9) One Dimensional Settlement

9) One Dimensional Settlement

1. Consolidation and Settlement

   • Initial state: fully saturated soil, higher volume
     • V=Δx*Δy*Δz
   • Final state: fully saturated soil, lower volume
     • V=[Δx(1-εxx)*Δy(1-εyy)*Δz(1-εzz)
   • Consolidation - process of water expulsion

2. One dimensional settlement behaviour

   • Spring analogy

3. Horizontal movement in wide embankments is prevented by the adjacent columns of soil

4. Measurement of soil settlement

   • Soil is loaded over a 24h period and the displacement is noted
   • After 24h the load is doubled until the desired load is reached
   • Oedometer apparatus:

5. Relationship between volume strain and axial strain/ voids ratio

   • εv=εzz
     • Confined compression
     • εv=-ΔV/V
     • εv=-(VsΔe/Vs(1+e0))

6. Theory of consolidation

   • A load on top a fully saturated soil will cause water expulsion
   • Time dependant
     • Coarse grained soils - fast
     • Fine grained soils - slow
   • Soil gets stiffer with increasing load
   • Settlement is partly recoverable with unloading

7. One dimensional soil behaviour

8. Consolidation Terms

   • Preconsolidation pressure - maximum effective stress that has been applied to the soil
   • Over consolidated - current effective stress < preconsolidated stress
   • Normally consolidated - current effective stress = preconsolidated stress

9. Estimating preconsolidation pressure

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