Retaining walls are rigid walls used for supporting soil laterally so that it can be retained at different levels on the two sides. The soil got a natural angle of repose and when it exceeds the range a retaining wall structure has to be provided.
They are vertical or near vertical structures constructed to hold soil between two terrains when the slope exceeds the natural one. The slope can be vertical or steep or much above the range of angle of repose.
Also read : Retaining walls – All Types, Materials, features and uses
In this article we are mentioning about some special type of retaining walls
Gravity retaining walls are made of stone, bricks, concrete or any other heavy material. Gravity walls are made with or without mortar They are designed to counter the earth pressure by their self weight. Following are the special types of gravity retaining walls.
a) Crib retaining wall
b) Bin retaining wall
c) Gabion retaining wall
Crib Retaining walls
Crib retaining wall or crib lock retaining wall is one of the oldest types of retaining wall. They consist of cribs or cells made of timber, concrete, and plastic/fibres. The cribs or interlock areas are filled with free-draining materials or earth back-fill, eliminating the hydro-static pressure and enabling a free escape of water.
Most common materials used for crib wall construction is
- Timber crib retaining walls
- Precast crib retaining walls
Timber crib retaining walls
Timber crib walls use timber to form the cells of the crib. The cells are filled with free-draining stone materials for maintaining the mass of the wall. Water drainage can happen freely through the cribs. The timber sections are interlocked to make the walls.
They can also be planted with trees to create a natural appearance. These types of walls are ok up to a height of 5-6 mtrs and mostly used for landscape walls etc.
Precast concrete crib retaining walls
This system consists of a precast concrete header and stretcher units. They are erected to form precast crib retaining walls.
Precast concrete cribs are the cheapest form of earth-retaining systems and are used for landscaping structures, plant terraces, and other works with heights around 10- 20 mtr with proper professional design.
They do not require any skilled labour to do the erection. Trees or shrubs are planted to give natural and excellent looks. Crib walls are erected for small curves and are considered a very flexible material.
Bin retaining walls
Steel bin walls are made from corrugated steel sheets and are usually bolted together and then filled with crushed rock or other free-draining material. They are mostly used for bank erosion protection, holding encroaching slopes, breakwaters, etc. They can resist unforeseen ground movements that may cause failure to other types of retaining walls.
Gabion Retaining walls
Gabion retaining wall systems are one of the oldest forms of gravity wall. Gabion walls are manufactured by factory fabricating a galvanised hexagonal wire mesh of varying diameters into box cages. These box cages are site filled with locally available stones and fully closed and laid in a pattern as per design. They are used in areas where the foundation conditions are not favourable for adopting any other retaining structures. The concept of a gabion wall is to increase the shear capacity of rock by providing the box cages. They can accommodate substantial ground movements without failures. Gabion boxes are free-draining structures that can reduce hydro-static pressure drastically.
The main advantage of these types of systems is that they do not need an exclusive foundation structure. Gabion walls are installed directly over the surface in specified patterns according to design requirements.
The mesh is PVC protected or coated with special coatings to protect from rusting in areas subjected to continuous water flow.
These walls provided a Good visual appeal of the product and the satisfying rock finish look.
Gabion walls are erected mainly for soil stabilisation behind the wall. They can also act as a cover wall. The gabion boxes are stacked in layers with a proper design. They are a very economical alternative for concrete retaining walls and rock anchors for soil stabilisation works and slope protection works.