Influence of Clear Edge Distance and Spacing of Piles on Failure of Pile Cap

Abstract

The design and dimensioning of pile cap is a challenging task depending upon shape and thickness of cap, soil strata, pile dimension and their locations in plan. A pile cap is a reinforced concrete structural rigid slab, which distributes column forces to a group of individual piles as per rivet formula. The main assumption in rivet formula is that the pile cap should be rigid enough to distribute load uniformly. Most of the pile cap are designed by short-cut or thumb rule procedures for spacing of piles, thickness of pile cap and minimum edge distance of pile cap from pile center or edge. In the present paper, finite element analysis of pile cap is performed to capture the behavior of pile cap under axial load and moment. The focus of this study is to find adequacy of the clear edge distance for pile cap, as there are very few guidelines available. In case of minimum clear edge distance, a large amount of tensile stresses are developed at edge of pile cap, which may not acceptable. It is observed that providing 100 mm or 150 mm or 250 mm as clear edge distance suggested by most of the codes is inappropriate. However, it should be at least half of the diameter of pile used to accommodate the stresses developed at the edge as proposed in this paper depending upon the mathematical model of structure. Moreover, the proposed suggestions are well agreement with the experimental results.