Introduction to shallow foundations- Design issues

Question 1

What is are foundations?

Answer 1

They constitute the part of the structure at the interface between the foundation soil and the structure itself.

Question 2

What are the 5 roles of foundations?

Answer 2

1. The foundation transfers vertical (e.g. the weight of the building) and horizontal (e.g. wind forces) forces to the ground.
2. The foundation controls the amount of movement in the building due to changes in stress in the ground or changes in water level
3. Prevents damage to adjacent structures.
4. Transmits the load beneath zones affected by seasonal change.
5. Prevents damage to structures due to subsequent changes in the use of the building

Question 3

What is a steel column designed to operate at?

Answer 3

Working stress of 150 MPa

Question 4

What is a concrete column designed to operate at?

Answer 4

10 MPa

Question 5

What is the range at which soil strength varies?

Answer 5

5 kPa - 1000 kPa

Question 6

What should we consider when designing a foundation in terms of settlement?

Answer 6

It should be kept within allowable limits

Question 7

Define bearing capacity

Answer 7

Capacity of the ground to resist loads, such as: dead, live, wind, inclined thrusts and uplift, water table and earthquake forces

Question 8

What can happen if a foundation is designed poorly?

Answer 8

The building could start to crack/tilt due to differential settlement of the foundations (fails serviceability limit criteria)

Question 9

What is a differential settlement?

Answer 9

Non-uniform movement of the underlying soils

Question 10

What are the two problems we need to investigate when designing a foundation?

Answer 10

• Settlement = Soil compressibility
• Failure = Shear strength

Question 11

When a soil fails how does it fail?

Answer 11

Soils generally fail in shear

• At failure, shear stress along the failure surface reaches the soil shear strength.

Question 12

Give two examples of soils failing in shear

Answer 12

1. Excessive displacement causing building to collapse
2. Land slide