Geosynthetics

In landfills HDPE geomembranes (thickness higher or equal 2.0 mm) are used nearly exclusively. In groundwater protection, mainly 1.0 mm thick HDPE geomembranes are used. In tunneling applications, mostly geomembranes with a signal layer are installed. Steeper slopes can be accommodated by installing a geomembrane with structured surfaces. Needle-punched geosynthetic clay liners with mechanically bonded nonwovens (300 g/m²) as cover and carrier geotextiles are especially suitable for steeper slopes because they normally achieve higher interface friction angles than other geotextiles.

Sealing is indispensable for environmental and groundwater protection and contributes substantially to the fitness for use and service life of buildings. Geomembranes of varying thickness, depending on the intended purpose, are used as barriers to liquids and gases mainly in landfills and tunnel construction and in hydraulic engineering. Typically, geomembranes manufactured of various polyethylene formulations (e.g. different densities) are used. Thicknesses are generally more than 1.0 mm. Geomembranes are deployed and welded together by approved installers. In areas with reduced stresses, plastic sheets with thicknesses of 0.3 mm to 1.0 mm can be used. This would be applicable for non-permanent covers and, for example, pond applications. Geosynthetic clay liners are used in specific areas, with bentonite performing the sealing function.

Products:

• Carbofol®
• Bentofix®

In order to allow long-term drainage performance of the percolation layer, filter geotextiles are deployed to transmit shear stress on the percolation layer. Mechanically bonded nonwovens (see filtration) are especially suitable for filtration functions. Randomly entangled mesh matrices are especially suitable as drainage layers since they have a stable three-dimensional static structure. Shearing stresses can be transferred without damage, and thus the long-term hydraulic performance is maintained.

Drainage is the collection of precipitation, groundwater and other liquids or gases which have to be discharged. Drainage systems are supplied as single elements or composites consisting of at least one filtering layer and one percolation layer. The latter takes up the liquid and discharges it with a minimum loss of pressure. Surface drainage systems are frequently combined with sealing systems, e. g. in landfills, and waterproofing applications, like underground car parks or tunnels. Geosynthetic drainage systems substitute expensive mineral drainage layers.

Product:

• Secudrain®

Mechanically bonded nonwovens are especially suitable for this function since they adjust themselves very well to irregular subsoils and also to soft soils due to their high elongation capacity. This elongation capacity is important to accommodate the penetration of a stone. The fibres lay themselves around the stone and prevent the nonwoven structure from being damaged.

Geotextiles separate adjacent soil types or fill materials preventing them from becoming intermixed. They are used in the form of durable, robust nonwoven or woven fabrics and/or composites manufactured of synthetic raw materials able to withstand high loads. Common applications include road and railway construction, hydraulic engineering, and construction of riding and sports grounds. The selection of the appropriate product depends on the grain size distribution of the base course materials and the expected operational loads.

Product:

• Secutex®

Thick mechanically bonded nonwovens have proven to be very good protection layers. Secutex® PP nonwovens with a mass per unit area of > 800 g/m² e. g. are used as a sole protection layer for geomembranes. However, in fields of application where lower loads occur, mechanically bonded nonwovens with a mass per unit area of higher or equal 300 g/m² are used.

Geomembranes, coated and non-coated structures need to be protected against mechanical damage. Without protection layers, damage would occur from sharp-edged irregularities of the underground or the filling material. Nonwovens and composites are used as protection against mechanical damage. Composites include nonwovens reinforced with wovens, double-sided wovens and composite nonwovens with mineral fillings. The effectiveness of protection depends on the thickness of the geosynthetics and their mass per unit area as well as their resistance to perforations by impact or compression. Nonwovens and composites are used in a variety of applications including landfills and tunnels for the protection of geomembranes. Such protection elements have also been installed successfully in pipe construction.

Product:

• Secutex®

Mostly geogrids and wovens are used as reinforcing elements. Reinforcing elements, where the reinforcing elements are made of yarns of slit films (e. g. wovens), are more susceptible to installation damage than reinforcing elements made of polymer ribs with rigid crossing points. Furthermore, stretched geogrids have lower initial elongations than wovens, for example, and hence generate an immediate force transfer without construction elongation.

When used for reinforcement purposes, geotextiles, geogrids and composites are placed below or between soil layers to take up tensile forces and thereby improve mechanical properties. They are preferably used in supporting structures based on the principle of “reinforced soil” or for stabilizing earth banks on types of soil with a poor load-bearing capacity. In many cases this makes expensive constructive measures, a soil exchange or the installation of an additional soil layer, unnecessary.

Products:

• Secugrid®
• Combigrid®

Mechanically bonded nonwovens are especially suitable for this function if the nonwoven thickness is at least 30 times larger than the selected opening size. This has been determined by inspecting mechanically bonded nonwovens which have been in service for relatively long periods of time. A thickness adjusted to the opening size allows a depth filtration and prevents the development of a filter cake at the interface between geotextile and soil which would reduce the water permeability. The water permeability of the mechanically bonded nonwoven adjusted to the soil is hence ensured in the long term.

A geotextile filter layer withholds solid components, whilst allowing liquids to pass almost freely perpendicular to the filter plane.
It is differentiated between the mechanical strength (soil retention capacity) and the hydraulic filter effectiveness both with the aim to achieve a water drainage with a minimum loss of pressure.

The requirements can also be fulfilled by a mineral filter. However, geotextile filter layers have proven to be the most suitable and economic alternative.

Like in mineral filter layers, the filter length of the geotextile filters (thickness of the geotextile) can affect the long-term mechanical and hydraulic filter effectiveness. Filters are mainly used in hydraulic engineering and drainage systems.

Products:

• Secutex®
• Terrafix®

Due to their very good flexibility, mechanically bonded nonwovens are especially suited because they allow a robust handling due to the optimal stress/strain behaviour and adjust well to the subgrade. Moreover, the flexible system deforms optimally during wave impact absorbing the impacting forces. The three-dimensional needle-punched nonwovens are furthermore particularly abrasion-resistant.

In geotechnology and hydraulic engineering, earth materials in particular are “packed” in flexible tubes, sacks and containers. Here geosynthetics perform separating, filtering, protecting and/or reinforcing functions, depending on the type of application involved. The materials used include nonwovens, wovens, geogrids and composites.

Product:

• Soft Rock® (Terrafix®)