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50th Ghana Institution of Engineers (GhIE) Annual Conference, Koforidua, Eastern Region, Ghana, March 2018

GHIE@50: ENGINEERING GHANA’S SUSTAINABLE DEVELOPMENT

AN APPRAISAL ON THE USE OF GEOFOAM AS GEOTECHNICAL SOLUTION IN CONSTRUCTION

P. Ackah & K. G. Bempong [Associated Consultants Ltd., Accra]

REFEREED PAPER

Geofoam is preferred and increasingly used in engineering applications. This growth is due to the inherent material properties such as low density, good insulation, low hydraulic conductivity, strength and deformation properties that complement soil behaviour. It is also environmentally friendly and relatively cost effective. This paper is an overview of a specific geofoam material called Expanded Polystyrene (EPS), which is a type of rigid plastic foam. EPS is an ultra-lightweight geosynthetic material successfully used in reducing settlement below embankments, reducing lateral pressure on sub structures, and reducing stresses on underground utilities.

Introduction Construction on soft ground pose serious threat to civil engineering structures due to compressibility and low shear

strength of such foundation soils. In roadworks, large volume of suitable material is needed and if not available locally,

the quality material is transported over long haulage distances increasing the total cost of the project. Conventional

methods of filling with earth materials (heavyweight) is done in thin lifts with repeated compaction requiring

considerable time, construction equipment, and tests to ensure adequate level of compaction. In the case of soft soils

condition, after surcharging the soil, significant waiting time is required for dissipation of pore water pressures

subsequently resulting in primary consolidation. The use of lightweight fill on soft ground for mitigation of settlement

and potential instability has become increasingly popular with increased reporting of successful applications.

(Frydenlund & Aaboe 1996; Hovarth 1997; Stark et al. 2000, 2002; Mann & Stark, 2007; Arellano et al., 2010).

Lightweight materials include fly-ash, shredded tires, woodchips and expanded polystyrene (EPS) or extruded

polystyrene (XPS) geofoam. However with the exception of geofoam, these material have higher densities and

variability in their make-up (Foam-Control, 2017).

Table 1: Range in densities of typical lightweight fills (Elragi 2006)

Fill Type Range in Density (kg/𝒎𝟑)

EPS Geofoam 12 to 35

Foamed Concrete 355 to 770

Wood Fiber 550 to 960

Shredded Tires 600 to 900

Expanded Shale and Clay 600 to 1040

Fly-ash 1120 to 1440

Boiler Slag 1000 to 1750

History Geofoam was first used for settlement control in 1972 for the approach to Flom Bridge in Norway (Frydenlund, 1991).

The embankments rested on a 3m thick layer of peat over 10m of sensitive marine clay. Before using EPS geofoam,

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settlement rates of the order of 200-300 mm annually were recorded. Little or no settlement were recorded after

replacing with 1m thick EPS. Due to its success, its use spread to many countries such as USA, Japan and Canada.

In 1989, it was used in the USA for slope stabilization on Highway 160 in the Colorado State. The first EPS geofoam

(15m high) application in Japan was an embankment fill in 1985 (Yamanaka, et al., 1996) where 470 cubic meters

were utilized in the project. (Miki, H., 1996). Germany use of EPS geofoam in highway construction occurred in

March of 1995 to minimize the differential settlement of a bridge approach (Hillmann, 1996). EPS geofoam as a

lightweight fill material was first introduced in 1992 in Malaysia (Mohamad, 1996). Currently, EPS find its use in

road embankment, railway embankments, bridge abutment, widening vertical walls, widening embankments for steep

slopes, protection of structures etc.

Geofoam Geofoam mainly of two types (EPS or XPS) is a block or planar rigid cellular foamed polymeric material used in

geotechnical engineering applications (ASTM D4439). This geosynthetic product is approximately 1% the weight of

soil and less than 10% the weight of other lightweight fill alternatives as presented in Table 1. It can quickly be placed

with no need for compaction or waiting for consolidation to occur. It is flexible, easy to handle and often requires no

special equipment during construction. It is unaffected by adverse weather conditions and moisture. Relatively, the

EPS geofoam is the commonest material choice for most projects due to its cost effectiveness, environmentally

friendly and range of applications (Duskov 1997).

EPS Geofoam Manufacturing Figure 1 shows the processes the raw material or resin used for the molding of EPS geofoam are manufactured. The

end product of the manufacturing process results in EPS beads which are fed to an expansion vessel containing an

agitator and a steam input. The resin beads are expanded into "pre-puffs" by injecting steam. The expanded beads are

then released into a bed dryer to get rid of moisture. The pre-puffs are then stored in fabric storage bags to allow them

to stabilize to atmospheric temperature and pressure. They are then transferred into block mold of various sizes. Steam

is then injected into the mold under controlled pressure to soften the polymer structure of the pre-puff. The heat from

the steam and the applied pressure causes the pre-puffs to further expand. Since the block mold is a confined

environment, the expanding pre-puffs reduce the void space between individual particles and fuse (bond) together to

form an expanded polystyrene (EPS) block. Figure 2 shows the formation stages of EPS geofoam.

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Figure 1: BASF Inc. production method of Styropor

expanded polystyrene (EPS) slabs and blocks.

(Koerner 2005)

Figure 2: Formation stages of geofoam

(adapted after Mandal 2017)

Material Properties and Test Methods Geofoams properties and test methods are grouped into physical, mechanical, thermal and endurance categories. The

physical specification by ASTM standards for the various grades of EPS and XPS is as shown in Table 2. The

commonly manufactured dimensions of geofoam according to the ASTM D6817 is presented in Table 3.

Table 2: Physical property requirements of geofoam (ASTM D6817)

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Table 3: Commonly manufactured dimensions of geofoam by ASTM D6817 (after Koerner 2005)

Dimension(mm) EPS Types XPS Types

Length 1219-4877 1219-1743

Width 305-1219 406-1219

Thickness 25-1219 25-102

Design and Construction Considerations The densities of geofoam is much lower than that of water (1000 kg/m3). This may lead to uplift forces due to buoyancy

effect resulting in failure at the construction stage. Probable solution involves provision of adequate surcharge or

controlling ground water levels to ensure stability against uplift.

Loading-deformation behavior is generally determined by laboratory testing. The compressive strength attained for

geofoams at strain of 1% 5% and 10% are shown in Table 2. It can be observed that compressive strength increases

as density increases. Loading-deformation behavior is affected by temperature, with compressive strength increasing

with decreasing temperature and vice versa (BASF, 1987). Horvath (1994) reported that over a range of temperature

(0-450C), the variation in strength is about ±20% relative to results obtained from laboratory test.

Other than compression, EPS specimens are routinely tested for tension, flexure and shear. The Flexural strength

are used as a quality control test (i.e. how well the expanded polyhedral were fused during manufacture). The flexural

strength increases with density of the material in table 2. Tensile strength of EPS material can be an indication of the

quality of prepuff and any recycled EPS geofoam used. (Horvath 1995b). Tensile properties are similar to that

described by the Flexural strength. EPS fails in tension as a crack on tension side appears at the moment of failure.

EPS geofoam is susceptible to long term creep settlement when a constant stress level is applied. A number of

factors affect the creep behavior of EPS Geofoam, for example density. Creep deformations decrease with density

increase (Sun 1997). To this end, after the I-15 project, Utah Department of Transportation installed instrument arrays

to gather long term performance data of the geofoam fills to inform future designs and construction guidance for

geofoam construction.

The interface shear strength between geofoam to geofoam and geofoam to sand interfaces slightly decreases with

increasing normal stress. A relatively strong adhesive bond developed between that of geofoam surfaces and in place

concrete. The effect of density on interface strength of geofoam is however negligible. During construction, barbed

metal plates or binder plates are sometimes used to attach foam layers to each other to develop more interface shear

resistance. However, tests have showed the plates helped in maintain the blocks in position during placement and not

provide resistance. (Bartlett et al.2000; Sanders et al. 1996). During construction, placing of EPS geofoam must be

accurate. There should be minimum amount of gaps between the individual and successive geofoam layers. The

existence of gaps create stress concentration in the contact areas leading to excessive immediate strains and large

creep. This affect the overall settlement hence decreasing the design life of the pavement structure (Negussey and

Elragi, 2000a).

Polystyrene is inherently hydrophobic, hence preventing the absorption of water due to its closed cell structure.

However, water can enter the small voids between the fused particles. The amount absorbed depends on factors such

as type, density and duration of exposure to moisture. The absorption rate is about 1% per year in volume. (BASF

1978). This level of moisture absorption does not compromise the desired low density feature nor adversely affect the

strength and deformation properties of geofoam. Notwithstanding, increased moisture absorption degrades the thermal

conductivity of geofoam. In designing, conservative allowance is made considering a long term water content in the

EPS by 3-5% by volume which produce increase in thermal conductivity of between 15-25% (Horvath, 1993b). Even

under extreme cases of exposure to water leading to increment in the coefficient of thermal conductivity, EPS remains

an efficient thermal insulator compared to soil.

EPS is a poor conductor of heat (excellent heat insulator) consisting of approximately 98% air and 2% polystyrene

(BASF Corp 1997). Unlike geofoams, the thermal resistance (R-value) of soil and concrete are less than 0.1m3. Factors

such as temperature, density and moisture content significantly affect the R value (Van Dorp 1988; Negussey 1997;

Elragi, 2006).

Exposing geofoam to ultraviolet (UV) leads to discoloration and dusting on the surface. This diminishes the strong

bond (interface strength) between the geofoam and cast in place concrete. Researchers such as (Sheeley 2000; Bartlett

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et al.2000) has reported by removing the degraded surfaces by power washing before concrete pouring re-establishes

adhesion bonding and maximum interface strength.

At the construction stage, EPS geofoam must be protected from high temperatures, concentrated load, combustible

products (eg. carbon dioxide), potential spills of petroleum based fuels and solvents (eg. diesel fuel). EPS would melt

when exposed to temperatures in excess of 1500C. Again it will dissolve upon encountering petroleum products hence

requires a protective cap of concrete (100mm thick) or geomembrane. Since geofoam has no nutritional value (BASF

1990), it does not attract ants, termites and rodents. However, borate is added to geofoam to prevent insect attack and

boring intrusion (eg I-15 project). Flame retardant additive can also be added to EPS beads if desired. Table 4 shows

some of the chemical reagents and corresponding EPS resistant.

Table 4: Selected EPS Resistant Behavior (after Elragi 2006)

Source of Attack Resistant Behavior

Salt Water (Sea Water) Resistant

Alkali Solutions Soaps Resistant

Caustic Soda Solutions Resistant

Bitumen (Air Blown) Resistant

Alcohol Resistant

Micro Organisms Resistant

Paraffin Oil, Vaseline, Diesel Oil Limited Resistance

Petrol (Super grade) Non Resistant

Strong Oxidizing Acids Non Resistant

Fuming Sulphuric Acid Non Resistant

Organic Solvents Non Resistant

Standards and Design Manual Table 5 provides the guide and design considerations of the appropriate EPS geofoam properties. The three standards

for EPS geofoam is ASTM D6817 Standard Specification for Rigid Cellular Polystyrene Geofoam, D7180 Standard

Guide for the Use of EPS Geofoam in Geotechnical Projects and D7557 Standard Practice for Sampling of EPS

Geofoam Specimens. Similarly, some manufacturers also design their own conceptual guides for analysis and design

(Geo Tech 1998). There exist other design manuals for EPS such as Draft European standards (1998), Public Works

Research Institute (1992), Ministry of Construction and Norwegian Road Research Laboratory (1992). Again, Federal

Highway Administration (FHWA) and National cooperative highway research program (NCHRP) have two

documents (FHWA NHI-06-019 and NCHRP Project 24-11) detailing the design procedures for lightweight fills.

Table 5: Selected ASTM Standards for geofoam (after Negussey 1997)

Handling and Installation EPS Geofoam block are large but easy to handle. It can be field cut or trimmed to fit to size by either a chain saw or

hot wire. Material delivery is accompanied by a detailed set of installation drawings from the manufacturer.

Geofoam installation does not require much training but care should be taken not to allow for operation of

equipment directly on the surface of the geofoam fills. Generally, geofoam blocks should be staggered to interlock

Property Standard

Density C-303 , D1622

Thermal Conductivity C-177, C-518

Compressibility D-1621

Flexural C-203

Tensile/Adhesion D-1623

Vapor Transmission E-96

Absorption C-272

Thermal Expansion D-696

Combustion; O2 Index D-2863

Insulation Specification C-578

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so that joints between block layers are not made continuous. Blocks can be interconnected with barbed plates,

gripper plates or suitable adhesive.

Application and Use Major applications of EPS geofoam is based on consideration of its relevant engineering properties, cost, durability

and environmental factors. Horvath (1995) functional classification for EPS are lightweight fill, compressible

inclusion, thermal insulation and small amplitude wave damping. Table 6 presents some selected properties of

geofoam corresponding to an application of geofoam in solving geotechnical problems.

Table 6: Selected EPS geofoam applications (Hovarth 1992)

Application Density Compressibility Damping Insulation Cohesion

Slope stabilization

Embankments

Bridge Approaches

Earth Retaining Structures

Bridge Abutment

Flood Control Levees

Buried Pipes

Railways

Slope Stabilization

Figure 3 shows the use of EPS geofoam in slope stabilization. In a slope stability problem two forces namely driving

and resisting forces are considered. To ensure stability, the driving force is reduced by removing a portion of the

existing soil and replacing it with lightweight EPS geofoam. For a soil with friction, the foam is positioned in a way

to increase the overall factor of safety. This can be achieved by placing the foam fill to take the shape of the slip

surface. NCHRP 24-11 recommends a factor of safety of 1.5 against global slope stability failure to be used for design.

EPS

Original slope

Driving block

Resisting block

Center of rotation

Resisting berm

Figure 3: Slope stabilization using EPS Geofoam

An embankment of height 21m for an emergency truck escape ramp in Hawaii was constructed in 1994 using EPS

geofoam (Mimura and Kimura, 1995). Originally, the project was designed as an earth fill embankment with extensive

geotextile reinforcement and wick drains to overcome stability problems and to reduce settlement. At construction

stage, the pertaining site conditions were found to be worse than expected hence 13500 m3 of geofoam was used as

lightweight fill to replace the earth embankment. In 1997, the reconstruction of Interstate 15 (I-15) in Salt Lake City

Utah, utilized geofoams instead of mechanically stabilized earth (MSE) to improve stability of embankment. This

application of geofoam eliminated stability concerns at the bridge abutments and reduced the construction time by up

to 75% (Barlett et al. 2000).

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Embankment

Large settlements may be experienced upon constructing over soft or loose soils. EPS geofoam can be used to replace

soft soils or in place of heavy fill materials to reduce loading on underlying soils and adjacent structures. In the I-15

project, the design of MSE embankments loads predicted induced primary settlements of about 1m which exceeds all

strain tolerance for buried utilities (Bartlett et al. 2000). Replacement of MSE with EPS geofoam reduced the large

settlement to minimum. It also enabled buried utilities to remain in-place, eliminating possible expensive interruption,

replacement, or relocation. Another application of the EPS geofoam was to mitigate settlement (300mm) of bridge

approach embankments constructed over compressible 30m thick layer of silty clay soils at Maine Turnpike Beech

Ridge overpass (Snow & Nickerson 2014). Another advantage for the geofoam used was to allow the overpass to be

built on a fast-track schedule.

Soft soil

EPS GEOFOAM

pavement

Base

Sand leveling-layer

Concrete slab

Figure 4: Building embankment on soft soil using EPS geofoam.

Foundation

EPS geofoam can be used as a compensating foundation to reduce the load on underlying compressible soils and

minimize building settlement along with potential bearing capacity problems (EPS Industry Alliance, 2012). The

foundation of an emergency staircase of an overpass was reported by Ojima et al 1996. The existing ground was

underlain by soft clay. Deep foundation could not be considered due to the existence of a four meter diameter sewer

pipe below the footing of the staircase. An alternate solution was utilizing 3m height EPS geofoam. In Port-Said,

Egypt the overburden soils is underlain by very thick layer of soft clay. Abdelrahman and Elragi (2006) used a physical

model to study the behavior of EPS with different thickness and densities over soft clay in order to reduce settlement.

They concluded that construction on soft clay which EPS as a lightweight material as replacement material of soft soil

beneath a raft foundation is an effective way to control settlements and moments.

Buried Pipes and Culverts

The low mass density ranging between 10-40 kg/m3 of geofoam reduce vertical and horizontal loads on buried pipes

and culverts under highway fills (Vaslestad, 1990; Sun et al., 2009). The earth pressures imposed on deeply buried

pipelines and culverts is significantly affected by soil arching. In the case of geofoams, “imperfect trench” method

involves installing compressible geofoam inclusion above the relatively rigid pipeline or culvert as shown in figure 5.

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EPS Geofoam

pipe

Ground

Figure 5: Stress reduction on buried pipe utilizing EPS geofoam.

Two full uplift tests conducted by Bartleet & Lingwall (2014) concluded that geofoam cover system developed about

four times less uplift force than that of the corresponding soil backfill. Similar results were reported by Choo et al

(2007), where 30-60 % reduction in lateral soil-pipe forces was recorded when geofoam was used as a lightweight

trench backfill cover for pipe undergoing horizontal displacement.

Retaining and Buried Walls

Geofoam is preferred for compressible inclusions because it is non-biodegradable. Inclusion of EPS geofoam as

backfill behind retaining and buried wall greatly reduces the lateral earth pressure on the structure (Ertugrul &

Trandafir 2011, 2013). For compressible inclusion applications, stiffness of the geofoam in the primary direction of

displacement is the critical property. Hovarth 1998 reported that the minimum EPS density of economical balance

between stiffness and durability is approximately 12kg/m3.

Soil cover or pavement

section

Retaining wall

or Abutment

Drain pipe

Granular backfill

EPS GEOFOAM

Figure 6: Geofoam retaining wall

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Cases of EPS Failures Reported applications of geofoam in geotechnical works include embankment and pavements (Hovarth 1997; Stark

et al. 2000 2002; Frydenlund & Aaboe 1994), slope stability (Mann & Stark 2007; Arellano et al., 2010). However

failures in its project application have also been reported (Horvath 1999; Duskov 1997).

Hovarth (1999) reported on number of failures involving EPS block geofoam used as lightweight fill, primarily for

roads. He attributed the cause of failures to lack of thorough understanding of all factors that must be considered when

designing and specifying block molded EPS as a geofoam product for such applications.

Duskov (1997) reported on the premature pavement failure which occurred in Matlingeweg, Rotterdam. EPS

geofoam was incorporated in the reconstruction of the road to reduce the resulting settlements of the existing subgrade.

Since the settlement were not uniform, a portion of the reconstructed road used only a single layer of EPS

blocks 500 mm thick. The remaining portion used two layers of blocks. One month after the road was opened to

traffic, cracking was observed on the portion of the road with 500 mm thick EPS subbase. Investigation conducted

revealed the EPS blocks had shifted at their joints. Movements between blocks in the vertical (up to 5 mm) and

horizontal (resulting in gaps as much as 20 mm wide ) were found. Movements resulting in failure occurred due

to lack of full contact and interaction between blocks.

A case of unexpected block flotation was reported in Thailand (Hovarth 1999). In Thailand, during the service life

of the project, occurrence of flood caused EPS geofoam used as a fill in pavement structure to float. This damaged the

overlying pavement structures requiring reconstruction.

Cost Analysis Comparison of cost between earth fills and geofoams requires a complete review of the conditions and geometry.

Beyond the easily determined direct costs, less tangible costs (improved life cycle costs to pavement, reduced

construction time, elimination of utility relocation) must also be included in the evaluation. Again other factors such

as availability locally and knowledge in its application may influence the total costing. An attempt is made by Lin et

al (2010) to compare labor and material prices for soil and EPS geofoam. Figure 7-8 adopted after Lin et al (2010)

illustrates the design for 800m long roadway expansion project in Taipei.

Figure 7: Traditional design

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Figure 8: EPS design

In the traditional design, earthen material is required to fill the expansion volume as shown in figure 7. Likewise, EPS

is used as an alternative fill material in figure 8. Table 8-9 compares the cost benefits of using tradition method or

EPS in 800m long roadway expansion project in Taipei.

Table 7: Cost analysis of traditional soil filling.

Item Unit

price

NT$

Retaining wall (Type A, average

H =3.1 m)

Retaining wall (Type B, average

H =3.6 m)

Quantity Price NT$ Quantity Price

NT$ Excavation 111 9.68 m3 1,074 13.84 m3 1,536

Backfill 672 6.08 m3 4,086 8.8 m3 5,914

Permeable material

backfill

500 0.34 m3 170 0.4 m3 200

Rebar f y ≥ 2,800 9,955 0.16 t 1,593 0.14 t 1,394

Foundation

formwork

372 0.8 m2 298 1.18 m2 439

Structure formwork 372 6.21 m2 2,310 7.18 m2 2,671

Concrete 80 kg / cm2 1,520 0.27 m3 410 0.41 m3 623

Concrete 240 kg /

cm2

1,770 2.33 m3 4,124 3.98 m3 7,045

Rail pile, length = 6

m

2,585 1 m width 2,585 —

Energy dissipation

block

256 1-m width 256 1-m width 256

Type B guardrail 1,502 1-m width 1,502 1-m width 1,502

Rebar f y ≥ 4,200 9,998 — 0.13 t 1,300

H-beam, length = 8 m 11,500 — 1-m width 11,500

Backhoe 6,000 0.4 day 2,400 0.4 day 2,400

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Crane 10,000 0.3 day 3,000 0.3 day 3,000

Manpower 2,000 2 manpower-

day

4,000 1.8 manpower-

day

3,600

Total price/m

28,438 NT$/m 43,380 NT$/m

Table 8: Cost analysis of filling with EPS geofoam.

Item Quantity Unit

Unit price NT$

Price NT$

EPS backfill 2 m3 2,200 4,400

H-beam 1 m 11,500 11,500

RC slab 1.5 m2 1,000 1,500

RC foundation 0.5 m3 2,000 1,000

Gravel permeable material 0.5 m3 500 250

Drainpipe 1 m 50 50

Energy dissipation block 1 m 256 256

Type B guardrail 1 m 1,502 1,502

Concrete 240 kg / cm2 1.3 m3 1,770 2,301

Backhoe 0.1 day 6,000 600

Crane 0.05 day 10,000 500

Manpower 0.6 manpower-day 2,000 1,200

Total price/m 25,059 NT$/m

From the analysis, it was observed that the cost for using soil as fill material were higher for both type A & type B.

This was estimated to cost NT$ 28,438/m (US$960.9) and NT$43380 (US$1465.8) respectively. However, the use of

EPS for construction reduced the cost to NT$25,059 (US$846.7).

Conclusion The use of geofoam technology provides varying applications in embankment fill, retaining wall backfill, bridge

abutment, compensating foundation, slope stabilization. The technology is limited because the material cost only is

typically more expensive than soil on a cost-per-unit-volume basis. However, in comparing the overall cost of the

project, for example reduced field installation and construction cost, accelerated construction, minimum field quality

control testing and no relocation of utilities: geofoam is a cost effective alternative and recommended as lightweight

fills over soft ground and protecting underground structures. It is therefore proposed that cheaper and faster ways

Vertical EPS Geofoam embankment fill Bridge pier extending through EPS geofoam fill

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could be employed in difficult construction sites in Ghana with the application and use of Geofoam technology.

Furthermore, it could be employed for reinstating excavations across roads where services are buried to reduce the

possibility of settlement as seen around on our roads.

Protecting buried pipes in transportation infrastructure using EPS Geofoam

Stockpiled EPS Geofoam on site using Backhoe Installing geomembrane over EPS Block on the

Roaring River Slough project, USA.

Figure 9: Some applications of EPS geofoam in construction

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Carousel MALL, Syracuse NY Norway 1987, Extreme flood event

Figure 10: Cases of EPS failures

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Contact details

Name of Principal Author: Priscilla Ackah

Address: Associated Consultants, Box M259, Accra

Tel: +(233)-302-237-528 Fax: +(233)-302-237-500

Email: prisack2a@yahoo.com

Name of Second Author: Kwabena Bempong

Address: Associated Consultants, Box M259, Accra

Tel: +(233)-302-237-528 Fax: +(233)-302-237-500

Email: kgbem69@gmail.com