DESIGN AND CONSTRUCTION GUIDELINES FOR ALTERNATIVE LIGHTWEIGHT BACKFILL FOR MECHANICALLY STABILIZED EARTH WALLS
Alternative lightweight backfill
for Mechanically Stabilized Earth (MSE) walls include but are not limited to
cellular (foamed) concrete, foamed glass aggregate, geotechnical polyurethanes,
expanded lightweight aggregate concrete and expanded polystyrene (EPS), which
are alternative to lightweight aggregate. The use of alternative lightweight fill for
MSE walls has grown in popularity in recent years due to its effectiveness in
reducing fill weight on soft soils and the limited availability of lightweight
aggregate. They have also become more
popular alternatives for lightweight embankment backfill (Ruttanaporamakul 2014), due to their relatively
low density when compared to traditional backfill (Anderson et al. 2012; Miller
et al. 2004; Saride et al. 2010).
The advantages of alternative lightweight
fill include reduced vertical and lateral loads, minimized settlement, accelerated
installation rate and improved fill uniformity with no compaction required, and
may reduce cost by circumventing conventional ground improvement techniques. Some alternative lightweight fills are
pervious and free draining while some are impervious and most of them provide thermal
studies have shown that alternative backfill can be used as MSE backfill. Anderson et al. (2012) described the use of
lightweight cellular concrete for an MSE railway embankment with steel
reinforcement. An additional advantage
of cellular concrete in this case study was its ability to be pumped long
distances, which was critical in the tight construction space. Although alternative backfill has been used
successfully in MSE wall construction, its application is currently limited due
to relatively high cost, lack of knowledge among owners and practitioners in the
suitability and selection of alternative backfill material, interaction of the
backfill with MSE reinforcement, and design and installation of those
materials. Therefore, there is a need for design and construction guidelines
for the increased use of alternative backfill in MSE walls in practice.
The main objective of
the proposed research is to develop design and construction guidelines for the use
of alternative lightweight backfill in MSE walls with extensible and
inextensible reinforcements. The guidelines will cover suitability and material
selection criteria, engineering properties for various alternative backfills, critical
design considerations, interaction of alternative backfill with reinforcements,
and installation considerations.
The benefits of developing the
guidelines for use of alternative backfill in MSE applications are to:
provide an alternate to potentially costly ground improvement techniques to
support embankments or structures,
differentiate the mechanical behavior between lightweight aggregates (which fit
in with conventional MSE design) and alternative lightweight fill such as
cellular foam concrete,
improve safety and economy through comprehensive and consistent design and
construction considerations using alternative lightweight backfill, and
to owners through accepted national standards governing the design and
installation of alternative lightweight fill.
Stark et al. (2004) provided design
guidelines and material/construction standards for EPS block geofoam as a
lightweight fill alternative in roadway embankments. This RNS calls for a similar document for alternative backfill
for MSE walls. Several studies have been
conducted to evaluate the advantages of alternative backfill for MSE
walls. For example, Hatami and Witthoeft
(2007) evaluated the potential of EPS inclusions in MSE walls, showing a 75%
reduction in lateral earth pressure compared to traditional backfill material
using numerical simulations.
The proposed research consists of
the following tasks:
Task 1: Review Literature and
Assess Current Practices
This task includes a comprehensive
review of national and international practices for use of alternative
lightweight backfill in MSE applications and transportation earthworks.
Task 2: Identify Gaps in Current
Practices and Perform Appropriate Studies
After the literature review and the
assessment of current practices, identify and list gaps in material properties,
design, and construction/installation of current practices. Perform appropriate
studies to bridge the gaps for development of design and construction guidelines.
Task 3: Develop Design and
Construction Guidelines for Use of Alternative Lightweight Backfill in MSE Walls
Develop comprehensive guidelines for use of alternative lightweight
backfill in MSE applications. The guidelines should include but are not limited
to material selection, engineering design properties, required material
characteristics for use as alternative lightweight backfill, lab and field
testing requirements, design methods for extensible and inextensible
reinforcements, installation guidance, and environmental suitability of the
Note: an experimental field phase may be
required (estimated to cost additional $300,000) depending on the results of
the first study.
This research will serve as a basis
for development of an implementation plan to be included in FHWA GEC-11 Design
and Construction of MSE wall and Reinforced Soil Slopes.
Federal and State DOTs, Researchers; representatives from the following departments have indicated this RNS is a critical need: Ohio Department of Transportation, California Department of Transportation, Nebraska Department of Roads, Louisiana Department of Transportation and Development, Kentucky Transportation Cabinet, Idaho Transportation Department, and Oregon Department of Transportation.
|Sponsoring Committee:||AKG50, Transportation Earthworks
|Research Period:||24 - 36 months|
|RNS Developer:||Willie Liew, P.E. M.ASCE, Tensar International; Stacey Kulesza, Ph.D. M.ASCE, Kansas State University; Jie Han, the University of Kansas|
|Source Info:||Anderson, J., Bartlett, S., Dickerson, N., and Poepsel, P. (2012). “Development of seismic design approach for freestanding freight railroad embankment comprised of lightweight cellular concrete.” GeoCongress 2012. http://ascelibrary.org/doi/pdf/10.1061/9780784412121.177 |
Hatami, K., Witthoeft, A. (2007). “Reduction of backfill earth pressure in reinforced soil walls using geofoam.” Transportation Research Board 86th Annual Meeting.
Priddy, L. and Newman, J. “Full-scale field testing for verification of mechanical properties of polyurethane foams for use as backfill in PCC repairs.” Journal of Materials in Civil Engineering, 22(3), 254-252.
Miled K, Roy RL, Sab K. Compressive behavior of an idealized EPS lightweight concrete: size effects and failure mode. Mech Mater 2004; 36(11), 1031-46.
Ruttanaporamakul, P. (2014). Evaluation of Lightweight Geofoam for Mitigating Bridge Approach Slab Settlements. Ph.D. dissertation, the University of Texas at Arlington.
|Index Terms:||Backfilling, Backfill soils, Mechanically stabilized earth, Design, Earth walls, |
|Cosponsoring Committees:||AKG80, Geosynthetics|
Bridges and other structures