Numerical investigation of the effect of shaft surface geometry of tapered pile group with circular and square cross-sections on bearing capacity and group efficiency inquiry

Piles with a gradually decreasing cross-section area from pile top to the tip is called tapered piles. Making this change in pile geometry could improve pile behavior in terms of axial compression load bearing, compared to conventional uniform cross-section piles. The beneficial effect of shaft taper pile on the capacity and performance of axially loaded single piles is well documented in the literature. However, the behavior of tapered pile groups has been rarely investigated experimentally and numerically. In this study, a numerical investigation of single tapered pile and pile group behavior based on an experimental investigation in geotechnical centrifuge is conducted. This investigation included both circular and square cross-sections for tapered pile and 2x2 pile group. The results of experimental and numerical modeling highlight the considerable advantage of circular and square tapered piles over the uniform cross-section ones in terms of axial compressive load-bearing capacity. Although the surface area of the circular tapered piles is smaller than square ones, the results surprisingly imply upon an increase in the axial bearing capacity. In numerical simulation, pile group efficiency of tapered pile and shear stress distribution in the soil medium around the pile are investigated. Moreover, the effect of shaft surface geometry of tapered pile with circular and square cross-sections on axial compression load-bearing capacity is also investigated. The findings of numerical simulations indicate that the concave corners of the pile cross-section impose negative effect on shear stress mobilized on the pile surface. In addition, the pile group efficiency of tapered piles is generally lower than corresponding values for uniform cross-section piles. Also, the group efficiency of all tapered pile groups was almost equal to unity, meaning that the load carried by the group is equal to the sum of the load carried by individual similar piles.