Impedance Functions for Double-D-Shaped Caisson Foundations

TL;DR: In this paper, the authors proposed solutions for stiffness estimation of double-D shaped caisson foundations embedded in three different types of ground profiles (stiffness variation along the depth): homogeneous, linear and parabolic).

Abstract: This article proposes solutions for stiffness estimation of Double-D shaped caisson foundations embedded in three different types of ground profiles (stiffness variation along the depth: homogeneous, linear and parabolic). The approach is based on three dimensional finite element analyses and is in line with the methodology adopted in Eurocode 8-Part 5 (2004)- lumped spring approach. The method of extraction of various stiffness values from the finite element model is described and followed by obtaining the closed form solutions. Parametric study revealed the nominal effect of embedment length of Double-D caisson and hence only the width and diameter effects are included in the suggested formulations. The obtained closed form solutions are presented in terms of multiplication factors for Double-D caissons. Final stiffness terms for a given width and diameter of a Double-D caisson can be conveniently estimated by multiplying the proposed formulations to the circular shaft solutions available in literature. Applicability of the proposed formulations is demonstrated by considering a typical bridge pier supported by Double-D caissons. The proposed formulations requires minimum amount of input parameters and can be used during the tender design to arrive at the required geometry of such foundations.