What geomembrane properties are most important to protect EPS Geofoam?
Part 1: Geomembranes as a component of EPS Geofoam applications
In late 2019, we published a blog defining the concept of geomembranes for protection of Expanded Polystyrene (EPS) Geofoam for transportation applications. Geofoam is widely gaining acceptance as a lightweight fill material used as an alternative to compacted earthen fill to improve subsurface stability and/or to counteract factors that make the fill more difficult or expensive to place, such as when:
- It is adjacent to structures when compaction from vibration is undesirable.
- It is in tight workspaces, such as adjacent to angular surface.
- It is in difficult to place areas, such bridge abutments.
- Subsurface conditions require extensive improvement to carry load from compacted overburden.
- Absorption of active earth pressure is needed when used against a wall.
- It is cost prohibitive to acquire select backfill materials.
In recent years, most Geofoam applications have been in the transportation industry. Inherent in transportation are hydrocarbon fuels that can be spilled or leaked. Additionally, more than 90% of the roads in the U.S are paved with petroleum-based asphalt. Geofoam is a hydrocarbon and is miscible with other hydrocarbons. In other words, Geofoam dissolves in contact with many hydrocarbons, losing its ability to function as a lightweight fill.
In transportation, Geofoam is used in conjunction with the high-strength, gasoline-resistant, 9832 XR-5 Geomembrane, which protects it from hydrocarbons.
Geomembrane performance requirements for protecting Geofoam
The normal layout is to place the Geofoam on a geomembrane. When the Geofoam installation is complete, the geomembrane is configured to completely encapsulate the Geofoam. Any hydrocarbons or water is shed off the geomembrane.
The geomembrane is expected to perform in active construction sites and provide durability, including:
- Puncture resistance from placement and from long-term use.
- Abrasion resistance to withstand installation activity.
- Resistance to spilled hydrocarbons, including most fuels such as gasoline, diesel, etc.
- Resistance to water and acidic/basic soils and aggregates.
- Tensile strength of sheet and seams to withstand placement and shear loading from adjacent backfill.
XR-5 Geomembrane Installation over Geofoam, Interstate I5.
Caltrans, California, USA
Source: Seaman Corporation
To create a specification, a more in-depth review of the requirements of a geomembrane used to protect Geofoam from damage due to contact with hydrocarbons is needed. Here are the features of the application and the performance demands on the geomembrane.
- The geomembrane will encompass the Geofoam blocks, requiring it to bend at 90-degree angles and conform to the shape of the blocks. Property needed: Flexibility
- Field seams need to be eliminated or minimized. Property needed: Flexibility
- Geofoam blocks are laid initially on top of the geomembrane at the base, and then completely enclose the Geofoam. The geomembrane will be against the subgrade and the overburden. Property needed: Puncture resistance, both dynamic and long-term static.
- The geomembrane is deployed on a construction site and must have robust mechanical properties. Property needed: Puncture resistance, abrasion resistance and yield tensile (sheet and seams).
- Upon backfilling, the geomembrane will encounter shear forces from the backfill, creating tensile loading. Property needed: Yield tensile.
- Any hydrocarbon vapors in the context of contaminated soils prior to cleanup and residue compounds will likely be present. Property needed: Long-term resistance to vapor intrusion form hydrocarbon contaminated soils
- Similarly, hydrocarbon spills in the context of contaminated soils prior to cleanup and residue compounds will likely be present. Property needed: Long-term chemical resistance to hydrocarbon contaminated soils
- The final closure of the Geofoam encapsulation is normally a field seam along the top of the geofoam structure. This loads the closing seam in shear, which results from the vertical backfill, creating frictional tensile, as discussed on the sheet in No. 5 above. Property needed: Seam strength = sheet strength.
The second part of this series, geomembrane material specifications for Geofoam applications will be presented to address all the requirements.