inspection of the subgrade has been undertaken and deemed suitable and in accordance with the specifications by the CQA engineer.
E5.2.3 Panel placement, overlaps
The GCLs shall be installed such that the panels are anchored at the crest of the slope and are continuous down side walls/slopes. The panels should also be continuous across the base or the cover. The
arrangement of the GCL panels should be according to a predetermined layout plan to minimise the amount of end overlaps.
Overlap joints between panels shall be formed by overlapping the panels by a minimum of 300 mm and sealed by bentonite paste or powder/granules (sometimes referred to as accessory bentonite). The overlap zone shall be kept clean and shall not be contaminated with loose soil or other debris. There shall be no folds or wrinkles in the overlap zone and no traffic or walking shall occur on the completed overlap.
Bentonite used for overlapping shall comply with the same specifications as the bentonite used in the GCL delivered to the site (same rule applies for sealing penetrations and repairs). Research has demonstrated that adequate bentonite between overlapped panels is critical to obtaining good hydraulic performance at the overlap (Cooley and Daniel 1995, Daniel et al. 1997, Benson et al. 2004). In the case of composite liners, particular care should be taken to avoid contaminating the upper surface of the GCL with bentonite powder. The presence of loose bentonite may affect welding of overlying geomembranes and may also influence interface friction.
If the slope design includes any transverse overlaps, intermediate anchorage of the panels on the slope will be needed. In this case, panels should be placed in a roofing tile fashion. The sealing of the panels shall be conducted in the same fashion as for parallel overlaps. Overlaps must be at least 1500 mm for any transverse overlaps (across the slope) and 300 mm for parallel overlap (downslope) to cater for possible movement. If settlement is likely to be significant such as in capping, the overlaps should be increased to allow for the predicted settlement. The entire surface area of every roll shall be inspected by the CQA engineer (for example, during
unrolling/installation) to ensure that there is no damage or other faults in the material (such as significant and obvious variability in thickness/mass per unit area, initial moisture content of the GCL). If damage is identified, it will need to be repaired according to the specifications put in place for the site.
Wrinkles are in general undesirable, as they increase the likelihood of poor intimate contact between the GCL and the geomembrane or subgrade material. In the event that wrinkles occur in the GCL or where wrinkles extend to the edge of the roll due to manufacturing tolerances, they will need to be removed prior to installation of any material cover.
Geosynthetic clay liners installed on slopes are required to be fixed in anchor trenches. This is done to secure the geosynthetic clay liner and prevent it from sloughing or slipping down the inside side slopes during construction or service. A normal minimum requirement is that the anchor trench must be at least one meter back from the top edge of the slope. The front edge of the trench is to be rounded to prevent the development of stress concentrations on the GCL or any other geosynthetics for that matter. The geosynthetic clay liner should be laid on the inside wall and base of the trench only and the trench should be cleared of any debris, gravel or loose material before tte GCL is installed. The trench should be backfilled and compacted with low hydraulic conductivity soils. GCLs shall not be installed in wet weather or windy conditions.
It is very important to ensure that the GCL is not left exposed to rain. In this respect, it is essential that covering and confinement activities be coordinated with GCL installation. If the deployed GCL panels have hydrated prematurely (for example, during rainfall) without confinement, then the GCL panels shall be replaced.
E5.2.3.1 Soil cover placement
Where a soil cover is placed directly on the GCL, the soil cover specification shall account for the compatibility of the GCL and the cover soil. The soil shall also be free of debris, roots, sharp objects and any other item which may under the overburden stress penetrate or tear the GCL. Disturbance of the overlap area during placement must be avoided. It may be necessary to place the cover soil in this area manually. The cover should not be pushed or graded in a direction that may cause the overlap to move. The geosynthetic clay liner shall not be trafficked directly.
E5.2.3.2 Geomembrane cover placement
Where a geomembrane is placed directly on the GCL, it should be placed immediately following deployment and acceptance of the GCL.
Siting, design, operation and rehabilitation of landfills
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E5.3 Repairs
If the GCL has been damaged during installation, it can be repaired by patching a new piece of GCL of the same material type and thickness extending 500 mm beyond the damaged area in each direction. The patched area must be augmented with bentonite powder or
granules/paste as per normal jointing requirements.
E.6
Quality
E6.1 Manufacturing specifications and quality
control
The quality of the geosynthetic clay liner (GCL) shall be in accordance with the requirements of the Geosynthetic Research Institute (GRI) — GCL3. The minimum
specifications for quality GCL products are contained in GRI Test Method GCL3 Standard Specification for ‘Test Methods, Required Properties, and Testing Frequencies of Geosynthetic Clay Liners (GCLs)’. These specifications were developed by the Geosynthetic Research Institute (GRI), with the cooperation of geosynthetic clay liner manufacturers. The specifications set forth a set of minimum physical and mechanical properties that must be met, or exceeded by the geosynthetic clay liner being manufactured.
Note that, currently, there are no Australian
manufacturing specifications. In this respect GRI GCL3 represents best practice. However, it should be stressed that the GRI requirements represent a minimum. Higher requirements may be necessary in certain applications and the onus is on the engineer of record to establish if higher requirements are necessary and to specify according to the particular engineering requirements. Further note: always refer to the latest version of this specification).
In addition to the above, the following bentonite specifications shall be verified every 50 tonnes of the product:
Property Range or value
Montmorillonite content > 70 wt% Carbonate content* < 1–2 wt%
Bentonite form Natural Na-bentonite or > 80 wt% sodium as activated bentonite Particle size Powdered (e.g. 80%
passing 75 micron sieve) or Granulated (e.g. < 1% passing 75 micron) Cation exchange capacity ≥ 70 meq/100 g (or
cmol/kg) Free swell index ≥ 24 cm3/2g
* Carbonate here implies calcite, calcium carbonate or other soluble or partially soluble carbonate minerals.
A statement on the origin of the bentonite must be included, as well as certified copies of the quality control certificates issued by the bentonite supplier and reports on the tests conducted by the manufacturer to verify the quality of the bentonite used to manufacture the
geosynthetic clay liner (GCL) rolls assigned to the project. The geotextile components of the GCL must also have been through a QC programme. The manufacturer’s geotextile QC program should be available for auditing.
E6.2 Construction quality control (CQC)
Installation of the geosynthetic clay liners must be undertaken by GCL installers with extensive installation experience and competence with the specified GCL. In the case of installation of multi-component liners composite, they shall provide sufficient evidence of installation experience and competence with other geosynthetics. In either case, they must provide experience records prior to any installation.
E6.3 Third-party CQA consultant
Construction quality assurance (CQA) is defined as a planned system of activities that provide assurance that the geosynthetic clay liner was fabricated and installed as specified in the design.
It is an important factor in ensuring that design and installation of the GCL are done in accordance with the standards and specifications agreed with EPA. For this purpose, an independent, third-party CQA consultant having experience with geosynthetic clay liners and knowledgeable of geosynthetic clay liner characteristics