GCL Installation Guide: Lapping, Anchoring & Repair

A geosynthetic clay liner (GCL) is a factory-made sandwich of sodium bentonite between two geotextiles. It self-seals when hydrated and is widely used alone or under HDPE geomembrane. The three things that decide its performance are: keeping it dry before covering, sealing every overlap, and anchoring it properly on slopes.

1Material at a Glance

GCL replaces 300–600 mm of compacted clay with a 6–8 mm thick product — less excavation, faster placement, and it self-heals around minor punctures.

2Site Conditions — Protect It from Water

• Keep rolls dry: store off the ground under cover; cut open only what you can place the same day.
• No standing water on the subgrade when placing — hydrated bentonite cannot be reworked.
• Place the cover layer (soil or next geosynthetic) as soon as practical after each day's placement.
• In rainy seasons, schedule placement in 1–2 day windows with cover material standing by.

3Panel Placement & Lapping

• Unroll panels parallel to the slope on slopes; on flat floors, lay with the long edge in the direction you will cover next.
• Overlap 150–300 mm between panels — less than 150 mm risks seam leakage; more than 300 mm wastes material.
• Keep the overlap area clean; do not let soil or gravel sit between the two panels.

4Sealing the Overlaps

• Apply granular sodium bentonite ≈ 0.4 kg per linear metre along the overlap before closing the two panels.
• Fold the top panel over and secure with the factory lap tape, pressing firmly the full length.
• On slopes steeper than 1:3, add mechanical fastening (staples or pins) at 300–500 mm spacing along the overlap.

5Slope Anchoring

• Dig an anchor trench at the crest (500 mm wide × 500 mm deep minimum), lay the panel into it, backfill and compact — never leave the panel just lying over the crest.
• Leave 200–300 mm slack per 10 m of slope for shrinkage and subgrade settlement.
• If the slope exceeds 1:2, anchor the GCL at the crest before placing the HDPE layer above it, and check that the GCL has not slid during welding work.

6Repair & Composite Lining with HDPE

• Damaged areas: cut out the damaged panel section and patch with a new piece, overlapping 300 mm on all sides and sealing the perimeter with bentonite and lap tape.
• In a GCL + HDPE composite system, place HDPE directly above the GCL with a 100 mm+ overlap and weld as normal — the GCL provides the second line of defence.
• Log every repair with a photo and location for the QC record.