Part I: Selection and Design of Rigid Inclusions

Abstract

The use of rigid inclusions (RIs) as a ground improvement technology has become widely accepted as a cost-effective solution to support structures and embankments on sites with marginal, compressible ground. Rigid inclusion elements are defined as stiff, columnar, slender, vertical, discrete elements typically installed in regularly spaced groups. The term RI can apply to a variety of materials, but the primary focus of this paper is on cementitious, cast-in-place RIs. Thousands of structures throughout the United States are supported on RIs; however, there currently exists no industry-wide standard for the selection, design, and verification of RIs. When evaluating, recommending, and specifying RI ground improvement methods, practitioners should understand the fundamental mechanics involved, as well as the applicability and limitations of RIs. The purpose of this document is to provide commentary guidelines that address general concerns regarding the selection and design of RI systems for ground improvement. The development of this document is the result of a collaborative effort of the Rigid Inclusion Task Force of the Deep Foundations Institute (DFI) Ground Improvement Committee. This document (Part I) describes the fundamental mechanics of RIs for ground improvement and discusses the state-of-the-practice for the design of RIs in the United States. A subsequent document (Part II) will discuss construction and verification considerations of RIs.