Foundation Engineering Study Notes

Foundation Engineering

Understanding Foundation Engineering and Types

Soil as Foundation Material
  • Geotechnical engineers consider soil fundamental for supporting structures.

Introduction to Foundation

  • Definition of Foundation:
    • Structural member that supports a structure.
    • System affected by loading from soil or rock.
  • Materials Used: Concrete, Steel, Wood.

Types of Foundations

Shallow vs. Deep Foundations

  • Shallow Foundations:

    • Suitable for firm soil and light loads.
    • Types include Spread Footings, Mat Foundations.

  • Deep Foundations:

    • Include Driven Piles, Drilled Shafts, Auger Cast Piles.

Factors Affecting Foundation Choices

  • Primary Factors:
    • Subsurface soil, groundwater conditions, structural requirements.
  • Secondary Factors:
    • Building codes, surrounding structures, construction risks.

Types of Shallow Foundation

  • Square and Rectangular Footings.
  • Examples include Circular Foundations, Continuous Footings, and Combined Spread and Strip Footings.

Advantages and Disadvantages of Shallow Foundations

  • Advantages:
    • Simple construction, cost-effective, low expertise required.
  • Disadvantages:
    • High risk of settlement, susceptible to pullout and torsion, not suited for irregular terrains.

Types of Structural Settlements

  • Uniform Settlements: Equal settlement across foundation.
  • Tilting Settlements: Uneven distribution causes tilting.
  • Differential Settlements: Varying settlements can damage structures.

Reduction of Settlement

  • Design Considerations:
    • Modify structure, increase stiffness or flexibility, lighten loads.
  • Practical Considerations:
    • Modify foundation using wider or multiple footings, mat foundations for poor soils, deep foundations.

Bearing Capacity of Soils

  • Key Theories:
    • Meyerhof, Terzaghi, Hansen, Vesic.

Terzaghi Bearing Capacity Equation

  • For General Shear Failure:
    • For strip footings: q_1 = 1.0cN' + D
      ho + 0.5BN'
    • For square footings: q = 1.3cN' + D
      ho + 0.4
      ho BN'
    • For circular footings: q_1 = 1.3cN' + D
      ho + 0.3
      ho BN'
  • Bearing Capacity Factors (Nc, Nq, Ny):
    • Values depend on shear failure types and friction angle.

Practical Application Example

  • Calculating ultimate bearing capacity for a square footing.
  • Example given with dimensions and conditions for a footing at specific depth.