2. The structures which are constructed to
retain the earth or other loose material which
are unable to stand vertically by itself are
called as “retaining walls”.
They can also be used to support grounds at
different levels on both sides of wall.
The material retained by wall is called as
“backfill”.
3. On the basis of shape & mode of resisting
pressure due to backfill.
1. Gravity retaining wall
2. Semi-Gravity retaining wall
3. Cantilever retaining wall
4. Counterfort retaining wall
5. Buttress wall
4. •The walls which resists the earth pressure due to backfill by its own
weight.
•They are constructed with stone masonry or plain concrete.
5. • The size of section of a gravity retaining wall may
be reduced if a small amount of reinforcement is
provided near the back face. Such walls are
known as Semi-gravity retaining wall.
6. • Cantilever retaining walls are made of reinforced cement concrete.
• The wall consist of a thin stem and a base slab cast monolithically.
7. • Counterfort retaining walls have thin vertical slabs, known as
Counterfort, spaced across the vertical stem at regular intervals.
• Counterforts tie vertical stem with the base slab.
•The purpose of providing Counterfort is to reduce shear force
&bending moment in the vertical stem & the base slab.
8. • It is similar to the Counterfort retaining wall in which Counterfort,
called as buttresses are provided on the opposite side of the backfill &
act as compression struts.
9. • Sliding Failure
There are 5 • Overturning Failure
types of
modes of • Bearing capacity Failure
failure
• Shallow shear Failure
• Deep shear Failure
10.
11. Sliding failure is nothing but sliding of wall away from
backfill when there is shearing failure at the base of
wall.
The Factor of safety against sliding is,
< 1.5
where,
µ = coefficient of friction = tan δ
= vertical & horizontal components of
resultant R of weight of wall & earth
pressure
12.
13. Overturning failure is rotation of wall about
its toe due to exceeding of moment caused
due to overturning forces to resisting forces.
The Factor of safety against overturning is
given by,
< 1.5 - 2.0
where,
= sum of resisting moment about toe
= sum of overturning moment about
toe
14.
15. The pressure exerted by resultant vertical
force at toe of wall must no exceed the
allowable bearing capacity of the soil.
The pressure distribution is assumed to be
linear.
The maximum pressure is given by,
The Factor of safety against bearing failure is,
< 3.0
where,
= allowable bearing pressure
16.
17. This type of failure occurs along a cylindrical
surface ABC passing through the heel of
retaining wall as shown in above fig.
The failure takes place because of excessive
shear stresses along the cylindrical surface
within the soil mass.
The FOS against horizontal sliding is lower
than that for shallow shear failure.
However, FOS against sliding is greater than
1.5, shallow shear failure is not likely to
occur.
18.
19. This type of slope failure occurs along a
cylindrical surface ABC as shown in above fig,
when there is a weak layer of soil under the wall
at a depth of about 1.5 times ht. of wall.
The critical failure surface is found by trial &
error method.
For the backfills having slope i less than 10º, it
has been seen that critical failure surface DEF
passes through the edge of heel slab as shown in
above fig.
In this condition possibility of excessive
settlement should also be checked.
21. The castle village is located in historic Washington
heights section of Manhattan.
The wall is owned by Castle village owner’s
corporation.
Five buildings, 575 unit co-operative housing
complex is located on the top of hill behind the wall.
On Thursday, May 12, 2005 at approx 4:00 pm, a
portion of a 65 foot high stone retaining wall on side
of bluff rising above Hudson river suddenly collapsed.
About 10 minutes later second larger collapse
followed as 150 feet section of 800 foot long wall and
covered Henry Hudson parkway.
Fortunately, there were no deaths or even injuries.
22. The collapse was cause of structural failure
resulting from increased pressure developed
behind the wall due to build up of ground water
throughout the years.
Langan Engg. & Environmental services was the
firm inspecting, evaluating and making
recommendations about & repair certain areas of
retaining walls.
The retaining wall has moved about 2 feet from
its initial position when it was constructed.
Hence this case is remarkable case of sliding of
retaining wall.
23.
24.
25.
26. The landslide triggered due snow melt caused
this retaining wall failure.
It was due to overturning of wall due to
excessive overturning moment caused by
pressure generated by snow melt.
It fell on the carriageway & Unfortunately it
fell onto a truck, killing the driver.
