Cantilever retaining walls can safely be used for a height not more than A. 3 m B. 4 m C. 5 m D. 6 m

The correct answer is: C. 5 m.

Cantilever retaining walls are a type of retaining wall that is supported by its own weight and the weight of the soil it retains. They are typically used for low retaining walls, up to 5 m in height.

The maximum height of a cantilever retaining wall is limited by the following factors:

• The strength of the soil: The soil must be strong enough to support the weight of the wall and the soil it retains.
• The type of soil: The type of soil will affect the stability of the wall. For example, clay soils are more stable than sandy soils.
• The groundwater table: The groundwater table must be below the base of the wall to prevent the wall from becoming unstable.
• The seismic activity: The seismic activity in the area will affect the design of the wall.

Cantilever retaining walls are a cost-effective and efficient way to retain soil. They are easy to construct and require minimal maintenance. However, they are not suitable for all applications. For example, they cannot be used in areas with high seismic activity or where the groundwater table is high.