General Specification for HDPE Liner

1. Scope of works

The scope of works covered by this specification is for the supply, installation and testing of HDPE (High Density Polyethylene) geomembrane. The scope of work includes the following items:

• Supply, delivery and installation of the specified premium grade HDPE geomembrane liner

• Provision of all administration, management, supervision, labour and equipment to perform the installation to the manufacturer's recommendations

• Supply of all approved HDPE geomembrane welding and QA/QC testing equipment

• Provision of QA/QC certificates for raw materials, manufactured materials, site works and site testing as detailed in this specification

• Installation, testing, submittals for approval and commissioning of all HDPE geomembrane lining as detailed in this specification

2. Experience

The installer shall, at the time of tendering, provide evidence of ability and experience to supply and install the specified HDPE geomembrane lining. The installer must have at a minimum five (5) years continuous experience in the installation of HDPE sheet. Full details of experience must be lodged at the time of tender for approval by the principal. Failure to demonstrate prior use and vast experience with the specified materials will be grounds for rejection of any tender.

3. Membrane manufacturer and supply

3.1 Material specifications

The geomembrane shall be premium grade HDPE or equivalent. The membrane shall be manufactured by flat-cast extrusion process only, and consist of a single resin being 100% virgin with a narrow molecular distribution. Carbon black shall be added to the resin for ultraviolet resistance. The membrane shall be manufactured to the following approximate ratios: HDPE 97.5% / Carbon Black 2.5%.

All membrane shall be provided in rolls of a minimum width of 6.8 metres. Each roll shall be labelled with the following identifying data:

• Name of manufacturer and type

• Material thickness

• Roll number

• Roll length

• Roll weight

• Roll width

• Cross reference numbers to raw material batch and all laboratory certified reports

• The manufacturer's approved QA stamp and the technician's signature

The material shall be free from holes, blisters, folds, undispersed raw materials, and any sign of contamination by foreign matter.

3.2 QA/QC requirements for membrane raw materials

All raw material supplied to the manufacturer shall be delivered in rail car batches and must be supplied with test certification from the raw material supplier. The certification must state the results of tests which confirm the quality of the resin. The raw material supplier must also confirm that each batch of resin is all of the same type and is 100% virgin. Each batch of resin shall be given an identification (batch) number and remain on file to keep track of all rolls manufactured from each batch.

The use of any off-spec, recycled or blended resins will not be considered.

Prior to production, the membrane manufacturer tests the raw material batches to certify that the raw material supplier test results identify the singular resin. The manufacturer shall provide certification and all available test results for raw materials prior to delivery of materials to site.

Resin lot test requirements:

3.3 QA/QC requirements for membrane manufacturing

The manufacturing process shall be a fully automated flat-cast extrusion process controlled by a fully computerised system. The control system shall provide for the continuous monitoring of temperature, pressure and speed.

Thickness: Each roll shall be tested automatically and evenly over its entire surface area. The minimum parameters acceptable for testing each roll shall be 6,000 thickness point checks. The acceptable thickness for each roll shall not be greater than -10% of the specified material thickness.

Sheet quality: Each roll shall be tested automatically by high voltage over its entire surface area for any point of electrical continuity through the thickness of the sheet. The high voltage scanner shall be capable of detecting any pinhole, void or significant reduction of electrical resistance. Any roll detected to have holes or electrically conductive inclusions shall be rejected and not sent to site.

Each roll delivered to site shall be provided with a roll test data report carrying the manufacturer's laboratory QA/QC approval seal. Membrane property minimum specifications and roll test values shall be verified against the following ASTM methods:

The following items shall be tested in both machine and cross direction:

4. Subgrade preparation

All subgrade surfaces over which the HDPE flexible membrane shall be placed will be prepared as follows: the area to be lined shall be smooth and free of stones, rocks, roots, sticks and any sharp objects or debris of any kind. The surface shall provide a firm, unyielding, uniform base for the membrane. The surface shall be compacted to a density to allow the movement of vehicles, welding equipment and personnel without causing rutting or other detrimental effect. The area to be lined shall not be affected by rising groundwater or ponding of water. The earthworks contractor shall complete subgrade preparation to the approval of the lining contractor.

5. Installation of flexible membrane

The installer shall install the membrane as per the recommended methods of the membrane manufacturer. The membrane panel layout will be the responsibility of the installer's site manager, in conjunction with the principal's approval. Individual panels of membrane shall be overlapped with adjacent sheets by a minimum of 50mm.

The membrane liner shall terminate within an anchor trench located 0.5 metres from the top of the embankment. Once the membrane is in place the anchor trench must be backfilled and suitably compacted to prevent slippage of the membrane.

The membrane installer shall be responsible for making allowances considered necessary to accommodate variations in temperature and weather conditions.

6. Field welding of flexible membrane

All welds require a minimum of 50mm overlap. Two types of welding methods are approved.

6.1 Primary welding method — split hot-wedge fusion

All primary welds shall utilise the split hot-wedge fusion welding method. The split hot-wedge welder shall be a fully automated device comprising a heated copper wedge, pressure rollers and electronic controls. The copper wedge shall be controlled and constantly monitored by a programmable controller with an audible off-temperature alarm and a variable speed drive unit. The copper wedge shall create two contact fusion areas of a minimum width of 10mm with a 2mm minimum wide void between each parallel weld zone. This void shall be created over the entire seam length to allow for field weld pressure testing.

6.2 Secondary welding method — surface extrusion

All secondary welds shall utilise surface extrusion hand welders. The minimum width of the surface extruded bead shall be 15mm. The surface extrusion welder shall be semi-automated and equipped with electronic controls which constantly monitor outputs for both preheat and HDPE extrudate. The unit shall be capable of pre-heating the sheet just prior to the casting of HDPE extrudate over the upper and lower section of the weld zone.

The extrusion rod shall be manufactured from the same resin type used in the manufacture of the membrane. All physical properties shall be identical to those possessed by the membrane raw material. The manufacturer shall provide certified test data with each batch of welding rod. All rod supplied shall be packed to prevent the ingress of moisture and other contaminants.

6.3 General site welding

The installer shall be responsible for regularly checking, calibrating and recording the following:

• Preheat temperature at the nozzle

• Internal barrel temperature

• Split copper wedge temperature

• Split copper wedge speed

6.4 Weld preparation

The installer shall ensure that prior to any primary or secondary welding, weld zones are clean, free from moisture, dust, and any other foreign matter. All weld zone surfaces shall be cleaned or abraded no more than 60 minutes prior to the commencement of welding any seam.

6.5 Trial welds

Trial welds shall be made on fragment pieces of membrane to verify that welding machine parameters are set to produce satisfactory welds. Such trial welds shall be made prior to actual field welds at the beginning of each working day. Samples shall be cut from the trial weld using a calibrated die cutter and tested on a calibrated tensiometer in shear and peel.

7. Testing of wedge fusion welds

Destructive testing: Trial welds shall be run at the beginning of each working day. The trial weld sample shall be a minimum 1.0m long by 0.3m wide with the weld centred lengthways. Four 25mm wide samples shall be cut using a calibrated die cutter and tested in shear and peel. Destructive seam tests shall also be performed at random locations during installation at a minimum of one sample every 300 metres.

Non-destructive testing: 100% of all wedge welds will be tested by air channel pressure testing. The procedure is as follows:

1. Seal both ends of the seam to be tested

2. Insert needle into the channel created by the wedge welder

3. Connect air pump and pressurise the channel to a minimum of 20 PSI and maintain for approximately two (2) minutes

4. If loss of pressure exceeds 10% or does not stabilise, locate the faulty area, repair with surface extrusion weld and re-test

5. Remove the APT kit

7.1 Testing of surface extrusion welds

Destructive testing: Trial welds shall be run at the beginning of each welding period. The trial weld sample shall be a minimum 0.5m long by 0.3m wide. Four 25mm wide samples shall be cut and tested in shear and peel using a field tensile tester.

Non-destructive testing: 100% of all surface extrusion welds will be tested using a high voltage spark gun. The procedure is as follows:

6. Area of weld must be clean and dry

7. Patch is to be heat tacked firm

8. Overlap area to be abraded (minimum 10mm)

9. Copper wire to be inserted at overlap of material

10. Surface weld to be carried out

11. Allow to cool

12. Point HVST at weld, moving slowly over the welded area

13. If a spark shows, repair and retest

8. QA/QC certificates and records

The installer shall provide the principal with the following at completion of the works:

• Certification and test results of raw materials from the raw material supplier

• Certification and test results of raw materials from the membrane manufacturer

• Roll test data reports for each roll of material

• HDPE welding rod test reports

• Daily installation reports for each welder and technician, including trial test weld records, wedge weld records, surface extrusion weld records, weld peel and tensile test records, air channel pressure test records, and patch, repair and HVT records

• Completed as-built drawing including roll numbers, panel layout, seam locations and repair locations

9. Independent testing

The principal may at their own discretion and cost require the installer to extract random samples of sheet and welded seams. Standard frequencies are:

• Material samples: 1 sample per roll

• Weld samples from site: 1 sample for every 300 metres of seam

All independent tests shall be undertaken by an approved testing authority experienced in HDPE flexible membrane testing. Results are subject to review and confirmation by the membrane manufacturer.