Learning Objectives:
1) Explain the difference between the UU, the CD, and the CU triaxial tests.
2) Compute the the undrained cohesion or undrained shear strength from UU test results.
3) Explain why the undrained shear strength tends to be lower in an unconfined compression test than in a UU triaxial test.
4) Compute the undrained shear strength from the vane shear test.
5) Compute the undrained shear strength from the Su/sigma ratio.
6) Select the appropriate shear strength (drained or undrained) for use in design for a given engineering loading scenario.

Critical questions to answer:
1) Why is the failure envelope flat in a UU triaxial test or an unconfined compression test?
2) Which assumptions to we make when we perform a UU triaxial test or an unconfined compression test? Are these assumptions valid? Why or why not?
3) Why is the undrained shear strength typically lower in an unconfined compression test than in a UU triaxial test?