HDPE Geomembrane UK — Technical Specification Guide

High-density polyethylene (HDPE) geomembranes are the most widely used lining material for large ponds, reservoirs, landfill cells, and containment basins in the UK. Their combination of chemical resistance, durability, and weldability makes them the specification of choice for civil, environmental, and industrial engineers. This guide covers the key technical parameters, standards, and installation requirements for HDPE geomembranes.

Browse our HDPE pond liner range or request a technical specification.

GRI-GM13 — The Key Standard for HDPE Geomembranes

GRI-GM13, published by the Geosynthetic Research Institute, sets out the minimum property values for HDPE geomembranes used in geotechnical and environmental applications. Properties tested include:

Property	Test Method	0.75mm MARV	1.0mm MARV	1.5mm MARV
Density	ASTM D792	0.940 g/cm³ min	0.940 g/cm³ min	0.940 g/cm³ min
Tensile Strength (yield)	ASTM D6693	11 kN/m	15 kN/m	22 kN/m
Tensile Strength (break)	ASTM D6693	20 kN/m	27 kN/m	40 kN/m
Elongation at yield	ASTM D6693	12%	12%	12%
Elongation at break	ASTM D6693	700%	700%	700%
Puncture Resistance	ASTM D4833	240 N	320 N	480 N
Tear Resistance	ASTM D1004	93 N	125 N	187 N
Carbon Black Content	ASTM D4218	2–3%	2–3%	2–3%

MARV = Minimum Average Roll Value

Smooth vs Textured HDPE

HDPE geomembranes are available in smooth and single or double-sided textured configurations:

Smooth HDPE

• Lower interface friction angle (typically 10–15° with sand or gravel)
• Suitable for horizontal or gently sloping applications
• Easier to seam — uniform surface aids hot-wedge welding
• Lower cost per m²

Textured HDPE

• Higher interface friction angle (typically 20–30° with granular materials)
• Required for slopes steeper than approximately 3:1 (H:V) to prevent slip failure
• Used on side slopes of ponds, landfill cells, and embankments
• GRI-GM13 textured: tensile strength slightly lower than smooth due to surface treatment

Welding Methods for HDPE Geomembranes

Hot-Wedge Welding (Fusion Welding)

The primary seaming method for HDPE. A heated wedge passes between the two sheets, melting the surfaces, which are then fused under roller pressure. Produces a dual-track weld with an air channel between tracks for non-destructive air pressure testing.

• Temperature: typically 300–400°C depending on ambient conditions and machine speed
• Speed: approximately 1–3 m/min
• Produces a seam with approximately 100% of parent material strength

Extrusion Welding

Used for patches, difficult geometries, and where hot-wedge access is limited. Extruded HDPE filler material is deposited into the joint. Slower and requires more skill than hot-wedge welding.

Seam Testing Methods

Non-Destructive Testing

• Air pressure test — dual-track hot-wedge seams: inflated to 200–250 kPa for 5 minutes, pressure loss ≤10 kPa acceptable
• Vacuum box test — extrusion welds and patches: vacuum applied at 20–35 kPa, soapy water reveals any leak points
• Spark testing (electrical continuity) — for identifying pinholes in the membrane body

Destructive Testing

Typically conducted at a frequency of 1 per 150m of seam (minimum). A 25mm-wide sample is tested in both peel and shear modes:

• Seam peel strength: minimum 70% of parent material (GRI-GM13)
• Seam shear strength: minimum 100% of parent material tensile strength

Subgrade Preparation

Correct subgrade preparation is essential for HDPE performance. Requirements include:

• Removal of sharp stones, roots, and debris to a depth of 150mm
• Smooth, compacted surface — no voids or soft spots
• Geotextile protection layer (300–600 g/m² minimum) on granular subgrades
• Subgrade acceptance documented by the CQA inspector

View our HDPE pond liner range → | Request a technical specification →

Complete GRI-GM13 Property Requirements for HDPE Geomembranes

GRI-GM13 (Geosynthetic Research Institute) specifies the minimum average roll values (MARVs) that all HDPE geomembranes must meet. The following table gives the complete property set for the most commonly specified thicknesses:

Property	Test Method	0.75mm	1.0mm	1.5mm	2.0mm
Density (g/cm³)	ASTM D792	≥0.940	≥0.940	≥0.940	≥0.940
Tensile Strength — Yield (kN/m)	ASTM D6693 Type IV	11	15	22	29
Tensile Strength — Break (kN/m)	ASTM D6693 Type IV	20	27	40	53
Elongation at Yield (%)	ASTM D6693	12	12	12	12
Elongation at Break (%)	ASTM D6693	700	700	700	700
Puncture Resistance (N)	ASTM D4833	240	320	480	640
Tear Resistance (N)	ASTM D1004	93	125	187	249
Carbon Black Content (%)	ASTM D4218	2–3	2–3	2–3	2–3
Carbon Black Dispersion	ASTM D5596	Cat 1 or 2	Cat 1 or 2	Cat 1 or 2	Cat 1 or 2
OIT — Standard (min)	ASTM D3895	100	100	100	100
OIT — High Pressure (min)	ASTM D5885	400	400	400	400
Oven Aging — OIT Retention (%)	ASTM D5721+D3895	55	55	55	55
UV Resistance — OIT Retention (%)	ASTM D7238+D5885	50	50	50	50
Stress Crack Resistance (hours)	ASTM D5397 App X1	200	200	200	200

OIT = Oxidative Induction Time — a measure of antioxidant content and UV stability. Higher OIT = longer resistance to thermal and UV oxidation.

Smooth vs Textured HDPE — When to Specify Each

HDPE geomembranes are available in three surface configurations, each with different interface friction properties:

Smooth HDPE

Manufactured with a flat, polished surface. Typical interface friction angle with compacted granular fill: 8–12°. Suitable for:

• Horizontal pond bases with no slope stability concerns
• Ponds with gentle side slopes (flatter than 5:1 H:V)
• Applications where ease of seaming is prioritised over slope friction

Smooth HDPE is easier to weld (uniform surface contact with hot-wedge machine) and produces more consistent seam quality. Cost is typically 10–15% lower than textured per m².

Single-Sided Textured HDPE

One surface textured (typically the soil contact face), one smooth (top face for easier seam preparation). Interface friction angle with compacted fill: 18–25°. Use where:

• Side slopes between 3:1 and 2:1 (H:V)
• Textured face placed against subgrade for slope stability
• Smooth face upward for easier seam preparation at overlaps

Double-Sided Textured HDPE

Both surfaces textured. Interface friction angle 20–30°. Use where:

• Side slopes steeper than 2:1 (H:V)
• Both liner faces in contact with friction materials
• Maximum slope stability is required regardless of surface position

Formal slope stability analysis required for slopes over 3:1 in ponds deeper than 2m. Consult a geotechnical engineer.

HDPE Panel Deployment Procedure

Correct deployment sequence is critical to avoid wrinkles, stress concentrations, and installation damage:

1. Subgrade acceptance: CQA inspector confirms subgrade is smooth, free of sharp objects, compacted, and dry. Geotextile underlay placed over subgrade.
2. Panel layout plan: Panels numbered and positioned to minimise seam frequency. Seams should not cross at pond corners — offset by minimum 1.5m.
3. Deployment direction: Deploy up slope — roll panels from base to crest. Avoid dragging panels over rough surfaces.
4. Anchor trench: Begin deployment at anchor trench. Feed liner into trench before unrolling down slope.
5. Ballasting: Weight liner edges with sandbags or earth to prevent wind displacement. Never use stones on the liner surface.
6. Seam preparation: Clean seam zones with isopropanol. Remove all dust, moisture, and debris within 150mm of seam line.
7. Trial weld: Run a trial weld on a scrap panel at the start of each day and after any parameter change. Test trial weld before proceeding.
8. Production welding: Weld in consistent direction. Mark weld direction and machine settings on CQA log sheet for each seam.
9. Testing: Air pressure test all dual-track seams same day as welding. Vacuum box test all extrusion welds. Record all results.
10. Final inspection: Walk all panel surfaces looking for deployment damage, wrinkles under tension, and untested areas. Spark test if required by CQA plan.

Thermal Expansion Calculation Example

HDPE has a linear thermal expansion coefficient of approximately 1.5 × 10⁻⁴ per °C (150 microstrain/°C). For a 50m × 30m pond with HDPE installed at 10°C ambient, exposed to summer surface temperatures of 60°C:

• Temperature delta: 60 − 10 = 50°C
• Linear expansion: 1.5 × 10⁻⁴ × 50 = 0.0075 (0.75%)
• Length change on 50m dimension: 50 × 0.0075 = 375mm
• Width change on 30m dimension: 30 × 0.0075 = 225mm

This 375mm potential expansion in one direction must be accommodated by adequate slack in the liner deployment or it will generate tension loads at the anchor trench. Always deploy HDPE with approximately 1% slack on each slope to accommodate thermal movement. In cold installations (below 5°C), increase slack allowance to 1.5–2%.

Interface Friction Angles — Reference Table

Liner Surface	Against Sand (°)	Against Gravel (°)	Against Compacted Clay (°)	Against Geotextile (°)
Smooth HDPE	8–12	10–14	6–10	12–18
Single-sided textured HDPE	18–25	20–28	15–22	18–26
Double-sided textured HDPE	22–30	24–32	18–26	20–28
EPDM (smooth)	14–20	16–22	12–18	16–22

HDPE vs EPDM vs Butyl for Civil Applications — Comparison

Factor	HDPE	EPDM	Butyl
Seaming method	Hot-wedge weld	Adhesive tape	Adhesive tape
Seam testability	Full (air pressure)	Limited	Limited
CQA documentation	Full GRI-GM13	Limited	Limited
Tensile strength (1.0mm)	15 kN/m	~9 kN/m	~8 kN/m
Elongation at break	700%	350–450%	350–420%
Chemical resistance	Excellent	Good (no oils)	Good (no oils)
UV resistance	Excellent (C black)	Excellent	Excellent
Design life	40–60 years	25 years	Lifetime
Typical cost/m²	£2.80–4.00	£2.80–4.50	£3.50–5.50
Best for	SuDS, reservoirs, civil	Wildlife, koi ponds	Premium garden

Case Study: SuDS Attenuation Pond — 1,200m² HDPE, Residential Development

Project: 180-unit residential development, South East England, 2024.
Pond specification: 1,200m² attenuation pond, designed for 1-in-100-year + 40% climate change storm event.
Liner: 1.0mm smooth HDPE, GRI-GM13 compliant; 1.0mm single-sided textured HDPE on 3:1 side slopes.
Seaming: Hot-wedge fusion welding throughout; extrusion welding at pipe penetrations.
Testing: 100% air pressure testing of all dual-track seams; vacuum box at all extrusion welds; 8 destructive tests (1 per 150m).
CQA: Full CQA documentation submitted to LLFA as part of drainage consent package.
Outcome: First-time LLFA approval; zero seam failures on testing; 5-year maintenance agreement in place.