BENTOMAT Geosynthetic Clay Liners

Geosynthetics

General information about BENTOMAT Geosynthetic Clay Liners

General information

Geosynthetic clay liners, also known as bentonite mats, are composite geotextile materials that have been in use for many years as a successful natural method for sealing against liquids and gases in a wide variety of applications. The spectrum ranges from landfill sites and road construction through to water engineering structures and the construction of storage and rainwater retention basins. In contrast to the traditional construction method, using mineral sealing materials such as clay, bentonite mats provide consistently high product quality and significant economic benefits.

BENTOMAT Geosynthetic Clay Liners are normally made up of three components:

  1. The geotextile top layer,
  2. the granulated bentonite and
  3. the geotextile base layer.

As a rule, the geotextiles consist of a mechanically-bonded, non-woven fabric on one side and a woven geotextile on the other. All the components of the layers are mechanically bonded by needle-punching over their entire area and are filled uniformly with bentonite granules.

This ensures that the bentonite stores well and prevents material loss and rearrangement during transport and installation. The use of bentonite granules instead of the conventional bentonite powder avoids the problem of dust production.

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The main component of BENTOMAT is the mineral sodium bentonite, which is 90% montmorillonite. Bentonite is a volcanic clay mineral that formed naturally during the course of 200 million years under the influence of water and pressure.

Only high quality bentonite in granular form is used for the manufacture of BENTOMAT Geosynthetic Clay Liners.

The excellent swelling capacity of bentonite when it comes into contact with moisture is responsible for the quick and reliable sealing effect of the BENTOMAT.

This special property of bentonite allows the sealing layer to repair itself securely if it becomes mechanically damaged during installation or later use.


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BENTOMAT structure
BENTOMAT cross-section

With mineral clay sealing layers, layer thicknesses of up to 100 cm are required. BENTOMAT achieves a comparable sealing effect with a thickness of just 1 cm. As well as conserving natural raw materials and reducing excavation, the thinner BENTOMAT Geosynthetic Clay Liners also allow comparatively larger volumes of waste to be deposited in landfill sites.

The use of bentonite mats is therefore more environmentally friendly and more cost-effective than the conventional method of construction. Because BENTOMAT is industrially manufactured and is therefore subject to continuous quality monitoring, it guarantees a sealing layer that has constant and uniform properties.

BENTOMAT Geosynthetic Clay Liners are quick and easy to install. BENTOMAT is supplied in rolls and laid with an overlap, requiring no expensive welding work. The required overlap width of 30 cm is marked on the mat during manufacture.

In order to achieve the same sealing effect in the overlap area as in the rest of the liner, a layer of loose bentonite granules is strewn, on site, in the marked overlap area. In order to maximise the sealing performance, bentonite mats require permanent loading with a suitable fill material laid in a layer at least 30 cm thick.

This overburden also ensures that the BENTOMAT Geosynthetic Clay Liners are kept permanently moist and are protected from mechanical damage.

When dimensioned correctly, BENTOMAT Geosynthetic Clay Liners can also be laid on steep slopes. The mechanical needle-punching of the components across the entire area of the liner creates a firm bond and a high internal shear angle.

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BENTOMAT is a brand-name product made by CETCO, the world's leading manufacturer of bentonite mats, and we are CETCO’s exclusive sales partner in Germany.

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BENTOMAT CL

BENTOMAT CL has been specially developed for applications with particularly stringent requirements in terms of sealing performance. This innovative product incorporates an HDPE membrane that is bonded across the whole area of the bentonite mat to create a multi-layer product.

The membrane provides additional protection against unwanted drying out and against root penetration. With its combination of bentonite mat and sealing membrane, BENTOMAT CL is a sealing system with in-built redundancy that satisfies the highest safety requirements.

BENTOMAT CL is the perfect solution when it comes to greater depths of standing water, because the flow through geosynthetic clay liners increases at higher hydraulic gradients. With the addition of an HDPE membrane, this effect is significantly impeded without having to forgo the benefits of a bentonite mat.

As a composite made of mineral sealing material with a sealing membrane bonded to it, BENTOMAT CL is a multi-layer product that offers the highest level of reliability.

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BENTOMAT CL structure
BENTOMAT CL cross-section

BENTOMAT CL is the ideal solution for applications where the hydraulic performance of traditional geosynthetic clay liners is inadequate and a conventional combination sealing system would be uneconomical.

The standard HDPE membrane used is 0.50 mm thick and is usually adequate for most types of application. Where more stringent requirements apply, in landfill sites or tank pits for example, BENTOMAT CL is available with thicker membranes, up to 2.50 mm thick, and with a textured surface if required.

For thicknesses greater than 1.00 mm, the membranes can also be welded together by a professional craftsman in order to achieve the best possible seal.

Fuctionality of BENTOMAT Tondichtungsbahnen

Functions

Sealing

As a sealing element, BENTOMAT Geosynthetic Clay Liners protect the environment, structures and people from the harmful effects of liquids and gases. This is particularly true in the case of landfill sites and road, tunnel and water engineering construction. The sealing properties of BENTOMAT Geosynthetic Clay Liners are largely determined by the quality of the bentonite used.

The excellent sealing effect achieved by BENTOMAT is due to the limitation of the natural swelling behaviour of the bentonite as it absorbs water. The filaments of the non-woven geotextile base layer strengthen the BENTOMAT uniformly as a result of the needle-punching across the entire area of the liner and keep the natural swelling action within strict limits. The fill material used to provide a permanent overburden further reinforces this effect.

Since the bentonite cannot swell freely under these conditions, the resulting swelling pressure closes the pores in the grain structure of the clay and creates a sealing effect.

A side effect of the swelling capacity is that if minor mechanical damage is caused to the liner, a so-called “self repairing effect” comes into play, whereby the leaking area seals itself automatically.

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Areas of application of BENTOMAT Geosynthetic Clay Liners

Applications

Landfill and contaminated sites

In order to avoid the risk of environmental hazards, waste material in landfill sites and waste disposal facilities must be stored permanently and safely. The relevant technical regulations specify suitable systems for sealing the base and upper surface of landfill sites.

Geosynthetic clay liners are used in base and surface sealing systems, in the technical barrier and in intermediate and temporary sealing layers.

The selection of a geosynthetic clay liner for use as a sealing element in a landfill site is made in accordance with the project-specific suitability assessment made by the relevant waste management authority.

This certification of suitability is important because the clay liner forms an essential component in a coordinated sealing system. The certification of suitability is deemed to have been successfully completed if a nationally recognised suitability approval has been issued by the German states (LAGA Ad-hoc-AG “Deponietechnik”) for a sealing component or a sealing system.

The BENTOMAT GDA clay liner has been issued with a LAGA suitability approval for the construction of mineral sealing layers in surface sealing systems for landfill classes 1 and 2.

Landfill class 1 and contaminated sites
Landfill class 2
Water engineering structures

One of the classical fields of application for geosynthetic clay liners is in water engineering. Here they are used to prevent water losses, to separate ground and surface water, and to ensure the static stability of structures.

Water engineering structures that require sealing include for example storage basins, ponds, dams, dykes or canals.

The selection of a geosynthetic clay liner for use as a sealing element in water engineering structures is made in accordance with the project-specific requirements.

When used in the construction of navigable waterways, clay liners require proof of suitability in accordance with the requirements of the German Federal Waterways and Research Institute and the RPG Guidelines for Testing Geotextiles for Navigable Waterways.

Sealing ditches
Road and traffic route construction

The types of application for geosynthetic clay liners in road and traffic route construction are far ranging. In the field of groundwater protection, they are used in traffic areas to prevent the harmful effects caused by the ingress of substances that are hazardous to water.

In retention basins, bentonite mats are employed for the purpose of delaying the discharge of surface water and protecting the groundwater.

When bentonite mats are used for groundwater protection purposes, they require certification in accordance with the German RiStWag guidelines for construction engineering measures in water abstraction areas.

Sealing of water basins (such as drainage basins)

Advantages of BENTOMAT Geosynthetic Clay Liners

The advantages of BENTOMAT Geosynthetic Clay Liners

  • Consistent product characteristics
  • Full-coverage needle-punching
  • Self-repairing effect
  • Excellent sealing
  • Many areas of application
  • Conservation of natural resources
  • Cost-effective installation
  • Cost-effective sealing system
  • Low transport costs
  • No dust generation during installation


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Additional advantages of the BENTOMAT CL clay liners
  • Superior sealing performance compared to conventional clay liners.
  • The sealed surface is impervious to root penetration.
  • Drying out is effectively prevented.
  • Redundant sealing system to meet the highest safety and reliability requirements.
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Installation of BENTOMAT Geosynthetic Clay Liners

Installation instructions for BENTOMAT Geosynthetic Clay Liners

  1. Lifting equipment with a cross beam and suitable for lifting loads of at least 1300 kg is required for unloading and laying the clay liners. The rolls, even if still packaged, must be stored in dry and weatherproof conditions.
  2. The material may be laid only by qualified personnel.
  3. It must always be laid in dry weather.
  4. The subgrade must be flat, even and free of foreign bodies, surface water, rubble, roots, and pointed or sharp edged stones.
  5. The liners must always be laid without creasing and in the direction of incline.
  6. The overlap areas must be installed neatly and with particular care.
  7. The bentonite granules must be distributed evenly in the overlap areas.
  8. From the point of view of stability, it may be necessary to secure the bentonite mat at the top edge of the incline.
  9. Extra care must be taken in the area of pipe penetrations and connections.
  10. To prevent the material from swelling before the overburden is applied, it must be covered with suitable material immediately after laying.
  11. The covering material must be “end tipped” onto the liner.
  12. Vehicles must not drive directly on to areas that have already been laid.
  13. The required overburden must cover the entire area of the BENTOMAT.

Our detailed installation and laying instructions for BENTOMAT Geosynthetic Clay Liners must also be observed.

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Geosynthetics
Picture Mr Stefan Bermüller
Mr Stefan Bermüller

Sales Director Geosynthetics

Telephone: +49 (0) 911 64200-49stefan.bermueller@beco-bermueller.de

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