Two-pile interaction factor revisited

Abstract

A rigorous analytical method is developed for calculating the interaction factor between two identical piles subjected to vertical loads. Following the scheme proposed by Muki and Sternberg, the problem is formulated by decomposing the pile soil system into an extended soil mass and two fictitious piles. With the consideration of the compatibility condition that the axial strain of the fictitious pile be equal to the corresponding strain average over the extended soil, a Fredholm integral equation of the second kind governing the unknown axial forces along fictitious piles is established and then solved using numerical procedures. The real pile head settlement is subsequently calculated based on the determined fictitious pile forces and finally, the desired pile interaction factor is derived. Comparison with existing solutions confirms that the conventional interaction factor approach does tend to overestimate the interaction and may cause considerable errors for long compressible piles. Numerical results for the interaction factor between two piles in both semi-infinite and finite layered soils are presented over a wide range of pile and soil parameters, and also the settlement behaviour of a 3 × 3 pile group embedded in a semi-infinite soil is studied by virtue of the newly established interaction factor.