Describe Raft Slabs for foundations & when and where they are used,
-a thick slab to bear the load across a large surface area
-they are used when the soil is weak or unstable but the ground still must be bearable
-used for commercial buildings
Advantages of Raft foundation
-Relatively cheap
- can be used with poor ground conditions
Disadvantages of raft foundation
-Susceptible to edge erosion
- poor at supporting point loads
Describe pad foundations
When pads and columns are placed close together, reinforcing longitudinal stiffness.
Advantages of pad
-shallow foundation
-requires little excavation
-reinforcement for tension and shear can be added
disadvantages of pad foundation
- limited suitability for framed buildings
-foundation size can be too large to manages high point loads
-deep excavation required
Describe pile foundations & where they are used
Where slender vertical columns are used to transfer the load of structure down to the soil.
Used where heavy points exceed bearing capacity, low bearing subsoil
Advantages of pile foundation
- Made off site in a factory
-No excavation required
-suited to framed construction
-can transfer loads in variable ground conditions
Disadvantages of pile foundations
Noisy installation & vibration
High cost compared to shallow foundations
Complex design- needs specialised expertise
How are loads transmitted in end bearing
End bearing: the load is transferred directly to the base of the pile once a solid layer is penetrated
How are loads transmitted in skin friction
The load is supported by the frictional resistance between contact (of the surface) and the soil
Types of pile
Bored Pile - cylindrical tube is drilled then poured
Displacement - driven into the ground ( no excavation required)
