The Chartership Forum

Soil Mechanics / 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 you will understand

  • 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. What a test must reproduce

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

  2. Consolidation and permeability tests

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

  3. Strength tests

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

Module summary
  • A test is meaningful only if it reproduces the field drainage condition and stress path, on a representative sample.
  • The oedometer gives Cc, Cr, σ′c and cv; permeameters give k; strength tests give su or c′, φ′.
  • Triaxial UU/CU/CD map onto short-term and long-term field cases; in-situ tests add realism and volume.
  • Procedures and correlations are standard-dependent and must be checked against the current edition.
Teaching basis and review status

These are educational models and exercises. Check their assumptions before using the results. The full technical content and every diagram have not yet been independently verified.

Concrete and steel calculations retain their stated first-generation Eurocode teaching basis. Use the standards and amendments specified for your project; do not mix generations without an appropriate design basis.

Read the lesson register and outstanding review notes

Check your understanding

Practice

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

Check yourself

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

Practice

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?