Minet Geotextile

APPLICATIONS OF GEOTEXTILES

1. UNDERGROUND AND ROAD FOUNDATION IMPROVEMENT
2. PAVEMENT EXTENSION
3. UNDERGROUND DRAINAGE
4. PROTECTION AGAINST EROSION
5. WALLS AND SLOPES
6. SECURITY FACILITIES
7. SILT FENCES AND LANDSCAPE PROTECTION
8. RAILROADS

1. UNDERGROUND AND ROAD FOUNDATION IMPROVEMENT

a) Application domains
Both woven and nonwoven geotextiles can be efficiently used in repairing/stabilising national primary roads, secondary roads, unpaved or paved (access roads, forest roads, construction roads), parking areas, industrial courtyards etc. Geotextiles fulfil four main functions: separation, filtration, drainage and/or reinforcement. The type of geotextile you choose depends on the functions required for the stabilisation of your project.

b) Reasons for designing (geotextiles)
The main reason for road pavement structure deficiencies is the contamination of the gravel foundation and the subsequent loss in gravel resistance. When the gravel is laid on a weak soil, the inferior layer gets contaminated with soil. In time, heavy traffic and vibrations make the gravel from the pavement’s base penetrate the ground and lead to the ascending migration of silt and clay. In humid areas, construction traffic causes the pumping of humid underground soil into the covering gravel. All these conditions reduce the effective thickness of gravel, destroying the road support and diminishing their efficiency and life. It has been settled that road supports can be efficiently stabilised by using a combination of geotextiles and gravel.

c) Advantages
A geotextile laid between the underground and the base/sub-base foundation leads to numerous advantages, such as:

It prevents the contamination of sub-base and base levels with fine particles/small material;
It enables the use of free drainage and open filtration materials, structurally more efficient;
It increases road drainage;
It reduces the depth of excavations necessary for the removal of improper materials from the underground;
It reduces the preparation needs of the area;
It saves weather-caused interruptions as work can be performed in nearly any weather conditions;
It expands the life of pavement structures;
It prevents pavement deficiencies;
It reduces maintenance and reparation costs.

d) The separation/stabilisation application
The separation is the geotextile’s function of preventing the soil of the underground or the base foundation mix with the covering material of the gravel (sub-base, base, remblai/ embankment etc.). This is the geotextile’s most important function for roads, especially when building on weak or moderately resistant soils (CBR>3).

Generally, in case of weaker soils (1<CBR<3) and/or humidity, more resistant woven and nonwoven geotextiles are used to stabilise the roads. Therefore, as important as separation, a well-chosen geotextile for separation and the covering base layer with free drainage can improve the filtration and the drainage of the underground, providing a means of hydrostatic pressure dispersion with an excess of pores. In some cases, the geotextile can also provide reinforcement.

In case the stress conditions on the remblai/embankment section of the pavement cause global deficiencies of the underground foundation or stability (such as embankment on soft surfaces (CBR < 1%), then the primary function of the geotextile is reinforcement. If necessary, reinforcement plans specific for a particular area should be drawn using standard geotechnical techniques. The woven geotextile with high reinforcement module/coefficient can be taken into consideration. A separation geotextile is also necessary under any open structure geosynthetic as a geogrid or a geocell when placed over a soft soil.

As demonstrated by the Road Construction and Civil Engineering softwares, geotextiles can increase the medium life of the pavement and can eliminate 30% or more of the requires thickness of gravel for an unpaved road or any other unpaved surface as, for example, a storing courtyard. Using flexible methods of pavement design, the AASHTO software also enables a reduction of the thickness of pavement structural section and/or can considerably increase the life of the pavement.

2. PAVEMENT EXTENSION

a) Application domains
The maintenance and renewal of road coating for national roads, city streets, parking areas, storing courtyards, airport pavements, footbridge deck membrane systems etc.

b) Reasons for designing (geotextiles)
The deterioration of the pavement is greatly due to the water under the pavements that softens the underground and, thus, destroys the structural capacity of the pavement. A pavement with a soaked foundation for only 10% of the time, will have merely 50% of the life of a pavement with a foundation protected from water. A great quantity of this water penetrates the surface of the pavement through cracks and pores. The long-term output of a reconditioned pavement surface is determined by the following phenomena: bending fatigue, natural ageing, gutter formation, road wear, temperature-induced cracks and reflection cracks.

c) Advantages
When a geosynthetic product for the intermediate layer is placed between the layers of the pavement, this system of the product becomes an integral part of the road section, forming a barrier against water infiltration and absorbing the shocks in order to reduce reflection cracks and fatigue cracks of the new surface layer AC (air cooling).

The effect of geosynthetics for the intermediate layer as to the durability of the new pavement and the asphalted cover surfaces is a complex mechanism determined by a series of factors: the type of geosynthetic, the type of mixture and the thickness of concrete for the asphalt, the linking layer, the surface of the existing pavement and the quality of the construction as a whole.

It is not possible to evaluate the output of geosynthetic products for the intermediate layer taking into account only their tensile strength. The main factors contributing to a longer life of roads are: the impermeabilisation function of the product for bitumen-impregnated pavement, the considerably improved uniformity of the bond and the advantages of crack delay in the intermediate tension-absorption layer.

3. UNDERGROUND DRAINAGE

a) Application domains
Geotextiles have replaced graded soil filtres for the drainage of all structures, including subdrains, water evacuation channels, interception drains, pavement edge drains, drains for walls and embankments, drains for evacuating collected/detected alkaline substances, sports field drains, etc.

b) Reasons for designing (geotextiles)
For maximum efficiency, the filtre fabric must enable liquids to flow through the geotextile into the drainage tools (granular soil and/or perforated pipe) given the durability of the drainage system design. Meanwhile, the fitre fabric must retain upstream fine soil particles and prevent their migration or their flowing through the pipes into the drainage system. A certain filtre fabric can be selected following four main criteria:

Retention criterion: - the filtre fabric openings must be small enough to prevent excessive migration of soil;
Permeability criterion: - the filtre fabric must be permeable enough to allow liquids to pass through it without a significant reduction in flow;
Clogging criterion: - the filtre fabric must have a significant number of pore openings, such that if soil particles block or clog a few openings path the flow of the filter geotextile fabric will be greater than the required system permeability.
Survivability criterion: - the filtre fabric must exhibit adequate strength, chemical resistance and environmental resistance, to prevent it from becoming damaged during installation and throughout the design life of the drainage system.

c) Advantages
In comparison with conventional granular soil filtres, geotextiles have more advantages, ensuring:

Compact and continuous filtre;
Reduced excavation;
Reduced environmental impact;
Simplified and better quality construction;
Reduced construction time;
A substantial reduction as to the cost of the materials.

Geotextiles also permit/allow the use of freely calibrated base materials, with open drainage, much more efficient from a structural viewpoint.

4. PROTECTION AGAINST EROSION

a) Application domains
Geotextiles have replaced graded soil filters used under banks of rocks and other trimming materials. Usual applications include: drainage sewers, shorelines, rivers, coastline protection, artificial channels, and anti-erosion systems for bridges and embankments. Typical applications include: drainage channels, shorelines, rivers, coastline protection, artificial channels and protection systems against bridge and embankment erosion.

b) Reasons for designing (geotextiles)
The actual control of the destructive erosion of shorelines, riverbanks, drainage ditches and artificial channels has always been a problem. This is due to the necessity of an exterior protective and resistant layer to absorb wave and stream energy, and the necessity for an interior protective layer, traditionally as a crush filtre to prevent bank soil erosion. This interior layer must play a difficult role, as it has to fulfil two, often opposite, tasks: on the one hand, it needs to be fine enough to act as a filtre on the bank soil, and, on the other hand, to be coarse enough to prevent the occurrence of a great differential pressure between the bank and the exterior water levels. These problems can be overcome with the use of a properly designed filtration geotextile, installed to cover the exposed bank surface. In order to choose the geotextiles for shoreline erosion control one has to know the filtration mechanisms, the installation tensions/forces and the long-term durability requirements. Filtration mechanisms will be based on soil graduation, the characteristics of geotextile pore dimension and the stream conditions. While design criteria are well established for geotextile filtres, the special character of erosion control applications must be carefully considered when choosing the most appropriate geotextile for the specific conditions of a certain area. The (geotextile) design relations are complicated due to reversible flow conditions in applications for coastal erosion control.

c) Advantages
In comparison with conventional granular soil filtres, geotextiles have more advantages, ensuring:

Compact and continuous filtre;
Reduced environmental impact;
Simplified and better quality construction;
Reduced construction time;
A substantial reduction as to the cost of the materials.

5. WALLS AND SLOPES

a) Application domains
Geotextiles are used for walls and steep slopes, to maximise usable construction areas, to extend roads, construction sites, storing courtyards, earth-filled steep slopes, for landslide repairs etc. Geotextiles are also used for the reinforcement of protection embankments and foundations on soft soil.

b) Reasons for designing (geotextiles)
Walls and slopes allow property owners to maximise the use of their land. Geotextile-fortified earth walls and slopes are not only an interesting solution from a technical viewpoint for fortified earth structures, but more importantly, a cost-cutting alternative to rigid concrete walls and slopes. This is an interesting solution from a technical viewpoint as the trial stress applied to geotextile-fortified earth walls and slopes demonstrated that the tear stress is highly above present design technologies’ achievements.

c) Advantages
In comparison with conventional methods, woven geotextiles have significant advantages, such as:

Quick and easy construction;
The possibility of using remblai materials on the construction site;
A flexible structure with a very high load capacity;
A substantial cost reduction in comparison with conventional retaining walls and slopes;
Lower costs than a geogrid earth-fortification system.

6. SECURITY FACILITIES

a) Application domains
Security facilities such as municipal and risky remblais, embankments, channels, water reservoirs, waste water treatment lagoons, waste safety basins, waste reservoirs, tunnels, maintenance etc.

b) Reasons for designing (geotextiles)
Intermediate geomembrane layers are between 20 and 100 inches thick. Relatively thin intermediate layers can be easily damaged, both during the installation of the sealant systems and after construction, if there is no proper mechanical protection. Furthermore, it gives off gas and liquids under the intermediate layer in surface and waste embankment systems that need to be drained. Geotextiles with very good physical properties and a consistent product quality are needed for surface and waste embankment systems cleaning projects. In environmental applications, geotextiles must have these qualities when exposed to chemically harsh conditions.

c) Advantages
Geotextiles are an integral part of security systems and have a wide range of environmental applications, including the filtering of effluent and gas collecting systems, intermediate geomembrane layer/lining protection against damage and puncture and reinforcement. By the use of an unwoven needlepunched geotextile combined with the intermediate layers, the danger of deterioration of the (geomembrane) lining system can be substantially reduced.

7. SILT FENCES AND LANDSCAPE PROTECTION

a) Application domains
Silt fences are used in any construction site that can potentially lead to earth sediment flow in storm water. Landscape protection products are used for weed control and for separation in landscape preservation application.

b) Reasons for designing (geotextiles)
Many construction activities disturb the vegetation, and the surface soil is exposed to storm water erosion. This sediment often contaminates surrounding areas and ends up forming overland flows, rivers and lakes, killing fish and any other aquatic life form. In order to contain this dangerous sediment, a barrier must be properly placed to control overland flow. Geotextile silt fences have been specially designed for this task.

c) Advantages
Temporary silt fences play a key-role in the construction industry and provide a low-cost environmental protection. Silt fences filtre and control overland flow, containing silt and allowing clean water to flow though the fabric. Silt fence fabrics are made of woven or unwoven polypropylene threads or fibres treated to be UV-resistant. In case of landscapes, unwoven products play the role of a weed-barrier while allowing water and nutrients to reach to the plants’ roots.

8. RAILROADS

a) Application domains
Geotextiles are generally used under the ballast for main railroad tracks, secondary railroad tracks, heavy-duty railroad tracks, crossovers, bridge access points, brake systems etc. Geotextiles are used for the construction of new railroads or for the repairing of existing railroads.

b) Reasons for designing (geotextiles)
Maintaining the form of railroad platforms is essential for the efficient functioning of railways. The fine sub-soil particles that pump into the covering gravel can create an uneven railroad platform, resulting into a potential serious derail. When choosing the appropriate geotextile for the given conditions, one should carefully consider the special character of railroad platform stabilisation. Designing is complicated by the dynamic and turbulent flow existing under the railroad platforms. The dynamic hydraulic conditions also impose taking into account the long-term durability for abrasion, filter stability and installation tensions/forces.

c) Advantages
Geotextiles can fulfil four functions vital for the preservation of railroad platforms’ output: separation, drainage, filtration and reinforcement. As a separator, the geotextile preserves the designed thickness and the structural integrity of the platform ballast. Without separation, ballast thickness is reduced by gravel perforation into the sub-soil. As for drainage and filtration, the geotextile can control the water that enters through the ballast. The water from the separation surface between the ballast and the sub-soil is exposed to the load of the wheels’ dynamic stress causing the pumping of fine sub-soil particles into the ballast. As for the reinforcement, the geotextile can absorb the tensile effort induced at the base of the ballast, thus imposing a side-limit. It has been proved that geotextiles are a cost-effective method of extending the ballast life, thus ensuring the structural integrity of railroad platforms.