Testing of geosynthetic barriers - Clay
Testing of Geosynthetic Barriers - Clay
The definition of a geosynthetic clay liner (GCL), taken from EN ISO 10318, is: “A factory-made composite consisting of geosynthetic materials and clay materials with sealing (low filtration) capacity (e.g. bentonite) shaped in strips, used where touching the ground or other material during grading or building works”.
Geotextiles (and geotextile-related products), in contrast to geosynthetic barriers, are basically fabrics which are permeable to fluids such as water and gas.
BTTG™ offer an unrivalled testing service for Geosynthetic Barriers, both polymeric (geomembranes) and clay (geosynthetic clay liners), to manufacturers, consulting engineers, contractors and landfill operators among others. We are able to perform a wide range of mechanical, hydraulic and durability tests. The tests are co-ordinated and carried out by the High Performance Materials (HPM) department in custom designed premises in Trafford Park, Manchester. The laboratory building contains three separately conditioned laboratories and a large preparation area with a loading bay to handle samples directly from site and from manufacturers.
BTTG™ is the UK’s leading laboratory for testing geosynthetic materials and was the first UK laboratory to be UKAS accredited for any geosynthetic tests. BTTG™ hold UKAS accreditation to ISO 17025 for an extensive range of geosynthetic tests, including opinions and interpretations. View our schedule of UKAS accredited tests.
The principals of commonly performed tests
Where two or more standards have been grouped together under one heading, the test methods are not necessarily identical, nor would they produce the same results, but they follow similar principals of test.
Geosynthetic Clay Liners
Mass per unit area
BS EN 14196; BS EN 965; ASTM D5261; ASTM D5993
Specimens of known area are cut from the samples and weighed. Mass per unit area is calculated.
BS EN ISO 9863-1; BS EN 964-1; ASTM D5199
The nominal thickness is determined by measuring the distance that a moveable plate is displaced from a parallel surface by the material while under a specified pressure.
BS EN ISO 10319; BS 6906: Part 1; ASTM D4595; ASTM D6768
Specimens of a specified width are clamped across their entire width with a specified gauge length and pre-tension, and strained at a specified rate until rupture occurs. Tensile strength per unit width and percentage extension (where appropriate) are measured.
Grab tensile strength
The central portion of a rectangular specimen is clamped at a set gauge length and an increasing load is applied at a constant speed until rupture occurs. Grab tensile strength and apparent elongation (%) are measured.
BS EN ISO 12236; BS 6906: Part 4; DIN 54307; ASTM D6241; ASTM D4833
Specimens for test are clamped between circular rings with a specified internal diameter and a puncture probe of known dimensions is pushed centrally against and normal to the fabric at a specified speed until failure of the specimen occurs. Push through force and plunger displacement / elongation (%) (where appropriate) are measured.
BS EN ISO 13426-2; ASTM D6496, ASTM D4632 (Mod.); ASTM D413 (Mod.)
Rectangular specimens are prepared and the two layers of geotextile separated by hand over a sufficient length to allow them to be clamped in the jaws of a tensile machine at a specified gauge length. The jaws are run at a set speed and the peel strength measured.
Sample material is dried in an oven at a specified temperature. The percentage moisture content is calculated from the loss in mass of the material as a percentage of the dry mass.
Index flux / Hydraulic conductivity
ASTM D5887; ASTM D5084 (GRI)
This test involves permeation of a circular specimen of known diameter. The specimen is set up in a flexible-wall permeameter, subjected to defined total stress and back pressure for a specified period of time. Flow is initiated using water by raising the pressure in the influent side of the specimen. The hydraulic conductivity / flux is determined when inflow and outflow are approximately equal (+/-25%).
ASTM D5890; USP NFX VII
A known weight of bentonite is added in small increments at specified time intervals to a graduated cyclinder containing de-ionised water. After all the bentonite has been added, the cyclinder is left undisturbed for a minimum specified period before recording the volume level of the hydrated clay.
The test uses a known amount of bentonite taken from the GCL and hydrates it with distilled water. The test container is a cicular mould with a porous base plate and porous cover plate with an extension rod that imposes a dead weight stress on the test material. Swelling readings are measured with a dial gauge over a known period of time.
A specified ratio of bentonite and water is mixed into a slurry and poured into the cylinder of the apparatus. The cylinder is pressured and as water drains from the bottom of the cylinder a filter cake is formed. The filtrate is allowed to flow over a specified period before being collected over a known, specified period. A lower amount of filtrate collected indicates the more effective at sealing and therefore less permeable.
Montmorillonite content (Methylene blue capacity)
API RP 131; VDG P69
The methylene blue capacity is an estimate of the cation exchange capacity of the bentonite. A well dispersed sample of the bentonite is titrated with methylene blue solution until a blue ‘halo’ appears around a drop of dyed bentonite solids on paper.
Water absorption of bentonite
The amount of water absorbed over a fixed time interval by a known weight of dried bentonite is determined. The test uses a sintered aluminium oxide plate that sits in distilled water to within a specified distance from the top of the plate. The bentonite for test is placed on filter paper on top of the plate and left for a given period of time. The increase in weight of the bentonite is used to calculate the percentage water absorption.