Shallow Foundations Revision Checklist

Terzaghi’s Bearing Capacity Equation (inc shape factors etc)

- estimates the maximum stress (ULS) that a shallow strip foundation can carry in theory

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What are the three components of the equation – what do they physically represent – internal cohesion (Nc), overburden effect (Nq) and internal friction/confinement (Nγ)

What are the main assumptions - smooth, infinite, flexible strip foundation on a semi-infinite, weightless, plastic medium

What case is the equation for – General Shear (dense, stiff soils) and what happens when the soils is less dense or looser? Be able to describe, sketch and explain local and punching shear cases as well as General Shear.

Applying to different cases

What is the analysis case I am considering – drained (usually long term) or undrained (short term in fine grained soil such as clay). Choose the appropriate N values.

Do I know or need to estimate the unit weight of the soil at each level?

Where is the water table - >2B below FL (neglect) or within 2B or above FL – need to adjust the unit weights to buoyant values.

Is there an overburden (FL below OGL) and can it be relied upon in practice – if it might be excavated or poorly backfilled should I neglect it?

Usually a sketch to show the expected FL, the OGL and the water table will help get this right and then list any assumptions you are making.

What shape is the foundation – it if is not a