4) Effective Stress

4) Effective Stress

1. Loaded soil

   • By water - Soil becomes saturated, does not compress
   • By load - soil compresses

2. Total normal stress

   • σv=F/A=γd

3. Pore water pressure

   • uw=γd

4. Effective normal stress

   • σ`=σv-uw

5. Only apples to fully saturated soils

   • All measurable effects of change in stress is due to changes in effective stress

6. Drainage dependant

7. Changes in effective stress

   • σ` increases
     • Soil compresses, ground surface settles
   • σ` decreases
     • Soil swells, ground surface heaves
       • Surface flooding, basement flooding, uplift of buildings, failure of retaining structures, failure due to reductions in bearing capacity