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RETAINING WALLS
BY
K.P.VINEETH
 What is retaining wall
 Parts of retaining wall
 Types of retaining wall
 Earth pressures
 Principles of the design of retaining wall
 Drainage of back fills
 Theories required to solve problem
 Design of retaining wall
Contents
What is a Retaining wall?
Retaining wall is a
structure used for
maintaining the
ground surfaces at
different elevations on
either side of it.
All permanent walls and components shall be
designed for a minimum service life of 75 years.
Corrosion protection is required for all permanent
and temporary walls in aggressive environments.
Retaining walls are usually built to hold back soil
mass.
They are also provided to maintain the grounds at
two different levels.
PARTS
STEM
or
Wall Slab
TOE HEEL
KEY
BACKFILL
FRONT
Types of retaining walls
1. Gravity Retaining Walls
2. Semi-Gravity Retaining Walls
3. Cantilever Retaining Walls
4. Counter fort Retaining Walls
The “gravity wall” provides stability by
virtue of its own weight , and therefore,
is rather massive in size.
It is usually built in stone masonry, and
occasionally in plain concrete
Gravity Walls
 The thickness of wall
is also governed by
need to eliminate or
limit the resulting
tensile stress to its
permissible limit .
 Plain concrete
gravity walls are not
used for heights
exceeding about 3m,
for obvious economic
reasons.
 Stress developed is very low.
 These walls are so proportioned
that no tension is developed
anywhere and the resultant of
forces remain within the middle
third of the base.
Semi-Gravity Walls
Semi-gravity walls resist
external forces by the
combined action of self
weight, weight of soil
above footing and the
flexural resistance of the
wall components.
concrete cantilever wall is an
example and consists of a reinforced
concrete stem and a base footing.
These walls are non-proprietary.
Cantilever Wall
 The “Cantilever wall ” is the
most common type of
retaining structure and is
generally economical for
heights up to about 8m.
 The structure consists of
vertical stem , and a base
slab, made up of two
distinct regions, viz., a heel
slab and a toe slab
 “Stem” acts as a vertical
cantilever under the lateral
earth pressure
 “Heel slab” acts as a
horizontal cantilever under
the action of weight of the
retained earth (minus soil
pressure acting upwards from
below)
 “Toe slab ” acts as a
cantilever under the action of
resulting soil pressure acting
upward.
 It resists the horizontal
earth pressure as well as
other vertical pressure by
way of bending of various
components acting as
cantilevers.
 May be L shaped or T
shaped.
Counterfort Wall
 Stem and Heel slab are strengthened by
providing counterforts at some suitable
intervals.
 The stability of the wall is maintained
essentially by the weight of the earth on
the heel slab plus the self weight of the
structure.
 For large heights, in a
cantilever retaining
wall, the bending
moments developed in
the stem, heel slab and
toe slab become very
large and require large
thickness.
 The bending moments
can be considerably
reduced by introducing
transverse supports,
called counterforts.
Counterfort wall are placed at regular
intervals of about1/3 to ½ of the wall
height, interconnecting the stem with
the heel slab.
The counterforts are concealed within
the retained earth on the rear side of the
wall.
Type equation here.
This wall is
economical for
heights above
(approximately) 7m.
The counterforts subdivide
the vertical slab (stem)
into rectangular panels
and support them on two
sides(suspender-style),
and themselves behave
essentially as vertical
cantilever beams of T-
section and varying depth.
EARTH PRESSURES
 PRESSURE AT REST
 ACTIVE EARTH PRESSURE
 PASSIVE EARTH PRESSURE
PRESSURE AT REST
When the soil behind the wall is
prevented from lateral movement
(towards or away from soil) of wall,
the pressure is known as earth
pressure at rest.
PRESSURE AT REST
This is the case when wall has a
considerable rigidity.
Basement walls generally fall in
this category.
ACTIVE EARTH PRESSURE
If a retaining wall is allowed to move
away from the soil accompanied by a
lateral soil expansion, the earth
pressure decreases with the increasing
expansion.
ACTIVE EARTH PRESSURE
A shear failure of the soil is resulted with
any further expansion and a sliding
wedge tends to move forward and
downward. The earth pressure associated
with this state of failure is the minimum
pressure and is known as active earth
pressure.
PASSIVE EARTH PRESSURE
If a retaining wall is allowed to move
towards the soil accompanied by a lateral
soil compression, the earth pressure
increase with the increasing compression
in the soil.
Principle of the design of
retaining wall
SLIDING:
Ability of the retaining wall structure to overcome the
horizontal force applied to the wall
Factor of safety = 1.5
OVERTURNING:
Ability of the retaining wall structure to overcome the
overturning moment created by the rotational forces
applied to the wall.
Factor of safety = 1.5
BEARING CAPACITY:
Ability of the underlying soil to support the weight of the
retaining wall structure.
Factor of safety = 2.0
 NO TENSION:
There should be no tension at the base of the
wall.
when the eccentricity (e) is greater than b/6 ,
tension develops at the heel
DRAINAGE OF THE BACK FILL
DRAINAGE
Sand + Stone Filter
Weepers
Or
Weep Holes
DRAINAGE
Drainage Pipes f 100-200 mm @ 2.5 to 4 m
DRAINAGE (Alternate)
Perforated Pipe
Suited for short walls
RANKIE’S THEORY
Assumptions
• The soil mass is semi-infinite, homogeneous, dry and
cohesionless
• The ground surface is plane which may be horizontal
or inclined.
• The back of the wall is vertical and smooth(No
shearing stresses are developed between the wall
and soil).
• The wall yields about the base and satisfies the
deformation conditions for plastic equilibrium.
When soil surface is horizontal:
d = 0


sin1
sin1


=ahC
H
H/3

When soil surface is inclined:
H
H/3
d
dd
dd
d 22
22
coscoscos
coscoscos
cos


=aC
Coulomb’s Theory
Assumptions
• The back fill is homogeneous, dry ,cohesionless ,
isotropic and ideally plastic material.
• The slip surface is plane which passes through the
heel of the wall.
• The wall surface is rough. The resultant earth
pressure on the wall is inclined at an angle of δ to
the normal to the wall, where δ is the angle of the
friction between the wall and the backfill.
• The sliding wedge itself acts as rigid body.
where KA is the active earth
pressure coefficient.
DESIGN OF RETAINING WALLS
General proportions of gravity
retaining wall
When surface is inclined:
When surface is horizontal:
General proportions of cantilever
retaining wall
 Bulkheads are very similar in design and
construction as standard retaining walls.
The primary difference in definition
between a bulkhead and retaining wall is
that a bulkhead is retaining earth on one
side, and is partially surrounded by water
on the other.
 Materials used in the construction of bulkheads
vary, but generally are the same as those used for
the construction of the piers.
 Masonry is often used as a bulkhead material.
Masonry can take the form of brick, block, or poured
concrete.
 The largest problem with the bulkhead systems is
erosion of the backfill area. As the backfill begins to
erode, the granular surface is affected, as is the
drainage. The increase in hydrostatic pressure,
coupled with the lateral forces of the earth itself,
tend to push the units over.
Disadvantage:
What is anchored bulkhead?
If tie rods or anchor rods are anchored
close to the upper ends of sheet pile walls, the sheet
pile walls are called bulkheads or anchored sheet pile
walls. The tie or anchor rods are buried in the backfill
at a considerable distance from the back of the wall.
The ties or anchored rods reduce the lateral
deflection, the bending moment and the depth of
penetration.
Anchored Bulkhead
Anchored bulkhead are extensively used in water front
structures. They are constructed by driving a row of sheet pile
to the required depth. The soil in front of the wall is dredged
out to required depth in front of the wall and behind the wall it
is backfilled by suitable soil. The wall is supported at the top by
tie rods and at the bottom by passive earth resistance.
How Anchored Bulkhead determined?
In anchored bulkheads the depth of penetration is
determined by:
 The free earth support method
 The fixed earth support method
In free earth support method
the depth of penetration is not
sufficient to provide end
restraint. The wall is assumed
to be freely supported by tie
rods at the top and by the
passive earth resistance of soil
at the bottom. The forces
acting on the wall as well as
the deflected shape of the
wall are shown in Fig.1 below.
Free Earth Support Method:
T = Tension in the tie rod per unit length
d = Depth of penetration below dredge line
pa = Active pressure in the wall
ppm = Mobilized passive resistance = ppF
The depth of penetration d is found out by taking moment of all forces
about the line of action of the tie rod.
Or, Pa×23(h+d)−a−Ppm×23(d+h)−a=0
Once d is known, the tension in the tie rod is found out by summing all
the horizontal forces i.e.,
pa – ppm – T = 0
In order to guard excess dredging, scouring and presence of pockets of
weak soils the depth of penetration is increased by 20 to 40 %. With this
increasing the depth of penetration, a factor of safety of 1.5 to is
ensured.
Fixed Earth Support Method:
 In fixed earth support method, the depth of
penetration is adequate and soil below the dredge
line provides considerable anchorage. The wall acts as
propped cantilever beam and cannot rotate
freely at its lower end as shown in Fig.3 and the point
of contra flexure lies close to the dredge line.
 Prevention of free rotation at the bottom develops
full passive resistance at the back of the wall above
the lower end. This resistance is replaced by a
concentrated force RD at 0.2 d above the lower end of
the pile
Analysis:
In the analysis, two beams, one above the point of
contraflexure and another below the point of contraflexure, are
considered. The position of the point of contraflexure, y is a
function of angle of internal friction of the soil ɸ. For sands, y is
given by,
ɸ 20 30 40
Y 0.25h 0.08h -0.006h
For approximate analysis 'y' may be assumed as zero and the point of
contrafiexure lie at the dredge level.
By considering the upper beam, the unknown forces RC and T can be found out by
∑M and ∑H = 0.
. In the case of lower beam as shown in Fig.3 force RD and depth of
penetration d are not known.
. By taking moment of all forces about the base of the pile the depth of
penetration can be
found out. The depth of penetration thus obtained by fixed earth support
methodis increased by 20 to 40 %.
1.Check the stability of a cantilever concrete retaining
wall having a stem thickness of 0.4m uniform
throughout, 6.0m height bed block thickness 0.8 m
and a projection of 2.5 m on the heel side and 1.5 m on
the toe side. The unit weight of the wall material is
25kN/m3. The soil has a unit weight of 18 kN/m3 and an
angle of internal friction of 360.Take in to account a
uniform surcharge on the ground of 50kN/m2. The
ground level on the toe side is 1.2 m high above the
base of the wall
Questions
2.A gravity retaining wall is shown
in Fig. 3. Calculate the factor of
safety with respect to
overturning and sliding, given the
fallowing data:Wall dimensions: H
= 6 m, x1 = 0.6 m, x2 = 2m, x3 = 2 m,
x4 = 0.5 m, x5 = 0.75 m,x6 =0.8m, D
= 1.5 m.Soil properties:
γ1 = 16.5kN/m3,φ 1' = 320, 2 =
18kN/m3,φ 2' = 22, c2'=40kPa. Use
the Rankine active earth pressure
in your calculations.
3.Figure 1 shows a section of a
cantilever wall with dimensions and
forces acting there on. Check the
stability of the wall with respect to
(a) overturning, (b) sliding, and (c)
bearing capacity.
4.For the cantilever retaining wall shown in
Fig. 2, let the fallowing data be given:Wall
dimensions: H = 6.5 m, x1 = 0.50 m, x2 = 1.2
m, x3 = 1.35 m, x4 = 2.1 m, x5 = 1.0 m,D = 2.0
m, Φ= 150.Soil properties: 1 = 19.5kN/m3,
φ1' = 360, 2 = 17.0 kN/m3, φ2' = 10, c2'= 50
kPa.Calculate the factor of safety with
respect to overturning, sliding and bearing
capacity.
Retaining walls

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Retaining walls

  • 2.  What is retaining wall  Parts of retaining wall  Types of retaining wall  Earth pressures  Principles of the design of retaining wall  Drainage of back fills  Theories required to solve problem  Design of retaining wall Contents
  • 3. What is a Retaining wall? Retaining wall is a structure used for maintaining the ground surfaces at different elevations on either side of it.
  • 4. All permanent walls and components shall be designed for a minimum service life of 75 years. Corrosion protection is required for all permanent and temporary walls in aggressive environments. Retaining walls are usually built to hold back soil mass. They are also provided to maintain the grounds at two different levels.
  • 6. Types of retaining walls 1. Gravity Retaining Walls 2. Semi-Gravity Retaining Walls 3. Cantilever Retaining Walls 4. Counter fort Retaining Walls
  • 7. The “gravity wall” provides stability by virtue of its own weight , and therefore, is rather massive in size. It is usually built in stone masonry, and occasionally in plain concrete Gravity Walls
  • 8.  The thickness of wall is also governed by need to eliminate or limit the resulting tensile stress to its permissible limit .  Plain concrete gravity walls are not used for heights exceeding about 3m, for obvious economic reasons.
  • 9.  Stress developed is very low.  These walls are so proportioned that no tension is developed anywhere and the resultant of forces remain within the middle third of the base.
  • 10. Semi-Gravity Walls Semi-gravity walls resist external forces by the combined action of self weight, weight of soil above footing and the flexural resistance of the wall components.
  • 11. concrete cantilever wall is an example and consists of a reinforced concrete stem and a base footing. These walls are non-proprietary.
  • 13.  The “Cantilever wall ” is the most common type of retaining structure and is generally economical for heights up to about 8m.  The structure consists of vertical stem , and a base slab, made up of two distinct regions, viz., a heel slab and a toe slab
  • 14.  “Stem” acts as a vertical cantilever under the lateral earth pressure  “Heel slab” acts as a horizontal cantilever under the action of weight of the retained earth (minus soil pressure acting upwards from below)  “Toe slab ” acts as a cantilever under the action of resulting soil pressure acting upward.
  • 15.  It resists the horizontal earth pressure as well as other vertical pressure by way of bending of various components acting as cantilevers.  May be L shaped or T shaped.
  • 16. Counterfort Wall  Stem and Heel slab are strengthened by providing counterforts at some suitable intervals.  The stability of the wall is maintained essentially by the weight of the earth on the heel slab plus the self weight of the structure.
  • 17.  For large heights, in a cantilever retaining wall, the bending moments developed in the stem, heel slab and toe slab become very large and require large thickness.  The bending moments can be considerably reduced by introducing transverse supports, called counterforts.
  • 18. Counterfort wall are placed at regular intervals of about1/3 to ½ of the wall height, interconnecting the stem with the heel slab. The counterforts are concealed within the retained earth on the rear side of the wall. Type equation here.
  • 19. This wall is economical for heights above (approximately) 7m. The counterforts subdivide the vertical slab (stem) into rectangular panels and support them on two sides(suspender-style), and themselves behave essentially as vertical cantilever beams of T- section and varying depth.
  • 20. EARTH PRESSURES  PRESSURE AT REST  ACTIVE EARTH PRESSURE  PASSIVE EARTH PRESSURE
  • 21. PRESSURE AT REST When the soil behind the wall is prevented from lateral movement (towards or away from soil) of wall, the pressure is known as earth pressure at rest.
  • 22. PRESSURE AT REST This is the case when wall has a considerable rigidity. Basement walls generally fall in this category.
  • 23. ACTIVE EARTH PRESSURE If a retaining wall is allowed to move away from the soil accompanied by a lateral soil expansion, the earth pressure decreases with the increasing expansion.
  • 24. ACTIVE EARTH PRESSURE A shear failure of the soil is resulted with any further expansion and a sliding wedge tends to move forward and downward. The earth pressure associated with this state of failure is the minimum pressure and is known as active earth pressure.
  • 25. PASSIVE EARTH PRESSURE If a retaining wall is allowed to move towards the soil accompanied by a lateral soil compression, the earth pressure increase with the increasing compression in the soil.
  • 26. Principle of the design of retaining wall
  • 27. SLIDING: Ability of the retaining wall structure to overcome the horizontal force applied to the wall Factor of safety = 1.5
  • 28. OVERTURNING: Ability of the retaining wall structure to overcome the overturning moment created by the rotational forces applied to the wall. Factor of safety = 1.5
  • 29. BEARING CAPACITY: Ability of the underlying soil to support the weight of the retaining wall structure. Factor of safety = 2.0
  • 30.  NO TENSION: There should be no tension at the base of the wall. when the eccentricity (e) is greater than b/6 , tension develops at the heel
  • 31. DRAINAGE OF THE BACK FILL
  • 32. DRAINAGE Sand + Stone Filter Weepers Or Weep Holes
  • 33. DRAINAGE Drainage Pipes f 100-200 mm @ 2.5 to 4 m
  • 35. RANKIE’S THEORY Assumptions • The soil mass is semi-infinite, homogeneous, dry and cohesionless • The ground surface is plane which may be horizontal or inclined. • The back of the wall is vertical and smooth(No shearing stresses are developed between the wall and soil). • The wall yields about the base and satisfies the deformation conditions for plastic equilibrium.
  • 36. When soil surface is horizontal:
  • 38.
  • 39.  When soil surface is inclined:
  • 41. Coulomb’s Theory Assumptions • The back fill is homogeneous, dry ,cohesionless , isotropic and ideally plastic material. • The slip surface is plane which passes through the heel of the wall. • The wall surface is rough. The resultant earth pressure on the wall is inclined at an angle of δ to the normal to the wall, where δ is the angle of the friction between the wall and the backfill. • The sliding wedge itself acts as rigid body.
  • 42. where KA is the active earth pressure coefficient.
  • 44. General proportions of gravity retaining wall When surface is inclined:
  • 45.
  • 46. When surface is horizontal:
  • 47. General proportions of cantilever retaining wall
  • 48.  Bulkheads are very similar in design and construction as standard retaining walls. The primary difference in definition between a bulkhead and retaining wall is that a bulkhead is retaining earth on one side, and is partially surrounded by water on the other.
  • 49.  Materials used in the construction of bulkheads vary, but generally are the same as those used for the construction of the piers.  Masonry is often used as a bulkhead material. Masonry can take the form of brick, block, or poured concrete.
  • 50.
  • 51.  The largest problem with the bulkhead systems is erosion of the backfill area. As the backfill begins to erode, the granular surface is affected, as is the drainage. The increase in hydrostatic pressure, coupled with the lateral forces of the earth itself, tend to push the units over. Disadvantage:
  • 52. What is anchored bulkhead? If tie rods or anchor rods are anchored close to the upper ends of sheet pile walls, the sheet pile walls are called bulkheads or anchored sheet pile walls. The tie or anchor rods are buried in the backfill at a considerable distance from the back of the wall. The ties or anchored rods reduce the lateral deflection, the bending moment and the depth of penetration. Anchored Bulkhead
  • 53. Anchored bulkhead are extensively used in water front structures. They are constructed by driving a row of sheet pile to the required depth. The soil in front of the wall is dredged out to required depth in front of the wall and behind the wall it is backfilled by suitable soil. The wall is supported at the top by tie rods and at the bottom by passive earth resistance.
  • 54. How Anchored Bulkhead determined? In anchored bulkheads the depth of penetration is determined by:  The free earth support method  The fixed earth support method
  • 55. In free earth support method the depth of penetration is not sufficient to provide end restraint. The wall is assumed to be freely supported by tie rods at the top and by the passive earth resistance of soil at the bottom. The forces acting on the wall as well as the deflected shape of the wall are shown in Fig.1 below. Free Earth Support Method:
  • 56.
  • 57. T = Tension in the tie rod per unit length d = Depth of penetration below dredge line pa = Active pressure in the wall ppm = Mobilized passive resistance = ppF The depth of penetration d is found out by taking moment of all forces about the line of action of the tie rod. Or, Pa×23(h+d)−a−Ppm×23(d+h)−a=0 Once d is known, the tension in the tie rod is found out by summing all the horizontal forces i.e., pa – ppm – T = 0 In order to guard excess dredging, scouring and presence of pockets of weak soils the depth of penetration is increased by 20 to 40 %. With this increasing the depth of penetration, a factor of safety of 1.5 to is ensured.
  • 58. Fixed Earth Support Method:  In fixed earth support method, the depth of penetration is adequate and soil below the dredge line provides considerable anchorage. The wall acts as propped cantilever beam and cannot rotate freely at its lower end as shown in Fig.3 and the point of contra flexure lies close to the dredge line.
  • 59.
  • 60.  Prevention of free rotation at the bottom develops full passive resistance at the back of the wall above the lower end. This resistance is replaced by a concentrated force RD at 0.2 d above the lower end of the pile
  • 61. Analysis: In the analysis, two beams, one above the point of contraflexure and another below the point of contraflexure, are considered. The position of the point of contraflexure, y is a function of angle of internal friction of the soil ɸ. For sands, y is given by,
  • 62. ɸ 20 30 40 Y 0.25h 0.08h -0.006h For approximate analysis 'y' may be assumed as zero and the point of contrafiexure lie at the dredge level. By considering the upper beam, the unknown forces RC and T can be found out by ∑M and ∑H = 0. . In the case of lower beam as shown in Fig.3 force RD and depth of penetration d are not known. . By taking moment of all forces about the base of the pile the depth of penetration can be found out. The depth of penetration thus obtained by fixed earth support methodis increased by 20 to 40 %.
  • 63. 1.Check the stability of a cantilever concrete retaining wall having a stem thickness of 0.4m uniform throughout, 6.0m height bed block thickness 0.8 m and a projection of 2.5 m on the heel side and 1.5 m on the toe side. The unit weight of the wall material is 25kN/m3. The soil has a unit weight of 18 kN/m3 and an angle of internal friction of 360.Take in to account a uniform surcharge on the ground of 50kN/m2. The ground level on the toe side is 1.2 m high above the base of the wall Questions
  • 64. 2.A gravity retaining wall is shown in Fig. 3. Calculate the factor of safety with respect to overturning and sliding, given the fallowing data:Wall dimensions: H = 6 m, x1 = 0.6 m, x2 = 2m, x3 = 2 m, x4 = 0.5 m, x5 = 0.75 m,x6 =0.8m, D = 1.5 m.Soil properties: γ1 = 16.5kN/m3,φ 1' = 320, 2 = 18kN/m3,φ 2' = 22, c2'=40kPa. Use the Rankine active earth pressure in your calculations.
  • 65. 3.Figure 1 shows a section of a cantilever wall with dimensions and forces acting there on. Check the stability of the wall with respect to (a) overturning, (b) sliding, and (c) bearing capacity.
  • 66. 4.For the cantilever retaining wall shown in Fig. 2, let the fallowing data be given:Wall dimensions: H = 6.5 m, x1 = 0.50 m, x2 = 1.2 m, x3 = 1.35 m, x4 = 2.1 m, x5 = 1.0 m,D = 2.0 m, Φ= 150.Soil properties: 1 = 19.5kN/m3, φ1' = 360, 2 = 17.0 kN/m3, φ2' = 10, c2'= 50 kPa.Calculate the factor of safety with respect to overturning, sliding and bearing capacity.