# 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:

• Sd > Rd / 2

Swedish annex

• Sd > 2 Rd / 3

# Cohesionless soil

For cohesionless soil the calculation can be performed with regard to peak pressure sounding where the characteristic peak pressure qck 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 γR,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 = γR,s Σ 2,3 / Cd log ((σ0d' + Δσd') / σod') Δz
• Cd = 1,5 qcd / σod'
• qd is the peak pressure qd = qk / γM
• σod' is the effective pressure at the middle of each layer,
• σod' = γ (d + z) above ground water level
• σod' = γ (d + h) + γ' (z – h) below ground water level
• Δσd' is the vertical stress increase and is calculated with the 2:1 method
• Δσd'= 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 = γR,s (Δσd' / Ed) Δz
• Δσd' is the vertical stress increase and is calculated with the 2:1 method
• Δσd'= Δq /((1 + z / B') (1 + z / L'))
• Δq is the load at ground level
• Ed is the E-modulus
• Ed = Ek / γM
or
• Compression modulus Md = Mk / γM

# 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 γR,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 σc'  the compression modulus is constant with the value Mo. The compression modulus will then fall to a lower value Mwhich will be constant until the pressure reached σL'. 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 = γR,s Σ(Δσ' / M) Δz
• 0 < Δσ' ≤ σcd'
• s = γR,s Σ(σd' - σod') / Mo Δz
• σcd' < σd' ≤ σLd'
• s = γR,s Σ[(σcd' - σod') / Mo + (σd' - σcd') / ML] Δz
• σd' > σLd'
• s = γR,s Σ[(σcd' - σod') / Mo + (σLd' - σcd') / ML + 1 / M' ln((σd' - σLd') M' / M+ 1)] Δz
• σd' = σod' + Δσd' = σod' + Δq /((1 + z / B') (1 + z / L'))
• σod' is the effective pressure at the middle of each layer
• σod' = γ (d + z) above ground water level
• σod' = γ (d + h) + γ' (z – h) below ground water level
• Δσd' 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 γR,s will consider uncertainties in the calculation model.

The settlement s is calculated layer wise as:

• s = γR,s ((σd' - σod') / Md) Δz
• σd' = σod' + Δσd' = σod' + Δq / ((1 + z / B´) (1 + z / L´))
• Δσd' is the vertical stress increase and is calculated with the 2:1 method
• Δq is the load at ground level
• σod' is the effective pressure at the middle of each layer as above
• Md is the compression modulus Md = M/ γM or the E-modulus Ed = Ek / γM