Episode 5 – Mechanically Stabilized Earth Walls: Extensible vs. Inextensible Reinforcement

MSE wall performance depends heavily on the type of reinforcement used. Two categories dominate practice:

• Inextensible reinforcement (steel strips, steel grids, welded wire mats)

• Extensible reinforcement (polymeric geogrids or geotextiles)

Their behavior under load is very different:

• Inextensible reinforcements mobilize their strength at very small strains, often before the soil reaches its own peak strength.

• Extensible reinforcements, on the other hand, require larger strains to reach peak strength — after the soil has already mobilized most of its shear strength.

This distinction changes how walls are designed and built:

• No mixing of extensible and inextensible reinforcements within the same wall.

• Design approach matters:
  • Rankine method → extensible reinforcements with <10° face batter.
  • Coulomb method → extensible reinforcements with ≥10° batter or significant surcharge loads.

• Height restrictions (BC Ministry of Transportation & Transit):
  • Extensible walls → maximum 9 m
  • Inextensible walls → maximum 12 m

Getting this wrong can lead to incorrect stress assumptions, unsafe designs, or excessive deformations.