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GeoSpec® Lightweight Fill
Ground fill applications where lightweight fill is required

GeoSpec® Lightweight Fill

GeoSpec® lightweight fill material is expanded polystyrene (EPS) geofoam
used in ground fill applications where a lightweight fill material is required
to reduce stresses on underlying or adjoining soils/structures.   EPS
geofoam has been used in projects involving roads, bridge approach fills,
embankments, levees, berms, foundations, landscaping, etc., worldwide
for over 50 years.

GeoSpec fill material can be designed to support high compressive loads,
but has a density less than 1% of traditional earth materials.  It can be
designed to meet a wide range of geotechnical engineering specifications
with a typical density range of 11 kg/m3 (0.7 pcf) to 40 kg/m3 (2.5 pcf)
providing a range of compressive resistance properties. The table
below provides GeoSpec fill material type designations and
material properties as per ASTM D6817, Standard Specification for
Rigid Cellular Polystyrene Geofoam

Material Property Test Method Units D6817 GeoSpec Type Designations1
Product Density,
Compressive Resistance2
Minimum @ 1% strain
Compressive Modulus
Flexural Strength
Limiting Oxygen Index
% 24 24 24 24 24 24
Additional Compressive Resistance Properties3
Compressive Resistance
Minimum @ 5% Deformation
Compressive Resistance
Minimum @ 10% Deformation

1. The material properties for GeoSpec lightweight fill material are third party certified by Intertek.
2. Compressive resistance at 1% strain is within the elastic limit for the GeoSpec types in the above table and is accepted as the design compressive resistance to limit long-term deformation under structural load.
3. Compressive resistance at 5% and 10% strain in the above table are provided for applications where the intended end-use requires long-term deformation under structural load - i.e., a compressible product.

The required GeoSpec fill material type should be specified based upon the required compressive
resistance for a specific project.  GeoSpec fill material offers the following benefits to maximize
onsite installation efficiency:

GeoSpec Construction Principles
The following information identifies key issues in each step in the construction process that will need to
be addressed in order to ensure a quality GeoSpec fill material installation.  The steps that will be
addressed are as follows:

Site Preparation:
Ideally, the bottom of the first layer of GeoSpec fill material block should be placed above the mean height
of the water table, where possible. Any water at or near the ground surface must be pumped off until the
GeoSpec fill material block is covered by material whose weight is sufficient to prevent flotation.

The bottom layer of GeoSpec fill material block must be supported over its entire lower face, so a plane
surface, inclined as appropriate, must be prepared. Departures from planarity may not exceed ± 10 mm in
3 meters (3/8” in 10 feet). The levelling material used is generally sand; its thickness depends on the
ground and the machines to be employed. Once GeoSpec fill material blocks are in place, they should be
covered as soon as possible. Suitable drainage measures must be taken. On sloping sites this is particularly
important. If there is any possibility of flooding, buoyancy effects must be considered.

For buoyancy calculations, GeoSpec fill material density may be taken as no more than the dry unit weight of
the product - e.g. 22 kg/m3 (1.38 pcf), but for load calculations the density of material with moisture content
must be assumed. Using the appropriate calculation methods, the designer must confirm that the road system
– including earthworks and the supported structures – is stable with respect to shear due to differential
settlement, slip, and flotation.

Conditions while the system is under construction must also be taken into account and the designer must
assume the most unfavourable conditions. Any water at or near the ground surface must be pumped off until
the GeoSpec fill material block is covered by material whose weight is sufficient to prevent flotation. Once
GeoSpec fill material blocks are in place, they should be covered as soon as possible. Suitable drainage
measures must also be taken during construction. On sloping sites this is particularly important.

Block Shipment, Handling and On-Site Storage

The types of trucks used to deliver to site (e.g. closed or flat bed trailers), the loading of the trailers and
the sequencing of delivery must be coordinated with Plasti-Fab well in advance of delivery. Typically,
GeoSpec fill material is delivered in trailer load quantity in standard closed trailers. The blocks are not normally
packaged – i.e. plastic wrap not required – unless on-site storage for a period of time is anticipated.

Damage can occur during shipment and handling on site.  Damage which occurs during delivery should be
identified to Plasti-Fab personnel immediately.

At all stages of construction, GeoSpec fill material should be handled in such a manner so as to minimize
possible damage to blocks. GeoSpec fill material is easily positioned at the work site. Lifting or transporting
blocks in any manner that creates dents, holes or broken edges should be avoided.

If GeoSpec fill material blocks are to be stockpiled on site until placement, a secure storage area should be
designated for this purpose. No traffic on the geofoam blocks should be permitted, especially vehicles
or on-site equipment. The blocks should be stored away from any heat source or construction activity
produces heat or open flame. GeoSpec fill material blocks stored on site should be secured with sand
bags or similar “soft” weights to prevent their being dislodged by wind.

GeoSpec fill material contains a flame-retardant additive. However, it may ignite when exposed to
open flame or welding activities that are not part of the construction activities. Therefore, until the GeoSpec
fill material block has been completely covered by the pavement system – i.e. non-combustible aggregate
cover material – smoking and the use of any tools that may create an open flame in the proximity
of GeoSpec fill material should be forbidden.

Block Layout and Placement
The block layout shall be designed so that the following general design details are taken into account:

Limited study of interface friction between geofoam to geofoam as well as geofoam to other commonly
used construction materials indicates that anchorage between geofoam blocks may be redundant due
to geofoam interface friction angles and vertical loads on blocks from the completed structure above. The
table below provides some examples of published values.

Interface Peak Factor Residual Factor
Foam-Foam, 20 kg/m3 (dry) 0.85 0.70
Foam-Foam, 30 kg/m3 (dry) 0.85 0.65
Foam-Cast in Place Concrete 2.36 1.00
Foam-Textured HDPE Membrane 1.00 ~1.00
Foam-Smooth HDPE Membrane 0.29 0.23
Foam-Smooth PVC Membrane 0.70 0.40

If the calculated resistance forces along the normally horizontal surfaces between layers of GeoSpec fill
material blocks are insufficient to resist horizontal driving or imposed forces, additional resistance between
blocks is required to supplement the interface friction. When needed, Plasti-Fab recommends the use
of barbed gripper plates at the rate of two fasteners per geofoam block in order to prevent movement
during the construction process.

Pavement Construction
In general, pavement construction can occur in a normal manner with only a few cautions related to the
use of GeoSpec fill material. The most critical step in the process is the placement and compaction of the first
layer of soil above the GeoSpec fill material.

As a rule, the subgrade of the road distributes the load on and protects GeoSpec fill material block, while
its surface constitutes the road formation. During construction, loads imposed by traffic may not
exceed limits set according to the thickness of material over the GeoSpec fill material block. Vehicles and
construction equipment, such as earth moving equipment, must not be operated directly on the surface of

It is also suggested that vibratory compaction equipment not be used within 508 mm (20 inches) vertically
from the top surface of blocks. It has been found that plate vibratory has been the most suitable for
compaction of unbound material in the pavement system.

Alternatively, loads can be spread though a 127 to 152 mm (5 to 6 inch) thick reinforced concrete slab formed
in situ on the top surface of the GeoSpec geofoam. However, compacted layers of gravel materials may
be used instead to provide required load distribution. But in any case, traffic in direct contact with the
GeoSpec lightweight fill material block is not permissible and loads imposed must not exceed design
compressive load characteristics of the GeoSpec fill material.

For additional technical information applicable to construction using GeoSpec fill material, contact your
Plasti-Fab Technical Sales Representative.