Cantilever Retaining Wall

Cantilever retaining wall operate on the principles of leverage, their stem is substantially thinner, and the majority of their resistance to sliding and overturning comes from the weight of the backfill dirt.

The most typical style of earth-retaining structure is the cantilever retaining wall.

Two different ground surface elevations are maintained by using earth slopes and earthen retaining structures.

What is Cantilever Retaining Wall?

Cantilever walls are constructed from reinforced concrete and have an L-shaped or inverted T-shaped base.

By transferring the vertical stress behind the wall to the foundation, the collapse caused by the background pressure of the same soil mass is avoided.

The weight of the soil in front of the wall (and the resulting vertical stress) supports the T-shaped foundation, increasing its stability.

Sometimes the base of the foundation has a “key” that sticks to the ground to prevent it from sliding and collapsing.

As compared to other styles of retaining wall, cantilever walls take up less space once constructed that are suitable for retaining heights up to 5 meters.

They are not particularly suited to retaining existing slopes, however, they do not provide temporary support during building construction as they take up space behind the wall.

Purpose of Cantilever Retaining Wall:

The purpose of a cantilever retaining wall is to hold the soil in a generally vertical or nearly vertical position, but on a steeper slope, it would naturally accept.

To determine the pressure applied to the wall at any given point, consider the following:

• The size of the water table.
• Nature and soil type.
• Movement of water in the soil.

Types of Cantilever Retaining Walls:

1. Cantilever wall without toe (L shaped).
2. Cantilever wall with another heel (Inverted L shaped).
3. Cantilever wall with the key.
4. Cantilever wall on abutment (Wing wall).

Parts of Cantilever Retaining Wall:

Stem:

The vertical upright section of the cantilever wall that supports or restrains the lateral confinement is referred to as the stem.

The ratio of the stem is slimmer.

The base of the stem may be thicker than the rest of the stem at times, but this is not always the case.

Toe:

The bottom footing is buried in the ground up against the exterior of the wall, away from where the soil mass needs to be kept in place.

Heel:

The heel is also a component of the foundation footing that is buried in the ground.

The heel’s length is noticeably longer to increase the wall’s weight.

By acting as a component of the wall and adding weight to the footing, the earth above the heel behaves as part of the wall increasing the restoring moment against the moment induced by the lateral force of the retaining mass.

Key:

It is a modest, barrier structure of a retaining wall that is occasionally built on footings to improve passive lateral forces, and resist sliding and shearing.

Methods to Build the Cantilever Retaining Wall:

The limit equilibrium approach is commonly used to study cantilever walls.

The designer uses this method to determine the active and passive ground pressures on either side of the wall.

 If necessary, water and other charges are also added, there are two methods for limiting equilibrium analysis:

a) Free earth approach for cantilever walls:

This strategy is the simplest, the overturning and resisting moments need to be balanced as required.

 On the side to be placed, active earth pressures are often expected, and on the side to be excavated, passive earth pressures.

The necessary embedment for a safety factor of 1 is thus reached at the zero-moment point.

The method’s drawback is that shear loads are not distributed equally.

Therefore, it is advisable to multiply the embedment obtained for FS=1 by about 1.2. (To obtain a wall embedment with a safety factor of 1).

b) Fixed earth method for cantilever walls:

The fixed earth method balances the shear and overturning moments, however, the static earth method’s analytical results are relevant in specific circumstances.

Finding important key points about how the static earth approach works balances rotational moments and shear forces.

It is assumed that there are active earth forces on the excavation side and passive earth pressures on the side that is positioned beneath the pivot point.

Given the restricted number of closed-form solutions with the fixed earth method, Winkler spring analysis is advised instead of the more common fixed earth solution.

c) Practical recommendations for cantilever walls:

To establish a sufficiently safe construction, wall embedment for cantilever walls is often needed in the range of 1.5 times the excavation height.

Although rapid excavation is a benefit of cantilever walls, the typical maximum depth is about 15 feet or less (4.5 m).

Beyond that depth, more rigid and expensive wall elements will be required to keep horizontal wall displacements within acceptable limits.

Although deep cantilever walls have been used successfully with small sections, their effectiveness frequently results from observed soil strengths exceeding conservative design estimates.

When constructing deep cantilever walls, horizontal wall movements must be carefully considered.

Specifications of Cantilever Wall:

Cantilever Retaining Wall is constructed cost-effectively using the prestressing process.

 Reinforced cantilever walls can be built up to a height of 6,000 meters.

 It is possible to apply any long-lasting material to the surface to enhance the appearance of the wall, but it should be remembered that these finishes are only aesthetic and do not enhance the structural integrity of the wall.

Cantilever wall defects:

• Effect Groundwater can negatively affect the construction and stability of a wall, whether it is static or percolating through the soil.
• In clayey soils, slip circle failure can occur with cantilever walls, especially if there is significant overburden.
• Poor-quality materials were used in the cantilever construction.
• Cantilever wall reinforcement has a low design.
• Errors in water table elevation, nature, and soil type.
• The flow of water into the soil.

Detection of Cantilever Wall Failure:

• A cantilevered wall should be sloped.
• The surface or wall of the cantilever wall should be curved.
• Wall structural cracks.
• Washed cantilever wall.

Advantages of Cantilever Retaining Wall:

1. Cantilever walls provide a clear excavation path.
2. Cantilever walls do not require tiebacks to be installed below neighbouring properties.
3. A more straightforward method of construction is provided by cantilever walls.

Disadvantages of Cantilever Retaining Wall:

1. For cantilever walls, the maximum excavation is typically 18 feet (6 m).
2. Generally, cantilever walls should not be used adjacent to adjacent buildings.
3. Passive earth resistance must be activated to control side wall displacements.
4. Deep cantilever excavations may require significantly improved wall stiffness. This may reduce the options for excavation sites.

Conclusion:

The many stability failure modes must be taken into consideration while designing cantilever retaining walls.

 At every location of the structure, the reinforcing of the wall components must offer sufficient structural strength.

Section Under: Retaining Walls