DFI Magazine September/October 2020 - 101

Rigid inclusions being installed for tanks,
energy facilities in Connecticut (credit: Keller)

FEATURE

ARTICLE

Panel on Soil Improvement by Rigid Inclusions
Rigid Inclusions (RIs) are cementitious columns that are
significantly stiffer than the surrounding soil and are used to
improve ground performance. The use of RIs has gained
widespread acceptance, but common misconceptions or concerns
can exist among engineers who are less familiar with RI differences
from piles regarding their design and behavior. To address issues
related to RIs, a panel was assembled for an interactive discussion
during the American Society of Civil Engineers' (ASCE) GeoCongress held in February. This article reviews the panel's
discussion of various RI uses and RI design and reinforcement
needs. The panel, made up of DFI and ASCE members, consisted of
six practitioners and one academic:
José Clemente (moderator), Ph.D., P.E., D.GE, Bechtel
Corporation
Tanner Blackburn, Ph.D., P.E., Keller Foundations
Jie Han, Ph.D., University of Kansas
Roberto Lopez, P.E., Malcolm Drilling
Morgan NeSmith, P.E., Berkel & Company
Timothy Siegel, P.E., G.E., D.GE, Dan Brown and Associates
Sonia Swift, Menard Group USA
RIs are not structurally connected to the superstructure. Instead, a
load-transfer fill mat or platform is typically installed between the

MODERATOR

top of RIs and the bottom of a superstructure. This arrangement
allows for load sharing with the surrounding soil.
Topics discussed at the panel included stress distribution
between RIs and soil, the use of RIs for settlement control and
liquefaction mitigation, performance and design of RIs under
seismic loading, and the need for steel reinforcement of RIs. Quality
assurance/quality control (QA/QC) issues were also discussed, as
briefly summarized in this article from the panelists.

Settlement Control
Initial development of RIs in Europe in the 1970s was to support
area loads such as highway embankments, tank foundations and
structures on mat foundations. RIs continue to be used extensively
for these applications. Typically, the main geotechnical consideration has been settlement reduction. Because of their load-sharing
capabilities, RIs carry part of the foundation load (fig. 1), reducing
stresses on the soil and consequently reducing total and differential
settlements. Additional benefits can be derived when RIs are
installed in granular soils by using displacement methods that can
result in densification of the soil surrounding the RIs. Serviceability
limit state (settlement) design is employed, and the RIs are typically
not reinforced. Use of RIs for settlement reduction has been
extended to carry concentrated loads under footings in a manner
analogous to a pile. In these cases, the bearing capacity of the RIs
becomes a geotechnical consideration that must be accounted for.

José Clemente, Ph.D., P.E., D.GE, Bechtel Corporation

DEEP FOUNDATIONS * SEPT/OCT 2020 * 101

DFI Magazine September/October 2020

Table of Contents for the Digital Edition of DFI Magazine September/October 2020