FAQ about Typar®

What are the differences between nonwoven and woven geotextiles?

Nonwoven geotextiles are made of directionally or randomly orientated fibres, filaments or other elements, mechanically and/or thermally and/or adhesively bonded. 

Woven geotextiles are produced by interlacing two or more sets of yarns, fibres, filaments, tapes or other elements.  

What are the differences between needlepunched and thermally bonded nonwoven geotextiles?

Needlepunched geotextiles are produced by entangling continuous or short fibres by needles. This so called mechanical bonding can be improved by additional thermal bonding. 

Thermally bonded geotextiles are produced by bonding randomly or directionally orientated fibres by thermal treatment.

Which role does the polymer play in the properties of the geotextile?

Different polymers are used for the production of geotextiles. The selection of a polymer depends mainly on properties like melting point, density, melt flow index etc that influence the different production processes.

Usually the polymer is modified using additives and stabilizers in order to improve the characteristics. It is the final manufactured product that is of primary interest to the end user.

What is the difference between geotextiles and geosynthetics?

Geosynthetics is the generic term for products where at least one component is made from a synthetic or natural polymer used in contact with soil and/or other materials in geotechnical and civil engineering applications.

Geotextiles are planar, permeable, polymeric textile products and are one type of geosynthetics.

What is the filtration function?

The restraining of soil or other particles subjected to hydrodynamic forces while allowing the passage of fluids into or across a geosynthetic.

What does clogging, piping, blocking and blinding mean?

During the filtration function some smaller particles are not retained by the geotextile filter. The passage of these particles into the drainage system is called piping; the retention of these particles in the structure of the geotextiles is called clogging. Particles, which are larger than the geotextile pores, may blind or block these openings at the surface. Clogging and blinding will reduce the permeability and should be limited.

What requirements does a geotextile need to fulfil as a filter?

The first requirement for a geotextile is to survive the installation-related stresses, which means that a high damage resistance is needed.

Then, to ensure high filtration performance:

• Appropriate pore size and pore size distribution
• A water permeability higher than the soil being filtered
• An adequate permeability even under pressure
• A high durability

Why is DuPont™ Typar® SF one of the best filters of the market?

Even though DuPont™ Typar® SF has a three-dimensional structure, the Typar® SF filters are so thin that the risk of clogging is highly reduced. The longer the path of the soil particles through a geotextiles’ structure, the higher the risk of clogging.

• Typar® SF is pre-compressed. Pore size and permeability can be measured in the laboratory and show no change under the pressure of the covering soil.
• Typar® SF has a very high number of pores of different shape, size and size distribution similar to the particle size distribution of soil.
• Typar® SF has a high damage resistance.
• Typar®  SFhas a very high uniformity even at low unit weights so that the filtration function is guaranteed over the entire surface of the product.
• Typar® SF has a high initial modulus that ensures high discharge capacity when used in composite drainage materials. 
• Typar®  SF  is predicted to be durable for a minimum of 100 years in all natural soils

What is the separation function?

The preventing from intermixing of adjacent dissimilar soils and/or fill materials by the use of geosynthetics. As defined by European standards, the separation function is always used in conjunction with another function.

What requirements does a geotextile need to fulfil as a separator?

• The first requirement for a geotextiles is to survive the installation-related stresses which means that a high damage resistance is needed
• A High initial modulus to prevent excessive deformations
• An appropriate pore size and pore size distribution
• A water permeability higher than the soil being filtered
• A high durability

What are the benefits of using DuPont™ Typar® SF as a separator?

• Improves of the load bearing capacity by separating fine-grained subgrade from the aggregate base
• Helps increase the bearing capacity by preventing the loss of aggregate into soft subgrade
• Helps increase of compaction degree
• Reduces the deterioration through frost heave effects
• Eradicates the need to remove weak subgrade
• Maintain the drainage capacity of the aggregate base
• Prevents migration of fine particles
• Reduces deformations (rutting)
• Results in longer lifetime of construction.

Why is the energy concept so important?

Tests confirmed a close correlation between energy absorption and damage during installation. As a damaged geotextile cannot perform any function if it is destroyed during installation this property is one of the major performance parameters of any geotextile.

What is the energy absorption and how is it measured?

The energy absorption of a geosynthetic can be described as the combination of its elongation and its applied strength. It is usually measured during the standard tensile strength test.

What is the difference between theoretical energy and actual potential energy?

• Energy absorption, W The work done in elongating a specimen to a given tensile stress or strain in a tensile test. It is relevant for products whose tensile strength is not calculated based on thickness. It is given by the integral of (the area under) the stress/strain curve to the chosen point, and expressed in kJ/m²
• Energy absorption index, W-index An approximate and theoretical calculation of energy absorption at maximum load W-index = 0,5 (Tmax. max e)

Why does the energy absorption describe best the performance of geosynthetics?

The energy absorption index is a simplified and theoretical approach. As the result differs highly from the measured energy absorption (some products benefit from calculated additional energy while other products loose some of the measured energy), the real measured energy absorption should be used. The “real” energy absorption can be easily determined during tensile strength tests