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David Arellano, Ph.D., P.E.Associate ProfessorThe University of Memphis

Lightweight Fill Applications & Considerations

50th Annual Southeastern Transportation Geotechnical Engineering ConferenceNovember 6, 2019Chattanooga, Tennessee

Outline• Lightweight Fill as a Ground Modification Technology

• Overview of Various Lightweight Fill Materials• Example Lightweight Fill Embankment Applications

• Framework of Design Methodology• Preliminary Selection of Lightweight Fill Materials

• What Lightweight Fill Type is the Best?

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What is considered a lightweight fill?

• A fill material that has a lower unit weight than the unit weight of locally available compacted natural soil fill.– Compacted natural soil fill unit weight typically ranges from about 115‐140 pcf (FHWA GEC 013 2017).

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Lightweight Fill as a Ground Modification Technology

• Ground modification: the alteration of site foundation conditions orproject earth structures to provide better performance under design and/or operational loading conditions (USACE 1999; FHWA GEC 013 2017).

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Nike  Warehouses, Memphis

Ground Modification Functions (FHWA GEC 013 2017)

• Increase shear strength and bearing resistance• Increase density• Decrease permeability• Control deformations (settlement, heave, distortions)• Increase drainage• Accelerate consolidation• Decrease imposed loads• Provide lateral stability• Increase resistance to liquefaction• Transfer embankment loads to more competent subsurface 

layers5

Evaluation of Ground Modification Alternatives

6(FHWA GEC 013 2017)

Combination Ground Modification Technologies

7(FHWA GEC 013 2017)

Nike  Warehouses, Memphis

Overview of Various Lightweight Fill Materials

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Density and Specific Gravity for Various Lightweight Fill Materials

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Basalt 30 to 70 0.5‐1.1Foamed Glass Aggregate (FGA) 15 to 20 0.2‐0.3

(FHWA GEC 013 2017)

CategoriesFills with Unconfined  Compressive Strength

• Geofoam• Cellular concrete

Granular Lightweight Fills

• Wood fiber• Blast furnace slag• Boiler slag• Fly ash• Shredded tires• Foamed glass aggregate 

(FGA)• Expanded shale, clay & 

slate (ESCS)• Pumice, basalt

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Manufactured materials

Geofoam: expanded‐polystyrene block

11AL DOT

Cellular Concrete

• Concrete made with hydraulic cement, water and preformed foam to produce a hardened material.

• Preformed foam is created by diluting a liquid foam concentrate with water in predetermined proportions and passing this mixture through a foam generator.

12Photos courtesy of Aerix Industries. 

Cellular Concrete

Permeable Non‐Permeable

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Provided by Mainmark

Photos courtesy of Aerix Industries. 

Cellular Concrete: Properties 

• Wet Density Range: 20 to 80 pcf • Compressive Strength Range: 10 

to 300 psi, depending on density • Water Absorption: 1.4 to 15 psf, 

depending on density • Freeze‐thaw Resistance, 100 

Cycles: 92 to 98%, depending on density 

• Coefficient of Lateral Earth Pressure: Negligible for vertical loads applied directly over the foamed concrete. Lateral pressures from adjacent soil mass may be transmitted undiminished. 

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Photo courtesy of S.F. Bartlett

(FHWA GEC 013 2017)

Tire Shreds

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• Dry Density: 21 to 53 pcf loose and 30‐73 pcf compacted 

• Angle of Shearing Resistance: 19°to 30°

• Cohesion Intercept: 100 to 230 psf, use 0 for design 

• Compressibility: 5 to 40 percent vertical strain over a range of 200 to 4,200 psf vertical stress 

• Permeability: 0.5 to 60 cm/sec • Type A Gradation (ASTM D6270): 

8‐inch maximum dimension; 100% passing 4‐inch, a minimum of 95% passing 3‐inch, a maximum of 50% passing the 1.5‐inch, and a maximum of 5% passing the 0.2‐inch sieve 

• Coefficient of Lateral Earth Pressure: 0.25 to 0.47 

https://www.dot.ny.gov/divisions/engineering/technical‐services/technical‐services‐repository/shreds_rolling.jpg

(FHWA GEC 013 2017)

Wood Fiber• Moist Density: 45 to 60 pcf • Angle of Shearing Resistance: 

– Sawdust – 25° to 27°– Hogfuel – 31°– Wood Chips – 30° to 49°

• Permeability: 1 x 10‐5m/s • Compressibility: Loose volume 

reduces 40 percent on compaction. 

• Vertical subgrade reaction coefficient: 1300 to 1450 psi in top 2 feet, roughly corresponding to a CBR of 1 

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https://www.google.com/search?rlz=1C1GCEU_enUS819US819&biw=1280&bih=692&tbm=isch&sa=1&ei=ZMWXXIe1GdC7tgWezb0g&q=wood+chip+fill+photos&oq=wood+chip+fill+photos&gs_l=img.3...72436.72436..73346...0.0..0.53.53.1......1....1..gws‐wiz‐img.‐6sfYoh03us#imgrc=pp2nfXxZOy5HlM:

(FHWA GEC 013 2017)

Expanded shale, clay & slate (ESCS)• Dry Density, Compacted: 50 

to 65 pcf • Dry Density, Loose: 40 to 54 

pcf • Angle of Shearing 

Resistance: 35° loose, 37° to 44° compacted 

• Grain Size Gradation: 3/16 to 1 inch 

• Permeability: High • Coefficient of Subgrade 

Reaction: 33 to 37 pci loose, 140 to 155 pci compacted 

17(FHWA GEC 013 2017)

Publication #6600.4 Revised June 2008 ESCS

Pumice, Basalt• Unit weight range 

(compacted): 30‐70 lb/ft3

• Water absorption: 9% basalt

18(www.Garibaldi Pumice.com) Photos courtesy : Roch Player

Fly Ash

• Density Range, Compacted: 70 to 90 pcf 

• Shear Strength: 33° to 40°,       c = 0, for Type F; Class C is self‐hardening, so the shear strength will vary as it cures 

• Permeability: Range of 1 x 10‐6 to 1 x 10‐9 m/s 

• Compressibility: Cc = 0.05 to 0.37, Ccr = 0.006 to 0.04 

• Grain Size Range: 0.005 to 0.074 mm 

• Specific Gravity: 1.9 to 2.5 • Atterberg Limits: Non‐plastic 

19(FHWA GEC 013 2017)

Report No. FHWA‐IF‐03‐019

Air‐Cooled Blast Furnace Slag

• Compacted Moist Density: 70 to 94 pcf, varies with size and gradation 

• Gradation: Can be graded to any specified size from 4 inches down. 

• Angle of Shearing Resistance: 35° to 40°

• Permeability and Compressibility: Depends on final specified gradation. Generally similar to gravel and sand. 

20(FHWA GEC 013 2017)

http://www.nationalslag.org/blast‐furnace‐slag

Boiler Slag• Dry Density, Loose: 60 to 78 pcf • Dry Density, Compacted: 82 to 102 

pcf • Optimum Moisture: 8 to 20% 

(Stroup‐Gardiner and Wattenberg‐Komas 2013b) 

• Angle of Shearing Resistance: 38° to 42°

• Coefficient of Permeability: 0.3 to 0.9 mm/s 

• Grain Size Range (Percent Passing): 90 to 99% on #4, 62 to 89% on #8, 16 to 46% on #16, 4 to 23% on #30, 2 to 12% on #50, 1 to 7% on #100, and 0 to 5% on #200 (Stroup‐Gardiner and Wattenberg‐Komas 2013b) 

• Atterberg Limits: Non‐plastic • Compressibility: Comparable to sand, 

at same relative density 21

(FHWA GEC 013 2017)

https://www.acaa‐usa.org/AboutCoalAsh/WhatareCCPs/BoilerSlag.aspx

Foamed Glass Aggregate (FGA)

22Table and photo courtesy of T.A. Loux of AeroAggregates.

Example Lightweight Fill Embankment Applications

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Rte 1 & 9, Jersey City, NJ

Port of Longview, Longview, WA

Geofoam

Photos: Insulfoan/Sutmoller

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Cellular Concrete

Colton Crossing, CAFigure and photo courtesy of Steven F. Bartlett

Foamed Aggregate Glass

Navy yard Access Project, Philadelphia, PAPhoto courtesy of T.A. Loux of AeroAggregates.

Basalt

SB405 RSSRenton, WAFigure and photo courtesy Roch Player.

• Road construction over poor soils

• Road widening• Bridge abutment• Bridge underfill• Culverts, pipelines & buried

structures• Compensating foundations• Rail embankment

• Landscaping & vegetative green roofs

• Retaining and buried wall backfill

• Slope stabilization• Stadium & theater seating• Levees• Airport runway/taxiway• Foundations for lightweight

structures

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Summary of Applications

• Special applications: Noise and vibration damping Compressible application Seismic application Permafrost embankments Rockfall/impact protection

• ????????

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Summary of Applications

Framework of Design Methodology

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Functions of Lightweight Fill Materials

• Lightweight Fill• Thermal insulation• Compressible inclusion• Damping• Low earth pressure fill for retaining

structures• Structural support

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Application:Road embankment oversoft ground

Application:Retaining wall

Application:Integral abutment

Design by Function

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Design‐By‐Function Approach

• “Assessing the primary function that the lightweight fill will serve and then calculating the required numerical value of a particular property for that function” (Koerner 1998).

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Lightweight Fill Embankments Over Soft Soil Ground Conditions

• Design and construction of embankments over soft ground is based on avoiding failureduring construction by providing adequate stability and limiting postconstruction settlement to desirable amounts (Hunt 1986).

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What is failure?

What is Failure?

• The term “failure” is a loss of function. • Failure or loss of function may occur as either a – serviceability failure (the serviceability limit state, SLS) or a 

– collapse failure (the ultimate limit state, ULS).

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Examples of Failure• An embankment over soft 

soil may experience a serviceability failure due to excessive total or differential settlement that develops over time and which produces premature failure of the pavement system. 

• An embankment over soft soil may experience a collapse failure through either a rotational (slope stability), lateral spreading, or bearing capacity failure mechanism. The collapse failure may involve at least partial, if not total, collapse.

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Overall Design Goal• The overall design goal is to satisfy the following equations for 

the ULS and SLS respectively:– ULS: resistance of embankment to failure > embankment loads producing failure

– SLS: estimated deformation of embankment ≤ maximum acceptable deformation

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How does use of lightweight fill achieve design goal?

• When utilizing normal soil for the embankment, the resistance and stiffness of the soft soil foundation must be increased artificially using soft ground treatment techniques to be able to resist the loads with acceptable deformations and meet ULS and SLS requirements.

• With lightweight fill, the approach is to reduce the loads acting on the soft soil and accept the natural resistance (strength and compressibility) of the existing soft foundation soil as it exists to meet ULS and SLS requirements.

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Application: Roadway EmbankmentFunction: Lightweight Fill

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H=1 ftGeofoam or SoilEmbankment

Soft soil subgrade

q=applied stress

Soil embankment:Soil unit weight ≈120 lb/ft3q=(H)(unit weight)=(1ft)(120 lb/ft3)= 120 lb/ft2

Lightweight fill embankment: Unit weight ≈ 1 to 90 lb/ft3q=(H)(unit weight)=(1ft)(1 to 90 lb/ft3)= 1 to 90 lb/ft2

Summary of Overall Design Process

1. Identifying the potential failure mechanisms that need to be considered for the required function(s) and application.

2. Identifying the engineering properties that influence the failure mechanisms

3. Identifying the loads that need to be considered in the analysis of each failure mechanism

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Summary of Overall Design Process (cont.)

4. Evaluating existing design methods typically used in practice to analyze each failure mechanism

5. Developing a design method for analyzing those failure mechanisms for which existing design methods are not available or suitable.

6. Determining tolerable performance criteria for each failure mechanism such as min. FS or max. settlement

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Identify Failure Mechanisms & Performance Criteria 

• Allowable total settlement• Allowable differential settlement• Factor of safety for slope stability• Factor of safety for overturning• Factor of safety for sliding• Factor of safety for bearing capacity• Factor of safety for seismic stability• Factor of safety against hydrostatic uplift• Factors of safety against pavement cracking and rutting 

41Obtained from www.GeoTechTools.org

Identify Material Characteristics • Fill type• Fill density• Flammability• Fill water content (water absorption)• Fill creep• Fill susceptibility to petroleum products• Fill allowable load• Fill permeability• Freeze/thaw resistance• Flexural strength• Fill friction angle• Fill cohesion• Fill modulus/compressibility• Fill coefficient of lateral earth pressure• Fill gradation• Other unique material characteristics applicable to each type of 

lightweight fill (see design/analysis procedure summaries in www.GeoTechTools.org ) 

42Obtained from www.GeoTechTools.org

Settlement?

Major Components of a Lightweight Fill Embankment

Lightweight Fill Mass

OVERBURDEN MATERIAL(PAVEMENT SYSTEM)

FOUNDATION SOIL

FILL MASS

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Design must consider the interaction of the various components.

Design Phases (5)Preliminary Embankment

Arrangement

External (global) Stability

Internal Stability

Pavement System Design

Final Embankment Design

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These phases consider the interaction of the major components of the embankment.

Lightweight Fill Embankment Design Framework

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Preliminary Selection of Lightweight Fill Materials

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Subsurface Conditions 

• Site stratigraphy• Depth to groundwater table• Soil compressibility• Soil initial void ratio• Soil shear strength• Soil variability

47Obtained from www.GeoTechTools.org

Loading Conditions 

• Traffic surcharge• Fill/soil load• Structure load• Water pressures• Earthquake acceleration and duration• Wind load 

48Obtained from www.GeoTechTools.org

Geometry

• Lift thickness• Fill arrangement• Side slope inclination• Overlying pavement thickness• Transition zone 

49Obtained from www.GeoTechTools.org

Preliminary Selection of Lightweight Fill Materials

• Settlement will typically be the most critical issue when lightweight fills are considered. 

• Based on settlement criteria (SLS requirements), can evaluate various lightweight fill types to determine which ones will satisfy settlement. – SLS: estimated deformation of embankment ≤ maximum acceptable deformation

• Evaluate settlement of various lightweight types or determine a maximum unit weight that will satisfy settlement requirements.

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Example: Settlement

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H=5 ftEmbankment

3100 , 1.7, 0.3, 0.04, 1.5sat o c r

Claylb e C C OCRft

3

Tolerable settlement: 4 in.

Estimated max. unit weight of embankment fill: 30

Potential lightweight fills: cellular concrete, foamed glass aggregate, geofoam

lbft

Lightweight Fill Type Selection Factors

• The basic cost of the material. • Transportation costs. • Quantity of material. • Availability of materials. • Placement and/or compaction costs could be 

higher than for soil fill. • Availability of the materials. • Construction methods. • Durability of the fill deposits.• Environmental concerns.• Geothermal properties. 

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Alternative analysis

(These are cost factors from FHWA GEC 013 2017)

Table 3-12. Typical Cost Ranges for Lightweight Fills (FHWA GEC 013 2017)

Costs do not include intangible benefits!

Intangible Benefits• Material cost per volume of some lightweight fills is greater than

conventional soil.

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boobook48.blogspot.com1024

Photo courtesy of Aerix Industries

Intangible Benefits Reduced field installation time and placement in adverse

weather conditions resulting in accelerated construction Shorter time roadway is not in service Easily adaptable to use of phased construction Minimum field quality control testing

On many projects, the intangible benefits of using more expensive lightweight fill materials more than compensate for the fact that the material unit costs are greater than that of traditional earth fill material.

(NCHRP 24-11(01))55

Preliminary Design

• Once the preferred lightweight fill alternative has been selected perform preliminary design.

• If the preferred lightweight fill type does not adequately meet the performance criteria of a failure mechanism, perform preliminary design with the 2nd preferred lightweight fill type.

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The geotechnical “system”. BWC = Build With Confidence (Harr 1987; Holtz 1989).

BWCSampling Testing Analysis Criteria

TolerableApplication of

Previous

Experience

in Area

Especi

ally

of Pro

ject Construction

Monitoring (Arellano)

Judgment(Arellano)

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1. Engineering judgment without relevant experience is weak.2. Engineering judgment without relevant data is foolish.3. Good judgment needs good data and evaluated experience.4. Good judgment is essential for the effective use of information technology tools.5. Good judgment is central to geotechnical engineering, even in the information age.

From Allen Marr, Ph.D., P.E., F.ASCE, NAE, "Geotechnical engineering and judgment in the information age," GeoCongress 2006, Geotechnical Engineering in the Information Technology Age. Included in GEOTECHTOOLS website.

What Lightweight Fill Type is the Best?

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What Lightweight Fill Type is the  Best?

• The one that meets project’s technical and economical objectives.

• Combinations of different lightweight fill types and/or ground modification technologies?

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Geotechnical Research

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SR‐57 Bridges Over Sr‐23, CSXT & IC RR, Union Pacific Railroad and Scott Street, Memphis, TN: Proposed instrumentation of  geofoam  embankments between bridges.

Embankment 1: 280 ft long, 8‐26 ft high.Embankment 2: 115 ft long, 42‐44 ft high.

Geotechnical Research

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Resonant column tests : lightweight cellular concrete.

Lake 2018

Dyer 2019

Lauderdale 2020

Tipton 2021

Madison2022

* Jackson

* Memphis/Shelby Co

TN

KY

MO

AR

MS

Date by county nameis expected year ofcompletion by Mayof that year.

2017‐2022: 5 yrs.

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Seismic and Liquefaction Hazard Maps for Northwestern Tennessee

Department of Housing and Urban Development National Disaster Resilience Award.

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Thank You!

David Arellano, Ph.D., P.E.Associate ProfessorThe University of Memphis104 Engineering Science Building Memphis, TN 38152 901‐678‐3272darellan@memphis.edu