Geofoam Use in Road and Bridge Approach works

 

What is Geofoam ?

¡  Geofoam is expanded polystyrene (EPS) or extruded polystyrene (XPS) manufactured into large lightweight blocks.

¡  The primary function of geofoam is to provide a lightweight void fill below a highway, bridge approach, embankment or parking lot.

¡  EPS Geofoam minimizes settlement on underground utilities.

¡  EPS Geofoam is used widely as compared to XPS Geofoam.

¡  Since the manufacturing of XPS causes emissions of CFCs and HFCs harmful to the nature.

Geofoam Blocks

¡  The blocks vary in size but are often 2 m x 0.75 m x 0.75 m.

APPLICATIONS

 

¡  SLOPE STABILIZATION:

                To reduce the tendency of failure of portion of the soil, the crest of the slope is excavated and replaced by the super lightweight material EPS geofoam.

¡  Alternative solutions:

•       Changing of the slope inclination,

•       Buttressing the toe of the embankment using soil nailing

•       Any other solution that may affect the geometry of the slope or the surrounding land or may not be feasible for many reasons.

¡  REDUCING LATERAL PRESSURE ON RETAINING STRUCTURES

•       To reduce:

ü  static earth pressure acting behind an abutment during and after construction of the backfill

ü  the dynamic earth pressure due to earth-quakes and traffic loads after the construction

•       Finite element analysis, showed 85% reduction in the overall bending moment when utilizing 12kg/m3 EPS geofoam.

•       The 20kg/m3 geofoam showed 70% reduction compared with the case of no geofoam.

COMPRESSIBLE INCLUSION AGAINST EXPANSIVE SOIL

¡  Expansive soils or swelling soils are those soils that have the tendency to increase in volume when water is available and to decrease in volume if water is removed.

¡  Upon soil heave EPS geofoam compresses according to its own stress strain relation.

¡  The geofoam will also act as a form for the slab.

¡  EMBANKMENT FILL TO REDUCE SETTLEMENT

•       Figure shows a situation of constructing a new embankment on soft ground.

•       Large settlement can be experienced under the load of the conventional embankment fill.

Existing utility line: damaged if not designed for large deflections.

 ¡  WIDENING EMBANKMENTS

•       The self-standing property will reduce the additional space without the need of a retaining wall.

¡  STRESS REDUCTION IN BURIED PIPES

•       The compressible inclusion of EPS geofoam may be utilized to reduce loading above rigid conduits.

•       Thin layers of EPS geofoam are placed some 0.5m above the rigid conduit. 

¡  PAVEMENT AND RAILWAY INSULATION

•       The cycle of winter freezing and spring thawing of soil can affect transportation facilities such as roads and railroads.

•       This is because the ground surface heaves as a result of freezing and settles upon thawing. 

Geofoam for roadway
embankments as an alternative to ground improvement

¡  Maintenance is not required.

¡  All weather resistant.

¡  The overall time for construction is typically much shorter and less.

¡  Saving cost of heavy equipments.

¡  In consideration of these benefits, the typically higher unit cost of geofoam is usually more than offset by savings when overall project costs are considered.

ADVANTAGES OF GEOFOAM

¡  Super lightweight material

¡  Most versatile lightweight materials available.

¡  Low density/ high strength: Geofoam is 1% to 2 % the density of soil with equal strength.

¡  Predictable behavior: Geofoam allows engineers to be much more specific in the design criteria. This is very different than other lightweight fillers, such as soil, that can be very variable in composition.

¡  Inert: Geofoam will not breakdown, so it will not spread into surrounding soils,  no leachates.

¡  Reused: Geofoam can also be dug up and  reused.

¡  Limited labor required for construction: Geofoam can be installed by hand using simple hand tools. This eliminates the investment and operating cost of heavy machinery.

¡  Cuts down on construction time: Geofoam is quick to install and can be installed during any type of weather, day or night, resulting in faster installation time. It can arrive at the job site prefabricated and ready to place and is easily inventoried and handled.

¡  Installation is not delayed by weather.

¡  It maximizes onsite installation efficiency.

¡  Insect and Mold Resistant

¡  Proven Performance

¡  Maintenance Free

¡  Contains no CFC, HCFC, or HFC. Thus environment friendly.

DISADVANTAGES OF GEOFOAM

¡  Fire hazards: Untreated Geofoam is a fire hazard.

¡  Vulnerable to petroleum solvents: If Geofoam comes in contact with a petroleum solvent, it will immediately turn into a glue-type substance, making it unable to support any load.

¡  Buoyancy: Forces developed because of buoyancy can result in a dangerous uplift force.

¡  Susceptible to insect damage: Geofoam should be treated to resist insect infestation. If it is not, insects such as ants can burrow into the Geofoam, weakening the material.

Present Scenario and Scope

¡  Has been used around the world as a fill for more than 30 years.

¡  In India, some industries manufacturing geotextiles also manufacture geofoam blocks.

¡  However use of geofoam is not seen on a large scale in India.

¡  Scope: Soft soils in India are found near marine and river delta deposits.

 

Properties

•       Density

•       Compression

•       Tension

•       Creep

•       Flexural

•       Thermal Resistance

•       Flammability        

•       Water Absorption        

•       Resistance to Attacks

•       Durability

•       Inertness Properties        

•       Energy Absorption        

•       Acoustical properties        

•       Environmental Effect

Density

¡  Can be considered to be the main index of its properties

¡  Cost of manufacture is considered proportional to density

¡  For practical civil applications it ranges between 11 and 30 kg/m3

Compression

Tension

¡  Tensile strength of EPS material can be an indication of the quality of fusion of the prepuffs and any recycled EPS geofoam used in the process.

¡  It increases with density widely used as a quality control test in EPS geo-foam manufacturing plants

Flexure

¡  Widely used as a quality control test in EPS geo-foam manufacturing plants.

¡  The maximum stress is calculated assuming the material is linear elastic up to failure.

¡  The material fails in tension as a crack on the tension side appears at the moment of failure.

Creep

¡  Susceptible to time dependent creep deformation when a constant stress level is applied

¡  Dependent on

§  Density -- the creep decreases as density increases

§  Stress -- lower the stress, lesser is the creep deformation

Thermal Resistance and Flammability

¡  Poor conductor of heat and therefore excellent for heat insulation

¡  Combustible

Water Absorption

¡  Low

¡  Depends on:

§  Density

§  Fusion

Resistance to Attacks

¡  Sensitive to attack by solvents

¡  Most acids and their water solutions do not attack polystyrene; however strong oxidizing acids do

¡  Does not attack ants, termites, etc but is not resistant to them

¡  Not susceptible to fungal attacks and bacterial growth

Environmental Effect

¡  EPS geofoam is made of polystyrene beads and polystyrene is not biodegradable and chemically inert in both soil and water

¡  Does not contaminate the ground and ground water

¡  Recyclable material

¡  Does not use CFCs or HCFCs in its manufacture like other polymeric foam

¡  Good energy absorber,

¡  Inert and does not attack metals in contact with it,

¡  Reduces transmission of airborne sound

Design and Construction Considerations

¡  Buoyancy  

¡  Concentrated Loads        

¡  Chemical Attack        

¡  Flammability        

¡  Insect Infestation        

¡  Moisture Absorption        

¡  Gaps Between Blocks        

¡  Immediate Deformation

¡  Connections with Structural and Architectural Elements        

¡  Sliding        

¡  Blocks Alignment        

¡  Transition Zones 

Lightweight Material	Unit Volume Weight (tf/m3)*	Description
EPS Blocks	0.01 ~ 0.03	Ultra lightweight, expandable synthetic resins
Expanded Beads Mixed Lightweight Soil	0.7 approx. or more	Variable density; similar compaction and deformation characteristics to soil; can use excess construction soil
Air Foamed Mortar and Air Foamed Lightweight Stabilized Soil	0.5 approx. or more	Density adjustable; flow able; self-hardening; and can use excess construction soil
Coal Ash, Granulated Slag, etc	1.0 ~ 1.5 ap-prox.	Granular material; self hardening
Volcanic Ash Soil	1.2 ~ 1.5	Natural material
Hollow Structures	1.0 approx.	Corrugated pipes, box culverts, etc.
Wood Chips	0.7~ 1.0	Usually to be used below ground water level; anti leaching measures needed
Shells	1.1 approx.	Sized 12 to 76 mm; interlocking effects
Tire Chips	0.7~ 0.9	Usually used above ground water level; cover soil layer at least 0.9m is required

METHODS OF CONSTRUCTION

¡  Done in reference with ASTM D7180

¡  SUBGRADE PREPARATION:

1.  Clear and grub site.

2. Excavate existing soil if required.

3. At design engineer’s discretion, place geotextile over graded surface, i.e. soft soils, etc.

4. Dewater site as required.

5. Place a sand pad/leveling course over the prepared surface of 50 mm thickness minimum. Sand pad surfaces should be above ground water level at time of  EPS Geofoam placement.

¡  PLACEMENT:

1. Verify identification marks on face of the product. Field sampling and testing of the Foam-Control EPS Geofoam will be as specified by the Engineer. Properties of density and compressive resistance shall be verified in accordance with the specification.

2. Material is placed as required by the engineer and as shown on the drawings.

3. Blocks of Foam-Control EPS Geofoam should be placed tightly on the prepared sand pad/leveling course. For multiple layers of Foam-Control EPS Geofoam, successive layers of blocks are oriented at 90 degrees to previous layer.

4.  Geofoam must receive temporary ballast during all phases of construction to prevent displacement by wind or high water conditions.

5.  In order to facilitate construction during precipitation or when frost or icing is encountered, horizontal restraint (Geogripper) between layers of EPS Geofoam may be desired.

6.  Commence with the placement of permanent overlying materials as quickly as practical.

¡  Geogripper: Plates used to restrain EPS Geofoam from moving laterally in layer over layer applications. The plate shall be made of galvanized or stainless steel with two-sided multi-barbed design capable of piercing geofoam. Each plate shall be capable of a lateral holding strength of 60 lbs (approx 27 kgs)