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


Gravity Walls

2.4.1 Gravity Walls

Masonry walls

Gabion walls

Crib walls

RC walls

Counterfort walls

Buttressed walls


Gravity Walls

Unreinforced masonry wall


Gravity Walls

Gabion wall


Gravity Walls

Crib wall


Gravity Walls

Types of RC Gravity Walls


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


Embedded Walls

Types of embedded walls


Reinforced and Anchored Earth

2.4.3 Reinforced and anchored earth

Reinforced earth wall

Soil nailing

Ground anchors


Reinforced and anchored earth

Reinforced earth and soil nailing


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.


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


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


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


+=

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


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 :


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


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


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


Stability Analysis


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


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


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.

Technology

Earth retaining 2