FLOATING FOUNDATION - DEFINITION, PRINCIPLES

Floating foundation is based on the weight of the structure and the weight of soil and water excavated from the area. This is also known as the Caisson foundation. Generally, this type is used in soil having large settlement. For more articles CLICK HERE

FLOATING FOUNDATION

This type of foundation is constructed by excavating the soil and water, which is equal to the weight of the building to be constructed. Another name of the Floating foundation is Balancing raft or Partially compensated foundation.

Usually, this is used in soil having high moisture content undergoing heavy settlement. This foundation does not use footing. The superstructure is separated from the substructure in a way that the vertical pressure acting remains unchanged. These are also known as a raft foundation.

PRECAUTIONS TAKEN WHILE CONSTRUCTING

Since this is used in moisture soil the excavation should be done with proper care. Before the beginning of the excavation, The water present in the water table should be dewatered. Various methods are used for dewatering which results in the safe excavation.

After dewatering sides of the pit are supported by using sheet piles. This avoids the collapse of the ground. The weight of the water present in water is also calculated while digging. The settlement of such foundation is zero.

The deck system is constructed with the layout of the box beam frame.

EARTHQUAKE RESISTANT

Floating foundation the name itself says its Floating. This is an advantage in areas where an earthquake occurs.

The Building is placed on a lead rubber bearing. Floating foundation earthquake-resistant buildings are constructed. This consist of rubber and steel layers in which the core is made up of lead. These are attached by using steel plates. So during an earthquake, these Building moves above the ground and reduces damage and risks.

ADVANTAGES OF FLOATING FOUNDATION

• Used in soil having heavy or differential settlement.
• This is used in places with low shear strength.
•  Used in soft soil, where no hard strata found at a certain depth
• Even the factor of safety is high, this type is prefered with soil having a severe foundation.
• Protects from earthquakes.
• Reduces stresses.

FLOATING CAISSONS

Floating caissons are open at the top and are closed at the bottom. These are constructed and then transported to the site. Then installed in places. These are then allowed to sink by filling concrete,gravel etc. It can be used in the construction of dams, garage etc.

After reaching the targeted place these are filled with gravels. The main two part of this caisson is the concrete cap and the rip rap. The concrete cap is used to receive the loads and the rip rap is used to avoid the wear and tear.

These are made up of steel or reinforced concrete. The Floating caisson designed in rectangular, circular, elliptical or square shapes.

The principle behind the caisson is Archimedes principle.
when the body is immersed in the water an amount of water which is equal to the weight of the body is displaced.

W-U = 0

The caisson immersed in the water will become stable only if the metacentre is above the centre of gravity. The buoyant force acts through the centre of gravity. So while designing the caisson the stability should be taken into account. 

Since the floating foundation cost is less and they are easily transported, these are more prefered. They are precast or prefabricated. They have good quality.

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