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NAtioNAl CooperAtive HigHwAy reseArCH progrAm
Responsible Senior Program Officer: David A. Reynaud
January 2013
CONTENTS
Introduction, 1
Problem Statement, 2
Solution Alternatives, 3
Research Objective, 4
Key Research Products, 4
NCHRP Project 24-11(02)
Final Report, 5
How To Use This Digest, 5
Engineering Properties of
Block-Molded EPS Relevant to
Slope Stabilization, 5
Design Methodology, 6
Construction Practices, 20
Recommended EPS-Block
Geofoam Standard for Slope
Stability Applications, 21
Economic Analysis, 22
Summary, 23
Resources for Further
Information, 24
References, 25
Author Acknowledgments, 26
GUIDELINES FOR GEOFOAM APPLICATIONS
IN SLOPE STABILITY PROJECTS
This digest presents the results of NCHRP Project 24-11(02), “Guidelines
for Geofoam Applications in Slope Stability Projects.” The research was
performed by the Department of Civil Engineering at The University of
Memphis (UoM). David Arellano, Associate Professor of Civil Engineering
at UoM, was the Project Director. The other project investigators were
Timothy D. Stark, Professor and Consulting Engineer, Department of Civil
and Environmental Engineering at the University of Illinois at Urbana-
Champaign; John S. Horvath, Consulting Engineer and Professor, Civil
and Environmental Engineering Department at Manhattan College; and
Dov Leshchinsky, President of ADAMA Engineering, Inc., and Professor,
Department of Civil and Environmental Engineering at the University of
Delaware. The contractor’s final report for NCHRP Project 24-11(02) can
be accessed via TRB.org/NCHRP by linking to the project page.
Research Results Digest 380
INTRODUCTION
Geofoam is any manufactured material
created by an internal expansion process
that results in a material with a texture of
numerous, closed, gas-filled cells using
either a fixed plant or an in situ expansion
process (Horvath, 1995). From a technical
and cost perspective, the most successful
and predominant geofoam material used
as lightweight fill in road construction is
expanded polystyrene-block (EPS-block)
geofoam.
Geofoam is considered a type or cat-
egory of geosynthetic. As with most types
of geosynthetics, geofoam can provide a
wide variety of functions including thermal
insulation, lightweight fill, compressible
inclusion, fluid transmission (drainage),
damping, low earth pressure fill for retain-
ing structures, and structural support. Each
of these functions may have numerous
potential applications. Although the focus
of the present study is on the geofoam func-
tion of lightweight fill, the specific applica-
tion of this function is slope stabilization
and remediation of roadway embankments
subjected to slope instability. The fact that
geofoam can provide other functions—
even if not intended or not necessarily
desired in a particular project—should be
considered in the design of geofoam for
lightweight fills in road embankments. For
example, in addition to the lightweight fill
function, the functions of structural support
and thermal insulation should be consid-
ered during the use of EPS-block geofoam
as a lightweight fill material in slope stabi-
lization and repair.
The first project to use block-molded
EPS as a lightweight fill material is the Flom
Bridge project in Norway in 1972. The
EPS-block geofoam was used to rebuild a
road over soft soil that had chronic settle-
ment problems. In Europe, lightweight
fills such as EPS-block geofoam are rou-
tinely used to construct embankments over
soft foundation soils. In Japan, EPS-block
2
reduced inertial forces during seismic shaking.
Thus, the lower density of EPS-block geofoam
may alleviate the costs of soft soil removal (which
include the attendant disposal problems and costs);
soil improvement techniques; and/or the possible
need for an excavation support system, excavation
widening, and extensive temporary dewatering.
An example of the extensive use of the NCHRP
Project 24-11(01) reports is the large use of EPS-
block geofoam on the Central Artery/Tunnel (CA/T)
project in Boston. This project is the first major proj-
ect to use the NCHRP Project 24-11(01) research
results in practice (Riad, 2005). Another project that
used the NCHRP research results is the I-95/Route 1
Interchange (Woodrow Wilson Bridge Replacement)
in Alexandria, VA. These and other projects that have
been completed in the United States (e.g., the I-15
Reconstruction Project in Salt Lake City) demon-
strate that EPS-block geofoam is a technically viable
and cost-effective alternative to the construction or
remediation of stand-alone embankments over soft
ground. Additionally, Thompson and White (2005)
conclude that EPS-block geofoam may be a stabili-
zation technology that can be used as an alternative
to the use of stability berms to minimize the impacts
to environmentally sensitive areas where embank-
ments cross soft or unstable ground conditions.
FHWA has designated EPS-block geofoam as
a priority, market-ready technology with a deploy-
ment goal that EPS geofoam will be a routinely used
lightweight fill alternative on projects where the
construction schedule is of concern (FHWA, 2006).
FHWA considers EPS-block geofoam an innovative
material and construction technique that can accel-
erate project schedules by reducing vertical stress
on the underlying soil; thus, it is a viable and cost-
effective solution to roadway embankment widen-
ing and new roadway embankment alignments over
soft ground. In summary, EPS-block geofoam is a
market-ready technology that can contribute to solv-
ing the major highway problem in the United States
of insufficient highway capacity to meet growing
demand.
PROBLEM STATEMENT
A major transportation problem in the United
States is that current highway capacity is insuf-
ficient to meet growing demand; therefore, new
roadway alignments and/or widening of existing
roadway embankments will be required to solve
geofoam is also extensively used for lightweight fill
applications including in slope applications. Signifi-
cant research and development of the use of EPS-
block geofoam has been performed in Japan for
seismic loading applications (Horvath, 1999).
Although EPS-block geofoam for road con-
struction is an established technology and despite
the more than 30 years of extensive and continuing
worldwide use of EPS-block geofoam, it has been
underutilized in U.S. practice because a compre-
hensive design guideline for its use as lightweight
fill in roadway embankments has been unavailable.
There was, therefore, a need in the United States to
develop formal and detailed design documents for
use of EPS-block geofoam in roadway applications.
To meet this need, the American Association
of State Highway and Transportation Officials
(AASHTO), in cooperation with the Federal High-
way Administration (FHWA), funded NCHRP Proj-
ect 24-11(01), “Guidelines for Geofoam Applications
in Embankment Projects.” Conducted from July 6,
1999 to August 31, 2002, this research project’s objec-
tive was to develop a recommended design guideline
and a material and construction standard for the use
of EPS-block geofoam in stand-alone embankments
and bridge approaches over soft ground.
The results of this NCHRP project are presented
in two documents. NCHRP Report 529 includes
only the recommended design guideline and the
recommended material and construction for use
of geofoam in stand-alone roadway embankments
standard (Stark et al., 2004a). NCHRP Web Docu-
ment 65 includes the background and analyses used
to develop the recommended design guideline and
the material and construction standard, as well as a
summary of the engineering properties of EPS-block
geofoam and an economic analysis of geofoam
versus other lightweight fill materials (Stark et al.,
2004b).
EPS-block geofoam is unique as a lightweight
fill material because it has a unit weight that is only
about 1% of the unit weight of traditional earth fill
materials and that is also substantially less than
other types of lightweight fills (16 kg/m3 or 1 lb/ft3
versus 1,900 kg/m3 or 120 lb/ft3). In addition, geo-
foam is sufficiently strong to support heavy motor
vehicles, trains, airplanes, lightly loaded buildings,
and the abutments of bridges, if designed properly.
The extraordinarily low unit weight of EPS-block
geofoam results in significantly reduced gravity
stresses on underlying foundation soils as well as
3
the current and future highway capacity problem.
As noted by Spiker and Gori (2003), roadway con-
struction “often exacerbates the landslide problem
in hilly areas by altering the landscape, slopes, and
drainages and by changing and channeling runoff,
thereby increasing the potential for landslides.”
Landslides occur in every state and U.S. territory,
especially in the Pacific Coast, the Rocky Moun-
tains, the Appalachian Mountains, and Puerto Rico
(Spiker and Gori, 2003; TRB, 1996). Active seismic
activity contributes to the landslide hazard risk in
areas such as Alaska, Hawaii, and the Pacific Coast.
Spiker and Gori indicate that landslides are among
the most widespread geologic hazard on earth and
estimate that damages related to landslides exceed
$2 billion annually.
An additional application of EPS-block geofoam
as a lightweight fill that has not been extensively uti-
lized in the United States, but has been commonly
used in Japan, is in slope stabilization. The decades
of experience in countries such as Norway and Japan
with both soft ground and mountainous terrain have
demonstrated the efficacy of using the lightweight
fill function of EPS-block geofoam in both stand-
alone embankments over soft ground and slope sta-
bilization applications. The Japanese experience has
also involved the use of EPS-block geofoam when
severe seismic loading is a design criterion.
The recommended design guideline and the
standard included in the NCHRP Project 24-11(01)
reports are limited to stand-alone embankments and
bridge approaches over soft ground. The experience
in Japan has demonstrated that there are important
analysis and design differences between the light-
weight fill function for stand-alone embankments
over soft ground and slope stabilization applica-
tions. Therefore, a need exists in the United States
to develop formal and detailed design documents
for use of EPS-block geofoam for slope stabiliza-
tion projects. Slope stabilization projects include
new roadways as well as repair of existing road-
ways that have been damaged by slope instability or
slope movement. This need resulted in the current
NCHRP Project 24-11(02), the results of which are
summarized herein.
SOLUTION ALTERNATIVES
Slope stability represents one of the most com-
plex and challenging problems within the practice
of geotechnical engineering. The unique challenges
presented by the interactions between groundwa-
ter and earth materials, the complexities of shear
strength in earth materials, and the variable nature
of earth materials and slope loadings can combine
to make the successful design of a stable slope dif-
ficult, even for an experienced engineer. Over the
years, a wide variety of slope stabilization and repair
techniques have been used in both natural and con-
structed slopes. When implementing a slope stabili-
zation and repair design, the strategy employed by
the designer can usually be classified as (1) avoid the
problem altogether, (2) reduce the driving forces, or
(3) increase the resisting forces.
For any given project, the option of avoiding
the problem is generally the simplest solution; how-
ever, it is typically not a feasible option, especially
for roadways. In many cases, selecting an alternate
site or removing and replacing the problematic
earth material are simply not viable options. This
leaves designers with a choice between the remain-
ing two strategies for constructing a stable slope.
The resisting forces may be accepted as they are and
the design may be based on reducing the forces that
drive instability, or, conversely, the driving forces
may be accepted as they are and the design may be
based on improving the resisting forces sufficiently
to prevent failure of the slope.
Some of the more common design alternatives
to increase the resisting forces of a slope include
the installation of deep foundations—for example,
piles and drilled shafts—or other type of reinforc-
ing material to assist in restraining the unstable
slope material; the construction of “toe berms”
to add weight to the bottom portion of the slope;
chemical or biotechnical soil improvement methods
that increase the strength of earth materials; and/
or the installation of subsurface drainage to divert
groundwater away from the slope and increase the
effective stress, which increases the soil resisting
forces. Many of these procedures can be costly,
both in terms of actual installation costs, as well
as other indirect costs such as prolonged road clo-
sures, acquisition of additional right-of-way for
the new construction, and long-term maintenance
costs. However, some of these procedures do have
the advantage of having a relatively long history
of successful application. In many cases, design-
ers and contractors are somewhat familiar with
the approaches being used, enabling them to work
more efficiently when using a well-established
technology.
4
The simplest solution to reducing the driving
forces within a slope is simply to reduce the slope
inclination. This reduces the shear stress on the
material in the slope, making the entire slope more
stable. However, the costs of pursuing this solution
can be considerable, including right-of-way acquisi-
tion, earth material removal costs, and lane or road
closures during construction. For many slopes, par-
ticularly those in urban settings, flattening the slope
is simply not a feasible option. Other alternatives
that serve to reduce driving forces could be the
installation of subsurface drainage (which can serve
both to increase resisting forces and to reduce driv-
ing forces), installation of better surface drainage to
reduce infiltration from storm water accumulation,
and replacement of a portion of the natural slope
material with lightweight fill.
The latter alternative to reducing the driving forces
may encompass a wide variety of materials, both nat-
ural and man-made, that can significantly reduce the
weight of the upper portion of the slope, thus reduc-
ing driving forces that tend to cause slope instabil-
ity. A wide range of lightweight fill materials—such
as shredded tires, wood fiber, saw dust, ash, pumice,
air-foamed stabilized soil, expanded-beads mixed
with soil, and EPS-block geofoam—have been suc-
cessfully used as lightweight fill both in the United
States and globally. As might be expected, each type
of lightweight fill has its own unique advantages and
disadvantages that must be considered when evaluat-
ing alternatives for any design. The purpose of this
project is to provide guidance for slope stabilization
and repair utilizing EPS-block geofoam as a light-
weight fill material.
RESEARCH OBJECTIVE
The overall objective of this research was to
develop a comprehensive document that provides
both state-of-the-art knowledge and state-of-practice
design guidance to those who have primary involve-
ment with roadway embankment projects with design
guidance for use of EPS-block geofoam in slope
stability applications. The end users of the research
include design professionals such as engineers who
perform the design and develop specifications; own-
ers including FHWA, state DOTs, and local county
and city transportation departments that own, oper-
ate, and maintain the roadway; the manufacturers/
suppliers who supply EPS blocks; and the contrac-
tors who construct the roadway.
The general consensus that was reached at the
first International Workshop on Lightweight Geo-
Materials that was held on March 26 and 27, 2002,
in Tokyo is that although new weight-reduction tech-
niques for decreasing applied loads have recently
been developed, standardization of design and
construction methods is still required (“A Report
on the International Workshop on Lightweight
Geo-Materials,” 2002). The research results from
NCHRP Project 24-11(01) in conjunction with the
results of this project standardize the design guide-
lines for the use of EPS-block geofoam in various
U.S. highway applications.
KEY RESEARCH PRODUCTS
Successful technology transfer and acceptance
of a construction product or technique requires the
availability of a comprehensive and useful design
procedure and a material and construction standard.
Additionally, knowledge of the engineering prop-
erties of materials that will be incorporated in a
structure is also required to adequately design the
structure. Designers also need cost data related to
the proposed construction product or technique to
perform a cost comparison with other similar alter-
natives. One of the lessons learned with the use of
EPS-block geofoam on the CA/T Project in Boston
is the need to include a detailed numerical design
example to complement design guidelines.
Therefore, the five primary research products
required to ensure successful technology transfer
of EPS-block geofoam technology to slope sta-
bility applications in new and existing roadway
projects that are included in the project report are
(1) summary of relevant engineering properties;
(2) a comprehensive and usable design guideline;
(3) a material, product, and construction standard;
(4) economic data; and (5) a detailed numerical
example. In addition to these five primary research
products, an overview of construction tasks that
are frequently encountered during EPS-block geo-
foam slope projects and four case histories that
provide examples of cost-effective and successful
EPS-block geofoam slope stabilization projects
completed in the United States are included in the
project report.
These key research products facilitate the accom-
plishment of the overall research objective of this
study, which is to develop a comprehensive docu-
5
ment that provides design guidance to engineers,
owners, and regulators for the use of EPS-block geo-
foam for the function of lightweight fill in slope sta-
bility applications.
NCHRP PROJECT 24-11(02) FINAL REPORT
The contractor’s final report for NCHRP Proj-
ect 24-11(02) can be accessed via TRB.org/NCHRP
by linking to the project page. The following are the
report’s contents:
• Chapter 1—overview of EPS-block geofoam,
a summary of the NCHRP 24-11(01) study,
problem statement of the current project, and
the research objective.
• Chapter 2—summary of the research approach.
• Chapter 3—overview of EPS block engineer-
ing properties most relevant to the design of
slopes stabilized with EPS blocks.
• Chapter 4—design methodology developed
herein for slopes incorporating EPS-block
geofoam for the function of lightweight fill in
slope stability stabilization and repair.
• Chapter 5—overview of construction tasks
frequently encountered during EPS-block
geofoam slope projects.
• Chapter 6—background for understanding
the recommended EPS-block geofoam stan-
dard for slope stability applications included
in Appendix F.
• Chapter 7—summary of case histories that
successfully incorporated EPS-block geofoam
in slope stabilization applications.
• Chapter 8—cost information/cost estimate
for geofoam slope stabilization for the design
phase.
• Chapter 9—conclusions, recommendations,
and of future research.
• Appendix A—geofoam usage survey and its
responses.
• Appendix B—recommended design guide-
line for EPS-block geofoam slopes.
• Appendix C—two procedures developed for
optimizing the volume and location of EPS
blocks within the slope: one for landslides
involving rotational slides, and one for trans-
lational slides.
• Appendix D—results of the study performed
to determine the impact of typical centrifugal
loads on an EPS-block fill mass.
• Appendix E—design example demonstrating
the design methodology included in Chapter 4
and outlined in the design guideline included
in Appendix B.
• Appendix F—recommended standard for use
of EPS-block geofoam, which should facili-
tate DOTs in specifying and contracting for
the use of geofoam in slope stabilization and
repair projects.
• Appendixes G and H—example design details
and example slope stabilization specifications.
• Appendix I—draft of a contract special provi-
sion for price adjustment for EPS-block geo-
foam to minimize the impact of short-term oil
price fluctuations on the cost of EPS-block
geofoam during multi-phased projects.
• Appendixes J and K—Phase I and II work
plans.
• Appendix L—bibliography.
HOW TO USE THIS DIGEST
This digest provides a general overview of the
following key project research products that are
included in the project report: summary of engi-
neering properties of block-molded EPS relevant to
slope stabilization, general overview of the design
guideline for the use of EPS blocks for slope stabi-
lization and repair, an introduction to construction
practices frequently encountered during EPS-block
geofoam slope projects, an overview of the recom-
mended EPS-block geofoam standard for slope sta-
bility applications, and a summary of the economic
analysis related to EPS-block geofoam.
The intent of this digest is only to promote early
awareness of the project results in order to encour-
age implementation. This digest is not intended to be
used as a stand-alone document, so readers should
review the project report before implementing any
information included in this digest.
ENGINEERING PROPERTIES OF
BLOCK-MOLDED EPS RELEVANT
TO SLOPE STABILIZATION
The relevant engineering properties of block-
molded EPS for the application of lightweight fill
include physical, mechanical (stress-strain-time-
temperature), and thermal. A comprehensive over-
view of these engineering properties of EPS is
included in NCHRP Web Document 65 (Stark et al.
6
2004b). Additionally, the primary elements of the
molding process are included in NCHRP Web Doc-
ument 65 because the EPS-block molding process
can influence the quality and other performance
aspects of EPS-block geofoam to include the physi-
cal, mechanical, and thermal properties. Within the
web document, Chapter 3 provides an overview of
EPS-block engineering properties that are most rel-
evant to the design of slopes stabilized with EPS
blocks. These properties include shear strength and
density. Because limit equilibrium methods of slope
stability analysis are commonly used for analyzing
slopes, an overview of the various approaches avail-
able to model the strength of the EPS blocks in limit
equilibrium procedures of slope stability analysis is
also presented in Chapter 3.
Interface friction, primarily along horizontal sur-
faces, is an important consideration in external and
internal stability assessments under horizontal loads
such as in slopes and seismic shaking. Tables 3.1
and 3.2, which are included in Chapter 3 in the web
document, provide a summary of interface shear
strength data for EPS/EPS interfaces and EPS/
dissimilar material interfaces, respectively, which
are the two types of interfaces that are of interest for
EPS-block geofoam in lightweight fill applications.
If the calculated shear resistance along the hori-
zontal planes between EPS blocks are insufficient to
resist the horizontal driving forces, additional resis-
tance between EPS blocks is generally provided by
adding interblock mechanical connectors along the
horizontal interfaces between the EPS blocks or the
use of shear keys. The use of polyurethane adhe-
sives, which are used for roofing applications, could
be effective in providing additional shear resistance
between EPS blocks in the future once long-term
durability testing indicating that the shear strength
provided by adhesives will not degrade with time is
available.
DESIGN METHODOLOGY
Introduction
The recommended design guideline included
in NCHRP Report 529 and NCHRP Web Document
65 (Stark et al. 2004a; Stark et al. 2004b) is limited
to stand-alone embankments that have a transverse
(cross-sectional) geometry such that the two sides
are more or less of equal height as shown conceptu-
ally in Figure 1. Slope stability applications (some-
times referred to as “side-hill fills”) are shown in
Figure 2. As shown in Figure 2, the use of EPS-
block geofoam in slope applications can involve a
slope-sided fill [Figure 2 (a)] or a vertical-sided fill
[Figure 2 (b)]. The latter application is sometimes
referred to as a “geofoam wall,” and this applica-
tion is unique to EPS-block geofoam. The use of a
vertical-sided fill will minimize the amount of right-
of-way needed and will also minimize the impact
of fill loads on nearby structures. For vertical-sided
(b) Vertical-sided fill (Geofoam wall).
(a) Slope-sided fill.
Figure 1. Typical EPS-block geofoam applications in-
volving stand-alone embankments (Horvath 1995; Stark
et al. 2004a).
(a) Slope-sided fill.
(b) Vertical-sided fill (Geofoam wall).
Figure 2. Typical EPS-block geofoam applications
involving side-hill fills.
7
embankment walls, the exposed sides should be
covered with a facing. The facing does not have to
provide any structural capacity to retain the blocks
because the blocks are self-stable, so the primary
function of the facing is to protect the blocks from
environmental factors.
The recommended design procedure for the
use of EPS-block geofoam for slope stabilization
and repair is presented by initially introducing the
major components of an EPS-block geofoam slope
system and the three primary failure modes—that
is, external instability, internal instability, and pave-
ment system failure—which need to be considered
during design. An overview of the recommended
design procedure is then provided.
Major Components of an EPS-Block
Geofoam Slope System
Figure 3 shows that an EPS-block geofoam slope
system consists of three major components:
• The existing slope material, which can
be divided into the upper and lower slope.
Also, the slope material directly below the
fill mass is also referred to as the foundation
material;
• The proposed fill mass, which primarily
consists of EPS-block geofoam. In addition,
depending on whether the fill mass has sloped
(slope-sided fill) or vertical (vertical-sided
fill) sides, there is either soil or a protective
structural cover over the sides of the EPS
blocks; and
• The proposed pavement system, which
is defined as including all material layers,
bound and unbound, placed above the EPS
blocks.
Failure Modes
Overview. Potential failure modes that must be con-
sidered during stability evaluation of an EPS-block
geofoam slope system can be categorized into the
same two general failure modes that a designer must
consider in the design of soil nail walls (Lazarte
et al. 2003) and mechanically stabilized earth walls
(Elias et al. 2001). These failure modes are exter-
nal and internal failure modes. EPS-block geofoam
slope systems may also incorporate a pavement sys-
tem, so to design against failure, the overall design
process includes the evaluation of these three failure
modes and must include the following design con-
siderations:
• Design for external stability of the overall EPS-
block geofoam slope system configuration;
• Design for internal stability of the fill mass;
and
• Design of an appropriate pavement system
for the subgrade provided by the underlying
EPS blocks.
Table 1 provides a summary of the three failure
modes and the various failure mechanisms that need
to be considered for each failure mode. Each fail-
ure mechanism has also been categorized into either
an ultimate limit state (ULS) or serviceability limit
state (SLS) failure. The failure mechanisms are con-
ceptually similar to those considered in the design of
stand-alone EPS-block geofoam embankments over
soft ground (Stark et al. 2004a; Stark et al. 2004b) as
well as those that are considered in the design of soil
nail walls (Lazarte et al. 2003) and other types of
geosynthetic structures used in road construction—
for example, mechanically stabilized earth walls
(MSEWs) and reinforced soil slopes (RSS) (Elias
et al. 2001). Additionally, some of the failure
P a v e m e n t
S y s t e m
F i l l M a s s
( E P S b l o c k s a n d
s o i l c o v e r , i f a n y ) E x i s t i n g S l o p e M a t e r i a
l
( U p p e r S l o p e )
E x i s t i n g S l o p e M a t e r i a l
( L o w e r S l o p e )
E x i s t i n g S l o p e M a t e r i a l
( F o u n d a t i o n M a t e r i a l )
Figure 3. Major components of an EPS-block geofoam slope system.
8
Table 1. Summary of failure modes and mechanisms incorporated in the proposed design procedure for EPS-block
geofoam as a lightweight fill in slope stability application.
Failure
Mode
Limit
State
Failure
Mechanism Accounts for
External
Instability
ULS Static slope stability Global stability involving a deep-seated slip surface and slip
surfaces involving the existing slope material only (Figure 4).
Also considers slip surfaces that involve both the fill mass and
existing slope material (Figure 5).
ULS Seismic slope
stability
Same as for static slope stability but considers seismic-induced
loads.
SLS Seismic settlement Earthquake-induced settlement due to compression of the
existing foundation material (Figure 9) such as those resulting
from liquefaction, seismic-induced slope movement, regional
tectonic surface effects, foundation soil compression due to
cyclic soil densification, and increase due to dynamic loads
caused by rocking of the fill mass (Day 2002).
ULS Seismic bearing
capacity
Bearing capacity failure of the existing foundation earth material
(Figure 8) due to seismic loading and, potentially, a decrease in
the shear strength of the foundation material.
ULS Seismic sliding Sliding of the entire EPS-block geofoam fill mass (Figure 6) due to
seismic-induced loads.
ULS Seismic overturning Overturning of the entire embankment at the interface between
the bottom of the assemblage of EPS blocks and the underlying
foundation material as a result of seismic forces (Figure 7).
SLS Settlement Excessive and/or differential settlement from vertical and lateral
deformations of the underlying foundation soil (Figure 9).
ULS Bearing capacity Bearing capacity failure of the existing foundation earth material
(Figure 8) resulting in downward vertical movement of the
entire fill mass into the foundation soil.
Internal
Instability
ULS Seismic sliding Horizontal sliding between layers of blocks and/or between the
pavement system and the upper layer of blocks (Figure 10) due
to seismic-induced loads.
SLS Seismic load
bearing
Excessive vertical deformation of EPS blocks due to increase in
the vertical normal stress within the EPS-block fill mass due to
the moment produced by the seismic-induced inertia force.
SLS Load bearing Excessive vertical deformation of EPS blocks (Figure 11) due to
excessive initial (immediate) deformations under dead or gravity
loads from the overlying pavement system, excessive long-term
(for the design pavement system, excessive long-term (for the
design life of the fill) creep deformations under the same gravity
loads, and/or excessive non-elastic or irreversible deformations
under repetitive traffic loads.
Pavement
System
Failure
SLS Flexible or rigid
pavement
Premature failure of the pavement system (Figure 12), as well as
to minimize the potential for differential icing (a potential safety
hazard). Providing sufficient support, either by direct embedment
or structural anchorage, for any road hardware (guardrails,
barriers, median dividers, lighting, signage and utilities).
SLS=serviceability limit state
ULS=ultimate limit state
9
mechanisms shown in Table 1 are also included
in the Japanese design procedure that Tsukamoto
(1996) provides. The three failure modes are sub-
sequently described in more detail.
External Instability Failure Mode. Design for exter-
nal stability of the overall EPS-block geofoam slope
system considers failure mechanisms that involve
the existing slope material only as shown in Figure 4
as well as failure mechanisms that involve both the
fill mass and the existing slope material as shown in
Figure 5. The latter potential failure surface is simi-
lar to the “mixed” failure mechanism identified by
Byrne et al. (1998) for soil nailed walls, whereby
the failure surface intersects soil outside the soil nail
zone as well as some of the soil nails. The evalu-
ation of the external stability failure mechanisms
includes consideration of how the combined fill
mass and overlying pavement system interacts
with the existing slope material. The external sta-
bility failure mechanisms included in the NCHRP
Project 24-11(01) design procedure for stand-
alone EPS-block geofoam embankments consisted
of bearing capacity of the foundation material,
static and seismic slope stability, hydrostatic up-
lift (flotation), translation and overturning due to
water (hydrostatic sliding), translation and over-
turning due to wind, and settlement.
The Japanese design procedure specifically
considers the hydrostatic uplift failure mechanism
(Tsukamoto 1996). Many of the EPS-block geo-
foam slope case histories evaluated as part of this
NCHRP project include the use of underdrain sys-
tems below the EPS blocks to prevent water from
accumulating above the bottom of the EPS blocks
and, in some cases, incorporate a drainage system
between the adjacent upper slope material and the
EPS blocks to collect and divert seepage water,
thereby alleviating seepage pressures. Thus, based
on current design precedent, it is recommended that
all EPS-block geofoam slope systems incorporate
drainage systems. If a drainage system that will
P o t e n t i a l s l i p s u r f a c e 1
( G l o b a l s t a b i l i t y f a i l u r e )
P o t e n t i a l s l i p
s u r f a c e 2
P o t e n t i a l s l i p s u r f a c e 3
Figure 4. Static and seismic slope stability involving existing soil slope
material only.
Potential slip surface 2
Potential slip surface 1
Figure 5. Static and seismic slope stability involving both the fill mass and
existing soil slope material.
10
ensure that water from seepage or surface runoff
will not accumulate at or above the bottom of the
EPS blocks is part of the design, then analyses for
the hydrostatic uplift (flotation) and translation
due to water failure mechanisms that are included
in the NCHRP Project 24-11(01) design proce-
dure for stand-alone EPS-block embankments are
not required in slope applications. The final drain-
age system configuration should maintain positive
drainage throughout the slope, so the hydrostatic
uplift and translation due to water failure mecha-
nisms are not included in the current recommended
design procedure for slope applications. It should
be noted that in addition to a permanent drainage
system, temporary dewatering and drainage systems
need to be considered during construction.
Translation and overturning due to wind is a failure
mechanism that is considered in the NCHRP Project
24-11(01) design of stand-alone embankments incor-
porating EPS blocks. Wind loading is not considered
in the Japanese recommended design procedure for
the use of EPS blocks in slopes (Tsukamoto 1996). In
stand-alone embankments, the primary concern with
wind loading is horizontal sliding of the blocks; how-
ever, in slope applications, the EPS blocks will typi-
cally be horizontally confined by the existing slope
material on one side of the slope as shown in Figure 2.
Thus, wind loading does not appear to be a potential
failure mechanism for EPS-block geofoam slopes, so
the wind loading failure mechanism is not included
in the current recommended design procedure. How-
ever, it is recommended that additional research be
performed based on available wind pressure results
on structures located on the sides of slopes to further
evaluate the need to consider wind as a potential fail-
ure mechanism.
Potential failure mechanisms associated with
external instability due to seismic loads include
slope instability involving slip surfaces through
the existing slope material only (as shown in Fig-
ure 4) and/or both the fill mass and the existing
slope material (as shown in Figure 5); horizontal
sliding of the entire EPS-block geofoam fill mass
(as shown by Figure 6); overturning of a vertical-
sided embankment (as shown by Figure 7); bearing
capacity failure of the existing foundation earth
Figure 6. External seismic stability failure involving horizontal sliding of the entire
embankment.
Figure 7. External seismic stability failure involving overturning of an entire
vertical embankment about the toe of the embankment.
11
material due to static loads and seismic loads and/
or a decrease in the shear strength of the foundation
material (as shown in Figure 8); and earthquake-
induced settlement of the existing foundation
material (as shown by Figure 9).
In summary, Table 1 shows the external stability
failure mechanisms that are included in the proposed
design procedure consist of static slope stability,
settlement, and bearing capacity. Additional failure
mechanisms associated with external seismic stabil-
ity include seismic slope instability, seismic-induced
settlement, seismic bearing capacity failure, seismic
sliding, and seismic overturning. These failure con-
siderations together with other project-specific design
inputs such as right-of-way constraints, limiting
impact on underlying and/or adjacent structures, and
construction time usually govern the overall cross-
sectional geometry of the fill. Because EPS-block
geofoam is typically a more-expensive material than
soil on a cost-per-unit-volume basis for the material
alone, it is desirable to minimize the volume of EPS
used yet still satisfy external instability design cri-
teria concerning settlement, bearing capacity, static
slope stability, and the various seismic-related failure
mechanisms.
Internal Instability Failure Mode. Design for inter-
nal stability considers failure mechanisms within
the EPS-block geofoam fill mass. The internal insta-
bility failure mechanisms included in the NCHRP
Project 24-11(01) design procedure for stand-alone
embankments consists of translation due to water
and wind, seismic stability, and load bearing. As
previously indicated in the external instability fail-
ure mode discussion, translation due to water and
wind does not appear to be applicable to EPS-block
geofoam slope systems. The translation due to water
failure mechanism is not applicable provided that a
drainage system will ensure water from seepage or
surface runoff will not accumulate at or above the
bottom of the EPS blocks. Therefore, seismic stabil-
ity, which consists of seismic horizontal sliding and
seismic load bearing of the EPS blocks, and load
bearing of the EPS blocks appear to be the primary
internal instability failure mechanisms that need to
be considered in EPS-block slope systems.
Static slope stability is not an internal stability
failure mechanism for stand-alone embankments and
is not part of the internal stability design phase in the
NCHRP Project 24-11(01) design procedure for stand-
alone embankments because there is little or no static
Figure 8. Bearing capacity failure of the embankment due to general shear failure or local
shear failure.
Figure 9. Excessive settlement.
12
driving force within the EPS-block fill mass causing
instability. The driving force is small because the
horizontal portion of the internal failure surfaces is
assumed to be along the EPS-block horizontal joints
and completely horizontal while the typical static
loads are vertical. The fact that embankments with
vertical sides can be constructed demonstrates the
validity of this conclusion.
For geofoam slope applications, the potential
of the EPS-block fill mass to withstand earth pres-
sure loads from the adjacent upper slope material as
depicted in Figure 3 was evaluated as part of this study.
Horizontal sliding between blocks and/or between
the pavement system and the upper level of blocks
due to adjacent earth pressures is a failure mechanism
that needs to be considered if the adjacent slope is
not self-stable. Since the mass of the EPS-block fill
is typically very small, it may not be feasible for the
EPS fill to directly resist external applied earth forces
from the adjacent slope material. Because the inter-
face shear resistance of EPS/EPS interfaces is related
to the normal stress, which is primarily due to the
mass of the EPS blocks, the shear resistance between
blocks may not be adequate to sustain adjacent earth
pressures. Therefore, the design procedure is based
on a self-stable adjacent upper slope to prevent earth
pressures on the EPS fill mass that can result in hori-
zontal sliding between blocks. Although the design
procedure is based on a self-stable adjacent slope, it
may be possible to utilize an earth-retention system
in conjunction with an EPS-block geofoam slope sys-
tem to support a portion of the upper adjacent slope.
The primary evaluation of internal seismic sta-
bility involves determining whether the geofoam
embankment will behave as a single, coherent
mass when subjected to seismic loads. Because
EPS blocks consist of individual blocks, the col-
lection of blocks will behave as a coherent mass if
the individual EPS blocks exhibit adequate vertical
and horizontal interlock. The standard practice of
placing blocks such that the vertical joints between
horizontal layers of EPS blocks are offset should
provide adequate interlocking in the vertical direc-
tion. Therefore, the primary seismic internal sta-
bility issue is the potential for horizontal sliding
along the horizontal interfaces between blocks
and/or between the pavement system and the upper
layer of blocks as shown by Figure 10.
Load-bearing failure of the EPS blocks due to
excessive dead or gravity loads from the overlying
pavement system and traffic loads is the third inter-
nal stability failure mechanism. The primary con-
sideration during load bearing analysis is the proper
selection and specification of EPS properties so the
geofoam mass can support the overlying pavement
system and traffic loads without excessive immedi-
ate and time-dependent (creep) compression that can
lead to excessive settlement of the pavement surface
(an SLS consideration) as shown in Figure 11. The
load-bearing analysis procedure for stand-alone
embankments (Arellano and Stark 2009a; Stark
et al. 2004a; Stark et al. 2004b) is also included in
the design procedure for slope applications.
In summary, Table 1 shows the three internal
instability failure mechanisms that are evaluated in
the design guideline are seismic horizontal sliding,
seismic load bearing of the EPS blocks, and static
load bearing of the EPS blocks.
Potential
sliding
surfaces
Figure 10. Internal seismic stability failure involving horizontal sliding
between blocks and/or between the pavement system and the upper layer of
blocks due to seismic loading.
13
Pavement System Failure Mode. The objective of
pavement system design is to select the most eco-
nomical arrangement and thickness of pavement
materials for the subgrade provided by the underly-
ing EPS blocks. The design criterion is to prevent
premature failure of the pavement system such as
rutting, cracking, or similar criterion, which is an
SLS-type of failure (Figure 12) as well as to mini-
mize the potential for differential icing (a potential
safety hazard) and solar heating (which can lead to
premature pavement failure) in those areas where
climatic conditions make these potential problems.
Also, when designing the pavement cross-section
overall, consideration must be given to providing
sufficient support, either by direct embedment or by
structural anchorage, for any road hardware (i.e.,
guardrails, barriers, median dividers, lighting, sign-
age, and utilities).
In summary, the three failure modes that must
be considered during stability evaluation of an EPS-
block geofoam slope system include external insta-
bility, internal instability, and pavement system
failure. Table 1 provides a summary of the fail-
ure mechanisms that are evaluated for each failure
mode as well as a summary of the limit state that is
considered. The external instability failure mecha-
nisms that are included in the proposed design pro-
cedure consist of static slope stability, settlement,
and bearing capacity. Additional failure mechanisms
associated with external seismic stability include
seismic slope instability, seismic-induced settle-
ment, seismic bearing capacity failure, seismic
sliding, and seismic overturning. The three internal
instability failure mechanisms that are evaluated in
the design guideline are seismic horizontal sliding,
seismic load bearing of the EPS blocks, and static
load bearing of the EPS blocks. The design proce-
dure that is presented below provides the recom-
mended sequence for evaluating each of the failure
mechanisms shown in Table 1.
Overview of Design Procedure
Figure 13 shows the recommended design pro-
cedure for EPS-block geofoam slope fills. (Proce-
dures to analyze each step in Figure 13 are included
in the NCHRP Project 24-11(02) final report, avail-
able via TRB.org/NCHRP by linking to the project
page.) The design requirements of EPS-block geo-
foam slope systems are dependent on the location
of the existing or anticipated slip surface in relation
to the location of the existing or proposed roadway—
that is, slide mass located above the roadway as
shown in Figure 14 (a) or slide mass located below
Figure 11. Load bearing failure of the blocks involving excessive vertical
deformation.
Pavement crack
Figure 12. Pavement failure due to cracking.
14
1
Background investigation
including stability analysis
of existing slope
2
Select a preliminary type of
EPS and assume a
preliminary pavement system
design (if necessary)
3
Optimize volume & location
of EPS fill or assume a
preliminary fill mass
arrangement
5
Static slope stability
(external)
acceptable?
6
Seismic stability and
overturning (external)
acceptable?
7
Seismic stability
(internal)
acceptable?
8
Pavement system
design
9
Does required pavement system result in a change in
overburden stress compared to the preliminary pavement
system design developed in Step 2?
Return to Step 5
Yes
11
Settlement
(external)
acceptable?
12
Bearing capacity
(external)
acceptable?
10
Load bearing
(internal)
acceptable?
13
Design Details
No
Yes
Yes
Yes
Yes
Return to Step 3
Return to Step 3
No
No
No
No
Yes
Yes
OR
4
Modify optimized EPS fill as
needed for constructability
Yes
No
Will inter-block
connectors meet
Step 7 requirements?
Does slope include roadway
at head of slide?
(See Figure 14 (b))
-If yes, proceed to Step 8
-If no, skip to Step 10
Return to Step 8 and
modify pavement system
Return to Step 2 and use
EPS blocks with higher
elastic limit stress
Optimize volume &
location of EPS fill based
on required seismic
stability. Modify
optimized fill as needed
for constructability.
Recheck static slope
stability.
No
No
Figure 13. Steps in the design procedure for EPS-block geofoam slope fills.
15
the roadway as shown in Figure 14 (b). All steps
are required if the existing or proposed roadway is
located within the limits of the existing or antici-
pated slide mass and/or the existing or anticipated
slide mass is located below the roadway as shown in
Figure 14 (b)—that is, the roadway is near the head
of the slide mass.
If the existing or proposed roadway is located
outside the limits of the existing or anticipated slide
mass and/or the existing or anticipated slide mass
is located above the roadway as shown in Figure 14
(a)—that is, the roadway is near the toe of the slide
mass—the design procedure does not include Steps 8
and 9, which are directly related to the design of the
pavement system, because the EPS-block geofoam
slope system may not include a pavement system.
It is anticipated that EPS-block geofoam used for
this slope application will not support any structural
loads other than possibly soil fill above the blocks.
Therefore, only failure mechanisms associated with
the external and internal instability failure modes,
as shown in Table 1, are included in the modified
design procedure shown in Figure 13 if the existing
or proposed roadway is located outside the limits
of the existing or anticipated slide mass and/or the
existing or anticipated slide mass is located above
the roadway. The pavement system failure mode may
not be an applicable failure mode because if the road-
way is near the toe of the slide mass, stabilization of
the slide mass with EPS-block geofoam will occur
primarily at the head of the slide and, consequently,
the EPS-block geofoam slope system may not include
the pavement system. Therefore, Steps 8 and 9
of the full design procedure shown in Figure 13,
which involves the pavement system, may not be
required and are not part of the modified design pro-
cedure shown in Figure 13 if the roadway is near the
toe of the slide mass.
In summary, the full design procedure, which
is applicable if the existing or proposed roadway is
located within the limits of the existing or antici-
pated slide mass and/or the existing or anticipated
slide mass is located below the roadway, as shown
in Figure 14 (b), consists of all the design steps. If
the existing or proposed roadway is located out-
side the limits of the existing or anticipated slide
mass and/or the existing or anticipated slide mass
is located above the roadway as shown in Figure 14
(a), the design procedure does not include Steps 8
and 9, which are directly related to the design of the
pavement system, because the EPS-block geofoam
slope system may not include a pavement system.
Steps 8 and 9, which are associated with the pave-
ment system, are shaded in Figure 13 to help differ-
entiate between the complete design procedure that
includes Steps 8 and 9 and the modified procedure
shown that does not include Steps 8 and 9.
Figure 14 (a) does not imply that EPS blocks can
be placed near the toe of the slide where removal of
existing material and replacement with EPS blocks
would contradict the function of lightweight fill,
which is to decrease driving forces that contribute
to slope instability, and would instead contribute to
further instability. Therefore, Step 4 (static slope
stability) must be performed to ensure that the pro-
posed location of the EPS blocks will decrease driv-
ing forces and contribute to overall stability. The
stabilization of a slide above a roadway scenario as
shown in Figure 14 (a) is an alternative in which the
use of EPS blocks would still be the greatest benefit
near the crest of the slope above the roadway.
Figure 15 shows a design selection diagram that
can be used to determine whether to use the com-
plete procedure shown in Figure 13 or the modified
design procedure without Steps 8 and 9 shown in
Figure 13. In Figure 15, Level I of the decision dia-
gram indicates that the proposed design procedure is
applicable to both remedial repair and remediation of
existing unstable soil slopes involving existing road-
ways as well as for design of planned slopes involving
new roadway construction. Level II of the decision
diagram indicates that for existing roadways, the use
of EPS-block geofoam will typically only involve
unstable slopes, but for new roadway construction,
the use of EPS-block geofoam may involve an exist-
ing unstable slope or an existing stable slope that may
become unstable during or after construction of the
new roadway. Level III categorizes the location of the
existing or anticipated slide mass location in relation
(a) (b)
Figure 14. Location of slide mass relative to road-
way: (a) slide above roadway and (b) slide below
roadway. (Hopkins et al. 1988).
16
to the existing or proposed new roadway. Level IV
indicates the location of the roadway in relation to the
existing or anticipated slide mass.
Level V indicates the recommended design
procedure that can be used for design. As shown in
Figure 15, the complete design procedure shown in
Figure 13 is applicable if the existing or proposed
roadway is located within the existing or antici-
pated slide mass and the existing or anticipated slide
mass is located below the roadway as shown in Fig-
ures 14(b)—that is, the roadway is near the head of
the slide mass. The modified design procedure with-
out Steps 8 and 9 shown in Figure 13 is applicable if
the existing or proposed roadway is located outside the
limits of the existing or anticipated slide mass and/or
the existing or anticipated slide mass is located above
the roadway as shown in Figures 14 (a)—that is, the
roadway is near the toe of the slide mass.
One challenge of slope stabilization design with
lightweight fill is to determine the volume and loca-
tion of EPS blocks within the slope that will yield
the required level of stability or factor of safety at
the least cost. Because EPS-block geofoam is typi-
cally more expensive than soil on a cost-per-unit-
volume basis for the material alone, it is desirable
to optimize the volume of EPS used yet still sat-
isfy design criteria concerning stability. Therefore,
to achieve the most cost-effective design, a design
goal for most projects is to use the minimum amount
of EPS blocks possible that will satisfy the require-
ments for external and internal stability, so Steps 3
and 4 of the Figure 13 design procedure specifically
include the optimization of the volume and location
of the EPS blocks within the slope.
The determination of optimal volume and loca-
tion of EPS blocks will typically require iterative
Existing Roadway Proposed
New Roadway
Existing
Unstable
Slope
Existing
Unstable or Stable
Slope
Slide Mass
Below Roadway
Slide Mass
Above Roadway Slide Mass
Below Roadway
Slide Mass
Above Roadway
Roadway
Within Slide
Mass
Roadway
NOT
Within Slide
Mass
Roadway
Within Slide
Mass
Roadway
NOT
Within Slide
Mass
Roadway
Within Slide
Mass
Roadway
NOT
Within Slide
Mass
Roadway
Within Slide
Mass
Roadway
NOT
Within Slide
Mass
Complete Design
Procedure
(Figure 13)
Modified Design
Procedure
(Figure 13)
Complete Design
Procedure
(Figure 13)
Modified Design
Procedure
(Figure 13)
I
V
V
III
II
I
Figure 15. Design procedure selection diagram.
17
analysis based on various locations and thicknesses
until a cross section that yields the minimum vol-
ume of lightweight fill at the desired level of sta-
bility is obtained. However, other factors will also
impact the final design volume and location of EPS
blocks such as
• Construction equipment access to perform
excavation work,
• Ease of accessibility for EPS-block delivery
and placement,
• Impact on traffic if lightweight fill will be
incorporated below an existing roadway, and
• Right-of-way constraints and/or constraints
due to nearby structures.
It should be noted that although minimization of
EPS volume is the goal on most projects, for some
projects it may be desirable to maximize the use of
EPS. For example, economization of EPS volume
may not be a concern in some emergency slope repair
projects or projects with an accelerated construction
schedule.
The preliminary width and location of the EPS-
block geofoam fill mass within the slope will be
dependent on the results of the evaluation of the
preliminary geometric requirements of the proposed
EPS-block fill mass performed as part of Step 1. The
most effective location of the lightweight fill mass
will be near the head (upper portion) of the existing
slide mass or proposed slope because reducing the
load at the head by removing existing earth mate-
rial and replacing it with a lighter fill material will
contribute the most to reducing the destabilizing
forces that tend to cause slope instability. The loca-
tion of the fill mass within the slope selected in Step 1
is only preliminary because the location of the fill
mass as well as the thickness may change as various
iterations of the fill mass arrangement are evaluated
to obtain a fill mass arrangement that will satisfy the
design criteria of the various failure mechanisms that
are analyzed in each supplemental design step shown
in Figure 13.
In some projects, the volume and location of
EPS blocks within the slope will be constrained by
the previously indicated factors. For example, for
the case of the existing road that is located within the
existing slide mass and the existing slide mass that
is located below the roadway as shown in Figure 14
(b)—that is, the roadway is near the head of the slide
mass—the location of the EPS fill mass will typi-
cally be limited within the existing roadway loca-
tion because of right-of-way constraints. However,
in some projects the volume and location of EPS
within the slope may not be obvious and may require
that various iterations of the fill mass arrangement
be evaluated to obtain a fill mass arrangement that
will satisfy the design requirements of the various
failure mechanisms that are analyzed in each design
step shown in Figure 13. Therefore, as part of this
project, a study was performed to develop a proce-
dure for optimizing the volume and location of EPS
blocks within the slope to minimize the number of
iterations that may be required to satisfy the design
criterion.
In the NCHRP Project 24-11 (02) final report,
Appendix C presents two procedures for optimizing
the volume and location of EPS blocks within the
slope. One procedure is for slides involving rota-
tional slip surfaces, and the other for translational
slides. The purpose of the optimization methods is
only to obtain an approximate location within the
slope where the placement of EPS blocks will have the
greatest impact in stabilizing the slope while requiring
the minimum volume of EPS blocks. A separate static
slope stability analysis must be performed as part of
Step 5 of the design procedure as shown in Figure 13
with a better slope stability analysis method that pref-
erably satisfies full equilibrium such as Spencer’s
method. Step 5 is what should be relied on to verify
that the overall slope configuration meets the desired
factor of safety.
The design procedure is based on a self-stable
adjacent upper slope to prevent earth pressures on
the EPS fill mass that can result in horizontal sliding
between blocks. If the adjacent slope material can-
not be cut to a long-term stable slope angle, an earth-
retention system must be used in conjunction with
the ESP fill mass to resist the applied earth force.
Many of the EPS-block geofoam slope case his-
tories evaluated as part of this research included the
use of underdrain systems below the EPS blocks to
prevent water from accumulating above the bottom
of the EPS blocks and, in some cases, incorporated
a drainage system between the adjacent upper slope
material and the EPS blocks to collect and divert
seepage water, thereby alleviating seepage pres-
sures. Thus, based on current design precedent, it
is recommended that all EPS-block geofoam slope
systems incorporate drainage systems. It should be
noted that in addition to a permanent drainage sys-
tem, temporary dewatering and drainage systems
need to be considered during construction.
18
In addition to the technical aspects of the design,
cost must also be considered. Because EPS-block
geofoam is typically a more expensive mate-
rial than soil on a cost-per-unit-volume basis for
the material alone, it is desirable to optimize the
design to minimize the volume of EPS used yet still
satisfy the technical design aspects of the various
failure mechanisms. It is possible in concept to opti-
mize the final design of both the pavement system
and the overall EPS-block slope system consider-
ing both performance and cost so that a technically
effective and cost-efficient geofoam slope system
is obtained. However, because of the inherent
interaction among the three major components of
a geofoam slope system shown in Figure 3, over-
all design optimization of a slope incorporating
EPS-block geofoam requires iterative analyses to
achieve a technically acceptable design at the low-
est overall cost. In order to minimize the iterative
analysis, the design algorithm shown in Figure 13
was developed. The design procedure depicted in
this figure considers a pavement system with the
minimum required thickness, a fill mass with the
minimum thickness of EPS-block geofoam, and
the use of an EPS block with the lowest possible
density. Therefore, the design procedure shown in
Figure 13 will produce a cost-efficient design.
Summary
As shown in Figure 3, the design of an EPS-
block geofoam slope system considers the inter-
action of three major components: existing slope
material, the fill mass, and the pavement system.
The three potential failure modes that can occur due
to the interaction of these three primary components
of an EPS slope system and that must be considered
during stability evaluation of an EPS-block geofoam
slope system include external instability of the over-
all EPS-block geofoam slope system configuration,
internal instability of the fill mass, and pavement
system failure.
Design for external stability of the overall
EPS-block geofoam slope system considers fail-
ure mechanisms that involve the existing slope
material only, as shown in Figure 4, as well as
failure mechanisms that involve both the fill mass
and the existing slope material, as shown in Fig-
ure 5. The external instability failure mechanisms
that are included in the proposed design procedure
consist of static slope instability, settlement, and
bearing capacity. Additional failure mechanisms
associated with external seismic stability include
seismic slope instability, seismic-induced settle-
ment, seismic bearing capacity failure, seismic
sliding, and seismic overturning.
Design for internal stability considers failure
mechanisms within the EPS-block geofoam fill
mass. The three internal instability failure mecha-
nisms that are evaluated in the design guideline are
seismic horizontal sliding, seismic load bearing of
the EPS blocks, and static load bearing of the EPS
blocks.
The objective of pavement system design is to
select the most economical arrangement and thick-
ness of pavement materials for the subgrade pro-
vided by the underlying EPS blocks. The design
criteria are to prevent premature failure of the pave-
ment system as well as to minimize the potential for
differential icing (a potential safety hazard) and solar
heating (which can lead to premature pavement fail-
ure) in those areas where climatic conditions make
these potential problems. Also, when designing the
pavement cross section overall, consideration must
be given to providing sufficient support—either by
direct embedment or structural anchorage—for any
road hardware (i.e., guardrails, barriers, median
dividers, lighting, signage, and utilities).
Figure 13 shows the recommended design pro-
cedure for EPS-block geofoam slope fills (proce-
dures to analyze each step in Figure 13 are included
in the NCHRP Project 24-11(02) final report). All
steps are required if the existing or proposed road-
way is located within the limits of the existing or
anticipated slide mass and/or the existing or antici-
pated slide mass is located below the roadway as
shown in Figure 14 (b). If the existing or proposed
roadway is located outside the limits of the exist-
ing or anticipated slide mass and/or the existing or
anticipated slide mass is located above the roadway
as shown in Figure 14 (a), the design procedure does
not include Steps 8 and 9, which are directly related
to the design of the pavement system, because the
EPS-block geofoam slope system may not include a
pavement system.
For EPS blocks utilized in slope stabilization
and repair that do not support a pavement system or
heavy structural loads, the potential to utilize EPS
blocks with recycled EPS exists. The use of recycled
EPS blocks would be an attractive “green” product
that reduces waste by recycling polystyrene scrap
and would also reduce the raw materials costs in
19
the production of EPS. Arellano et al. (2009b) have
evaluated the mechanical properties of expanded
recycled polystyrene aggregate and are currently
evaluating the mechanical properties of EPS blocks
that consist of recycled polystyrene beads.
The design of an EPS-block geofoam slope sys-
tem requires consideration of the interaction among
the three major components of an EPS-block slope
system shown in Figure 3—that is, existing slope
material, fill mass, and pavement system. Because of
this interaction, the design procedure involves inter-
connected analyses among the three components. For
example, some issues of pavement system design
act opposite to some of the design issues involv-
ing external and internal stability of an EPS-block
geofoam slope system because a robust pavement
system is a benefit for the long-term durability of
the pavement system, but the larger dead load from
a thicker pavement system may decrease the factor
of safety of the failure mechanisms involving exter-
nal and internal stability of the geofoam slope sys-
tem. Therefore, some compromise between failure
mechanisms is required during design to obtain a
technically acceptable design.
However, in addition to the technical aspects of
the design, cost must also be considered. Because
EPS-block geofoam is typically a more-expensive
material than soil on a cost-per-unit-volume basis
for the material alone, it is desirable to optimize the
design to minimize the volume of EPS used yet still
satisfy the technical design aspects of the various
failure mechanisms. It is possible in concept to opti-
mize the final design of both the pavement system
and the overall EPS-block slope system consider-
ing both performance and cost so that a technically
effective and cost-efficient geofoam slope system is
obtained. However, because of the inherent interac-
tion among components, overall design optimiza-
tion of a slope incorporating EPS-block geofoam
requires iterative analyses to achieve a technically
acceptable design at the lowest overall cost. In order
to minimize the iterative analysis, the design algo-
rithm shown in Figure 13 was developed. The design
procedure depicted in this figure considers a pave-
ment system with the minimum required thickness, a
fill mass with the minimum thickness of EPS-block
geofoam, and the use of an EPS block with the low-
est possible density. Therefore, the design procedure
will produce a cost-efficient design.
Currently, no formal design guidelines to use
any type of lightweight fill for slope stabilization
by reducing the driving forces are available. There-
fore, the proposed recommended design guideline
that was developed herein for EPS-block geo-
foam can also serve as a blueprint for the use of
other types of lightweight fills in slope stability
applications.
An overview of the basis of the design proce-
dure shown in Figure 13 was introduced in a presen-
tation titled “A Framework for the Design Guideline
for EPS-Block Geofoam in Slope Stabilization and
Repair” at the 22nd Annual Meeting of the Tennes-
see Section of ASCE in 2009 and at the 89th Annual
Meeting of the Transportation Research Board
in January, 2010. The corresponding TRB paper
was published in 2010 in Transportation Research
Record 2170 (Arellano et al. 2010). The design pro-
cedure shown on Figure 13 was also presented at the
4th International Conference on Geofoam Blocks
in Construction Applications (EPS 2011 Norway)
(Arellano et al., 2011).
The research has revealed important analysis
and design differences between the use of EPS-
block geofoam for the lightweight fill function in
slope applications versus stand-alone applications
over soft ground. The primary differences between
slope applications versus stand-alone embankments
over soft ground are summarized below:
• Site characterization is usually much more com-
plex and difficult because it typically involves
explorations made on an existing slope and
concomitant access difficulties; the slope cross
section often consists of multiple soil and rock
layers that vary in geometry both parallel and
perpendicular to the road alignment; and piezo-
metric conditions may be very complex and
even seasonal in variation.
• The governing design issue is usually based on
a ULS failure involving the analysis of shear
surfaces using material strength and limit-
equilibrium techniques. SLS considerations
involving material compressibility and global
settlement of the fill are rarely a concern.
• There is always an unbalanced earth load,
often relatively significant in magnitude, act-
ing on the EPS mass that must be addressed
as part of the design process.
• Piezometric conditions are often a significant
factor to be addressed in design. In fact, if the
use of EPS geofoam is being considered to
reconstruct a failed or failing area, piezometric
20
issues typically contribute to the cause of the
failure in the first place.
• The volume of EPS placed within the overall
slope cross section may be relatively limited.
Furthermore, the optimal location of the EPS
mass within the overall slope cross section is
not intuitively obvious.
• The road pavement may not overlie the por-
tion of the slope where the EPS is placed, so
load conditions on the EPS blocks may be
such that blocks of relatively low density can
be used, which can achieve economies in the
overall design.
CONSTRUCTION PRACTICES
An overview of construction tasks that are
frequently encountered during EPS-block geo-
foam slope projects is included in Chapter 5 of the
NCHRP Project 24-11(02) final report. The con-
struction topics included in Chapter 5 include site
preparation; drainage; EPS-block shipment, han-
dling, and storage; construction QA/construction
QC of EPS blocks; block placement; backfill place-
ment between EPS blocks and adjacent earth slopes;
phased construction; accommodation of utilities
and road hardware; facing wall; earth retention sys-
tem; pavement construction; and post-construction
monitoring.
Figures and photographs that may aid in prepara-
tion of bid and construction documents are included
in Chapter 5. Additionally, Appendix G includes
various design details and Appendix H includes
example specifications utilized in geofoam proj-
ects. The construction details included in Appen-
dix G, which were obtained from actual geofoam
construction drawings used in projects throughout
the United States, can be used as a guide for devel-
oping site-specific drawings or details. The details
presented relate to a variety of geofoam issues such
as configuration of the EPS blocks, inclusion of util-
ities and roadway hardware, construction of a load
distribution slabs over the EPS, and construction of
facing walls.
In addition to ensuring that the correct EPS-
block-type is placed, it is also important to ensure
that the methods being used by the contractor to
construct the overall EPS-block geofoam slope
produce an acceptable slope system that complies
with the assumptions inherent in the recommended
design procedure. For example, the design proce-
dure assumes that the adjacent slope is self-stable
to prevent earth loads from developing on the EPS-
block fill mass and that an adequate drainage sys-
tem is provided to prevent hydrostatic and seepage
forces from developing within the EPS fill mass.
Therefore, it is necessary to monitor the construc-
tion process to ensure that the adjacent slope is
indeed stable and that the drainage system is con-
structed properly.
Lessons learned from four case histories are
presented in Chapter 7 to provide examples of cost-
effective and successful EPS-block geofoam slope
stabilization projects completed in the United States.
These case histories demonstrate that EPS-block geo-
foam can contribute to cost-effective and successful
slope stabilization and repair. For example, EPS-
block geofoam was selected by state DOT represen-
tatives or their representatives over a partial or total
slide material removal and replacement with another
earth material during the Colorado DOT (CDOT)
Highway 160 (Yeh and Gilmore, 1992), New York
State DOT (NYSDOT) State Route 23A (Jutkofsky
1998; Jutkofsky et al., 2000), and Wisconsin Bayfield
County Trunk Highway A (Reuter and Rutz, 2000;
Reuter, 2001) projects because the removal and
replacement procedure was too costly and because
of right-of-way limitations, concerns with impacting
adjacent environmentally sensitive areas, concerns
with the need to implement an extensive temporary
dewatering system during the removal and replace-
ment procedure, and the need to close the road during
the removal and replacement procedure. The CDOT
Highway 160 project also demonstrated that stabiliz-
ing a slope with EPS blocks can be especially cost
effective in comparison with traditional earth reten-
tion systems.
The Alabama DOT (ALDOT) State Route 44
(Alabama DOT, 2004) project showed that the
lower density of EPS blocks compared with other
types of lightweight fills such as expanded shale,
sawdust, and wood chips can yield a slope with the
desired stability while the alternative lightweight fill
materials cannot. The CDOT Highway 160 project
also demonstrated that EPS blocks can be placed dur-
ing the winter in cold weather climates when the water
level may be the lowest, thus minimizing the need for
an extensive temporary dewatering system during
construction.
All four case histories included the use of a drain-
age system below the EPS blocks to prevent water
from accumulating above the bottom of the EPS
21
blocks and, in some cases, incorporated a drainage
system between the adjacent upper slope material
and the EPS blocks to collect and divert seep-
age water, thereby alleviating seepage pressures.
Therefore, these case histories substantiate the rec-
ommendation included in the proposed design pro-
cedure of EPS-block geofoam slope systems that
all EPS-block geofoam slope systems incorporate
drainage systems to alleviate the need to consider
and design for hydrostatic uplift (flotation) and
translation due to water. Therefore, the hydrostatic
uplift and translation due to water failure mecha-
nisms are not included in the recommended design
procedure shown in Figure 13.
The literature search performed as part of this
study revealed that unlike the use of EPS-block
geofoam for stand-alone embankments over soft
ground, the U.S. case history experience with
EPS-block geofoam in slope stabilization is lim-
ited. However, it is anticipated that the results
of this project will facilitate the use of EPS-
block geofoam for slope stabilization and repair
in the United States and, consequently, designers
involved with slope stabilization and repair will
consider EPS-block geofoam as an alternative to
slope stabilization more in the future than they
have in the past.
In addition to a permanent drainage system, a
temporary dewatering and drainage system may be
required during construction to prevent flotation of
the EPS blocks caused by water collecting in and
around the area where the EPS blocks are being
placed. Additionally, adequate overburden such as
the use of “soft” weights should be applied to the
top of the blocks to prevent the blocks from being
picked up or displaced by high winds.
One issue that was raised as part of a slide cor-
rection project involved the payment quantity of
EPS block versus backfill material at the interface
between the EPS blocks and the adjacent cut slope.
To alleviate this potential pay quantity discrepancy,
it is recommended that the drawings specifically
show the limits of EPS block placement along the
EPS block and adjacent earth slope.
When necessary, an EPS-block geofoam fill can
be constructed in phases, allowing one portion of the
fill to be completed before beginning construction
on the next portion. The advantage of this approach
is that it can eliminate the need to completely close
down an existing roadway in order to repair the
unstable portion of a slope.
RECOMMENDED EPS-BLOCK
GEOFOAM STANDARD FOR SLOPE
STABILITY APPLICATIONS
A recommended standard for the use of EPS-
block geofoam for lightweight fill in slope stabi-
lization is included in Appendix F of the NCHRP
Project 24-11(02) final report. The objective during
this current project was to modify the NCHRP Proj-
ect 24-11(01) standard that is applicable to stand-
alone embankments over soft ground to make it
specific to geofoam usage in slope stability appli-
cations. The NCHRP Project 24-11(02) standard
included in Appendix F contains six key revisions
from the NCHRP Project 24-11(01) standard:
1. A commentary section was added.
2. The use of different minimum allowable
density values for individual manufacturing
QC/manufacturing QA (MQC/MQA) test
specimens versus a higher nominal or average
density of the block as a whole was eliminated
so that both the block as a whole and any test
specimen from within that block meet the
same criteria.
3. The minimum allowable values for compres-
sive strength were increased to reflect the
increase in these values included in ASTM
D 6817 (American Society for Testing and
Materials, 2007).
4. The requirements for flexural strength were
increased to be consistent with the change in
unifying block and test-specimen densities.
5. The wording related to the small-strain
modulus was changed from “Initial Tangent
Young’s Modulus” to “Initial Secant Young’s
Modulus” simply to correct semantics.
6. Two new, additional types were added: EPS130
and EPS160.
The primary issue related to the recommended
material and construction standard included in
the NCHRP Project 24-11(01) reports—NCHRP
Report 529 and NCHRP Web Document 65—that
was evident from the replies to the project ques-
tionnaire included in Appendix A of the NCHRP
Project 24-11(02) final report is the current confu-
sion between the NCHRP–recommended standard
and the ASTM D 6817 material properties. How-
ever, based on the consideration of knowledge
acquired over the approximately 60 years that
EPS has existed as a construction material and the
22
decade of actual project use and experience using
the standard for stand-alone embankments included
in NCHRP Report 529 and NCHRP Web Docu-
ment 65, the standards developed for the past and
current NCHRP studies are reasonable when imple-
mented properly in practice. Proper implementation
includes MQC/MQA laboratory testing performed
in accordance with well-established ASTM proto-
cols for test-specimen conditioning prior to testing,
numerical correction of all stress-strain curves for
machine compression, and graphical correction of
stress-strains for initial concavity as necessary.
As noted in a recent article that appeared in Geo-
Strata magazine, although alignment of the two
standards is preferred, the immediate need consists
of better educating stakeholders on the basis, ben-
efits, and limitations of both standards for structural
and non-structural applications (Nichols 2008).
ECONOMIC ANALYSIS
A review of existing available EPS-block geo-
foam cost data indicates that EPS-block geofoam
prices vary widely and that the price of EPS blocks
have substantially increased recently due to the sub-
stantial increase in the price of oil. Therefore, a draft
price adjustment contract special provision similar
to the special provisions that DOTs have used for
other construction materials such as bituminous
asphalt binder was developed as part of this proj-
ect and is included in Appendix I of the NCHRP
Project 24-11(02) final report. The purpose of the
adjustment contract special provision is to minimize
the impact of short-term oil price fluctuations on the
cost of EPS-block geofoam during multi-phased
projects.
In an effort to assist designers with designing
a cost-efficient EPS-block geofoam slope, the rec-
ommended design procedure for the use of EPS
blocks in slopes considers a pavement system with
the minimum required thickness, a fill mass with the
minimum thickness of EPS-block geofoam, and the
use of an EPS block with the lowest possible den-
sity. Therefore, the design procedure will produce a
technically and cost-efficient design, but, in addition
to the cost of the EPS blocks, the overall intangi-
ble benefits that the use of EPS-block geofoam can
contribute should also be considered as part of the
slope stabilization decisionmaking process. An in-
depth discussion of these benefits as well as other
issues related to the costs associated with EPS-block
geofoam construction is provided in Chapter 8 of
the NCHRP Project 24-11(02) final report and in
NCHRP Web Document 65 (Stark et al. 2004b).
When attempting to evaluate the feasibility of
using EPS-block geofoam for a slope stabiliza-
tion project, it is important to consider some of the
unique characteristics of EPS-block geofoam as
a construction material. For example, experience
has demonstrated that EPS-block geofoam can be
placed quickly. Once the site is prepared, the actual
process of moving and positioning the EPS blocks
requires minimal equipment and labor. EPS-block
geofoam blocks can be transported and placed eas-
ily, even at many project sites that would be inacces-
sible to heavy equipment. Although some specific
safety measures may have to be implemented, the
placement of EPS blocks can be continued in almost
any kind of weather, whereas many other slope sta-
bilization methods may be delayed by rain or snow.
The use of EPS-block geofoam may also facilitate
phased construction and may minimize disruption
to traffic by eliminating the need to close an existing
roadway in order to repair the unstable portion of a
slope or to widen an existing embankment.
DOTs are particularly interested in the benefit
of the accelerated construction that EPS-block geo-
foam can provide when constructing embankments
over soft foundation soils. In June 2002, FHWA in a
joint effort with AASHTO organized a geotechnical
engineering scanning tour of Europe (AASHTO and
FHWA, 2002). The purpose of the European scan-
ning tour was to identify and evaluate innovative
European technology for accelerated construction
and rehabilitation of bridge and embankment foun-
dations. Lightweight fills is one of the technologies
that was evaluated. One of the preliminary find-
ings of the scanning project is that lightweight fills,
such as geofoam, is an attractive alternative to sur-
charging soft soil foundations because the require-
ment of preloading the foundation soil can possibly
be eliminated and, therefore, construction can be
accelerated.
Another important consideration is the fact that
EPS-block geofoam is a manufactured construction
material that can be produced by the molder and
then stockpiled at a designated site until it is needed.
A DOT agency could potentially store a supply of
EPS blocks that could be used for emergency land-
slide mitigation or repair. Also, EPS blocks can be
molded in advance of the actual placement date and
can be either transported immediately when needed
23
or stockpiled at the site for immediate use. Thus,
the use of EPS blocks in slope application projects
can easily contribute to an accelerated construction
schedule.
The material cost per volume of EPS-block geo-
foam is greater than most other types of lightweight
fills and conventional soil fill. However, if the intan-
gible benefits of using geofoam are included in the
cost analysis—for example, reduced field installa-
tion and construction costs, shorter time roadway
is not in service, and minimum field quality-control
testing—geofoam is a cost-effective alternative to
constructing roadway embankments over soft ground.
On many projects, the overall immediate and long-
term benefits and lower construction cost of using
EPS-block geofoam more than compensate for the
fact that its material unit cost is usually greater than
that of traditional earth fill materials.
When performing an analysis to compare EPS-
block geofoam with other potential slope stabili-
zation alternatives, both tangible and intangible
benefits of utilizing EPS-block geofoam should be
considered when evaluating it as a potential alterna-
tive for a slope construction project. The benefit of
accelerated construction that the use of EPS-block
geofoam can provide has been a key contribution
to the decision to use EPS-block geofoam in proj-
ects such as the I-15 reconstruction project in Salt
Lake City; the CA/T Project in Boston; and the I-95/
Route 1 Interchange (Woodrow Wilson Bridge
Replacement) in Alexandria, VA (Nichols 2008).
Therefore, the benefit of accelerated construction
that the use of EPS-block geofoam can provide
should be evaluated since it has been a key factor
in the decision to use EPS-block geofoam in recent
projects in the United States.
The wide variance in price of EPS-block geo-
foam is perhaps one of the greatest hindrances to the
further adoption of EPS-block geofoam in the United
States. This wide variance in price may be attributed
to the number of potential factors that can impact
the cost of EPS-block geofoam. These potential fac-
tors are summarized in Chapter 8 of the NCHRP
Project 24-11(02) final report and include factors
related to manufacturing, design, and construction.
SUMMARY
A major transportation problem in the United
States is that current highway capacity is insuffi-
cient to meet the growing demand, so new roadway
alignments and/or widening of existing roadway
embankments will be required to solve the current
and future highway capacity problem. It is antici-
pated that the potential for landslides—which cur-
rently pose a major geologic hazard in the United
States—will increase as new roadway alignments
are constructed and/or existing roadway embank-
ments are widened. EPS-block geofoam is a unique
lightweight fill material that can provide a safe and
economical solution to slope stabilization and repair.
Benefits of utilizing EPS-block geofoam as a
lightweight fill material include the following:
• Ease of construction,
• Possible contribution to accelerated con -
struction,
• Ability to easily implement phased construction,
• Entire slide surface does not have to be removed
because of the low driving stresses,
• Can be readily stored for use in emergency
slope stabilization repairs,
• Ability to reuse EPS blocks utilized in tem-
porary fills,
• Ability to be placed in adverse weather
conditions,
• Possible elimination of the need for surcharg-
ing and staged construction,
• Decreased maintenance costs as a result of
less settlement from the low density of EPS-
block geofoam as well as excellent durability,
• Alleviation of the need to acquire additional
right-of-way for traditional slope stabiliza-
tion methods because of the ease with which
EPS-block geofoam can be used to construct
vertical-sided fills,
• Reduction of lateral stress on bridge approach
abutments,
• Excellent durability,
• Potential construction without utility reloca-
tion, and
• Excellent seismic behavior.
The benefit of accelerated construction that the
use of EPS-block geofoam can provide was a key
factor in the decision to use EPS-block geofoam in
projects such as the I-15 reconstruction project in
Salt Lake City; the CA/T Project in Boston; and the
I-95/Route 1 Interchange (Woodrow Wilson Bridge
Replacement) in Alexandria, VA (Nichols 2008).
EPS blocks utilized in slope stabilization and repair
may not support a pavement system or heavy struc-
tural loads, so the potential to utilize EPS blocks
24
with recycled EPS exists. The use of recycled EPS
blocks would be an attractive “green” product that
reduces waste by recycling polystyrene scrap and
would also reduce the raw materials costs in the pro-
duction of EPS (Horvath 2008).
Although the use of EPS-block geofoam for the
function of lightweight fill in stand-alone embank-
ments and bridge approaches over soft ground has
increased since the completion of NCHRP Proj-
ect 24-11(01), an additional application of EPS-
block geofoam for the function of lightweight fill
that has not been extensively utilized in the United
States but has been commonly used in Japan is in
slope stabilization applications. Therefore, a need
existed in the United States to develop formal and
detailed design documents, design guideline, and an
appropriate material and construction standard for
use of EPS-block geofoam for slope stabilization
projects. The slope stabilization projects include
new roadways as well as repair of existing road-
ways that have been damaged by slope instabil-
ity or movement. This need resulted in the current
NCHRP Project 24-11(02), the results of which are
summarized in this digest.
The overall objective of this research was to
develop a comprehensive document that provides
both state-of-the-art knowledge and state-of-
practice design guidance for engineers to facili-
tate use of EPS-block geofoam for the function of
lightweight fill in slope stability applications. The
completed research consists of the following five
primary research products: (1) summary of relevant
engineering properties, (2) a comprehensive design
guideline, (3) a material and construction standard,
(4) economic data, and (5) a detailed numerical
example. In addition to the five primary research
products listed above, an overview of construction
tasks that are frequently encountered during EPS-
block geofoam slope projects and a summary of four
case histories that provide examples of cost-effective
and successful EPS-block geofoam slope stabilization
projects completed in the United States is included the
NCHRP Project 24-11(02) final report.
The general consensus that was reached at the
first International Workshop on Lightweight Geo-
Materials held March 26 and 27, 2002, in Tokyo
is that although new weight-reduction techniques
for decreasing applied loads have recently been
developed, standardization of design and construc-
tion methods is required (“A Report on the Inter-
national Workshop on Lightweight Geo-Materials”
2002). The research results from NCHRP Proj-
ect 24-11(01), in conjunction with the results of
this project, standardize the design and construction
guidelines for the use of EPS-block geofoam in vari-
ous U.S. highway applications.
The purpose of this report is to provide those who
have primary involvement with roadway embank-
ment projects—design professionals, manufacturers/
suppliers, contractors, regulators, and owners—with
design guidance for use of EPS-block geofoam in
slope stability applications. The end users of the
research include engineers who perform the design
and develop specifications and owners, including
FHWA, state DOTs, and local county and city trans-
portation departments that own, operate, and main-
tain the roadway.
An example of the extensive use of the NCHRP
Project 24-11(01) research results related to stand-
alone EPS-block geofoam embankments overlying
soft ground is the large use of EPS-block geofoam
on the (CA/T) project in Boston (Riad 2005; Riad
et al. 2004; Riad et al. 2003; Riad and Horvath
2004). This project is the first major project to use
the NCHRP Project 24-11(01) research results in
practice. Another project that utilized the NCHRP
results is the I-95/Route 1 Interchange (Woodrow
Wilson Bridge Replacement) in Alexandria, VA. It
is anticipated that the deliverables of this NCHRP
Project 24-11(02) study related to EPS-block geo-
foam in slope stabilization and repair will also be
used and contribute to solving the major geologic
hazard of landslides, which are expected to increase
as new roadway alignments are constructed and/or
existing roadway embankments are widened as part
of the effort to meet the growing demand of high-
way capacity in the United States.
RESOURCES FOR FURTHER INFORMATION
The contractor’s final report of NCHRP
Project 24-11(02), “Guidelines for Geofoam Appli-
cations in Slope Stability Projects” is available via
TRB.org/NCHRP by linking to the project page.
The research results of NCHRP Project 24-11(01),
“Guidelines for Geofoam Applications in Embank-
ment Projects” are presented in NCHRP Report 529
and NCHRP Web Document 65, which are also
available on the TRB website (TRB.org). NCHRP
Report 529 includes only the recommended design
guideline and the recommended material and con-
struction standard for use of geofoam in stand-alone
25
roadway embankments. NCHRP Web Document 65
includes the background and analyses used to develop
the recommended design guideline and material and
construction standard as well as a summary of the
engineering properties of EPS-block geofoam and
an economic analysis of geofoam versus other light-
weight fill materials.
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Byrne, R. J., Cotton, D., Porterfield, J., Wolschlag, C.,
and Ueblacker, G. (1998). “Manual for Design and
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Day, R. W. (2002). Geotechnical Earthquake Engineer-
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Elias, V., Christopher, B. R., and Berg, R. R. (2001).
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FHWA-NHI-00-043, National Highway Institute,
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AUTHOR ACKNOWLEDGMENTS
This digest presents the results of NCHRP
Project 24-11(02), “Guidelines for Geofoam Appli-
cations in Slope Stability Projects.” The research
was performed by the Department of Civil Engi-
neering at The University of Memphis (UoM).
UoM was the contractor for this study, with the
Research Support Office of UoM serving as Fiscal
Administrator. Dr. David Arellano, P.E., Associ-
ate Professor of Civil Engineering at UoM, was
the Project Director. The other project investiga-
tors are Dr. Timothy D. Stark, P.E., D.GE, Profes-
sor and Consulting Engineer, Department of Civil
and Environmental Engineering at the University
of Illinois at Urbana-Champaign; Dr. John S. Hor-
vath, P.E., Consulting Engineer and Professor,
Civil and Environmental Engineering Department
at Manhattan College; and Dr. Dov Leshchinsky,
President of ADAMA Engineering, Inc., and Pro-
fessor, Department of Civil and Environmental
Engineering at the University of Delaware. The
final report for NCHRP Project 24-11(02) can be
accessed via TRB.org/NCHRP by linking to the
project page.
Drs. Arellano, Stark, Horvath, and Leshchinsky
gratefully acknowledge the contributions of the fol-
lowing project team members who worked under the
general supervision of Dr. Arellano at the University
of Memphis: Masood H. Kafash and Chuanqi Wang,
Research Assistants and Ph.D. Candidates; John B.
Tatum, Research Assistant and M.S. Candidate;
Dean M. Alavi and William B. Cupples, Undergrad-
uate Research Assistants; Beth Hoople and Ann R.
Meier assisted with editing and preparing the final
report manuscript.
Finally, the project team acknowledges the guid-
ance and contributions of the National Cooperative
Highway Research Program and the NCHRP Proj-
ect 24-11(02) panel in preparation of the project
final report and this digest.
Transportation Research Board
500 Fifth Street, NW
Washington, DC 20001
These digests are issued in order to increase awareness of research results emanating from projects in the Cooperative Research Programs (CRP). Persons
wanting to pursue the project subject matter in greater depth should contact the CRP Staff, Transportation Research Board of the National Academies, 500
Fifth Street, NW, Washington, DC 20001.
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to any previously published or copyrighted material used herein.
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given with the understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA, FMCSA, FTA, or Transit Development Corporation
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