fPP Geomembrane Liners

Installation is carried out to the project CQA plan and the manufacturer's installation guidance. A note on standards: GRI GM18, the specification for flexible polypropylene, was suspended in May 2004 and withdrawn in January 2007 over concerns that oxidative induction time could not reliably predict long-term durability in fPP, although it still appears on the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. Some manufacturers continue to state conformance to its physical property values. Where a project specification cites GM18, we will confirm in writing which edition is intended and what the material actually conforms to, rather than repeating a claim we cannot substantiate. Seam performance is evaluated under GRI GM19a and GM19b, which cover thermally bonded homogeneous and reinforced polyolefin geomembranes respectively - fPP is a polyolefin, so GM19a applies to this material.

Subgrade is proof-rolled and accepted in writing before deployment. It must be free of stones, roots, sharp protrusions, standing water and desiccation cracking beyond the limits in the project specification, and anchor trenches must be cut to profile and cleared of loose spoil. Non-reinforced sheet has no scrim to bridge a defect, so subgrade preparation carries more weight here than on a reinforced installation - the liner will conform to whatever is beneath it, including anything sharp.

Panels are deployed to the approved layout drawing with seams running up and down slopes rather than across them, and are temporarily ballasted against wind uplift from the moment of unrolling. Because fPP has a low coefficient of thermal expansion relative to polyethylene, it develops fewer wrinkles through the daily temperature cycle, but slack must still be managed deliberately: wrinkles combined with leaks are the dominant contributor to leakage in installed lining systems, so deployment aims to place the sheet flat rather than relying on the material's behaviour alone.

Field seaming is by hot wedge fusion for production seams and extrusion welding for details, patches and penetrations. fPP welds across a comparatively wide temperature window, which improves consistency in variable site conditions, but the permitted ambient range, preheat and machine parameters remain those set in the CQA plan and the manufacturer's guidance. 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, and each is tested before production welding resumes.

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

Where the specification requires leak location, method selection follows ASTM D6747, Standard Guide for Electrical Leak Location of Leaks in Geomembranes. Exposed-liner 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, and reviewable by a third party. 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.