Design Considerations
The design is established to provide a lightweight embankment that will carry the required highway load without overloading the subsoil and so cause settlement of the pavement structure above. A design can be established over a wide range of GeoSpec lightweight fill types providing compressive resistance which varies based upon expected compressive load. Design considerations that will also influence the GeoSpec lightweight fill material type used include the use of a concrete slab over the lightweight fill to distribute loads, the depth of gravel above the lightweight fill, pavement design and the expected traffic load over the road. At the same time the total load of the embankment fill must be kept below the level of load on the soft subgrade that would produce unacceptable settlement.
There are now numerous technical papers published to provide design assistance for the use of EPS geofoam in road construction. For example, in 2004 the National Cooperative Highway Research Program published NCHRP Report 529. This document provides design guidelines for EPS geofoam used in highway road embankment applications.
Several publications from ASTM International provide additional information on basic considerations for the use of expanded polystyrene (EPS) geofoam in geotechnical projects and guidance on quality assurance for EPS Geofoam blocks.
Construction Principles
Where blocks are placed on sloping terrain or where high fills are used, consideration should be given to anchoring the GeoSpec fill blocks. The table below provides some examples of published values for coefficient of interface friction between EPS geofoam and other materials.
| Interface |
Peak Factor |
Residual Factor |
| Foam-Foam, 20kg/m3 (dry) |
0.85 |
0.70 |
| Foam-Foam, 30kg/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.
Where possible, road embankment designs should provide positive drainage to the bottom of the embankment. Where there is a possibility of trapped water on one side of the embankment drainage must be provided through the embankment.
Typically, the embankment is sloped outward to the bottom as illustrated. Where drainage may not be adequate, consideration must be given to the buoyancy force lifting the unrestrained corner of the embankment. When buoyancy force is calculated use the actual density of the block – e.g. 22 kg/m3 (1.35 pcf).
Building an embankment with vertical sides is one way to minimize any buoyancy design problems. The greatest problem of flooding and buoyancy may be during the construction phase when drainage facilities are not complete and when the pavement has not been installed to ballast the GeoSpec lightweight fill material.
The side slope of a polystyrene embankment till should not be steeper than 2:1. The blocks are usually cut with vertical sides and the soil cover establishes the slope. It is 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.
For additional information on EPS geofoam construction principles see Plasti-Fab Product Information Bulletin No. 1002.
