Behaviour of Bituminous Geomembrane (BGM) Seams Exposed to Tensile Stress

In a recent presentation by Eric Blond of Eric Blond Consultant Inc., the critical differences between thermoplastic and bituminous geomembrane (BGM) seams were examined, focusing on the unique challenges of BGM seams. Eric discussed the mechanical continuity provided by bitumen and how its viscosity affects seam strength. The presentation highlighted significant seam performance reductions at elevated temperatures, backed by experimental data. Eric emphasized understanding BGM seam behaviour under stress and temperature variations, offering key recommendations for industries like mining, water containment, and landfill management to ensure seam integrity and reliability.

Key Points:

1. Seaming Differences:

• Thermoplastic Geomembranes: Seam creates a continuous material at the polymer scale.

• Bituminous Geomembranes (BGM): Seam binds geomembrane sheets to create a watertight plane. The seam strength is primarily dependent on the properties of the bitumen.

1. Mechanical Continuity:

• The bitumen is the only material connecting the BGM sheets.

• Seam strength relies on bitumen viscosity, defined by τ = μ (U/h) where τ is stress, μ is viscosity, h is the distance between planes, and U is the strain rate.

1. Experimental Work:

• Confirmed the seam performance depends on bitumen viscosity.

• Seams showed significant reductions in strength at elevated temperatures:

• Sheet Strength Retained: 76% at 40°C, 51% at 60°C, 45% at 80°C.

• Seam Shear Strength Retained: 68% at 40°C, 28% at 60°C, 8% at 80°C.

• Seam resistance is much lower than sheet resistance at higher temperatures.

1. Viscosity and Temperature Relationship:

• The relation between seam shear strength and temperature is exponential, similar to the relation between viscosity and temperature of bitumen.

• Properties of the bitumen control seam behaviour.

• Field conditions (constant stress) can lead to seam failure due to creep.

1. Creep Tests:

• Tests showed seams fail under constant tensile stress at various temperatures.

• Displacement rates and failure times depend on temperature and applied stress.

• Creep testing projected seam failures even at 10% of short-term strength at room temperature after a few days.

1. Field Implications:

• Short-term seam strength of BGM is highly sensitive to temperature.

• Seams exhibit viscous behaviour, implying predictable failure under constant stress.

• Design Considerations:

• BGM seams are reliable in static substrates (e.g., buildings).

• In-plane stress from substrate settlement poses challenges.

• Terminology: "Sealing" is more appropriate than "welding" for BGM seams.

Key Findings for Various Industries:

Mining:

• Environmental Protection: Mining operations often involve dynamic loads and variable temperatures, making BGM seams potentially vulnerable.

• Recommendations: Use BGM in stable, non-settling substrates or provide additional measures to minimize in-plane stress and temperature variations.

Water:

• Containment Structures: Dams and reservoirs need durable and reliable liners.

• Recommendations: BGM can be used effectively where substrates are stable. Temperature control and stress minimization are crucial to prevent seam failure.

Landfill:

• Liner Systems: Landfills require robust containment systems to prevent leachate leakage.

• Recommendations: Avoid using BGM in areas prone to significant settlement. Ensure proper temperature management and stress control to maintain seam integrity.

Conclusion:

The presentation highlights the importance of understanding the viscous behaviour of BGM seams under tensile stress and its implications for different industries. Proper application and environmental control are essential for maintaining the reliability of BGM in containment structures.