Geosynthetics for landfill in Malaysia.

Eight layers from subgrade up.

1. Prepared subgrade: compacted clay or stabilized native soil, ≥ 600 mm thick, k < 10⁻⁹ m/s.
2. GCL (Geosynthetic Clay Liner): bentonite layer encapsulated between two geotextile faces, k < 10⁻¹¹ m/s. Optional but increasingly specified as redundant barrier.
3. Primary HDPE geomembrane: 1.5-2.0 mm for non-hazardous landfill (MSW); 2.0-2.5 mm for hazardous. GRI-GM13 compliant. Hot-wedge dual-track seams + 100% air-pressure NDT.
4. Cushion geotextile: nonwoven PP 400-600 g/m² above the geomembrane to protect from puncture by drainage stone.
5. Leachate collection drainage: StrataDrain geocomposite or 0.3 m drainage gravel + perforated leachate pipe. ASTM D4716 transmissivity sized to the leachate generation rate.
6. Filter geotextile: nonwoven PP 200-300 gsm above the drainage layer to keep waste fines from clogging.
7. MSW or waste body
8. Closure cap (when filling complete): LLDPE 1.0-1.5 mm (chosen for flexibility under differential settlement) + drainage layer + topsoil + vegetation.

For hazardous landfill the regulatory standard adds a secondary HDPE liner + interlayer leak detection (often a thin leak-detection geomembrane sandwiched between the primary and secondary liners). The geoelectric leak detection sweep per ASTM D7007 is becoming a tender baseline.

What the Malaysian guideline requires.

The DOE landfill design guideline classifies landfills (Level 1 inert / Level 2 non-hazardous / Level 3 hazardous / Level 4 highly hazardous) and sets composite-liner minimums by class. The geosynthetic liner is one component within a composite barrier that also includes compacted clay (or GCL substitute) below the geomembrane. Final design must be approved by DOE at EIA / DEIA stage; our team prepares the EIA-compliant geosynthetic specifications and the construction QA plan as part of pre-tender deliverables.

The harder design problem.

Cap liner often gets less engineering attention than basal but is the system that fails first if mis-specified. The cap must accommodate differential settlement from the consolidating waste body (often 10-20% of waste depth over the post-closure period), maintain interface stability on the side slopes, and remain functional for the post-closure monitoring period (typically 30 years in Malaysia, longer for hazardous). LLDPE is preferred over HDPE for cap because of its lower stiffness; textured one side or both depending on slope; interface friction verified per ASTM D5321 against the cushion / cover soil pair.

Deeper technical reading.