Pile group are vastly used in marine structures for several applications. Loadings exerted to these structures are divided into two main categories: lateral loading and vertical loading. All researchers agree to use vertical piles in the case of pure vertical loading where as the use of batter piles in the case of lateral loading is still in doubt. The behavior of batter piles in a pile group is somehow two-faced. Although batter piles reduce the lateral displacement of the pile group under lateral loading but they also cause stress concentration in batter pile and pile head. Thereby complete understanding of batter and vertical piles is of great importance. In our research, different pile group configurations are analyzed numerically that based on the finite difference method. Soil is modeled as a mohr-coulomb continuous medium obeying model and piles and pile head are assumed to be elastic concrete. To validate the simulation, results from numerical modeling are compared to those from available experimental data and analytical solution.

A common reason for uneven settlement of existing struc- tures founded on pile foundations is negative skin fric- tion (NSF) developed along the piles.As a result of fill placement the soil surrounding the piles in soft ground settles more than the piles.In that case negative skin friction occurs producing pile settlement (down drag) and additional compressive force (down drag) due to the hanging effect around the pile.(NSF) is usually mobilized up to the shear strength of soil in most cases except at very close proximity to the neutral plane.The relative displacement between the settling subsoil and the pile shaft surface should not be more than a few millimeters to have even total settle- ment. Disregarding the effect of down drag forces on piles due to consolidation of the surrounding soil leads to damage in buildings and foundations. Many methods especially numerical simulation methods have been pro- posed to calculate the drag load on single piles. How- ever much less work has been done on drag load on a batter pile. Batter piles are commonly used to sup- port marine structures and deep foundations. Based on the experimental data from Hanna & Nguyen (1986) shaft resistance decreases by the increase of angle of in- clination for both compression and tension forces. On the other hand it was found from full scale results re- ported by Mayerhof (1973) that the shaft resistance ca- pacity for the pile increases due to an increase in the inclination angle. In this study the effect of negative skin friction on vertical piles and batter piles is investi- gated. The analysis was undertaken using Abacus soft- ware which is based on the Finite Element Method (FEM).A single vertical end-bearing and one skin friction pile under different earth surface loadings were analyzed and the drag load force was studied. Subsequently the per- formance of the single batter end-bearing and friction pile with different inclination angles between 0-300 was analyzed. After different combinations of the existed loadings in both surrounded areas of pile drag loading considering different cases. The vertical pile was mod- eled and its results were compared to those of previous studies for model validation. Then single batter piles with different angles were modeled using the results.