d) and soil density (Mandal et al., 2002). The tensile load capacity of the buried enlarged base pile in the sand was studied using physical modeling tests. Analysis of the results showed that the uplift tensile capacity of pile increases significantly with increasing the ratio of buried length to pile diameter more than two and also, increasing the relative density of the sand. The results also showed that the increase in the pile diameter leads to tensile load of the pile (Nazir et al., 2015). A series of laboratory study and numerical analysis of finite element were performed to evaluate the efficiency of enlarged base piles with increasing cross-section at different levels of the pile length in order to improve its uplift capacity. The results of the study showed that with increasing the cross-section of the pile at different levels, the tensile capacity of piles increased, and the amount of sand deformation around the pile decreased (Moayedi and Mosallanezhad, 2017).