helo
SOIL MECHANICS
“First Part” Third YEAR CIVIL
Prof. Dr. Mahmoud Mohammed El-Meligy
Soil Mechanics VERTICAL STRESSES
1 Copyright
© Dr. M. El-Meligy (2006) helo
Course Contents:
- Stresses in a Soil Mass (Page:3)
- Settlement of Soil (Page:19)
- Lateral Earth Pressure (Page:51)
- Subsoil Investigation (Page:68)
helo
Vertical STRESSES
Soil Mechanics VERTICAL STRESSES
3 Copyright
© Dr. M. El-Meligy (2006) helo
Vertical Stresses in a Soil Mass
INTRODUCTION
Overburden stresses.
Vertical Stress increase due to foundation loads
Two-dimensional Problems
- Stress due to strip load
Three-dimensional Problems
- Stress due to vertical point load
- Stress due to a circularly loaded area
- Stress below a rectangular area
- Stress due to triangular load on rectangular area
Newmark’s chart
Approximate method
Homework
Foundation Types
Shallow Foundation
Isolated Footing
Combined footing
Strip Footing
Raft Foundation
Deep Foundation
Out of scope of our study
Soil Mechanics VERTICAL STRESSES
4 Copyright
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Types of Shallow Foundations:
Isolated footing
Plan
Cross section
Combined footing
Cross section
Plan
Raft foundation
Strip footing
Soil Mechanics VERTICAL STRESSES
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OVERBURDEN STRESSES:
Pore water pressure
Effective stresses
Total stresses
Soil Mechanics VERTICAL STRESSES
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© Dr. M. El-Meligy (2006) helo
The total vertical stress is carried
partially by the pore water in the
void spaces and partially by the soil
solids at their points of contact
- Changes in effective stresses will induce volume changes. - Effective stress is also responsible for producing frictional resistance in
soils and rocks
satA hh 21
Total vertical
stress
'
AAA u
Unit weight = g
Saturated unit
weight = gsat
GWT
A
h1
h2
GL
AA uA
'
wsat hhhA
221
' )(
)(21
'
wsathhA
subhhA
21
' Submerged unit weight
Soil Mechanics VERTICAL STRESSES
7 Copyright
© Dr. M. El-Meligy (2006) helo
EXAMPLE:
Determine the total stress, pore water pressure, and effective vertical
stress at A, B, and D.
At D
σD = 6x16.5+13x19.25
σD = 349.25 kN/m2
σD = 13x9.81 =127.53 kN/m2
σD = 6x16.5+13x(19.2 – 9.81)
σD = 6x16.5+13x(19.2 – 9.81) = 221.72 kN/m2
Soil Mechanics VERTICAL STRESSES
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Vertical stress increase due to foundation loads:
Assumptions:
The soil mass is:
1- Elastic
2- Isotropic
3- Homogeneous
4- Semi-infinite medium
Rigid footing
Flexible footing
Soil Mechanics VERTICAL STRESSES
9 Copyright
© Dr. M. El-Meligy (2006) helo
0
2
4
6
8
10
12
14
16
18
0.0 1.0 2.0
De
pth
Vertical stress
Two-dimensional problems :
Stress due to strip load
Example using EXCEL:
Vertical stress d rad d deg b rad b deg z1 x1 B q t/m2
0.446353974 0.785398 45.02282 0.588003 33.70716 1 3 4 5
Variation of vertical stress with
depth at distance 3.0 m from C.L
of a strip load
2
B
2
B
q load/unit area
b
z
d+ve
Dsz
2cossin q
z
x
x1
z1
Soil Mechanics VERTICAL STRESSES
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Stress Isobars:
Vertical stress isobars under a flexible strip load
Pressure bulb
Soil Mechanics VERTICAL STRESSES
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Three-dimensional problems :
Stress due to vertical point load:
Stress due to a circularly loaded area:
CASE A : Vertical stress under the center of circular loaded area:
2
52
2 12
3
z
rz
Pz
2
3
2
21
11
z
B
qz
Soil Mechanics VERTICAL STRESSES
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Distribution of stresses under center of
flexible circular loaded area
CASE B : Vertical stress at any point in the soil:
Dsz can be obtained using the next table
CL
CL
Dsz
R r
q
z
Soil Mechanics VERTICAL STRESSES
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Variation of Dsz/q for uniformly loaded flexible circular area:
z/R r/R
0.0 0.2 0.4 0.6 0.8 1.0
0.0 1.000 1.000 1. 000 1.000 1.000 1.000
0.1 0.999 0.999 0.998 0.996 0.976 0.484
0.2 0.992 0.991 0.987 0.970 0.890 0.468
0.3 0.976 0.973 0.963 0.922 0.793 0.451
0.4 0.949 0.943 0.920 0.860 0.712 0.435
0.5 0.911 0.902 0.869 0.796 0.646 0.417
0.6 0.864 0.852 0.814 0.732 0.591 0.400
0.7 0.811 0.798 0.756 0.674 0.545 0.367
0.8 0.756 0.743 0.699 0.619 0.504 0.366
0.9 0.701 0.688 0.644 0.570 0.467 0.348
1.0 0.646 0.633 0.591 0.525 0.434 0.332
1.2 0.546 0.535 0.501 0.447 0.377 0.300
1.5 0.424 0.416 0.392 0.355 0.308 0.256
2.0 0.286 0.280 0.268 0.248 0.224 0.196
2.5 0.200 0.197 0.191 0.180 0.167 0.151
3.0 0.146 0.145 0.141 0.135 0.127 0.118
4.0 0.087 0.086 0.085 0.082 0.080 0.075
Soil Mechanics VERTICAL STRESSES
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Stress below a rectangular area:
Variation of I with m and n
L
y
B
xz
zyx
dydxzq
0 02
5222
3
2
3
),( nmIqz
z
Bm
z
Ln
Soil Mechanics VERTICAL STRESSES
15 Copyright
© Dr. M. El-Meligy (2006) helo
Stress below any point of a loaded flexible rectangular area:
Stress due to triangular load on rectangular area:
At point E1
Where:
At point E2
a
1
2 4
3 q
)( 4321)( IIIIqaz
q load/unit area
z
x
y
L
E1
E2
Dsz
Dsz
nm
nmL
LkLn
LkLn
kz
kzL
BL
zqEz 2
22
2
22
2
3
)(
)(
))((
))((ln
)(
21
22 Lzk
22 Bzm
222 LBzn
)(
1
222
22
)( 12tan
2
)(
2EzEz
BL
nz
nmk
mkzBLq
Soil Mechanics VERTICAL STRESSES
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© Dr. M. El-Meligy (2006) helo
NEWMARK’S CHART:
)(IVNqZ
c
No of cells
Uniform stresses
Influence value
c
Depth
scale
Soil Mechanics VERTICAL STRESSES
17 Copyright
© Dr. M. El-Meligy (2006) helo
Approximate (2:1) method:
Elevation
Plan
z
B 1
2
q
BxL
Dp
B+z
L
B
z/2 z/2
z/2
z/2
L
zLzB
LBqp
helo
Settlement of Soil
Soil Mechanics SETTLEMENT
19 Copyright
© Dr. M. El-Meligy (2006) helo
Settlement of Soil
Outline:-
- Introduction - Types of Foundation Settlement - Immediate Settlement - Consolidation Settlement - Primary Consolidation Settlement - Secondary Consolidation Settlement
INTRODUCTION:-
- 20 m Circular Base - 5m Out of Plumb (South) - Weak Clay Layer at 11m
Leaning tower of Pisa
Soil Mechanics SETTLEMENT
20 Copyright
© Dr. M. El-Meligy (2006) helo
TYPES OF FOUNDATION SETTLEMENT:-
Definitions:-
Immediate Settlement of a foundation: takes place during or
immediately after the construction of the structure. (All soil types)
Primary Consolidation Settlement: is the result of volume change of
saturated clayey soils due to the expulsion of water occupying the
void spaces at load application.
Secondary Consolidation Settlement: occurs at the end of primary
consolidation settlement due to the plastic adjustment of soil fabrics.
SETTLEMENT
Immediate Consolidation
Primary
Secondary
Soil Mechanics SETTLEMENT
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© Dr. M. El-Meligy (2006) helo
IMMEDIATE SETTLEMENT (ELASTIC SETTLEMENT):-
Based on the theory of elasticity:
Df
H
Settlement of flexible
footing
Settlement of rigid
footing
Footing B x L
Rigid base (Rock)
Soil
Elastic settlement of flexible and rigid footing
Q
Soil Mechanics SETTLEMENT
22 Copyright
© Dr. M. El-Meligy (2006) helo
Foundation on soil with infinite depth:-
If the depth of foundation Df = 0, H = ∞
The immediate settlement may be expressed as:
Where net stress
Es = Soil modulus of elasticity
Q = Applied load
µs = Soil Poisson’s ratio
B = Foundation width
I = Coefficient of shape and rigidity
IE
BpS s
s
e )1( 2
LB
Qp
Soil Mechanics SETTLEMENT
23 Copyright
© Dr. M. El-Meligy (2006) helo
Coefficient of shape and rigidity (I) for foundation on soil
with infinite depth:-
Shape & Rigidity
Coef. of shape and rigidity
Center Corner Perimeter of circle
Mid of L Average
Circle - Flexible 1.00 -- 0.64 0.85
Circle - Rigid 0.79 -- 0.79 0.79
Square - Flexible 1.12 0.56 0.76 0.95
Square - Rigid 0.82 0.82 0.82 0.82
Rectangle - Flexible
L/B = 2 1.53 0.76 1.12 1.30
L/B = 5 2.10 1.05 1.68 1.82
L/B = 10 2.56 1.28 2.1 2.24
Rectangle - Rigid
L/B = 2 1.12 1.12 1.12 1.12
L/B = 5 1.60 1.60 1.60 1.60
L/B = 10 2.00 2.00 2.00 2.00
Soil Mechanics SETTLEMENT
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Foundation on soil "with depth = H -":
Flexible Foundation:
Rigid foundation:
Where:
Ic = Influence coefficient
net stress
σ = Stress at mid layer
HE
Ss
avere
)(
c
s
e IE
BpS
LB
Qp
Soil Mechanics SETTLEMENT
25 Copyright
© Dr. M. El-Meligy (2006) helo
Foundation on multi-layered soil:-
Where:
s = Stress at middle of each layer
hz= height of each layer
Immediate settlement of sandy soil:
Use of Strain Influence Factor (SIF):
z
s
avere hE
S
)(
Df
Footing B x L
Soil
Elastic settlement calculation using SIF
Q
z1
z2
q = g Df
z
Iz
z
Es
Δz1
Δz2
Δz3
Δz4
Soil Mechanics SETTLEMENT
26 Copyright
© Dr. M. El-Meligy (2006) helo
According to the SIF method, the immediate settlement
may be calculated as:-
Where:
qo = Gross stress at foundation level
Iz = Strain influence factor
C1 = a correction factor for the depth of foundation
C1 = 1 – 0.5 [ q/ (qo - q) ]
C2 = a correction factor to account for the creep in soil
C2 = 1 + 0.2 log ( 10 time in years
For Square or circular foundation:
Iz = 0.1 at z = 0
Iz = 0.5 at z = z1 = 0.5 B
Iz = 0 at z = z2 = 2 B
For foundation with L/B ≥ 10
Iz = 0.2 at z = 0
Iz = 0.5 at z = z1 = B
Iz = 0 at z = z2 = 4 B
2
0
21 )(z
s
zoe z
E
IqqCCS
z1
z2
Iz
Soil Mechanics SETTLEMENT
27 Copyright
© Dr. M. El-Meligy (2006) helo
The soil modulus of elasticity may be evaluated by using:
- The Standard Penetration Test (SPT)
Es (kN/m2) = 766 N
- The Static Cone Penetration Resistance
Es = 2.0 qc
Range of material parameters for computing elastic
settlement:
µs Es MN/m2 Type of soil
0.2 - 0.4 10.35 - 24.15 Loose sand
0.25 - 0.4 17.25 - 27.60 Medium dense sand
0.3 - 0.45 34.50 - 55.20 Dense sand
0.2 - 0.4 10.35 - 17.25 Silty sand
0.15 - 0.35 69.00 -72.50 Sand and gravel
0.2 - 0.5
4.10 - 20.70 Soft clay
20.70 - 41.40 Medium clay
41.40 - 96.60 Stiff clay
Soil Mechanics SETTLEMENT
28 Copyright
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Example:
A soil profile consists of deep, loose to medium dense sand (gdry = 16
kN/m3 , gsat = 18kN/m3). The ground water level is at 4 m depth. A
3.5m x 3.5m square footing rests at 3 m depth. The total (gross) load
acting at the foundation level (footing weight + column load + weight of
soil or footing) is 2000 kN. Estimate the settlement of the footing 6
years after the construction using the strain influence factor (SIF)
method (Schmertman, 1978). End resistance values obtained from
static cone penetration tests are;
qc (kN/m2) Depth (m)
8000 0.00 – 2.00
10000 2.00 - 4.75
8000 4.75 - 6.50
12000 6.50 – 12.00
10000 12.00 – 15.00
Soil Mechanics SETTLEMENT
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Soil Mechanics SETTLEMENT
30 Copyright
© Dr. M. El-Meligy (2006) helo
2
0
21 )(z
s
zoe z
E
IqqCCS
Soil Mechanics SETTLEMENT
31 Copyright
© Dr. M. El-Meligy (2006) helo
PRIMARY CONSOLIDATION SETTLEMENT:
Fundamental of consolidation:
When a saturated clay is loaded externally, The water is squeezed out
of the clay over a long time (due to low permeability of the clay).
This leads to settlements occurring over a long time, which
could be several years.
time
settlement
Soil Mechanics SETTLEMENT
32 Copyright
© Dr. M. El-Meligy (2006) helo
Granular soils are freely drained, and thus the settlement is
instantaneous.
During consolidation
remains the same (=q) during consolidation.
u decreases (due to drainage) while ’
increases, transferring the load from water to the soil.
time
settlement
Soil Mechanics SETTLEMENT
33 Copyright
© Dr. M. El-Meligy (2006) helo
One Dimensional Consolidation:
• Drainage and deformations are vertical
• A simplification for solving consolidation problems
water squeezed out
reasonable simplification if the
surcharge is of large lateral extent
Soil Mechanics SETTLEMENT
34 Copyright
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One Dimensional Consolidation Lab Test:
Schematic diagram of consolidation test arrangement
Soil Mechanics SETTLEMENT
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Time-Deformation Plot
Soil Mechanics SETTLEMENT
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© Dr. M. El-Meligy (2006) helo
e-log v’ plot
loading
v’ increases &
e decreases
Soil Mechanics SETTLEMENT
37 Copyright
© Dr. M. El-Meligy (2006) helo
Normally Consolidated & Overconsolidated Clays:
• Normally Consolidated
Existing vertical effective stresses are the highest the soil has ever
experienced
“Young” deposits
• Overconsolidated
Existing vertical effective stresses is less than a previous maximum
Glaciation, erosion, pre-loaded
Preconsolidation pressure c’
c’ is the
maximum vertical
effective stress
the soil element
has ever been
subjected to
Soil Mechanics SETTLEMENT
38 Copyright
© Dr. M. El-Meligy (2006) helo
Graphical determination of c’:
Compression and swelling indices:
Soil Mechanics SETTLEMENT
39 Copyright
© Dr. M. El-Meligy (2006) helo
Cc ~ compression index:
1
2logv
v
c
eC
3
4logv
v
s
eC
Soil Mechanics SETTLEMENT
40 Copyright
© Dr. M. El-Meligy (2006) helo
SETTLEMENT CALCULATIONS:
average vertical strain =
average vertical strain =
Equating the two expressions for average vertical strain:
H
H
oe
e
1
consolidation
settlement
initial thickness of
clay layer
initial void ratio
change in void ratio
Soil Mechanics SETTLEMENT
41 Copyright
© Dr. M. El-Meligy (2006) helo
If the clay is normally
consolidated,
Primary consolidation settlement
The key for getting Sc
Soil Mechanics SETTLEMENT
42 Copyright
© Dr. M. El-Meligy (2006) helo
If the clay is overconsolidated, and remains so by the end
of consolidation,
If an overconsolidated clay becomes normally
consolidated by the end of consolidation,
Soil Mechanics SETTLEMENT
43 Copyright
© Dr. M. El-Meligy (2006) helo
TIME RATE OF CONSOLIDATION:
Average degree of consolidation:
Terzaghi Equation
Coefficient of consolidation
Cm2/sec
Excess pore
water pressure
Time
Soil Mechanics SETTLEMENT
44 Copyright
© Dr. M. El-Meligy (2006) helo
Average degree of
consolidation
Settlement at time t
after load application
Maximum consolidation settlement under a given
loading
Soil Mechanics SETTLEMENT
45 Copyright
© Dr. M. El-Meligy (2006) helo
Plot of time factor against average degree of consolidation
357.06.5
2
100
%1
100
%
4
U
U
Tv
Soil Mechanics SETTLEMENT
46 Copyright
© Dr. M. El-Meligy (2006) helo
Two types of problems are expected:
Determination
of Cv:
For U = 50%
Tv = 0.198
Time (log scale)
Problem
Settlement ?
Get Tv
Get U%
Get St
Time ?
U%
Get Tv
Get Time
2
dr
v
H
tCvT
Soil Mechanics SETTLEMENT
47 Copyright
© Dr. M. El-Meligy (2006) helo
SECONDARY CONSOLIDATION SETTLEMENT:
Occurs at the end of primary consolidation
Where:
ep = voids ratio at the end of primary consolidation
H = thickness of clay layer
t1 = time at the end of primary consolidation
t2 = time at which secondary consolidation is required
)log(1
2'
t
tHCSs
pe
CC
1
'
Secondary
compression index
Soil Mechanics SETTLEMENT
48 Copyright
© Dr. M. El-Meligy (2006) helo
Secondary consolidation settlement is more important in organic clays and
soft to very soft clays.
In overconsolidated inorganic clays the secondary compression index is
very small and of less practical significance.
- Absolute settlement
- Differential settlement
- Angle of distortion
EXAMPLE:
Estimate the primary consolidation settlement for the foundation shown
in Fig.
Soil Mechanics SETTLEMENT
49 Copyright
© Dr. M. El-Meligy (2006) helo
NC clay, then
= 2.5x16.5 + 0.5x(17.5-9.81) + 1.25x(16-9.81)
= 52.84 kN/m2
Using 2:1 approximate method at CL of clay layer
KN/m2
APPLICATIONS
- Water level lowering
- New building adjacent to an existing one
- Basement
- Increasing number of floors over existing building
- Variable thickness of clay layer
- More than one clay layer
cS'
''log
1 vo
vo
o
c
e
CH
'vo
45.13)25.32)(25.31(
300'
mx
Sc 044.084.52
45.1384.52log
8.01
32.05.2
CL of clay layer
helo
LATERAL EARTH PRESSURE
Soil Mechanics EARTH PRESSURE
51 Copyright
© Dr. M. El-Meligy (2006) helo
Outline:
- Introduction
- Earth pressure at rest
- Active earth pressure
- Passive earth pressure
Soil Mechanics EARTH PRESSURE
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Soil nailing Cantilever wall
Sheet pile wall
Soil Mechanics EARTH PRESSURE
53 Copyright
© Dr. M. El-Meligy (2006) helo
Earth Pressure at Rest:
The ratio h’/v’ is a constant known as coefficient of earth pressure at
rest (Ko).
At Ko state, there is no lateral strains.
For normally consolidated clays and granular soils,
Ko = 1 – sin
For overconsolidated clays,
Ko,overconsolidated = Ko,normally consolidated OCR0.5
From elastic analysis,
GL
υ
υ
1Ko Poisson’s
ratio
v’
h
Soil Mechanics EARTH PRESSURE
54 Copyright
© Dr. M. El-Meligy (2006) helo
v’
h
H
Z g
C
f
Retaining structure
KogH
ovo K' zv '
At rest earth pressure
H/3
R
At rest earth pressure diagram
Soil Mechanics EARTH PRESSURE
55 Copyright
© Dr. M. El-Meligy (2006) helo
Effect of water table:
ACTIVE & PASSIVE EARTH PRESSURE
H
hw
Kogh
w + K
og
sub (H-h
w)
GWT
gsub
g
gw
(H-hw)
Earth pressure
water pressur
e
R
Rw
At rest earth pressure diagram
A
B
Wall moves from soil away
ACTIVE STATE Wall moves
soil towards
PASSIVE STATE
Soil Mechanics EARTH PRESSURE
56 Copyright
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Active Earth Pressure:
v’
Initially (Ko state)
Failure (Active state)
active earth
pressure a
h
Active
state
Ko state
Failure
A
h
z
wall movement
decreasing h
v’
Soil Mechanics EARTH PRESSURE
57 Copyright
© Dr. M. El-Meligy (2006) helo
45 + /2
Rankine active failure wedge
Soil Mechanics EARTH PRESSURE
58 Copyright
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Major principal stress
Minor principal stress
Thus,
RANKINE ACTIVE
EARTH PRESSURE
245tan2
245tan2
31
c
'
1 v
a 3
245tan2
245tan2'
cav
245tan
2
245tan2
'
cva
245tan2
245tan2'
cva
Rankine active earth
pressure coefficient, Ka
aava KcK 2'
Soil Mechanics EARTH PRESSURE
59 Copyright
© Dr. M. El-Meligy (2006) helo
v’
h
H
z g
C
f
Retaining structure
- =
Earth pressure diagram
av K'aKc2
aKc2
a
aava KcK 2' zv '
Soil Mechanics EARTH PRESSURE
60 Copyright
© Dr. M. El-Meligy (2006) helo
H
zc
_
zc = depth of tension crack
Earth pressure diagram
Tension cracks
aKc2
a
aac KcKz 20 a
cK
cz
2
H
zc
Design active pressure diagram
Rankine active pressure diagram
Rankine active pressure diagram before cracks
occurrence
Rankine active pressure diagram for clay backfill behind retaining structure
Soil Mechanics EARTH PRESSURE
61 Copyright
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Passive Earth Pressure:
As the wall moves towards the soil,
Passive state
B
v’
h
Soil Mechanics EARTH PRESSURE
62 Copyright
© Dr. M. El-Meligy (2006) helo
45 - /2
Rankine passive failure wedge
Soil Mechanics EARTH PRESSURE
63 Copyright
© Dr. M. El-Meligy (2006) helo
Major principal stress
Minor principal stress
Thus,
PASSIVE EARTH PRESSURE
245tan2
245tan2
31
c
p 1
'
3 v
245tan2
245tan2'
cvp
Rankine passive earth pressure coefficient, Kp
ppvp KcK 2'
v’
h
H
Z
g
C
f
Retaining structure
Earth pressure diagram
R
pKc2
ppp KcKH 2
ppvp KcK 2' zv '
Soil Mechanics EARTH PRESSURE
64 Copyright
© Dr. M. El-Meligy (2006) helo
Case of inclined retaining structure:
Rankine active earth pressure for inclined granular backfill
For the passive earth pressure
R
H
H/3
W
GL
Soil
22
22
coscoscos
coscoscoscos
aK
aa Kz
aKHR 2
2
1
22
22
coscoscos
coscoscoscos
pK
R H
H/3
W
α
Soil Mechanics EARTH PRESSURE
65 Copyright
© Dr. M. El-Meligy (2006) helo
Active & passive earth pressure due to surcharge:
failure wedge
No lateral effect
p w
pk
wk
Soil Mechanics EARTH PRESSURE
66 Copyright
© Dr. M. El-Meligy (2006) helo
EXAMPLE:
For the retaining wall shown, assume that the wall can yield sufficiently
to develop active state. Draw the pressures diagrams and determine the
active force per unit length of the wall as well as the location of the
resultant line of action.
Ka(1) = tan2(45-15) = 0.333
Ka(2) = tan2(45-18) = 0.26
At z = 3 m
At z = 6 m
2' /48316 mkNxv 2' /1648333.0 mkNxa
2' /48.124826.0 mkNxa
2' /57.75)3)(81.919(316 mkNxv 2' /65.1957.7526.0 mkNxa
g=16 kN/m3
c1=0
f1=30
o
gsat=19 kN/m
3
c2=0
f2=36
o
GL
z 1
16 kN/m2
19.65 kN/m2
12.48
3.0 m
3.0 m
29.43 kN/m2
Soil
Water
2
helo
SOIL INVESTIGATION
Soil Mechanics SOIL INVESTIGATION
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SOIL INVESTIGATION
PURPOSE OF SOIL INVESTIGATION:
1. Selecting the type and depth of foundation
2. Evaluating the load-bearing Capacity of the foundation
3. Estimating the expected settlement
4. Determining the location of the water table
5. Predicting lateral earth pressure
6. Establishing construction methods
SOIL INVESTIGATION PROGRAM:
Collection of preliminary Information
Visual inspection
Site Investigation
Collection of preliminary information:
• Information regarding type of structure
• For buildings, approximate columns loads and spacing, basement
requirements are required.
• For bridges, approximate span lengths loads on piers and abutments
are required.
• General idea about of soil around the proposed site.
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Visual inspection:
Visual inspection of the site is required to obtain the following data:
1. General topography of the site.
2. Soil stratification from deep cuts.
3. Type of vegetation.
4. Ground water levels.
5. Reported problems in nearby buildings.
Site investigation:
Planning
Making test boreholes
Collecting soil samples
PLANNING:
The following tables:-
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Soil Mechanics SOIL INVESTIGATION
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Boring Types:
Auger boring
Continuous flight auger
Wash boring
Rotary drilling
Hand Auger
Auger Drilling
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Rotary wash boring
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Rotary wash boring
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Solid Augers
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Hollow stem augers
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Rotary wash borings
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Bucket auger borings
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SOIL SAMPLING:
Three types of soil samples:
Disturbed samples
Bulk samples (from auger cuttings or test pit excavations)
Drive samples (e.g., split-barrel)
Partially undisturbed
Continuous Hydraulic Push
Undisturbed samples
Push Tubes (Shelby, Piston, Laval, Sherbrook)
Rotary & Push (Denison, Pitcher)
Block Samples
SAMPLER TYPES:
• Split-Spoon Sampling
• Scraper Bucket
• Thin Wall Tube
• Piston Sampler
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Split-Spoon Soil Sampler
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Schematic diagram of thethin-wall tube sampler
Diagram of the sampling operation using the thin-wall
tube sampler
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Typical components of a hollow-stem auger
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Isometric drawing of the hollow-stem auger with the
center drag bit which can be used with soil sampling
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Schematic drawing of the Bishop sand sampler
Soil Mechanics SOIL INVESTIGATION
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Schematic diagram illustrating the operation of the Bishop
sand sampler
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OBSERVATION OF WATER TABLES:
The water levels in a borehole during field exploration should be
recorded.
In soils with high hydraulic conductivity, the water level in a borehole
will stabilize about 24 hrs after completion of the boring.
The depth of the water table can be recorded by lowering a chain or a
tape into the borehole.
In highly impermeable layers, the water level in a borehole requires
longer time to stabilize, hence a piezometer is used for accurate
measurement of water level.
Field Testing:
• Standard Penetration Test
• Vane Shear Test
• Cone Penetration Test
• Pressuremeter Test
• Dilatometer Test
Standard Peneteration Test (SPT):
General equipment and procedure
Corrections
Correlation between SPT and soil properties
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Correlation between Spt and Soil Properties:
• Relative density
• Effective stress friction angle
• Undrained shear strength
•
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CORING OF ROCKS:
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Rock core-drill set-up
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Diagram of two-types of core barrels
(a) Single tube (b) Double tube
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STRATIFICATION:
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Preparation Of Boring Logs:
The data gathered from each borehole is presented in the so called
boring log. The driller should include the following data in the site:
1. Drilling company.
2. Number and type of boring.
3. Date of boring.
4. Subsurface stratification by visual observation.
5. Water levels.
6. SPT results.
7. Number, type, and depth of samples.
After completion of lab tests, the geotechnical engineer prepare the
final log that include the data from the driller field log and test results.
Subsoil Explolration Report:
After all the required information has been compiled, a soil
exploration report is prepared.
Each report should include the following items:
1. The scope of the investigation.
2. A description of the proposed structure.
3. A description of the location of the site.
4. Geological setting of the site.
5. Details of the field exploration.
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6. General description of the subsoil condition.
7. Water-table conditions.
8. Foundation recommendations.
9. Conclusions and limitations of the investigation.
Some graphs should be attached to the to the report as:
1. Site location map.
2. A plan view of the locations of the borings.
3. Boring logs.
4. Laboratory test results.
الموقع العام وأماكن الجسات –( 1شكل)
)1جسـة (
)2جسـة (
مبنى
مبنى
شارع
شارع
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