1. Theory of Reinforced Concrete and Lab. II
12. Retaining Walls
TYPE OF RETAINING WALLS
EARTH PRESSURE
EARTH PRESSURE FOR COMMON LOADING
STABILITY OF RETAINING WALLS
by Prof. Jae-Yeol Cho
Theory of Reinforced Concrete and Lab. II
Fall 2009

2. 12. Retaining Walls TYPE OF RETAINING WALLS
hold back masses of earth or other loose material.
Arm
Continuous back drain,
Crushed stone
Crushed stone
Tile drain
Tile drain
Toe
Heel
(a) Gravity wall
(b) Cantilever wall
Counterfort
Weep hole
(c) Counterfort wall
Theory of Reinforced Concrete and Lab II Fall 2009

3. 12. Retaining Walls EARTH PRESSURE
Q>What would happen if a wall is built in contact with a solid,
such as rock?
If a vertical wall retains soil, the earth pressure is
(1)
where : unit weight of soil
: coefficient of earth pressure at rest
(depends on soil type and compaction)
0.4~ for uncompacted noncohesive soils.
(sands, gravels)
~ for compacted sands and gravels.
0.7~ for cohesive soil.
정지토압계수
Theory of Reinforced Concrete and Lab II Fall 2009

4. 12. Retaining Walls EARTH PRESSURE Sliding of Retaining Wall
usually, walls move slightly under the action of the earth pressure. ( 1% of wall height )
Active earth pressure
acts when the wall
move away from the fill.
Sliding plane
Passive earth pressure
acts when the wall
is pushed against the fill.
where is angle of internal friction
is the coefficient of intergranular friction
Theory of Reinforced Concrete and Lab II Fall 2009

5. 12. Retaining Walls EARTH PRESSURE Coefficient of Earth Pressure.
According to Rankine,
coefficient for active earth pressure is
(2)
coefficient for passive earth pressure is
(3)
where, is soil surface angle to the horizontal.
Rankine’s theory is valid only for noncohesive soils.
Theory of Reinforced Concrete and Lab II Fall 2009

6. 12. Retaining Walls EARTH PRESSURE Determination of
Refer to SOIL MECHANICS!
Theory of Reinforced Concrete and Lab II Fall 2009

7. 12. Retaining Walls EARTH PRESSURE FOR COMMON LOADING
Conditions of Loading
horizontal surface of fill
inclined surface of fill
- horizontal surface of fill carrying a uniformly distributed additional load
Theory of Reinforced Concrete and Lab II Fall 2009

8. 12. Retaining Walls EARTH PRESSURE FOR COMMON LOADING
Condition of Loading
the pressure of the soil ABOVE groundwater is determined as usual
the pressure of the soil BELOW groundwater is the sum of water pressure and soil pressure
(4,5)
Theory of Reinforced Concrete and Lab II Fall 2009

9. 12. Retaining Walls STABILITY OF RETAINING WALLS
Failure Modes of Retaining Walls
Individual parts may not be strong enough to resist the acting forces.
should be designed according to KCI Code
(usual load factors and strength reduction factors)
(2) The wall as a whole may be bodily displaced by the earth pressure. (External Stability)
should be checked based on ACTUAL earth pressure
and on service dead/live load  
Theory of Reinforced Concrete and Lab II Fall 2009

10. 12. Retaining Walls STABILITY OF RETAINING WALLS External Stability
(1) Safety against sliding
(6)
where,
f : coef. of friction
: component of the total
earth horizontal pressure P
: vertical component of P
In the figure R is total resultant and
W is the weight of wall plus soil resisting on the footing.
Theory of Reinforced Concrete and Lab II Fall 2009

11. 12. Retaining Walls STABILITY OF RETAINING WALLS External Stability
(2) Safe against bearing stability
The base plane ab, 1m wide
longitudinally, is subject to a
normal force Rv, and to a
moment about the centroid
(l/2 – a)Rv
Therefore, the following usual
formula can be used
(7)
Theory of Reinforced Concrete and Lab II Fall 2009

12. 12. Retaining Walls (a) Resultant in middle third
(b) Resultant at edge middle third
(c) Resultant outside middle third
Theory of Reinforced Concrete and Lab II Fall 2009

13. 12. Retaining Walls STABILITY OF RETAINING WALLS External Stability
(3) Safe against overturning
about the point b,
(8)
Resisting
moment
Overturning
moment
Theory of Reinforced Concrete and Lab II Fall 2009 13