Earth retaining 2
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Transcript of Earth retaining 2
EARTH RETAINING EARTH RETAINING STRUCTURES STRUCTURES
MARLIZA ASHIQIN BT KHAZALIMARLIZA ASHIQIN BT KHAZALI
TOPIC 4 : TOPIC 4 : LATERAL EARTH PRESSURE
COURSE LEARNING COURSE LEARNING OUTCOMEOUTCOME
• CLO 1 : Explain clearly the principle and CLO 1 : Explain clearly the principle and concept of geotechnical engineering (C4)concept of geotechnical engineering (C4)
• CLO 2 : Solve problems in soil stability CLO 2 : Solve problems in soil stability using appropriate method (C4)using appropriate method (C4)
LATERAL EARTH PRESSURE
Types of Retaining Wall
2.4.1 Gravity Walls
2.4.2 Embedded walls
2.4.3 Reinforced and anchored earth
LATERAL EARTH PRESSURE
Gravity Walls
2.4.1 Gravity Walls
Masonry walls
Gabion walls
Crib walls
RC walls
Counterfort walls
Buttressed walls
LATERAL EARTH PRESSURE
Gravity Walls
Unreinforced masonry wall
LATERAL EARTH PRESSURE
Gravity Walls
Gabion wall
LATERAL EARTH PRESSURE
Gravity Walls
Crib wall
LATERAL EARTH PRESSURE
Gravity Walls
Types of RC Gravity Walls
LATERAL EARTH PRESSURE
Embedded Walls
2.4.2 Embedded walls
Driven sheet-pile walls
Braced or propped walls
Contiguous bored-pile walls
Secant bored-pile walls
Diaphram walls
LATERAL EARTH PRESSURE
Embedded Walls
Types of embedded walls
LATERAL EARTH PRESSURE
Reinforced and Anchored Earth
2.4.3 Reinforced and anchored earth
Reinforced earth wall
Soil nailing
Ground anchors
LATERAL EARTH PRESSURE
Reinforced and anchored earth
Reinforced earth and soil nailing
LATERAL EARTH PRESSURE
Stability Criteria
2.5 Stability of Rigid Walls
Failures of the rigid gravity wall may occur due to any of the followings:
Overturning failure Sliding failure Bearing capacity failure
In designing the structures at least the first three of the design criteria must be analysed and satisfied.
LATERAL EARTH PRESSURE
The stability of the retaining wall should be checked against :
(ii) FOS against sliding (recommended FOS = 2.0)
(i) FOS against overturning (recommended FOS = 2.0)
Stability Criteria
moment Disturbing
momentResisting FOS =
H
wpV
R
Bc P 0.7) -(0.5 tan RFOS
++=
δ
LATERAL EARTH PRESSURE
Stability Analysis
Pp
Ph
∑ V
A
The stability of the retaining wall should be checked against :
2.3.1 FOS against overturning (recommended FOS = 2.0)
moment Disturbing
momentResisting FOS =
.. overturning about A
LATERAL EARTH PRESSURE
2.3.2 FOS against sliding (recommended FOS = 2.0)
Stability Criteria
H
wpV
R
Bc P 0.7) -(0.5 tan RFOS
++=
δ
Ph
∑ V
Pp
Friction & wall base adhesion
LATERAL EARTH PRESSURE
+=
B6e
B
R q V
b 1
2.3.3 For base pressure (to be compared against the bearing capacity of the founding soil. Recommended FOS = 3.0)
Now, Lever arm of base resultant
Thus eccentricity
R
Moment x
V
∑=
x - 2
B e =
Stability Criteria
LATERAL EARTH PRESSURE
Stability Analysis
Pp
Ph
∑ V
Base pressure on the founding soil
Stability AnalysisLATERAL EARTH PRESSURE
Figure below shows the cross-section of a reinforced concrete retaining structure. The retained soil behind the structure and the soil in front of it are cohesionless and has the following properties:
SOIL 1 : φu = 35o, γd = 17 kN/m3, SOIL 2 : φu = 30o, δ = 25o , γd = 18 kN/m3,
γsat = 20 kN/m3
The unit weight of concrete is 24 kN/m3. Taking into account the passive resistance in front of the wall, determine a minimum value for the width of the wall to satisfy the following design criteria:
Factor of safety against overturning > 2.5Factor of safety against sliding > 1.5Maximum base pressure should not exceed 150 kPa
Worked example :
Stability AnalysisLATERAL EARTH PRESSURE
SOIL 2
2.0 m
0.5 m
0.6 m
2.9 m
2.0 m
GWT
4.5 m
SOIL 1
SOIL 2
30 kN/m2
4.0 m
THE PROBLEM
LATERAL EARTH PRESSURE
Stability Analysis
P1P3
SOIL 2
2.0 m
0.5 m
0.6 m
2.9 m
2.0 mGWT
4.5 m
SOIL 1
SOIL 2
30 kN/m2
4.0 m
P2P4
PP
W41
W3
W2
W1
P5
THE SOLUTION
P6
LATERAL EARTH PRESSURE
Stability Analysis
271.035sin1
35sin -1
sin1
sin1o
o
1 =+
=+−=
φφ
aK
333.030sin1
30sin -1
sin1
sin1o
o
2 =+
=+−=
φφ
aK
00.330sin1
30sin 1
sin1
sin1o
o
2 =−+=
−+=
φφ
pK
Determination of the Earth Pressure Coefficients
LATERAL EARTH PRESSURE
Stability Analysis
LATERAL EARTH PRESSURE
Stability Analysis
OK is it thus 2.5, moment Disturbingmoment Resisting >=== 83.3
50.336
55.1288FOS
To check for stability of the retaining wall
(i) FOS against overturning > 2.5
(ii) FOS against sliding > 1.5
1.5 ..
60.75x 0.5 25tan .
R
P0.5 tan RFOS
o
H
pV <=+=+
= 34194180
9452δ
Thus it is not OK
LATERAL EARTH PRESSURE
Stability Analysis
+=
B6e
B
R q V
b 1
2.10 452.9
336.5 - 1288.55
RMoment
xV
==∑=
(iii) For base pressure
Now, Lever arm of base resultant
0.15 2.10 - 2.25 x - 2B
e ===
+=
4.50.15 x 6
4.5
452.9 qb 1
Thus eccentricity
Therefore
Stability AnalysisLATERAL EARTH PRESSURE
qb = 120.8 and 80.5 kPa
Since maximum base pressure is less than the bearing pressure of the soil, the foundation is stable against base pressure failure.
DISTRIBUTION OF BASE PRESSURE
80.5 kPa120.8 kPa
In conclusion the retaining wall is not safe against sliding. To overcome this the width of the base may be increased or a key constructed at the toe.