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Compressibility & Settlement
Settlement requirements often controlthe design of foundations
This chapter provides a generaloverview of principles involved insettlement analysis
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Case Studies
(a)Leaning Tower, Pisa
(b) Palacio de las BellasArtes, Mexico City
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Palace of Fine Arts in Mexico CitySettled 3m!
Lacustrine Clay deposited in former LakeTexcoco
Av. Water content 281%, Void Ratio 6.90
Groundwater withdrawal; increase ineffective stress
Resulting Consolidation
43-story Tower Latino Americana
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Settlement
Distortion Settlement (Immediate)
Consolidation (Time Dependent)Secondary Compression
time
Settlement
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Increase in Vertical Effective Stress
Due to a Placement of a fill
Due to an external load
fillfillzzf H += 0
( )inducedzzzf += 0
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Consolidation Settlement
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Laboratory Consolidation Test
v
v
Solids
Voids
Solids
Voids
Vs
VvV
v
Vs
1 Place sample in ring
2 Apply load3 Measure height change
4 Repeat for new load
V
Confiningstress
Before After
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Laboratory Consolidation Test
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Consolidation Test
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Compression Index andRecompression Index
c
eeC
zbz
bcc
)(log)(log
=
czdz
dc
r
eeC
)(log)(log
=
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Compression Ratio andRecompression Ratio
czbz
czbzcc
e
CC
)(log)(log
)()(
1 0
=
+=
czdz
czdzr
r e
CC
)(log)(log
)()(
1 0
=
+
=
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Consolidation Plot
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Consolidation Plot
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Consolidation Plot
5.5ft
2.0ft
tsfpsfftftpcfz 42.08360.2)4.621.128()5.5)(1.128( ==+=
=109.4(1+0.171)
= 128.1 pcf
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e0
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Normally and
Over-Consolidated Soils
czo = .. Normally consolidated
czo .. Under consolidated
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Over-Consolidation Margin &
Over-consolidation Ratio
zccm = .. Over-consolidationMargin
zo
cOCR
= .. Over consolidation ratio
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Typical Range of OC Margins
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Compressibility of Sand andGravels (Table 3.7)
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Example 3.3
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Settlement PredictionsN.C. Clays
+=
00
log1 z
zfcc H
e
C
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Settlement PredictionsO.C. Clays Case I
+=
00
log1 z
zfrc H
e
C
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Settlement PredictionsO.C. Clays Case II
+
+
+
=c
zfc
z
crc H
e
CH
e
C
log
1
log
1 000
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Ex. 3.4
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Example 3.4
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Ex. 3.5
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Example 3.5