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DESIGN AND CONSTRUCTION GUIDELINES FOR ALTERNATIVE LIGHTWEIGHT BACKFILL FOR MECHANICALLY STABILIZED EARTH WALLS

Description:

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 insulation.

Successful case 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.

Objective:

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.

Benefits:

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

  • provide confidence to owners through accepted national standards governing the design and installation of alternative lightweight fill.

Related Research:

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.

Tasks:

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 materials.

Note: an experimental field phase may be required (estimated to cost additional $300,000) depending on the results of the first study.

Implementation:

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.

Relevance:

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
Research Priority:High
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.
Date Posted:08/16/2017
Date Modified:02/19/2019
Index Terms:Backfilling, Backfill soils, Mechanically stabilized earth, Design, Earth walls,
Cosponsoring Committees:AKG80, Geosynthetics
 
Subjects    
Construction
Design
Materials
Geotechnology
Bridges and other structures

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