Foundation Engineering
CE 483
5. Settlement of
shallow foundations
Copy right reserved to Dr O. Hamza
CONTENTS
– Introduction
– Vertical stress increase in a soil mass
..caused by foundation load
– Elastic settlement calculation
– Consolidation settlement calculation
– Field test (Bearing capacity with
.Settlement consideration)
– References
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
2
Introduction
Copy right reserved to Dr O. Hamza
 Principal criteria for foundation design
 Types of settlements
 Things required to calculate settlements
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
3
Introduction
 Principal criteria for foundation design
When designing foundations, two
principal criteria must be satisfied:
1. Maintaining Stability
2. Limiting Settlement
Stability against
Bearing failure
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
4
Introduction
 Principal criteria for foundation design
When designing foundations, two
principal criteria must be satisfied:
1. Maintaining Stability
2. Limiting Settlement
Crack
Soft ground
Embankment and building constructed on
soft ground (highly comprisable soil)
5
Introduction
 Principal criteria for foundation design
Therefore, the allowable bearing
capacity qall should be the smaller of
the following two:
You learned how to
calculate this (see
previous chapter)
The safe pressure that does not
cause bearing failure
The safe pressure that does not
cause unacceptable settlement
You will learn (in this
chapter) how to
estimate settlement
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
6
Introduction
 Types of settlements
From structural consideration there are two types of settlements:
• Uniform settlement
• Differential settlement
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
should be within the acceptable
limit - given in the building code
7
Introduction
 Types of settlements
From geotechnical consideration, there are two types of settlements:
Immediate (or elastic) settlement,
(mostly during construction time)
Consolidation settlement (occurs over long period of time)
• Primary consolidation,
• Secondary consolidation,
End of Construction
Time, t
Settlement, S
8
Introduction
 Types of settlements
So, the total soil settlement ST may
be contain one or more of these types:
Immediate
settlement
elastic deformation
with no change in
water content
occurs rapidly
during the
application of load
occurs in sandy, silty
and clayey soils
Primary consolidation
settlement
decrease in voids
volume as porewater is squeezed
out of the soil
Secondary consolidation
or creep
due to gradual
changes in the
particulate
structure of the soil
occurs slowly
according to the
permeability
occurs very slowly,
long after the primary
consolidation is
completed
only significant in
saturated clays and
silts
most significant in
soft organic soils
9
Introduction
 Types of settlements
The total settlement of a foundation can then be given as:
ST = Se + Sc + Ss
What information do we need to know
to calculate these settlements?
10
Introduction
 Things required to calculate settlements
Methods used for settlement calculations
usually require to know the followings:
Net foundation load
q [kPa]
Foundation (net load q, type,
dimensions (B,L), Rigidity, …)
Vertical stress increase Ds in
soil caused by foundation load
Ds
Soil profile & parameters:
e.g. E, n, Cc, CR, …
Pressure bulb
11
Vertical stress increase in a soil mass
caused by foundation load







Pressure bulb
Stress due to a concentrated load
Stress due to a circularly loaded area
Stress due to vertical line load
Stress below rectangular area
Average vertical stress increases in a layer
Approximate method
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
12
Vertical stress increase in a soil mass caused by foundation load
 Pressure bulb
• Structure built on ground causes increase
in vertical stress (pressure) in the soil
below.
Net foundation load
q [kPa]
• This pressure increase is distributed
to the soil in the form of a pressure
bulb (or pressure isobars).
• The stresses Ds of the pressure
bulb is determined by elastic
theory.
Ds
Pressure bulb
13
Vertical stress increase in a soil mass caused by foundation load
 Pressure bulb
• The size and shape of the pressure bulbs depend on the size and shape of
the loaded area e.g. point load, circular or rectangular loaded area, …et.
q= 100 kPa
q= 100 kPa
B
2b
2B
0.2 q
Pressure bulbs under large
and small round foundations
Ds =
0.1 q
14
Vertical stress increase in a soil mass caused by foundation load
 Pressure bulb
Comparison between
Pressure Bulb for square
and strip footings
15
Vertical stress increase in a soil mass caused by foundation load
 Stress due to a concentrated load
Boussinesq solution (1885)
z
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
16
Vertical stress increase in a soil mass caused by foundation load
 Stress due to a circularly loaded area
z
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
17
Vertical stress increase in a soil mass caused by foundation load
 Stress due to vertical line load
z
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
18
Vertical stress increase in a soil mass caused by foundation load
 Stress below rectangular area
The vertical stress at a depth, z, below the
corner of a rectangular subject to uniform
pressure is:
l
b
Dsv = q. I
where:
q
l
b
D sv
decreases with depth z
q is the bearing pressure (net applied loading).
I is influence factor related to the shape of the loaded area.
It is given by the following equation (Newmark, 1935):
I
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
19
Vertical stress increase in a soil mass caused by foundation load
 Stress below rectangular area
n = 0.1
m
I
20
Vertical stress increase in a soil mass caused by foundation load
 Stress below rectangular area
To work out the vertical stress increase
below the center of foundation, use:
l=½L
b=½B
L
Dsv = 4 q. I
where:
L: foundation length
B: foundation width
l
b
B
l
b
DDssvv
21
Vertical stress increase in a soil mass caused by foundation load
 Stress below rectangular area
Q=1000 kN
Example problem
The figure shows 2.5m-square footing
constructed in sand layer underlain by
clay. Calculate the increase of effective
pressure in the clay layer (at the top,
middle and bottom) using Newmark
method.
1.5m
3m
2.5x2.5m
Dry sand
3m
Sand
3m
Clay
Key solution:
Let’s assume Ds’t , Ds’m and Ds’b represent
the increase in the effective pressure at the
top, middle, and bottom of the clay,
respectively, under the center of the
footing.
Bed rock
z
22
Vertical stress increase in a soil mass caused by foundation load
 Stress below rectangular area
Q=1000 kN
Key solution (cont..):
1.5m
3m
l = ½ L = b = ½ B = 2.5/ 2 = 1.25 m
Dry sand
Ds’ = 4 q. I
= 4 (1000/2.52) I
= 640 I
3m
m = l/z
n = b/z
Sand
D s ’t
3m
Z
2.5 x 2.5m
I
Ds’ [kPa]
4.5
Ds’m
Clay
D s ’b
Bed rock
z
6
7.5
From the chart
23
Vertical stress increase in a soil mass caused by foundation load
 Average vertical stress increases in a layer
q
• The increase in the vertical stress Ds’z in
soil caused by a load q, applied over a
limited area decreases with depth z
Compressible
Layer
z
Ds’z under the
center of foundation
varies parabolically
24
Vertical stress increase in a soil mass caused by foundation load
 Average vertical stress increases in a layer
q
• For settlement calculation, we can use the
average pressure increase Ds’av , using
weighted average method (Simpson’s
rule):
Compressible
Layer
z
where:
Ds’t , Ds’m and Ds’b represent the increase in the
effective pressure at the top, middle, and bottom of
the layer, respectively.
Ds’z under the
center of foundation
25
Vertical stress increase in a soil mass caused by foundation load
 Approximate methods
For wide uniformly distributed load,
such as for vey wide embankment
fill, the stress increase at any depth,
z, can be given as:
q kPa
GL
Ds z = q
z
Ds z
does not
decreases
with depth z
soil
26
Vertical stress increase in a soil mass caused by foundation load
 Approximate methods
For other cases, the vertical stress at any depth, z, can be
calculated using 2:1 linear distribution method.
q
2 vertical to
1 horizontal
B
2 vertical to
1 horizontal
Z
B+Z
2:1 method of finding stress increase under a foundation
27
Vertical stress increase in a soil mass caused by foundation load
 Approximate methods
decrease with depth z
Z
28
Vertical stress increase in a soil mass caused by foundation load
 Approximate methods
Average pressure increase
• For settlement calculation of a soil
layer we usually use the average
pressure increase Ds’av
• Based on the “Approximate Method”,
Ds’av can be considered at the middle
of the layer:
where Ds’m is the increase in the effective
pressure at the middle of the layer.
q
H
Compressible Layer
z
29
Vertical stress increase in a soil mass caused by foundation load
 Approximate methods
Example problem
The following figure presents a
rectangular foundation with length L=
3m and width B =2m. The net applied
pressure is 100kPa.
The ground profile consists of a clay
layer of H=4m high. Sand is presented
below and above this clay.
What is the increase of the effective
pressure Ds’ at the middle of the layer
caused by the foundation loading q ?
(use the approximate method)
q=100 kPa
Sand
1m
H
Clay
Sand
z
30
Vertical stress increase in a soil mass caused by foundation load
 Approximate methods
Example problem- key solution
Using 2:1 linear distribution of approximate method, Ds’
at the middle of the layer can be calculated from:
For Rectangular Foundation
where Z = ?
= ……
31
Elastic settlement calculation
 Contact Pressure and Settlement Profile
 Settlement based on general theory of Elasticity
 Elastic Settlement of saturated clay
 Elastic Settlement of sandy soil: use of strain
.influence factor
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
32
Elastic settlement calculation
 Contact Pressure and Settlement Profile
The contact pressure distribution and settlement profile under the
foundation are not uniform and will depend on:
• flexibility of the foundation (flexible or rigid).
• type of soil (clay, silt, sand, or gravel).
Contact pressure distribution
Contact pressure distribution
flexible
SAND
flexible
Settlement
profile
rigid
CESAND
481 - Geotechnical Engineering II - 2. Compressibility of Soil
CLAY
Settlement
profile
rigid
CLAY
33
33
Elastic settlement calculation
 Settlement based on theory of Elasticity
Settlement Se =
integration of
vertical strain ez
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
34
Elastic settlement calculation
 Settlement based on theory of Elasticity
For flexible shallow foundation
subjected to a net force per unit
area equal to Ds :
q
q
(flexible)
(based on elastic theory)
More details about the calculation
are given in Section 5.10 (Das,
2011).
rigid
35
Elastic settlement calculation
 Settlement based on theory of Elasticity
q
Thick
foundation
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
Thin foundation
36
Elastic settlement calculation
 Settlement based on theory of Elasticity
B
Due to the nonhomogeneous nature
of soil deposits, the magnitude of Es
may vary with depth. For that reason,
Bowles (1987) recommended using a
weighted average value of Es.
Es(1)
H
Es(2)
where:
Es(i) soil modulus of elasticity within a
depth Dz.
whichever is smaller
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
Es(3)
37
Elastic settlement calculation
 Elastic Settlement of saturated clay
Section 5.9 (Das, 2011)
38
Elastic settlement calculation
 Elastic Settlement of saturated clay
39
Elastic settlement calculation
 Elastic Settlement of sandy soil: use of strain
influence factor
(changes with depth)
(applied by the foundation)
(changes with depth)
40
Elastic settlement calculation
 Elastic Settlement of sandy soil: use of strain
influence factor
41
Elastic settlement calculation
 Elastic Settlement of sandy soil: use of strain
influence factor
is obtained from CPT test
1 ≤ L/B ≤10  by interpolation
we can find:
E
qc
qc
How about if there is no CPT
date available?
42
Elastic settlement calculation
 Elastic Settlement of sandy soil: use of strain
influence factor
Use
Note
43
Elastic settlement calculation
 Elastic Settlement of sandy soil: use of strain
influence factor
Maximum stain
influence factor
Izp
Initial value Iz0
Z1
Why does strain influence
factor take this shape?
The strain influence factor Iz
can be graphically presented
by this diagram
Z2
44
Elastic settlement calculation
 Elastic Settlement of sandy soil: use of strain
influence factor
Izp
Iz0
= Iz0
Z1
Z1
= Izp or Iz(m)
(required for the calculation of Izp)
Z2
Z2
=0
Depth of influence
45
Elastic settlement calculation
 Elastic Settlement of sandy soil: use of strain
influence factor
Izp
Iz0
Z1
L
Iz diagram
varies with L/B
Variables
Z2
46
Elastic settlement calculation
 Elastic Settlement of sandy soil: use of strain
influence factor
Izp
Izp
Izp
Iz0
Z1=0.5B
Z1
Z1=B
Z2 =2B
Z
Square
L/B = 1
z (Axisymmetric)
General case
1 ≤ L/B ≤10
Z2 =
Strip footing
10 ≤ L/B
(Plane strain)
2
z
Z2 = 4B
z
47
Elastic settlement calculation
 Elastic Settlement of sandy soil: use of strain
influence factor
Table summary of Iz profile
Z1
Z0
Z1
Z2
Z2
Z
* Calculated by interpolation between Case 1 and Case 3
48
Elastic settlement calculation
Z1
Z2
49
Elastic settlement calculation
 Elastic Settlement of sandy soil: use of strain
influence factor
Z1
Z2
2. General case
1 ≤ L/B ≤10
1. Square
L/B = 1
Z
Iz
Z
0
0.1
0
0.5B
Izp
2B
0
3. Strip
10 ≤ L/B
Iz
*
* I =
zp
2
*
0
Z
Iz
0
0.2
B
Izp
4B
0
* Calculated by interpolation between Case 1 and Case 3
50
Elastic settlement calculation
 Elastic Settlement of sandy soil: use of strain
influence factor
Z1
Z2
51
Class example
In preparation for
settlement calculation
using strain influence
method, the soil is divided
to smaller layers. Explain
why the soil is divided to 10
layers?
52
Elastic settlement calculation
 Elastic Settlement of sandy soil: use of strain
influence factor
Class example
A 3 m wide strip foundation on a
deposit of sand layer is shown along
with the variation of modulus of
elasticity of the soil (Es). The unit
weight of sand is 18 kN/m3.
Calculate the elastic settlement of
foundation using the strain
influence factor. Assume there is a
creep over a period of 10 years.
Solution
53
Elastic settlement calculation
 Elastic Settlement of sandy soil: use of strain
influence factor
Solution
First step is to plot the
variation of strain influence
factor Iz with depth (to scale).
Strip footing
10 ≤ L/B
Z
Iz
0
0.2
B=3
Izp
4B=12
0
= 18 x (1.5 + 3) = ….
54
Elastic settlement calculation
 Elastic Settlement of sandy soil: use of strain
influence factor
Solution (cont..)
Es profile is given.
We divide the soil
into a number of
layers depending on
the variation of Iz
and Es values with
depth.
Then prepare the
following table:
55
Elastic settlement calculation
 Elastic Settlement of sandy soil: use of strain
influence factor
Solution (cont..)
56
Elastic settlement calculation
 Elastic Settlement of sandy soil: use of strain
influence factor
More examples are given in
Das’s text book – Section 5.12
57
Consolidation settlement calculation
 Basic consolidation process
 Laboratory Consolidation Test
 Soil compressibility parameters
 Normally Consolidated and Overconsolidated Clays
 Calculation of Primary Consolidation Settlement
 Secondary Consolidation Settlement
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
58
Consolidation settlement calculation
 Basic consolidation process
When a saturated soil is loaded,
coarse soils
saturated soil
Settlement
GL
Fine soils
Time (months or years)
• in coarse soils (sand & gravel) the settlement takes place instantaneously.
How can this be explained?
• in fine soils (clay & silt): settlement takes far much more time to complete.
Why?
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
59
Consolidation settlement calculation
 Basic consolidation process
In coarse soils (sands & gravels) any volume change
resulting from a change in loading occurs immediately;
increases in pore pressures are dissipated rapidly due to
high permeability. This is called drained loading.
In fine soils (silts & clays) - with low permeabilities - the
soil is undrained as the load is applied. Slow seepage
occurs and the excess pore pressures dissipate slowly,
consolidation settlement occurs.
So, consolidation settlement: is decrease in voids volume as pore-water
is squeezed out of the soil. It is mostly significant in fine soil (clay & silt).
60
Consolidation settlement calculation
 Laboratory Consolidation Test
• Data obtained from laboratory testing can be used to predict
consolidation settlement reasonably, but rate is often poorly estimated.
• 1-D field consolidation can be simulated in Laboratory.
Wide foundation
simulation of 1-D field consolidation in Lab
GL
Sand or
Drainage layer
porous stone
undisturbed soil
specimen
Dia = 50-75 mm
Height = 20-30 mm
Saturated clay
field
lab
61
Consolidation settlement calculation
 Laboratory Consolidation Test
Typical results of laboratory
consolidation test
The study of the change in the
void ratio of the specimen with
pressure will allow us to find
soil compressibility parameters.
What are soil compressibility
parameters?
Effective pressure, s’ (log scale)
Typical plot of e against log s’
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
62
Consolidation settlement calculation
 Soil compressibility parameters
For one-dimensional compression and swelling there are simple
relationships between the void ratio, e, and the logarithm of the vertical
effective stress, s ‘.
CC and Cs are slopes of
the e–log s‘ plot
Cc
1
compression
index
void ratio, e
Cs
Cc
1
Cs : swell index
Note. Swell index (Cs)
may be also called
re-compression index (Cr)
Cs
or Cr
1
log s’
63
Consolidation settlement calculation
 Soil compressibility parameters
• These indexes are required for the calculation of field settlement
caused by consolidation.
• These indexes is best determined by the laboratory test results for void
ratio, e, and pressure s’ (as shown above).
• Several empirical expressions have been also suggested:
PI: Plasticity Index
LL: Liquid Limit
For undisturbed clays, Skempton (1944)
(Kulhawy and Mayne, 1990)
GS: Specific Gravity
e0 : in situ void ratio
For natural clays, Rendon-Herrero (1983)
64
Consolidation settlement calculation
 Soil compressibility parameters
Compression and Swell Indexes of some Natural Soils
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
65
Consolidation settlement calculation
 Normally Consolidated and Overconsolidated Clays
The upper part of the e –log s’ plot is somewhat curved with a flat
slope, followed by a linear relationship having a steeper slope.
• A soil in the field at some depth
has been subjected to a certain
maximum effective past pressure
in its geologic history.
• This maximum effective past
pressure may be equal to or less
than the existing effective
overburden pressure at the time
of sampling.
Void ratio, e
This is can be explained:
Effective pressure, s’ (log scale)
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
66
Consolidation settlement calculation
 Normally Consolidated and Overconsolidated Clays
Casagrande (1936) suggested a simple graphic construction to
determine the preconsolidation pressure s’c from the laboratory e–log
s‘ plot.
Void ratio, e
In general the overconsolidation
ratio (OCR) for a soil can be defined
as:
where s ’ is the present effective
vertical pressure.
If OCR > 1 overconsolidated soil
If OCR = 1 normally consolidated
s’c
Effective pressure, s’ (log scale)
67
Consolidation settlement calculation
 Calculation of Primary Consolidation Settlement
Let us consider a saturated clay layer of initial thickness Ho (or H), where the
average effective pressure increases, from s ’0 to s ’ 0 +Ds ’ causing
consolidation settlement Sc= DH.
average vertical strain =
Ground level (GL)
DH
Ho
q kPa
DH
Saturated clay
s ’0
e = eo
Ho
s ’ 0 + Ds ’
e = eo - De
Sand layer
Time = 0+
Time = 
68
Consolidation settlement calculation
 Calculation of Primary Consolidation Settlement
Consider an element of soil where the volume of solid,
Vs = 1 initially
De
eo
Vs
1
Time = 0+
Time = 
average vertical strain =
De
1  eo
69
Consolidation settlement calculation
 Calculation of Primary Consolidation Settlement
Equating the two expressions for average vertical strain,
consolidation
settlement
initial thickness of
clay layer
change in void ratio
DH
De
=
Ho
1  eo
initial void ratio
as, Sc = DH
How to get the changes in void ratio De ?
70
Consolidation settlement calculation
 Calculation of Primary Consolidation Settlement
For normally consolidated clay (s ’ 0 >s c’ )
OA or AD on the graph:
Thus,
where:
CC is “Compression Index” obtained from the slope
of the e–log s‘ plot. CC is soil parameter.
Note:
is also called
c
s c’ = Preconsolidation
pressure.
71
Consolidation settlement calculation
 Calculation of Primary Consolidation Settlement
For over-consolidated clay (s ’ 0 < s c’ )
There are two cases:
• Case (1): when s ’ 0 +Ds ’ ≤ s c’
• Case (2): when s ’ 0 +Ds ’ > s c’
c
s c’ = Preconsolidation
pressure.
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
72
Consolidation settlement calculation
 Calculation of Primary Consolidation Settlement
For over-consolidated clay (s ’ 0 < s c’ )
Case (1): when s ’ 0 +Ds ’ ≤ s c’
i.e. along the line BC on the laboratory rebound
curve.
Thus,
• Where CS is slope of rebound curve.
• CS or Cr is soil parameter and called “Swell Index”
or re-compression index.
c
s c’ = Preconsolidation
pressure.
73
Consolidation settlement calculation
 Calculation of Primary Consolidation Settlement
For over-consolidated clay (s ’ 0 < s c’ )
Case (2): when s ’ 0 +Ds ’ > s c’
i.e. along the line BC then CD.
Thus,
• CS = Swell Index or recompression index Cr
• CC = Compression Index
c
s c’ = Pre-consolidation
pressure.
74
Consolidation settlement calculation
 Calculation of Primary Consolidation Settlement
Example problem
A soil layer 3 m thick is consolidated under an effective vertical stress of
50 kPa at a void ratio of 0.891. If the compression index Cc of the soil is
0.138, what is the settlement, when the effective vertical stress is
increased to 100 kPa.
Key Solution
The consolidation settlement for a layer of thickness H can be represented
by the compression index Cc defined by:
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
75
Consolidation settlement calculation
Example problem
q
A soil profile is shown in the
figure.
If a uniformly distributed
load is applied at the
ground surface, what will be
the settlement of the clay
layer caused by primary
consolidation?
We are given that sc for the
clay is 125 kN/m2 and
Cs=1/6 Cc , where:
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
76
Consolidation settlement calculation
Solution
The important procedure for determining consolidation settlement is to
calculate:
• so‘ the initial effective pressure at the middle of compressible soil layer
• Ds ‘ the average net effective stress increase in the compressible soil layer.
For wide uniformly distributed load, such as given in the
question, the stress increase at any depth, z, can be given as:
Ds ‘ = q = 50 kPa
NOTE:
If the loaded area is limited (e.g. rectangular foundation) we will need to
compute the stress increase Ds ‘ within the soil mass using Boussinesq
method or other approach assuming elasticity.
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
77
Consolidation settlement calculation
Solution (cont..)
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
78
Consolidation settlement calculation
Solution (cont..)
79
Consolidation settlement calculation
 Time rate of consolidation
• You learned above how to calculate the ultimate settlement of
primary consolidation Sc (at the end of consolidation).
• However this settlement usually takes long time, much longer than
the time of construction.
• And we may need to know the settlement at a specific time.
End of Construction
End of primary consolidation
Time, t
Settlement, S(time)
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
80
Consolidation settlement calculation
 Time rate of consolidation
Permeable layer
Hdr
Hdr
H
Clay
Hdr
U = the degree of consolidation
Cv is obtained from laboratory testing
81
Consolidation settlement calculation
• In some soils (especially recent organic
soils) the compression continues under
constant loading after all of the excess
pore pressure has dissipated, i.e. after
primary consolidation has ceased.
• This is called secondary compression or
creep, and it is due to plastic adjustment
of soil fabrics.
• This settlement can be calculated using
the secondary compression index, Ca.
• The Log-Time plot (of the consolidation
test) can be used to estimate the
coefficient of secondary compression Ca.
CE 481 - Geotechnical Engineering II - 2. Compressibility of Soil
void ratio, e
 Secondary Consolidation Settlement
ep
De
t1 t2
82
Consolidation settlement calculation
 Secondary Consolidation Settlement
where:
ep void ratio at the end of primary consolidation.
H thickness of clay layer.
void ratio, e
• The magnitude of the secondary consolidation can be calculated as:
ep
De
• The general magnitudes of Ca is observed to
correlate with Cc as follows:
t1 t2
83
Field test (Bearing capacity with
settlement consideration)
 Plate load test
 Standard Penetration Test (SPT)
 Cone Penetration Test (CPT)
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
84
Field test (Bearing capacity with settlement consideration)
 Plate load test
Plate Load Test is a field test for
determining the ultimate bearing
capacity of soil and the likely settlement
under a given load (ASTM D-1194-72).
The Plate Load Test basically consists of
loading a steel plate placed at
the foundation level and recording the
settlements corresponding to each load
increment.
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Field test (Bearing capacity with settlement consideration)
 Plate load test
BF = width of the proposed foundation
Bp = width of test plate
Sp= settlement of test plate for a given intensity of load, q
SF = settlement of the foundation for a given intensity of load, q
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Field test (Bearing capacity with settlement consideration)
 Standard Penetration Test (SPT)
• Bearing Capacity for sandy soil can be based on SPT N value and
settlement consideration.
• Meyerhof (1956) proposed a correlation for the net allowable
bearing pressure for foundations with the standard penetration
resistance, N60.
87
Field test (Bearing capacity with settlement consideration)
 Standard Penetration Test (SPT)
• Bearing Capacity for sandy soil can be based on CPT value and
tolerable settlement.
• Meyerhof (1956) proposed a correlation for the net allowable
bearing pressure for foundations with the cone resistance, qc .
CE 483 - Foundation Engineering - 5. Settlement of shallow foundations
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References
1. Braja M Das, 2011, Principles of Foundation Engineering, 7th ed,
Chapter- 5.
2. Previous course materials and presentations at KSU.
3. Geotechnical on the web:
http://environment.uwe.ac.uk/geocal/foundations/founbear.htm.
4. Andrew Bond and Andrew Harris, 2008, Decoding Eurocode 7, London.
5. The Institution of Structural Engineers library:
www.istructe.org/resources-centre/library
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