In the “Guidelines for the specification of traffic areas”, a set of standard construction details are given for specific types of roads depending on their intended usage and service life. By including separation and reinforcement geosynthetic products in these standard construction details, a technically equivalent (or superior) design can be achieved by reducing the expensive mineral base course material thickness. If the subsoil of the intended road construction does not have sufficient bearing capacity, geosynthetic reinforcement can also be used in the stabilisation of the subsoil.

Separation

In the construction of most types of roads which are covered by
national classification systems, a frost protection layer and a base
course layer (typically gravel or crushed stone) are placed and
compacted over a prepared subgrade. National guidelines also stipulate a
bearing capacity requirement, based upon the long-term deformation
module (EV2). To achieve and maintain the required design performance,
the differing soil types (frost protection, base course and subsoil)
must be prevented from intermixing.

Secutex® polypropylene (PP) nonwoven geotextiles are specially
designed products for use in road construction as separation components.
They are robust, filter-stable products with high puncture resistance,
high tensile strength and high elongation properties. They are also
rated under the GRK (geotextile robustness classification) system for
puncture and resistance to installation damage. For further details on
the use of Secutex® geotextiles, please refer to the chapters
“Separation with geotextiles” and “Filtration with geotextiles”. The
high elongation capacity of the Secutex® nonwoven geotextiles ensures
excellent resistance to damage. This characteristic of Secutex® products
allows them to easily accommodate irregular or soft subgrades. When
covered with stone, the Secutex® nonwoven geotextile fibers are
reoriented around the stones, preventing damage to the nonwoven
structure.

 

Design cross sections

 

 

Reinforcing

Secugrid® geogrids are reinforcing geosynthetic products manufactured from high tensile strength extruded monolithic flat polymer bars with high strength welded junctions. Secugrid® absorbs tensile forces induced into the soil and distributes the stresses through the high tensile strength bars. This transfer of forces takes place by two distinct modes: interlock of the granular soil into the grid apertures which physically restrains movement of the granular base course material and frictional force transfer between the soil and the wide flat bars of Secugrid®. By absorbing the tensile forces induced by traffic loading on the road surface, the loading is distributed over a larger base area, minimizing localised pressures on the subsoil. An important feature of Secugrid® geogrids is the very high modulus (i.e. they are able to function at their design tensile loading at very low elongation). The high modulus minimises the deformation that can occur at the road surface. Secugrid® also has a very low susceptibility to long-term creep, ensuring the continued integrity of the road surface against deformation.

Soil reinforcement with Secugrid® can eliminate the need to remove and replace or chemically stabilise subsoils that do not have sufficient bearing capacity for the intended loading (ask for the Secugrid® calculation tool).

Combigrid® (a bonded composite of Secugrid® and Secutex® geotextiles) can be used if the geosynthetic product is required to provide reinforcement functions as well as separation-filter stability between cover layer and subsoil. The Secugrid® component of the composite provides reinforcement while the Secutex® nonwoven geotextile component provides separation and filter stability.

Drainage

On concrete pavements, cracks and damaged joint seals can allow surface water to penetrate the pavement slab and wash away the subsoil. The hydraulic undermining of the pavement slab can weaken the structure and lead to damage of the paving surface. When the subsoil also is low in permeability and unable to discharge the water that has penetrated the slab, water can build-up at the interface between the slab and the prepared subsoil. Cyclic traffic loading can then subject this water to alternating high and low pressures. This “pumping” action can drive soil out from under the slab, reducing the structural integrity of the pavement.

When installed between the pavement slab and its subsoil, Secutex® PP mechanically bonded nonwoven geotextiles provide a horizontal drainage path for water to discharge before it can cause damage to the road structure. As the drainage capacities of Secutex® geotextiles are considerably higher than that of engineered soils and as they are not affected by wash-out or pooling, they protect the integrity of the pavement against hydraulic damage. The thick threedimensional geotextile also acts as a cushion against traffic vibration, helping to prevent cracking, while the open porous structure of Secutex® aids the setting and curing of in-situ cast paving slabs.

Typically, a 500 g/m² product (Secutex® type R 504) is used for this application.

Long-term resistance

The raw material components used to produce Secugrid®, Combigrid® and Secutex® geosynthetics are carefully selected to ensure that their full performance is maintained during the entire service life.

Conclusion

For the construction of classified roads, geosynthetics are used to fulfill separation, reinforcement, filtration and drainage functions. Separation and soil filter stability can be achieved using Secutex® geotextiles, and the bearing capa city can be increased with either Secugrid® or Combigrid®. Other advantages of using Secutex® nonwoven geotextiles for the construction of concrete pavements include the prevention of cracks upon the casting of the paving slab, cushioning the slab from vibration damage during service, and protection against subgrade erosion.

A solid foundation starts with nonwoven geotextile products from NAUE.