Retaining Wall Structures: Classification and Construction Methods

Rigid Retaining Structures

Rigid structures have a rigid and stiff body. They move as a unit.

Types of Rigid Structures

• Gravity Walls

  These walls rely on their mass to resist lateral earth pressure.

  • Designed to avoid sliding and overturning.
  • Examples: In situ concrete walls, Masonry walls (often requiring drainage between the bricks), Rockfill.

• Cantilever Walls

  These walls use a structural stem and base slab to resist pressure.

  • Saves concrete compared to gravity walls.
  • Requires steel reinforcement.
  • Examples: Precast concrete walls, Green retaining walls.

• Counterfort Walls

  These walls use vertical supports (counterforts) connected to the stem and base.

  • The counterforts help support the bending moments.
  • Often used with reinforced earth (geosynthetics).
  • A toe piece can be added at the bottom to prevent overturning.

Drainage of Rigid Structures

Drainage is typically achieved by two methods:

1. Weep Holes: Holes in the wall that allow water to pass through.
2. Drainage Layer and Pipe: A drainage layer (often using geosynthetics) and a pipe to absorb and channel the water.

Flexible Retaining Structures

Flexible structures are built before excavation and are embedded in the ground (embedded walls). Their weight is generally not critical, but they experience significant bending moments. They allow excavation below the Groundwater Level (GWL) and are usually supported by props (struts, anchors, dead-men, etc.).

Types of Flexible Structures

Sheet Pile Walls

• They are usually steel piles, and occasionally precast concrete panels. The panels are very deep relative to their small thickness.
• They have a wavy shape to increase their flexural strength and rigidity (increasing the moment of inertia).
• They are driven into the soil by a vibratory hammer, or by a hydraulic crane if the soil is soft.
• They are very useful for temporary works, as the sheet piles can be extracted and reused.

Sheet Pile Construction Process

1. Positioning the sheet pile (using a guide wall).
2. Installation of the first sheet pile.
3. Installation of the second sheet pile.
4. Repetition of the process.
5. Extension of the sheet pile.

Diaphragm Walls

Diaphragm walls are usually cast-in-place concrete. The text notes that vibration must be used to drive the wall into the soil, which could potentially damage nearby structures.

Applications of Diaphragm Walls

• Permanent Works
• In urban areas
• Retaining Walls
• Deep basements and parking lots
• Deep, large-diameter shafts (e.g., for tunnels)

Diaphragm Wall Construction Method

1. Guide Wall Construction: To define the precise location of the panels.
2. Panel Excavation: Excavating non-successive panels.
3. Installing Stop Ends.
4. Panel Concreting.