This lecture introduces two different but important concepts related to effective stress: zero effective stress, and effective stress within the zone of capillary rise. The concept of critical gradient is introduced, and various terms including boiling, piping, heaving, and liquefaction are introduced. An example of computing the factor of safety against heave in an excavation is performed. The concept of capillarity in water is reviewed. The zone of capillary rise is discussed, and an example is performed where the effective stress is computed within the zone of capillary rise.

Critical Questions to Consider:
1) Why would zero effective stress be a bad thing in soil?
2) Why is pore pressure negative within the zone of capillary rise? Why would the actual pore pressure be affected by the degree of saturation of the soil?