3. What is Lateral Earth Pressure?
Lateral earth pressure is the pressure that soil
exerts in the horizontal direction.
4.
5. 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.
6. Other Forces Acting on the Wall
Aside from the earth pressure force acting on the wall,
other forces might also act on the wall and these are
superimposed onto the earth pressure force. For
example, these forces might include:
Surcharge load
Earthquake load
Water Pressure
7. Lateral Earth Pressure
The magnitude of lateral earth pressure depends on:
1. Shear strength characteristics of soil
2. Lateral strain condition
3. Pore water pressure
4. State of Equilibrium of soil
5. Wall and ground surface shape
8. Lateral Earth Pressure And Wall
Movement
Lateral earth pressure are the direct result of
horizontal stresses in the soil.
In order to understand the lateral earth pressure
we have to define the Coefficient of lateral earth
pressure, K.
9. Coefficient (K)
It is defined as the ratio of the horizontal effective stress,
σh to the vertical effective stress σv
K = σh/σv
10. 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)
11. 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)
12. At Rest Earth Pressure
Ko can be calculated as follows:
Ko = 1 – sin φ for coarse grained soils
Ko = .44 + .42 [PI / 100] for NC soils
Ko (oc) = Ko (NC) (OCR)1/2
for OC soils
13. 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.
15. 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.
19. Investigation and Testing
on-site
Cone penetration test
Standard penetration test
Monitoring well
piezometer
Borehole
Crosshole sonic logging
Nuclear densometer test
20. Investigation and Testing
Laboratory test:
Atterberg limits
California bearing ratio
Direct shear test
Hydrometer
Proctor compaction test
R-value
Sieve analysis
23. Earth Pressure Theories
Two classic Earth pressure theories has been put
forward in the eighteen and nineteen centuries by
Coulomb and Rankine respectively.
1) Coulomb’s(1776) Earth Pressure Theory
2) Rankine (1857) Earth Pressure Theory
These two theories are still in use in their original
form and in some modified forms to calculate the
earth pressure.
24. Coulomb’s Theory of Earth Pressure
• Assumptions;
– The backfill is a dry, cohesionless, homogeneous, isotropic soil.
– The backfill surface is planar and can be inclined.
– The back of the wall can be inclined to the vertical.
– The failure surface is a plane surface which passes through the heel of
the wall.
– The position and the line of action of the earth pressure are known.
– The sliding wedge is considered to be a rigid body and the earth
pressure is obtained by considering the limiting equilibrium of the
sliding wedge as a whole.
28. RANKINE THEORY (1857)
In original form the theory was developed for purely
non-cohesive soils (i.e. c = 0), but subsequently Bell
(1915) extended this theory to c-Φ soil as well.
29. ASSUMPTIONS
Soil is non-cohesive (c = 0) dry, isotropic and
homogenous.
Backfill is horizontal.
Wall is vertical,
Wall friction is neglected.
Failure is a plain strain problem.
35. :
Gravity Retaining Walls
Retaining wall that relies on their huge weight to retain
the material behind it and achieve stability against
failures.
Gravity retaining walls are much thicker in section.
Height must be 2 to 3 times than its width. .
37. Cantilever Retaining Walls
Cantilever walls are built of reinforced concrete and are typically
composed of a horizontal footing and a vertical stem wall.
Convert horizontal pressure from the soil sitting behind the wall into
vertical pressure and transfer it to the stem.
39. Anchored Retaining Wall
Any wall which uses facing units tied to rods or strips
which have their ends anchored into the ground is an
anchored earth wall
The anchors are like abutments
41. Soil nailing
Constructing a soil nailed wall involves reinforcing the
soil as work progresses in the area being excavated by
the introduction of bars which essentially work in
tension, called Passive Bars.
These are usually parallel to one another and slightly
inclined downward.
These bars can also work partially in bending and in
shear. The skin friction between the soil and the nails
puts the nails in tension.
44. GeoFoam is Use To Reduce
Lateral Stresses in Retaining
Structures
45. EPS GeoFoam
The manufacture of rigid plastic foams dates back to
the 1950s, with adaptation for geotechnical use
occurring in the early 1960s. In 1992, the category of
“GeoFoam” was
proposed as an addition to the variety of geosynthetics
already in existence. The most commonly used
GeoFoam material is a polymeric form called expanded
polystyrene (EPS), also known as expanded polystyrol
outside of the United States.
46. EPS GeoFoam
The most common method of producing EPS GeoFoam
is block molding, in which a mold is used to create a
prismatic rectangular block. Depending upon the
application, other mold shapes can be used, however it
is more common to shape the blocks post-production
(Horvath 1994). The raw material used to create
GeoFoam is referred to as expandable polystyrene, or
often resin, and is composed of small beads with
diameters similar to medium to coarse sand (0.2 to 3
mm).
