Settlement of Shallow Footings
Excessof VerticalStress
Stress Increment under Footing Subsoil Settlement due to Stress Change
Settlement Consists of:
• Immediate settlement: si– No volume change of subsoil, displacements only
• Settlement caused by primary consolidation: sp– Dissipation of pore-water pressure connected with
water flow and significant volume change of the soil• Settlement by secondary consolidation: ss
– Volume change due to secondary compression and u=0 – long-term development
Immediate Settlement
si
uu
i IEBqs ⋅⋅=
01 µµ ⋅=uI
Square
Circular
Settlement by Primary Consolidation
• Based on:– Oedometer modulus and subsoil composed of
individual layers,– Calculation of Origin Stress and Stress
Increment,– Calculation of Settlement:
i
n
i ioed
zi hE
s ⋅= ∑=1 ,
σi
n
i ioed
iorizi hEm
s ⋅⋅−
= ∑=1 ,
,σσ
Settlement by Secondary Consolidation
Calculation of Settlement ss
Coefficient of Secondary Consolidation:
Sand approx.0,00003-0,00006
Loess soil approx. 0,0004
Clay approx. 0,001
12 loglog1
tthh
s −⋅
∆=α
( )12 loglog tths ss −⋅⋅= α
Boussinesq - Point load
Boussinesq - Point load
2cos
RAR
βσ ⋅=
V / H Stress
Stress increment calculation
Stress increment calculation
Stress IncrementLarge Embankment Construction Footing Depth
Stress IncrementRe-construction Dewatering
Stress: Origin / Increment due to Vds
Vertical Stress Distribution
Distribution of vertical stress increment bellow indicated points -section
Uniform loaded rectangular area –site plan
Contact Stress Distribution
k = E/Edef . (t/l)3 If k > 1.0 Stiff Footing
Stress Increment Calculationσol/f
Rectangular / Strip Footing
StressIncrementCalculation
Circular Footing
Footing Depth – Stress Correction
Rectangular Footing
Strip Footing
Rock Base - Stress Correction
Rock Base