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Queensferry

Module 12

Laboratory and field testing

How the numbers are obtained: what each test measures, the drainage condition and stress path it imposes, and whether it represents the field problem you are designing for.

What this module covers

  • Explain that a test must reproduce the field drainage condition and stress path to be meaningful
  • Distinguish classification tests from performance (strength, stiffness, consolidation) tests
  • Read the compression and recompression indices and preconsolidation stress off an oedometer curve
  • Match triaxial test types (UU, CU, CD) to drained and undrained strength parameters
  • Choose an appropriate test for a required design parameter, and judge its representativeness

Lessons

  1. 12.1

    What a test must reproduce

    Drainage, stress path and representativeness — why the right test matters more than a precise one.

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  2. 12.2

    Consolidation and permeability tests

    The oedometer curve and reading Cc, Cr and σ′c; measuring permeability.

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  3. 12.3

    Strength tests

    Shear box, triaxial UU/CU/CD, and in-situ tests — what each yields.

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Module checkpoint

Check what you have taken in

3 questions

  1. Question 1

    On an oedometer virgin line, e = 0.98 at σ′ = 100 kPa and e = 0.80 at σ′ = 1000 kPa. What is Cc?

  2. Question 2

    Which test would you use to obtain the undrained shear strength su for end-of-construction stability of a clay foundation?

  3. Question 3

    A CU triaxial fails at σ1 = 260 kPa, σ3 = 140 kPa with a measured pore pressure u = 60 kPa. What is the effective minor principal stress σ′3, in kPa?