Foundation settlements Settlements of foundations

Foundation settlements
Settlements of foundations
Stress distribution below point load
Stress below strip load
Stress below strip load
2:1 - method
2:1 - method at corner of footing
Settlement below footing
Settlements in clay and silt
Based on lab tests
Settlements in sand
Based on in situ tests
Immediate settlements in clay
Estimate of modulus of elasticity in
clay
Determination of compression index
Determination of settlements from
compression test
Principle of settlement calculation
Settlement below footing
Determination of precosolidation
pressure
Determination of coefficient of
consolidation (logarithmic)
Coefficient of consolidation (square
root)
Secondary consolidation
Summary of settlement on clay
δ
T
= δ
Can be important
for soft clay
„
„
i
+ δ
p
+ δ
s
Important for
organic
Usually most
important
To get an accurate estimate of settlement
must have good estimate of σ’p
Important to adjust for 3-D effect (SkemptonBjerum Modification) δp= ψ δp, ψ ≤ 1.0
Settlement on Sand
„
Schmertmann's Method
Net bearing pressure
Strain influence factor at
midpoint of soil layer
I Δz
δ = C1C2C3 q ' ∑ ε
Es
⎛σ ' ⎞
C1 = 1 − 0.5⎜⎜ zD ⎟⎟
⎝ q' ⎠
⎛ t ⎞
C2 = 1 + 0.2 log⎜
⎟
⎝ 0 .1 ⎠
C3 = 1.03 − 0.03L / B ≥ 0.73
Thickness of soil layer
Equivalent modulus
Depth factor
Secondary creep factor
Shape factor
I εp = 0.5 + 0.1
q'
σ ' zp
Soil modulus from cone penetration
test (CPT)
Estimate of modulus of elasticity
from Standard penetration test (SPT)
Settlement analysis based on plate
load test
Estimate of settlements below
footing on sand
Settlements of footing on clay
qu = qu,0.3
Effect of plate diameter on bearing
capacity of plate on sand
qu = qu,0.3*B/0.3
Allowable settlement below building
Damage due to foundation
settlements
Floating foundation
Effect of ground water lowering from
tunnel on building settlements
Effect of trees on ground water near
building
Differential settlements between
adjacent buildings
Negative skin friction due to ground
water lowering
Swelling potential of soil below
building
Effect of pile installation on adjacent
building
Allowable differential settlements
below structure
Tolerable settlement of buildings
Definitions of
parameters for
differential
settlement
技術規範