Reinforcement of cantilever retaining wall.

Retaining wall design is crucial for giving support to slopes of soil, that would otherwise be unstable and run-off.   The different types of wall designs include Gravity, Semigravity, Cantilever and Counterfort. The precision in the design of such walls is important since they can be toppled by natural forces (hurricane & earthquakes) if ill-constructed. The soil that these walls support is known as backfill.

Tip 1: Understanding the Cantilever Beam
Reinforced Cantilever wall is shaped like an inverted T. The structure includes a vertical column which is essentially holding the backfill and a footing which horizontally rests on the ground and stabilizes the weight of the backfill. The part of the footing which is under the backfill is called the heel or the inner footing, whereas the exposed area is the toe or outer footing. The vertical length is called the stem and together the three compose the cantilever beam. The length of the entire structure usually ranges from 10 to 25 feet and is the most common wall design for resisting loose material.

Tip 2: Meaning of Reinforced Wall
Reinforced means to add extra strength to the structure and is mostly done by adding steel to the Cantilever beam. Steel and concrete have similar temperature expansion characteristics so one can avoid expansions or contraction within the structure. Therefore not only will steel add to the strength of the wall, it will also minimize the cracks that inevitably occur in concrete. The two are also complimentary since concrete is strong in compression and steel in strong in tension. You can also reinforce the cantilever wall by adding external buttresses. These are triangular slabs placed between the stem and the footing. Reinforcement can also be incorporated by adding a ground anchor to the cantilever footing for better stability. However these options are preferable in smaller retaining walls. If the Cantilever is more than 10-15 feet, steel reinforcement is the most favourable option.

Tip 3: Calculations to Consider
It is important that the steel emerges from the footer and rises up the vertical column for a well-constructed reinforced wall. There are a number of figures that need to be considered in order to design a Reinforced Cantilever wall and therefore most engineers use a computerized program for these calculations. The width of the footing is an important consideration since it essentially stabilizes the weight of the backfill. The length, width and height of the stem, the strength of the concrete and the steel respectively as well as the backfill properties such as density and angle are also included. Study of “stability moments” (resistance to overturning), is crucial in determining the appropriate design for reinforced walls with regard to the pressure the backfill puts on them and includes rigorous numerical analysis.

Tip 4: Improving the Wall
The calculations mentioned above can be performed in order to construct a well-designed reinforced cantilever wall. By increasing the friction angle of the backfill, the engineer can counteract the increase in unit weight. Also in order to increase the stability moment of the cantilever, the engineer can increase the thickness of the wall and hence it’s weight. Care should also be taken to avoid carbonation or steel corrosion, depending on the surrounding environment of the structure.

This video has nicely demonstrated about the detailed calculation step by step

Credits on this video: parag pal

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