There are numerous design considerations for EPS geofoam applications. These considerations include engineering properties and construction factors. This section presents some of the advantages and unique features of building with EPS geofoam, as well as precautions that must be followed.
EPS geofoam is manufactured in various unit weights that typically range from about 0.7 to 2.85 pounds per cubic foot (11.2 to 45.7 kilograms per cubic meter). As a result, they impart small dead load or stress to underlying soils, structures and utilities. This is especially advantageous where the existing soils are poorly suited to support additional loading (e.g., compressible clay, peats, etc.). In fact, existing loads can be significantly reduced by excavating and replacing native soils, which commonly weigh about 100 pounds per cubic foot (1,602 kilograms per cubic meter), with EPS geofoam. This can eliminate the need for specialized foundations or site preloading to reduce settlement and improve bearing capacity. The use of EPS geofoam over existing utilities can eliminate the need for utility relocation.
The use of EPS geofoam behind earth retaining structures, such as bridge abutments, can reduce lateral stresses.
EPS geofoam is available in a range of compressive resistances. A project designer can choose the specific type of EPS required to support the design loading while minimizing cost. Several different types of EPS geofoam can be specified on a single project to maximize savings. For example, higher strength EPS geofoam can be used in high applied stress areas while lower strength blocks are used in areas where the applied stresses are lower.
EPS geofoam design loads are recommended to not exceed the compressive resistance at 1% capacity. This limit controls the amount of long-term deflection, or creep, resulting from permanent ustained loads.
Note: Adequate soil cover, or a load distribution slab, may be needed to distribute heavy concentrated loads.
No special equipment is required when building with EPS geofoam. Blocks can often be carried and set in place by laborers or easily handled with mechanized equipment. This is an important consideration when the construction site is congested or does not have the clearances required for traditional placement or compaction equipment. EPS geofoam can be field cut using a hot-wire cutter, hand saw or chain saw. The EPS geofoam can be trimmed on site to accommodate the shapes of existing underground utilities and services.
EPS geofoam helps projects maintain extremely tight construction schedules. The ease and speed with which EPS geofoam can be constructed results in shorter construction time because of faster placement rates, reduced utility relocation and less disruption of traffic in urban areas. Additionally, adverse weather conditions typically do not affect placement rates of EPS geofoam.
In addition to other project costs, using EPS geofoam reduces the loading on adjacent supporting structures. Adjacent structures can be designed to be less robust and therefore less expensive. This is particularly important for underground utilities. Typically the higher cost of some types of lightweight fill materials is usually offset by savings when all of the project costs are considered, such as lower installation costs and lower maintenance. Available in a range of compressive resistances, EPS geofoam allows for economical project design.
EPS geofoam is considered a permanent material when correctly specified and installed.
EPS is an efficient thermal insulator. EPS has been used for many years as insulation for various building applications. Although some applications may not directly utilize the insulation value of EPS geofoam, this aspect should be considered in all designs.
EPS geofoam can be damaged when exposed to certain hydrocarbon chemical and may need protection. There are a number of hydrocarbon resistant geomembranes that are suitable for protection of EPS geofoam. Make sure that the geomembranes used are compatible with EPS. For example, polypropylene, polyethylene, chlorosulphonated polythylene (CSPE) and Ethylene Interpolymer Alloys (EIAs) are compatible geomembranes. If using EPS geofoam in a location with contaminated soils, laboratory testing should be performed to determine the nature of the contaminants and their possible effects.
Like many construction materials, EPS is combustible. EPS geofoam is manufactured with a flame retardant in North America. Appropriate precautions should be implemented at project sites if open flame procedures, such as welding, will be performed. In geotechnical finished applications EPS geofoam is protected from exposure by soil, concrete or other cover materials. When used within buildings, gypsum board or concrete should be used for protection. • EPS is combustible. • A flame retardant is part of EPS geofoam. This retardant inhibits the early stages of fire development.
EPS is susceptible to ultra violet degradation if exposed to sunlight for long periods of time. Degradation caused by prolonged exposure to sunlight is generally surficial (yellow colored dust) and does not cause detrimental property changes of practical importance. This discoloring can be removed by power washing or a grinder, if desired.
Wind speeds should be monitored during construction to determine if overburden weight restraints such as sandbags should be placed on top of the EPS geofoam to prevent the blocks from shifting.
Because of its closed-cell structure and light weight, EPS geofoam is buoyant. Care must be taken during design, construction and post-construction to ensure that the potential flotation forces are accounted for within the hydrological conditions of the site. Adequate surcharge, i.e., soil or pavement cover, or an alternate means of passive restraint must be provided against uplift. Alternately, the material can be installed above the water table or the water table can be lowered using suitable drains or other dewatering systems.
Drainage (generally a sand or gravel layer) can be provided between the EPS geofoam fill and the natural soils to reduce potential uplift forces. Providing for adequate drainage of groundwater and/or surficial waters below the EPS geofoam prevents water from infiltration and reduces the development of uplift forces.
EPS has a closed-cell structure that limit water absorption. When used in well-drained conditions, no change in EPS geofoam weight is expected over time. A slight increase in the weight of EPS geofoam can be expected over time due to water absorption if installed in a submerged application.
EPS geofoam can be reground, recycled and reused in many composite applications such as lightweight concrete, plastic lumber, weather resistant outdoor decks, fencing, drain field aggregate, etc.
Compared with traditional fill materials, fewer trucks with lighter loads are required to deliver EPS geofoam to a project site. This means less pollution from fuel emissions and less wear and tear on the nation’s roadways and infrastructure.
Traditional soil fills are constructed in thin lifts with repeated compaction. This requires considerable time, construction equipment, fuel to operate the equipment and testing to ensure adequate compaction. For soft soil conditions, significant waiting time is required after fill placement while the underlying foundation soil consolidates and settles. In contrast, EPS geofoam can be quickly placed with no need for compaction or waiting for consolidation to occur. Because each block is equivalent to the height of several soil lifts, construction proceeds more rapidly. In addition, EPS geofoam is unaffected by the normal range of climate and moisture conditions construction can proceed without regard to weather. Traditional soil fills have to be constructed and compacted within relatively narrow soil moisture conditions to achieve the desired dry unit weight. In addition, because gravity loads and the lateral forces that develop under static and seismic loads are proportional to backfill material density, i.e., the greater the backfill density, the greater these loads. The use of lightweight EPS geofoam significantly reduces these loads.