9.4. Importance of Effective Stress

Try these first

1. 1.

   What is the formula for effective stress?

   Hint

   Consider what each term in the formula represents.

2. 2.

   What happens to effective stress when pore water pressure increases?

   Hint

   Think about the relationship between total stress and pore water pressure.

3. 3.

   What does effective stress determine in soil?

   • Soil strength
   • Pore water pressure
   • Total stress

   Hint

   Think about what keeps the soil particles together.

4. 4.

   True or False: A rise in the pore water pressure always leads to an increase in effective stress.

   • True
   • False

   Hint

   Recall the effective stress equation.

5. 5.

   You have a soil column with a total stress of 30 kPa at a depth of 5 m and a pore water pressure of 10 kPa. Determine the effective stress.

   Hint

   Use the effective stress formula.

6. 6.

   In a scenario where excavation causes the total stress to increase by 15 kPa and the pore water pressure increases by 10 kPa, what happens to effective stress?

   Hint

   Think about the relationships between changes in pressure.