19791340 Lateral Earth Pressure

7/30/2019 19791340 Lateral Earth Pressure

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What is Lateral Earth Pressure?

Designing any retaining wall requir es

knowledge of lateral earth pressure, the pressure

developed by the backf i l l .

It is the force generated by the lateral earth

pressure that constitutes a large part of the

load that the wall must carry.

represents pressures that are to the

side (horizontal) rather than vertical


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Lateral Support

In geotechnical engineering, it is often necessary to

prevent lateral soil movements.

Cantilever

retaining wall

Braced excavation Anchored sheet pile

Tie rod

Sheet pile

Anchor


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Lateral Support

We have to estimate the lateral soil pressures acting on

these structures, to be able to design them.

Gravity Retaining

wall

Soil nailingReinforced earth wall


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Lateral Support

Reinforced earth walls are increasingly becoming popular.

geosynthetics


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Lateral Support

Crib walls have been used in Queensland.

Interlocking

stretchersand headers

filled with

soil

Good drainage & allow plant growth.

Looks good.


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Categor ies of Lateral Earth

Pressure


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Active/Passive Earth Pressures- in granular soils

smooth wall

Wall moves

away from soil

Wall moves

towards soil

A

B

Lets look at the soil elements A and B during the

wall movement.


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Active Earth Pressure- in granular soils

A

v

h

z

As the wall moves away from the soil,

Initially, there is no lateral movement.

v= z

h= K0v

= K0 z

vremains the same; and

hdecreases till failure occurs.

Active state


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v

decreasing h

Initially (K0 state)

Failure (Active state)


active earth

pressure


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v[h]active

Rankines coefficient of

active earth pressure

WJM Rankine

(1820-1872)


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v[h]active

A

v

h45 + /2

90+

Failure plane is at

45 + /2 to horizontal


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A

v

h

z


hdecreases till failure occurs.

wall movement

h

Active

state

K0 state


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Passive Earth Pressure- in granular soils

B

v

h

Initially, soil is in K0 state.

As the wall moves towards the soil,

vremains the same, and

hincreases till failure occurs.

Passive state


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v

Initially (K0 state)

Failure (Active state)


increasing h

passive earth

pressure


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v [h]passive

Rankines coefficient of

passive earth pressure


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v [h]passive

A

v

h

90+

Failure plane is at

45 - /2 to horizontal

45 - /2


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B

v

h


hincreases till failure occurs.

wall movement

h

K0 state

Passive state


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Earth Pressure Distribution- in granular soils

[h]passive

[h]active

H

h

KAHKPh

PA=0.5 KAH2

PP=0.5 KPh2

PA and PP are the

resultant active and

passive thrusts on

the wall


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Wall movement

(not to scale)

h

Passive state

Active state

K0 state


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Rankines Earth Pressure Theory

assumes:

There is no adhesion or friction between the wall and

soil

Lateral pressure is limited to vertical walls

Failure (in the backfill) occurs as a sliding wedge

along an assumed failure plane defined by .

Lateral pressure varies linearly with depth and theresultant pressure is located one-third of the height

(H) above the base of the wall.

The resultant force is parallel to the backfill surface.


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Rankines Earth Pressure Theory

Rankines Active earth pressure coefficient

Rankines Passive earth pressure coefficient


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The Coulomb Theory

Coulomb active earth pressure coefficient:

Coulomb passive earth pressure coefficient:


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The Coulomb Theory is similar to Rankine

except that:

There is friction between the wall and soil and takes this

into account by using a soil-wall friction angle of .

Note that ranges from /2 to 2/3 and = 2/3 iscommonly used.

Lateral pressure is not limited to vertical walls

The resultant force is not necessarily parallel to the

backfill surface because of the soil-wall friction value .


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Retaining Walls - Applications

Road

Train


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highway


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basement wall

High-rise building


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Gravity Retaining Walls

cobbles

cement mortarplain concrete or

stone masonry

They rely on their self weight to

support the backfill


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Cantilever Retaining Walls

They act like vertical cantilever,

fixed to the ground

Reinforced;

smaller section

than gravitywalls

19791340 Lateral Earth Pressure

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