HDPE Liner and PET Geotextile for Slope Protection in Pilibhit, Uttar Pradesh

For a slope protection project in Pilibhit, Uttar Pradesh, Ocean Non Wovens supplied and installed 13,200 sq m of Ocean HDPE Liner 1000 Micron for Vagmine Enterprises. With it, Ocean supplied 13,200 sq m of Ocean Non Woven Geotextile (PET) 1.8 mm, the cushion layer that goes with the liner. The HDPE liner keeps rainwater out of the slope; the geotextile protects the liner from the ground beneath and the cover above.

Project snapshot

Slopes in the Terai

Pilibhit lies in the Terai, the flat alluvial belt below the Himalayan foothills, on the border with Nepal. The Sharda and Deoha rivers cross the district, and the Central Ground Water Board puts its average annual rainfall at about 1,256 mm, most of it in the June to September monsoon. In heavy monsoons the rivers overflow and low ground floods.

In flat Terai country, the slopes that need protection are usually built ones: embankments, the banks of ponds, channels and reservoirs, and fill around structures. They are made of alluvial soil that erodes easily once it is wet. Rain that soaks into an embankment raises its pore water pressure and lowers its shear strength, and runoff cuts rills and gullies in the face. The Pilibhit project, carried out in 2024, needed protection against both without relying on stone pitching or concrete blocks.

What the HDPE liner does on a slope

An HDPE geomembrane is a continuous, welded polyethylene sheet that water does not pass through. Laid over a slope and anchored, it stops rainfall infiltrating the soil beneath, so the slope stays drier and keeps its strength, and it stops runoff reaching the soil face. Where the slope retains water, as on a pond or channel bank, it also stops seepage through the bank, which is what drives internal erosion (piping).

The 1000 micron (1 mm) grade was chosen for the following properties:

• Puncture and tear resistance: a 1 mm sheet takes the stress of soil cover and settlement on a slope better than the thinner pond grades.
• UV resistance: carbon black protects the sheet where it is exposed. GRI-GM13 measures this with ASTM D7238 (fluorescent UV exposure), checking how much of the antioxidant package remains afterwards.
• Chemical resistance: HDPE is unaffected by the salts, fertiliser residues and organic matter carried in agricultural runoff.
• Flexibility: the sheet follows minor settlement of the slope without cracking, where a rigid lining would.

The PET geotextile cushion

Ocean supplied the 13,200 sq m of Ocean Non Woven Geotextile (PET) 1.8 mm in the same quantity as the liner. A needle-punched polyester non woven of this thickness is the standard partner for an HDPE liner on a slope:

• Puncture protection: laid under the liner, it spreads the point loads from stones, roots and clods in the prepared slope. Laid over it, it protects the sheet from the cover soil.
• Drainage under the liner: the fabric carries small amounts of water and air sideways and downslope. In the Terai, where groundwater can sit close to the surface, this helps stop pressure building up beneath the sheet.
• Durability: polyester keeps its strength in buried service and resists creep.

Installation on the slope

The installation followed the sequence a lined slope needs:

1. Grading and compaction: the slope was trimmed and compacted to a smooth surface so the sheet would bear evenly, with no stress points.
2. Anchoring at crest and toe: anchor trenches lock the liner in place. Without them a liner on a slope can slip or balloon in wind.
3. Seam welding: panels were joined by hot-wedge welding. In standard practice every dual-track seam is air-pressure tested along its length (ASTM D5820), and samples are cut at intervals for peel and shear testing.
4. Protective cover: a thin soil layer was placed over the liner to protect it from mechanical damage and sunlight.

One design check deserves attention on any lined slope: the soil cover must not slide off the liner. The friction between soil, geotextile and a smooth HDPE sheet is lower than within the soil itself, so the slope angle, the cover thickness and whether to use a textured sheet are worked out from interface shear tests (ASTM D5321) before construction.

Compared with conventional slope protection

Rip-rap, stone pitching, gabion mattresses and concrete slabs armour the surface of a slope, but they let water through to the soil behind and need a great deal of stone, labour and haulage. A liner and geotextile system seals the slope against infiltration, arrives in rolls and goes down quickly, and follows the existing profile. Where the slope also faces fast-flowing water, it can be combined with a hard armour layer on top.

Ocean used the same 1000 micron grade for landslide prevention at Nanded, Maharashtra, and has supplied geosynthetics for slope protection on an NTPC project in Gurgaon.

Frequently asked questions

Why use an HDPE liner for slope protection?

It stops rainwater soaking into the slope. A drier slope keeps its shear strength and is less likely to slump or erode, and on water-retaining banks the liner also stops seepage through the bank.

Why is a geotextile laid with the HDPE liner?

The non woven geotextile cushions the liner against puncture from the ground below and the cover soil above, and it lets water and air beneath the liner drain away instead of lifting the sheet.

What thickness of HDPE liner is used on slopes?

1 mm (1000 micron) is common for slope and bank protection. Thicker sheets, 1.5 mm and above, are used where the liner carries heavy cover or contains hazardous liquids, as in landfills.

About Ocean Non Wovens

Ocean Non Wovens manufactures and supplies geomembranes, geotextiles, geogrids and other geosynthetics for slopes, embankments, highways, reservoirs and landfills across India. To discuss a slope protection or lining requirement, contact the Ocean team.