Strip / Pad / Piled Foundations

Question 1

Describe the process of constructing a strip foundation?

Answer 1

1. Dig trenches to a depth that reaches the required soil bearing strata.
2. Erect and place temporary supports
3. Pour concrete into the trenches.
4. On top of these concrete trenches, the loadbearing walls of the building can be erected.

Question 2

For buildings with insulated ground floors what is the general minimum foundation depth that is sufficient against the possibility of damage from ground movement due to frost heave?

Answer 2

450mm

Question 3

Why are strip foundations not commonly used when you have to excavate deep into the ground to reach soil with a higher bearing strata?

Answer 3

It is very expensive thus pad foundations (less excavation required) are used.

Question 4

What does the width of a concrete strip foundation depend on?

Answer 4

The Bearing Capacity of the soil and the loads that will be acting on the foundations

Question 5

What is shear failure?

Answer 5

Shear is caused by two opposing forces of the wall and the ground acting on and tearing or shearing the concrete (footing).

Question 6

Strip foundations on subsoils with poor bearing capacity need to be a lot wider than the wall they support. The alternative to widening the wall is adding…?

Answer 6

Steel reinforcement (means the foundation doesn’t need to widen as much).

Question 7

It is normal when using strip foundations to have a foundation depth of at least what?

Answer 7

0.9m minimum

Question 8

What depth is ‘topsoil’ (the weak top surface of land that needs to be removed before construction can begin)

Answer 8

Typically between 100-300mm

Question 9

Describe the process of constructing a pad foundation?

Answer 9

Pits are excavated down to the necessary level (the sides of the excavation are temporarily supported and isolated pads are cast in the bottom of the pits. The ground beams/foundation beams may be just below or at ground level.

Question 10

Describe the process of constructing a pile foundation?

Answer 10

Pits are excavated down to the necessary level, the sides of the excavation temporarily supported and isolated pads of concrete are cast in the bottom of the pits.

Question 11

What material is most used for temporary support for the sides of excavations in foundations?

Answer 11

Rough Sawn Timber

Question 12

Name the 4 different types of foundation (and describe them in your head)

Answer 12

1. Strip
2. Pad
3. Pile
4. Raft