Foundation Settlement

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Foundation Settlement By Kamal Tawfiq, Ph.D.,
P.E. Fall 2008
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Foundation Settlement
Total Foundation Settlement Elastic Settlement
Consolidation Settlement Stotal Se Sc

Foundation Type
(Rigid Flexible) Elastic Settlement or
Immediate Settlement depends on
Settlement
Location (Center or Corner)

Theory of Elasticity Elastic
Settlement Time Depended Elastic
Settlement (Schmertman Hartman Method (1978)
Elastic settlement occurs in sandy, silty, and
clayey soils.
By Kamal Tawfiq, Ph.D., P.E.
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By Kamal Tawfiq, Ph.D., P.E.
Consolidation Settlement (Time Dependent
Settlement)
Consolidation settlement occurs in
cohesive soils due to the expulsion of the water
from the voids. Because of the soil
permeability the rate of settlement may varied
from soil to another. Also the variation
in the rate of consolidation settlement depends
on the boundary conditions. SConsolidation
Sprimary Ssecondary Primary Consolidation
Volume change is due to reduction in
pore water pressure Secondary Consolidation
Volume change is due to the rearrangement of
the soil particles (No pore water
pressure change, ?u 0, occurs after the primary
consolidation)
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Elastic Settlement
2
Se Bqo (1 - µs) a
(corner of the flexible foundation)
2
Es
2
Se Bqo (1 - µs) a
(center of the flexible foundation)
Es
Where a 1/p ln ( v1 m2 m / v1 m2 - m
) m.ln ( v1 m2 1 / v1 m2 - 1 ) m
B/L B width of foundation L length of
foundation
By Kamal Tawfiq, Ph.D., P.E.
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3.0
2.5
a
aav
ar
2.0
a, aav, ar
1.5
For circular foundation a 1 aav 0.85 ar 0.88
1.0
3.0
2
8
4
3
5
6
7
10
9
1
L / B
Values of a, aav, and ar
By Kamal Tawfiq, Ph.D., P.E.
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Elastic Settlement Using the Strain Influence
Factor Schmertman Hartman Method (1978)
The variation of the strain influence factor with
depth below the foundation is shown in Figure 1.
Note that, for square or circular
foundations, Iz 0.1 at z 0 Iz 0.5 at z
0.5B Iz 0 at z 2B Similarly, for foundations
with L/B 10 Iz 0.2 at z 0 Iz 0.5 at z
B Iz 0 at z 4B
Se C1 C2 ( q - q) ? (Iz / Es ) ?z where Is
strain influence factor C1 a correction factor
for the depth of foundation embedment 1 -
0.5 q / (q - q) C2 a correction factor to
account for creep in soil 1 0.2 log
(time in years /0.1) q stress at the level of
the foundation q overburden pressure ? Df
Example
B x L
q
Df
Iz
Es
q ? Df
?Z1
?Z2
Is3
?Z3
Es3
Average Is
Average Es
?Z4
Depth, z
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