The image you've provided shows stress diagrams for a clay sample subjected to:

1. Consolidated-Undrained (CU) Test:

   • Application of cell pressure and drainage to back pressure of $100 \, \text{kN/m}^2$.
   • Application of axial load to failure in an undrained condition.

2. Drained (D) Test:

   • Similar cell pressures and drainage conditions, but the test allows for drainage during the application of axial load until failure.

To determine the shear strength parameters (cohesion $c$ and angle of internal friction $\phi$) for the clay, we can apply Mohr-Coulomb failure theory based on the total and effective stresses in each test. Here’s a general outline of steps to follow:

1. Extract Stress Values: From each test diagram, identify the confining cell pressure and the additional axial load at failure.

2. Calculate Deviator Stress: For each test, compute the deviator stress ($\sigma_1 - \sigma_3$) by subtracting the cell pressure from the applied axial stress at failure.

3. Determine Total and Effective Stresses:

   • In the CU test, use total stresses since it’s undrained.
   • In the drained test, use effective stresses, as pore pressures equilibrate.

4. Plot Mohr Circles: Using the calculated stresses, plot Mohr’s circles for each test condition and draw the failure envelope.

5. Calculate $c$ and $\phi$: Determine cohesion and friction angle based on the Mohr-Coulomb envelope that best fits the Mohr circles.

Would you like further detailed calculations or specific values from each step?

Expanding Questions

1. What are the differences in stress behavior between consolidated-undrained and drained tests?
2. How does pore water pressure affect shear strength in undrained versus drained conditions?
3. Can Mohr-Coulomb theory be applied to all soil types for shear strength analysis?
4. What is the significance of using a back pressure in these tests?
5. How does the presence of clay in soil impact its shear strength properties?

Tip

In soil mechanics, effective stress plays a crucial role in drained conditions, as it reflects the soil’s true ability to carry load by accounting for pore water pressure.