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Frequently Asked Questions
This is a compilation of the most frequently asked questions relating to GeoTech's products. If there is a question you have which is not addressed here, or if you would like more detail or reference information, do not hesitate to contact us at email@example.com.TerraLite Synthetic Lightweight Fill: TerraFlex® Synthetic Compressible Inclusion: GeoTech Insulated Drainage Panel: GeoTech Geoinclusion®: GeoTech Systems Corporation:
Responses to FAQs prepared by D. D. Van Wagoner, Vice President of Engineering
TerraLite Synthetic Lightweight Fill (Geofoam):
The most commonly used TerraLite in road construction is Type VIII, which is 1.25lb/ft^3 (20kg/m^3). This density costs from $40 - $45 a cubic yard ($50-58 a cubic meter) FOB Plant, depending on the raw material cost and quantity ordered. While this is certainly not "cheap as dirt," it turns out that it IS often cheaper than installing a field of wick drains, instrumentation, and the "cost" of waiting for months for the surcharging to take effect.
For example, the FHWA conducted a study of the costs associated with Geofoam fills, and found that they cost, on average, about $65 a cubic yard, installed. When surcharging, a typical 2 lane 20' high road embankment would cost from $400 to $750 per foot of road (and take many months). If Geofoam is used in the embankment (using 10.6 cubic yards/foot) to eliminate the need for surcharging, the installed cost of the geofoam would be range from $580 to $700 a foot, which is competitive with surcharging costs, AND the road is finished in mere WEEKS instead of MONTHS.
Yes, TerraLite Geofoam will immediately dissolve into a glue like substance when exposed to petroleum solvents. Geotechnical and Highway engineers have known this from the very first time Geofoam was used for a as a light weight fill, so they design against this possibility. In fact, in all the geofoam highway projects world wide, since the first use of this technology back in 1972, there has NEVER been a SINGLE failure caused by hydrocarbons attacking the integrity of the fill.
When designing a TerraLite fill, the engineer will typically specify welded geomembrane over the TerraLite to serve as a barrier to prevent this type of contamination. Concrete Load Distribution Slabs have also been used alone, in lieu of geomembranes, as solvent barriers.
Even though this type of incident has never happened, you would be in better shape with an EPS fill instead of a surcharged soil mass. Think the problem through: If there was an accident which saturated the soil with petroleum, it is likely that the road will be put out of commission regardless of construction technique in order to allow the contaminated soil to be removed to prevent it's contamination of the aquifer. If that road was built on TerraLite, and the TerraLite is melted, there will be LESS contaminated material to remove, and the road will be back in service MUCH FASTER after the TerraLite is replaced with new blocks.
Buoyancy, like hydrocarbon sensitivity, is something an engineer needs to factor into his design. There is more than one way to skin this cat. See the paper on Buoyancy elsewhere on this site.
Only if it is not treated to resist insect infestation.
It is well documented that there are certain species of ants which will nest within Geofoam. The material provides them no nutritional value, but is a soft, well insulated place which they prefer as a nesting site. Fortunately, there is a borax mineral compound which, when added to the TerraLite during the manufacturing process, makes the TerraLite impervious to this attack. Not all Geofoam suppliers have access to this technology, and it must be specified or the geofoam will be susceptible to this type of damage.
This can be of particular concern when the Geofoam fill is close to a wall or near the surface of the earth. If there are exposed faces of geofoam (behind precast concrete walls), it is also strongly suggested that TerraLite be specified.
Any contractor can install a TerraLite Fill. No special expertise, training, or equipment is needed. It can be done in ANY weather, day or night. Basically, all you do is "stack the blocks" in accordance with the engineers plans, which will show a means to build a fill without any continuous seams (alternating block orientation between layers and staggering blocks).
See sections 5 and 6 of the generic TerraLite specification for a detailed step by step discussion of subgrade preparation and block placement.
Nothing. Nothing. Nothing. Nothing. TerraLite does not decompose, nor do its physical properties undergo any change other than a possible change in density due to some water absorption. There have been numerous instances where Geofoam fills have been excavated after burial for over 10 years, and there has never been any evidence of the material decomposing, softening, or contaminating the surrounding soil. TerraLite is a non-biodegradable plastic.
TerraFlex™ Synthetic Compressible Inclusion:
TerraFlex™ is NOT the same thing as TerraLite, although it is MADE from TerraLite. There are critical differences in the material properties of TerraFlex™ and TerraLite that qualifies TerraFlex™ as an entirely different material and appropriate for applications where TerraLite would be wholly unsuitable.
TerraFlex™ is a synthetic compressible inclusion, that has been made especially elastic. Ordinary TerraLite has an elastic strain limit of only 1 percent. This means that if you compress it only one percent of it's starting height, it will undergo plastic (permanent) deformation. TerraFlex™ has an elastic strain limit of between 15 and 20 percent- it was developed specifically to be a soft, compressible material that will withstand many compressive cycles without permanent deformation.
The initial Young's Modulus of TerraFlex™ is less than 1/4th that of even the lightest (lowest density) TerraLite available. This means that it is 4x softer than the softest TerraLite. If you think you can use a low density TerraLite instead of TerraFlex, you are in for a bad surprise!
TerraFlex™ is elasticized through a mechanical process that creates an anisotropic elasticization along a sensitive axis. In the micro mechanics domain, the cellular structure is changed from a spherical shape into an ellipsoid, which accounts for the increased flexibility.
It is used in applications that can benefit from a material that will undergo "controlled yielding." For example, an earthen retaining wall will experience lower lateral pressures due to the controlled yielding of a layer of TerraFlex™ placing the earth in it's active state, mobilizing it's internal strength.
Integral Bridge Abutments built with an elastic layer of TerraFlex™ have a compressible volume that can accommodate the motion of the abutment into the embankment as the bridge deck heats and cools with the seasons.
TerraFlex™ has unit cost about twice that of TerraLite; however, since it is over four times more compressible than TerraLite, it costs only half as much as TerraLite to use as a compressible inclusion. Since it is typically installed as sheets against a wall (or bridge abutment), the cost for installation (and required excavation) is significantly less than what is required when using TerraLite blocks in place of TerraFlex.
TerraFlex™ is made into sheets measuring 4 feet x 4 feet x Thickness (varying from 2" to 30"). These sheets are usually installed between the structure and the soil, with a putty like adhesive used to hold the sheets against the structure until backfilling takes place. In soil arching applications, the TerraFlex™ can be cut into more narrow strips and placed over the buried conduit or pipeline as the compressible inclusion (See the paper on Soil Arching for more details)
GeoTech Insulated Drainage Panel:
GeoTech Insulated Drainage Panel is a exactly what the name suggests. It is distinctly different from other sheet drain systems in that it offers functionality as an insulator and compressible inclusion not found in any other prefabricated sheet drain system.
It has been tested in accordance with ASTM 4716 and has been found to have transmissivity suitable for use in virtually ANY soil condition. Other sheet drains clearly offer greater capacity, but when estimating the amount of drainage actually required for various hydraulic conditions, GeoTech's Insulated Drainage Panel can give design margins of 3 or more.
The drainage capacity of our Insulated Drainage Panel is determined by the thickness of the panel as well as the stress normal to the panel. The panels are available in thicknesses varying from 2 inches (5.08 cm) to 24 inches (60.96cm). The transmissivity (unloaded) will vary from 10gpm/ft to well over 30 gpm/ft, depending on thickness specified.
It is compatible with virtually ANY geotextile, since the textile is well supported by the bead matrix. That enables a designer to optimize the design of the hydrostatic pressure relief system.
It is an insulator (R=3.5 dry), which means that below grade interior spaces will be more comfortable for less energy, and dryer since the dew point is moved outside. Exterior applications can benefit from the insulating characteristics since the soil behind a wall exposed to freezing temperatures will not freeze and will not experience the lateral loads developed by the formation of ice lenses.
It can act as a compressible inclusion, which can accommodate the forces generated by swelling soils without imparting damaging loads to the foundation walls.
No other sheet drain alone can offer these benefits.
The Geoinclusion® is a revolutionary product consisting of a drainage component laminated to a compressible inclusion that can serve in a wide range of applications.
It has been used behind integral bridge abutments to accommodate the motion associated with the expansion and contraction of the bridge deck and to relieve hydrostatic pressure.
It has been used against building foundations and behind retaining walls to reduce the lateral pressures by relieving hydrostatic pressure and by allowing the soil's internal strength to be mobilized as the compressible inclusion undergoes "controlled yielding."
Like TerraFlex™ and GeoTech's Insulated Drainage Panel, the Geoinclusion® is made into sheets measuring 4 feet x 4 feet x Thickness (varying from 4" to 30"). These sheets are usually installed between the structure and the soil, with a putty like adhesive used to hold the sheets against the structure until backfilling takes place. The Geoinclusion® is easily trimmed at the factory or in the field with a hot wire cutter or saw.
It is an easy, cost-effective solution to the problems associated with the periodic (seasonal and daily) cycling of the abutment into and out of the embankment due to temperature variations of the bridge deck. In addition, the drainage component ensures there will be no hydrostatic pressure build up behind the abutment. Finally, the insulating properties of the compressible inclusion (TerraFlex) prevent the soil behind the abutment from freezing. For a 100m long bridge, a 12" thick piece of Geoinclusion® will do the job at each abutment, with a unit cost as low as $2.50 a square foot!
GeoTech Systems Corporation:
Yes. This web site has a number of useful documents, drawings, and specifications, and we are happy to respond to questions posed via telephone or e-mail. We can also provide "box lunch seminars" providing a product overview and discussion of methodology for applications.
No. None of our materials require any special equipment or expertise for installation. Any contractor can confidently install our materials, including TerraLite.
Call GeoTech Systems Corporation at (703) 759 0300 or e-mail us at firstname.lastname@example.org and we will refer you to an appropriate licensee from whom you can order the materials.
GeoTech Systems Corporation warrants for a period of 5 years that the GeoTech products will be free of manufacturing defects. The company will, at its option, either replace any material proven to be defective or refund the purchase price of the material. GeoTech systems Corporation does not assume any liability, direct or indirect, nor any consequential damages.
The above warranty is offered in lieu of all others, implied or expressed, and may be modified or extended only in writing by corporate officers of the company.
Last Modified: July 16, 2009