Influence of under-reamed pile groups arrangement on tensile bearing capacity using FE method

Under-reamed (Belled) piles are useful methods to increase the bearing capacity in deep foundations. They have some enlarged bases in their stems. They are suited for soils which are often subjected to considerable ground movements due to seasonal moisture variations. Also group arrangement is an effective parameter in application of these piles. In this paper using finite element software PLAXIS 3D Foundation, the group arrangement is investigated in order to reach the maximum bearing capacity. First the numerical model is verified, then some groups including 3, 5 and 7 piles with spacing/diameter (S/D) ratios of 4 to 12 for triangle, square and pentagon plan are subjected to tensile loading. The optimum S/D ratio which is related to the angle between piles in plan is obtained 9 for triangle and 5 for pentagonal arrangement. As a result pentagon arrangement comparing to square arrangement have 16% increases in bearing capacity in the same area with the same number of piles. Triangle arrangement is also more efficient than a symmetric square arrangement with the similar area. © 2014 ejge.