Lecture-8-Lateral-Earth-Pressures.pdf

What is Lateral Earth Pressure?
Lateral earth pressure is the pressure that soil
exerts in the horizontal direction.

Why We Study Lateral Earth
Pressure?
Lateral Earth pressure is an important parameter
for the design of bridge abutment, different types
of retaining walls (Such as gravity retaining walls,
cantilever walls, buttresses), sheet piles and other
retaining structures.
It is important because it affects the consolidation
behavior and strength of the soil also because it is
considered in the design of retaining
walls, basements, tunnels etc.

SIVA Copyright©2001
4
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

5
Lateral Support
We have to estimate the lateral soil pressures acting on
these structures, to be able to design them.
Gravity Retaining
wall
Soil nailing
Reinforced earth wall

6
Soil Nailing

7
Sheet Pile
Sheet piles marked for driving

8
Sheet Pile
Sheet pile wall

9
Sheet Pile
During installation Sheet pile wall

10
Retaining Walls - Applications
Road
Train

11
highway

12
basement wall
High-rise building

13
Gravity Retaining Walls
cobbles
cement mortar
plain concrete or
stone masonry
They rely on their self weight to
support the backfill

14
Cantilever Retaining Walls
They act like vertical cantilever,
fixed to the ground
Reinforced;
smaller section
than gravity
walls

Lateral Earth Pressure
There are 3 states of lateral earth pressure
1. Ko= At Rest
2. Ka= Active Earth Pressure
3. Kp= Passive Earth Pressure
(Passive is more like a resistance)

Earth Pressure At Rest
At rest earth pressure occur when there is no wall
rotation such as in a braced wall. (for example basement wall)

At Rest Earth Pressure
 Ko can be calculated as follows:
Ko = 1 – sin φ

Active Earth Pressure
Active earth pressure occurs when the wall tilts away
from the soil.
(for example a typical free standing retaining wall)
• In Active earth pressure the value of K is minimum.

Active Earth Pressure
Kacan be calculated asfollows:








2
45
tan2 
o
a
K


sin
1
sin
1



a
K

Passive Earth Pressure
Passive earth pressure occurs when the
wall is pushed into the soil.
And a wall pushed into the soil when a
seismic load pushing the wall into the soil or
a foundation pushing into the soil.
In Passive earth pressure the value of K is
maximum.

Passive Earth Pressure
Kp can be calculated as follows:
Kp = tan2 (45 + φ/2)


sin
1
sin
1



p
K

22
Active/Passive Earth Pressures
smooth wall
Wall moves
away from soil
Wall moves
towards soil
A
B
Let’s look at the soil elements A and B during the
wall movement.

Comparison of Three States of
Lateral Earth Pressure

WORK EXAMPLE 1
Calculate the resultant active thrust on a vertical
smooth retaining wall of height 5.4m. The water
table is well below the base of the wall.
Soil properties :
 = 30, c = 0,  = 20kN/m3

 Calculate Ka using appropriate equation.
o
 Calculate the lateral soil pressure, a = KaH.
 Find the resultant active thrust, Pa = ½ KaH2
 Determine the point of action at a height of H/3
above the base .








2
45
tan2 
o
a
K


sin
1
sin
1



a
K

Calculate the Rankine active force per unit
length of the wall shown below, and also
determine the location of the resultant.
5m
γ=15.7kN/m3
Φ’=30
c’=0
WORK EXAMPLE 2
Ans : Pa = 65.4kN/m , y = 1.67m

 coefficient of passive earth pressure, Kp
Lateral soil pressure, p = KpH
Resultant force per unit length of wall,
Pp = ½ KpH2
ii)
i)








2
45
tan2 
o
p
K


sin
1
sin
1



p
K

WORK EXAMPLE 3
For the retaining wall considered below, what is
the Rankine passive force per unit length of the
wall?
5m
γ=15.7kN/m3
Φ’=30
c’=0
Ans : Pp = 588.75kN/m , y = 1.67m

WORK EXAMPLE 4
Determine the active force per unit length of
the wall for Rankine state. Also find the location
of the resultant. (Das, 2010)
z
GWT
γ = 16 kN/m3
Φ’ = 30
c’ = 0
γsat = 18 kN/m3
Φ’ = 30
c’ = 0
3m
3m
Ans : Pa = 128.394kN/m , y = 1.78m

Lecture-8-Lateral-Earth-Pressures.pdf

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Lecture-8-Lateral-Earth-Pressures.pdf