Cantilever Retaining Walls | Civil Engineering Optional Notes for UPSC PDF Download

Definition

Construction and Function

• Construction: Typically constructed of reinforced Portland-cement concrete (PCC), cantilever retaining walls were the predominant type of rigid retaining wall from the 1920s to 1970s.
• Function: To retain soil at a slope steeper than it would naturally assume, usually at a vertical or near-vertical position. They are used to maintain two different ground surface elevations.

Design Considerations

• Height of the water table
• Nature and type of soil
• Subsoil water movements
• Type of wall
• Materials used in the wall's construction

Earth Pressure

• Active Earth Pressure: The pressure that tends to move or overturn the retaining wall.
• Passive Earth Pressure: Reactionary pressures that resist the movement of the wall.

Types of Cantilever Retaining Walls

Figure 1 :Typical reinforced concrete cantilever walls

2. Wall with Large Toe: Used when a large heel is not practicable.

Figure 2 : Typical reinforced concrete cantilever retaining walls

Reinforcement

• The main steel reinforcement occurs on the tension face of the wall.
• Nominal steel (0.15% of the cross-sectional area) is often included on the opposite face to control shrinkage in in-situ concrete work.
• Reinforcement requirements, bending, fabricating, and placing are detailed in sections on reinforced concrete.

Advantages

• Economic Height Range: 1.2 to 6.0 meters. Walls taller than this can be economically constructed using prestressing techniques.
• Aesthetic Finishes: Any durable facing material can be applied to improve appearance, but it does not add structural strength.

Failure Modes

1. Effect of Water: Groundwater behind the wall, whether static or percolating through subsoil, can adversely affect design and stability.
2. Slip Circle Failure: Common in clay soils, particularly with heavy surcharges.
3. Low-Quality Materials: Using substandard materials can lead to failure.
4. Insufficient Reinforcement: Inadequate reinforcement can compromise the wall’s integrity.
5. Design Errors: Mistakes in calculating the height of the water table, nature, and type of soil, and subsoil water movements.

Identifying Failure

• Sloping Position: The wall may lean or tilt.
• Curved Surface: The wall may exhibit a curve.
• Cracks: Visible cracks in the structure.
• Water Damage: The wall may be awash or show signs of water damage.

By understanding these aspects, engineers and constructors can ensure the proper design, construction, and maintenance of cantilever retaining walls to prevent failures and achieve long-lasting, stable structures.