General

If the settlement module is available settlements is calculated for all load cases according to [4] 2.6 and 3.53. Calculations of settlements shall include both immediate and delayed settlements.

The depth of the compressible soil layer to be considered may normally be taken as the depth at which the effective vertical stress due to the foundation load is 20% of the effective overburden stress. If the ratio between the bearing capacity of the ground to the applied serviceability loading is less than 2 the calculations should also take account of creep:

• S_d > R_d / 2

 Swedish annex

• S_d > 2 R_d / 3

Cohesionless soil

For cohesionless soil the calculation can be performed with regard to peak pressure sounding where the characteristic peak pressure q_ck is obtained or with regard to estimated modules or dilatometer results. If the latter method is used for settlement calculations of small footings relatively the soil depth the elasticity modulus E is recommended as it includes the effect of lateral extension while in other cases the compression modulus M can be used. The safety factor γ_R,d will consider uncertainties in the calculation model.

Peak pressure sounding

The settlement s is according to De Beer (1965) calculated layer wise as:

• s = γ_R,s Σ 2,3 / C_d log ((σ_0d' + Δσ_d') / σ_od') Δz
  • C_d = 1,5 q_cd / σ_od'
    • q_d is the peak pressure q_d = q_k / γ_M
  • σ_od' is the effective pressure at the middle of each layer,
    • σ_od' = γ (d + z) above ground water level
    • σ_od' = γ (d + h) + γ' (z – h) below ground water level
  • Δσ_d' is the vertical stress increase and is calculated with the 2:1 method
    • Δσ_d'= Δq / ((1 + z / B') (1 + z / L'))
      • Δq is the load at ground level.

Estimated modules

The settlement s is calculated layer wise as:

• s = γ_R,s (Δσ_d' / E_d) Δz
  • Δσ_d' is the vertical stress increase and is calculated with the 2:1 method
    • Δσ_d'= Δq /((1 + z / B') (1 + z / L'))
      • Δq is the load at ground level
  • E_d is the E-modulus
    • E_d = E_k / γ_M
      or
    • Compression modulus M_d = M_k / γ_M

Cohesive soil

For cohesive soil the calculation can be performed with regard to soil conditions based on laboratory tests where consolidation pressure and compression properties are evaluated. The safety factor γ_R,ds will consider uncertainties in the calculation model. The settlement s is calculated with regard to the compression modulus M.

Until the consolidation pressure reach σ_c'  the compression modulus is constant with the value M_o. The compression modulus will then fall to a lower value M_L which will be constant until the pressure reached σ_L^'. If the load is further
increased the compression modulus M will also increase as seen above.

The settlement s is calculated layer wise as:

• s = γ_R,s Σ(Δσ' / M) Δz
  • 0 < Δσ' ≤ σ_cd'

• s = γ_R,s Σ(σ_d' - σ_od') / M_o Δz
  • σ_cd' < σ_d' ≤ σ_Ld'

• s = γ_R,s Σ[(σ_cd' - σ_od') / M_o + (σ_d' - σ_cd') / M_L] Δz
  • σ_d' > σ_Ld'

• s = γ_R,s Σ[(σ_cd' - σ_od') / M_o + (σ_Ld' - σ_cd') / M_L + 1 / M' ln((σ_d' - σ_Ld') M' / M_L + 1)] Δz
  • σ_d' = σ_od' + Δσ_d' = σ_od' + Δq /((1 + z / B') (1 + z / L'))
    • σ_od' is the effective pressure at the middle of each layer
      • σ_od' = γ (d + z) above ground water level
      • σ_od' = γ (d + h) + γ' (z – h) below ground water level
    • Δσ_d' is the vertical stress increase and is calculated with the 2:1 method
    • Δq is the load at ground level.

Medium soil

With medium soil means soil types where both un drained and drained analysis has to be made e.g. silt and clay moraine. The settlement is calculated with regard to estimated modules or dilatometer results. For settlement calculations of small footings relatively the soil depth the elasticity modulus E is recommended as it includes the effect of lateral extension while in other cases the compression modulus M can be used.

The safety factor γ_R,s will consider uncertainties in the calculation model.

The settlement s is calculated layer wise as:

• s = γ_R,s ((σ_d' - σ_od') / M_d) Δz
  • σ_d' = σ_od' + Δσ_d' = σ_od' + Δq / ((1 + z / B´) (1 + z / L´))
    • Δσ_d' is the vertical stress increase and is calculated with the 2:1 method
    • Δq is the load at ground level
  • σ_od' is the effective pressure at the middle of each layer as above
  • M_d is the compression modulus M_d = M_k / γ_M or the E-modulus E_d = E_k / γ_M