Case Study: Application of Geomembranes and Geotextiles in the Construction of a Landfill Site – Taking Shenyang City Landfill as an Example

Project Background
With the accelerated urbanization and population growth in Shenyang City, the volume of municipal solid waste increased dramatically. The capacity of the existing Laohuchong Landfill was nearly exhausted. To meet the waste disposal needs for the next two decades, Shenyang City initiated an expansion and upgrade project for the Laohuchong Landfill. A core objective of this project was to build a high-standard, safe, and environmentally friendly modern sanitary landfill. The key technology involved using a composite liner system for full-site impermeability, ensuring zero pollutant leakage and protecting local groundwater and soil environment.

Products Applied

• HDPE Geomembrane: Used as the primary impermeable layer, selecting high-quality high-density polyethylene geomembranes with thicknesses of 1.5mm and 2.0mm.

• Polyester Filament Geotextile: Used as a protection layer and drainage/collection layer.

• GCL (Bentonite Geosynthetic Clay Liner): Combined with the geomembrane to form a composite liner system, providing self-healing properties and dual protection.

Specific Application Plan and Construction Steps

The landfill adopted a typical “double composite liner system” structure, from bottom to top, as follows:

First Layer: Base Layer and Leachate Collection & Removal Layer (Bottom)

1. Foundation Preparation: The base was leveled and compacted to achieve the required density.

2. GCL Installation: A bentonite geosynthetic clay liner was laid on the compacted subbase. Its swelling property upon hydration seals potential minor cracks caused by foundation settlement, serving as a secondary impermeable layer.

3. Primary Liner Installation: A 1.5mm thick HDPE geomembrane was laid over the GCL. This is the core of the entire impermeability system. All sheets were joined using dual-track fusion welding, and every seam underwent non-destructive (air pressure testing) and destructive (sample testing) tests to ensure integrity and watertightness.

4. Protection Layer Installation: A 600g/m² polyester filament geotextile was laid over the HDPE geomembrane. Its core functions are:

   • Puncture Protection: Prevents sharp edges in the overlying gravel layer from puncturing the underlying HDPE geomembrane under pressure.

   • Drainage/Collection: The geotextile’s excellent in-plane transmissivity helps quickly channel leachate laterally into the collection pipes.

5. Leachate Collection System Installation: A network of graded gravel and HDPE perforated pipes was placed over the geotextile to collect all leachate generated from waste decomposition and convey it to the treatment plant.

Second Layer: Slope Lining and Anchorage System

1. Slope Preparation and Anchor Trench Excavation: The slopes of the landfill cell were graded and an anchor trench was excavated along the top.

2. Slope Liner Installation: A GCL was laid on the slopes, followed by a 2.0mm thick (thicker for enhanced durability) HDPE geomembrane.

3. Slope Protection: A filament geotextile was also laid over the geomembrane on the slopes for protection.

4. Anchorage: The top edge of the geomembrane was buried within the pre-excavated anchor trench and backfilled with concrete to form a permanent seal.

Third Layer: Daily Operations and Final Capping

• Daily Cover: At the end of each day’s waste placement, HDPE geomembranes or polyethylene sheets were used for temporary covering to minimize rainwater infiltration, odor release, and fly breeding.

• Final Capping System: When a cell reached its final design grade, a complex final cover system was constructed, typically consisting of (from top to bottom):

  • Vegetative Layer

  • Topsoil Layer

  • Drainage Layer

  • Another HDPE Geomembrane (serving as the final impermeable layer to prevent water ingress into the waste mass)

  • Gas Collection Layer (often composed of geotextile and gravel to collect and convey landfill gas)

  • Waste Mass

Application Results

1. Outstanding Environmental Benefits: The composite liner system of “geotextile + geomembrane + GCL” achieved near 100% impermeability, effectively preventing highly concentrated leachate from contaminating groundwater sources and protecting the ecological environment in the Shenyang area, particularly against potential threats to groundwater.

2. Significant Social Benefits: Greatly reduced odor pollution and pathogen spread from the landfill, improving the living environment for surrounding residents, enhancing the city’s image, and contributing to Shenyang’s efforts in building a National Sanitary City.

3. Considerable Economic Benefits: Although the initial investment was high, the long-lasting impermeability system avoided potential future enormous costs for groundwater remediation and environmental cleanup. Simultaneously, the collected landfill gas could be utilized for power generation, enabling resource recovery.

4. Extended Service Life: The efficient leachate collection and removal system reduced hydrostatic pressure within the waste mass, improving landfill slope stability and indirectly extending the site’s operational life.

Conclusion
In the construction of Shenyang’s Laohuchong Landfill, the HDPE geomembrane, serving as the impermeable core, worked synergistically with the protection and drainage functions provided by the polyester filament geotextile, together forming a complete and reliable barrier system. This case fully demonstrates the critical role of modern geosynthetics in municipal environmental protection projects, serving as a model for ensuring the safe, durable, and efficient operation of major environmental infrastructure.