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Queensferry

Module 03

How a footing fails

The mechanism under the equation — and why it is exponential in friction.

What this module covers

  • Describe the three modes of bearing failure and say which soils produce each
  • Explain the failure mechanism beneath a footing in terms of the wedge, the fan and the passive zone
  • Explain why bearing capacity is so sensitive to the friction angle
  • Recognise when a general shear failure will not develop, and what happens instead

Lessons

  1. 3.1

    Three ways to fail

    Only one of them looks like failure.

    Start lesson →
  2. 3.2

    The mechanism beneath the footing

    A wedge, a fan and a passive zone — and where the exponential comes from.

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Module checkpoint

Check what you have taken in

2 questions

  1. Question 1

    Which zone beneath a footing produces the surface heave seen in a general shear failure?

  2. Question 2

    Using Nq = e^(π tan φ′) · tan²(45° + φ′/2), calculate Nq for φ′ = 35°. Give the answer to one decimal place.