rFPP Geomembrane Liners

Installation is carried out to the project CQA plan and the manufacturer's installation guidance. The manufacturer states that both grades meet the physical property values of GRI test method GM18, the specification for flexible polypropylene. A note on that standard: GM18 was suspended in May 2004 and withdrawn in January 2007 over concerns that oxidative induction time could not reliably predict long-term durability in fPP, although it still appears on the Geosynthetic Institute's published index and manufacturers continue to reference it. Where a project specification cites GM18, we confirm in writing which edition is intended and what the supplied material actually conforms to. Seam performance for reinforced polyolefin geomembranes falls under GRI GM19b, Specification for Seam Strength and Related Properties of Thermally Bonded Reinforced Polyolefin Geomembranes/Barriers, which is the correct seam reference for this material - not GM19a, which covers homogeneous sheet.

Subgrade is proof-rolled and accepted in writing before deployment, free of stones, roots, sharp protrusions, standing water and desiccation cracking beyond the project limits, with anchor trenches cut to profile and cleared of loose spoil. Panels are deployed to the approved layout drawing with seams running up and down slopes rather than across them, and are ballasted against wind uplift from the moment of unrolling. Because the scrim holds the sheet dimensionally stable, factory-fabricated panels arrive at the shape they were built to and can be positioned in a single operation, which is the principal programme advantage of reinforced material over roll goods.

Field seaming is by hot wedge fusion for production seams, with extrusion welding for details, patches and penetrations. The outer polypropylene plies weld well and give a workable temperature window, but permitted ambient conditions, preheat and machine parameters remain those set in the CQA plan and the manufacturer's guidance. Reinforced sheet requires particular attention to weld penetration: the scrim must remain fully encapsulated at the seam, and over-welding that exposes or damages the reinforcement compromises the property the material is specified for. Welding parameters qualified on one grade do not transfer to another without re-qualification.

Trial seams are produced on offcut material at the start of each shift, after any break exceeding the interval stated in the CQA plan, and following any change of operator, machine or ambient conditions. Each trial seam is tested before production welding resumes. Destructive samples are taken at intervals selected under GRI GM14, Guide for Selecting Variable Intervals for Taking Geomembrane Destructive Seam Samples Using the Method of Attributes, or GRI GM20 where control charts are specified. For reinforced material, peel testing is evaluated for scrim delamination rather than for film tear bond, and ply adhesion is assessed under ASTM D6636 per GRI GM15, Test Method for Determination of Ply Adhesion of Reinforced Geomembranes.

All production seams receive full-length non-destructive testing, with methods and acceptance criteria recorded in the CQA plan and field integrity evaluated in accordance with GRI GM29, Practice for Field Integrity Evaluation of Geomembrane Seams (and Sheet) Using Destructive and/or Nondestructive Testing. Dual-track seams with an air channel are pressure tested to ASTM D5820. Single-track seams, extrusion welds, patches, penetrations and detail work are vacuum box tested to ASTM D5641 or air lance tested to ASTM D4437 as appropriate to the detail.

Where leak location is specified, method selection follows ASTM D6747, Standard Guide for Electrical Leak Location of Leaks in Geomembranes. Exposed surveys are carried out to ASTM D7002 water puddle, ASTM D7703 water lance or ASTM D7953 arc testing; surveys after cover placement follow ASTM D7007 or, preferably, ASTM D8265, which controls site conditions, instrumentation and procedure and requires a voltage map in the final report — the strongest quality-control document obtainable at the conclusion of construction. On completion the handover package comprises mill certificates traceable to the supplied rolls, the subgrade acceptance record, the as-built panel layout, all trial seam, destructive and non-destructive test results, welder and equipment calibration records, the repair register, and the final QA/QC sign-off certificate that starts the warranty period.