You may confuse the retaining wall blocks with the normal walls you see around you covering the gardens or roadways but this is not the fact. The retaining walls are not usual walls and are not constructed for every situation. These walls differ in terms of their design, attributes, materials, and area of application. As you can infer from its name these walls are built to retain their structure against various kind of force. This force can either be exerted by earth, soil of some mountain or even water.
Unlike other walls these are built to provide safety against collapsing and slipping of soils and stones. These walls are usually made around roads that are in mountain areas so that these walls can prevent the soil of mountains from collapsing and damaging the road areas. These walls need not to be a part of some proper construction work like a building rather these can function as an independent structure and could be used to provide decorative and operational features of landscape. If this wall is a part of some construction work such as part of some building then you need to get permission from planning authorities if its height exceed than 1 meter. But if you are building these walls independently along the road then these walls height can exceed 2 meter heights and you do not even need to get permission for this. However, the basic requirement of sound structure must always be fulfilled regardless of the area of application. Furthermore, the building regulations and standard divisions (DCLG) has complete authority to remove such structures and walls which do not satisfy their standards of soundness and strength and can present any sort of danger. Therefore, the retaining wall must be strong enough to retain itself against the earth pressures. There are following types of earth pressures. Browse this website to find out more details.
Earth also provides pressure when the wall is static and material is in its original state this is known as earth pressure at static state. Then there are active and passive earth pressures. Active earth pressure is exerted when the wall is pushed away from the backfill whereas passive earth pressure is exerted when wall goes towards the backfill. Not only earth but water can also build up the pressure and the pressure of water is known as hydrostatic pressure. Therefore, these walls must have some sort of mechanism which keeps on draining the water like some sort of drainage or water holes so that these can reduce the force of water and the walls could maintain their form.