Foundation Engineering
What is Foundation Engineering?
The maximum average contact pressure between the foundation and the soil that will not cause shear failure in the soil.
Key formula / rule: Terzaghi's Ultimate Bearing Capacity (Strip Footing)
Key points
- Understand the principles of shallow foundation design.
- Differentiate between various types of shallow foundations.
- Apply bearing capacity theories to determine safe loads.
- Estimate foundation settlement.
Common exam trap
Ignoring settlement analysis, focusing only on bearing capacity.
Definitions
- Term
Bearing Capacity
- Meaning
The maximum average contact pressure between the foundation and the soil that will not cause shear failure in the soil.
- Term
Settlement
- Meaning
The downward displacement of a foundation due to the applied loads.
- Term
Factor of Safety (FoS)
- Meaning
The ratio of the ultimate bearing capacity to the allowable bearing capacity, ensuring a margin of safety against failure.
Learning objectives
Understand the principles of shallow foundation design.
Differentiate between various types of shallow foundations.
Apply bearing capacity theories to determine safe loads.
Estimate foundation settlement.
Select appropriate foundation types based on site conditions.
Formulae
- Name
Terzaghi's Ultimate Bearing Capacity (Strip Footing)
- Note
Where qu is ultimate bearing capacity, c is cohesion, q is surcharge pressure (γDf), γ is unit weight of soil, B is foundation width, and Nc, Nq, N_γ are bearing capacity factors depending on the angle of internal friction (φ).
- Expression
qu = cNc + qNq + 0.5γBN_γ
- Name
Allowable Bearing Capacity
- Note
FoS is the Factor of Safety, typically 2.5 to 3.
- Expression
qa = qu / FoS
- Name
Surcharge Pressure
- Note
Df is the embedment depth of the foundation.
- Expression
q = γDf
Prerequisites
Soil Mechanics: Soil properties (cohesion, friction angle, unit weight), stress-strain behavior.
Strength of Materials: Stress, strain, bending moment, shear force.
Structural Analysis: Load transfer mechanisms.
Common mistakes
Ignoring settlement analysis, focusing only on bearing capacity.
Incorrectly applying Terzaghi's bearing capacity factors.
Assuming uniform soil conditions when they are variable.
Using an inadequate factor of safety.
Not considering the influence of groundwater table.
Keywords
Shallow Foundation
Bearing Capacity
Settlement
Terzaghi
Footing
Raft Foundation
Factor of Safety
Practice preview
The ultimate bearing capacity of a soil is defined as the:…
easy
Which type of settlement occurs almost immediately after the application of load, primarily due to elastic deformation of the soil?…
easy
A concrete pile of 400 mm diameter is driven into a homogeneous clay layer. The undrained shear strength (c_u) of the clay is 50 kPa. If the pile is 10 m long and the adhesion factor (alpha) is 0.7, what is the approxima…
medium