11) Consolidation

11) Consolidation

1. Definition

   • Gradual reduction in volume of a fully saturated soil of low permeability due to drainage of some of the pore water until the excess pore water pressure has completely dissapated
     • Increase in effective stress

2. Occurs in fine grained soils

3. Caused by applied load

4. Occurs over a period of time

   • Occurs instantaneously for coarse grained soils

5. Time depends on the permeability of the soil

6. Leads to settlement over time

7. Process:

8. Terms

   • Preconsolidated stress (σpc)
     • Highest stress experienced in loading history
   • Normally consolidated soil
     • Soil experiencing highest loading
   • Over consolidated soil
     • Soil experiencing lower stresses than σpc
   • Over consolidation ratio
     • Level of consolidation

9. Coefficient of volume compressibility (Mv)

   • Mv=(ΔV/Vo)*(1/Δσ)
     • ΔS=MvH0Δσ
   • Coefficient of consolidation Cv

10. 1D consolidation

    • Solution for 2 way drainage
    • Governing equation

11. Calculation of settlement

    • Approximate expression for degree of settlement

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