Geotechnical Engineering

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UNIVERSITI MALAYSIA PAHANG Department of Civil
and Environmental Engineering

• Geotechnical Engineering
• BAA 3513
• Chapter 2 Lateral Earth Pressure Part 2

Muzamir bin Hasan, M.Eng. Lecturer
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The In-situ Stresses and the KO Condition
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The In-situ Stresses and the KO Condition
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The In-situ Stresses and the KO Condition
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The Active Earth Pressure

• When the earth (soil) actively pushes on the
  structure and moves it, this is called an active
  earth pressure condition. As the structure moves
  away, it decreases the confining stress s3 sH
  pa

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The Active Earth Pressure

• Using Mohrs graphical representation,

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The Active Earth Pressure
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The Active Earth Pressure
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The Active Earth Pressure

• A similar analysis can be performed for the
  active earth pressure of a saturated clay in
  undrained loading by using a Mohr circle to give
  the formula,

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The Active Earth Pressure

• The total force per foot length of wall, FA is
  given by the expression

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The Active Earth Pressure

• The total earth pressure is zero at a depth
  z2c/?, as shown in the figure.
• Above that level the soil is in tension. Below
  it, the soil is in compression. The depth of the
  tension zone can be found where the total force
  FA 0,

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The Active Earth Pressure (Backfill Cohesive
Soil with Horizontal Backfill)
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The Active Earth Pressure (Backfill Cohesive
Soil with Horizontal Backfill)
Depth at which the active pressure become 0
For undrained condition, f0,Katan2451 and ccu
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The Active Earth Pressure (Backfill Cohesive
Soil with Horizontal Backfill)

• After tensile crack

For undrained condition, f0,Katan2451 and ccu
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The Active Earth Pressure (Backfill Cohesive
Soil with Horizontal Backfill)

• Before tensile crack

For undrained condition, f0,Katan2451 and ccu
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The Passive Earth Pressure

• When the soil is passively being pushed by the
  structure, the earth is considered to be in a
  passive earth pressure condition. Using Mohrs
  graph, the passive pressure pp and the passive
  force Fp are,

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The Passive Earth Pressure
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The Passive Earth Pressure
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The Passive Earth Pressure (Backfill Cohesive
Soil with Horizontal Backfill)

• The passive earth pressure and force for granular
  soils is,

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The Passive Earth Pressure
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Summary of the Rankine Theory Formulas
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Summary of the Rankine Theory Formulas
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Example 8.1 (page 232)

• Calculate the Rankine active force per unit
  length of the wall shown in Figure 8.14a, and
  also determine the location of the resultant.

?15.7kN/m3 F30º c0
5m
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Solution
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Solution
5m
65.4lN/m
1.67m
26.17kN/m2
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Example 8.2 (page 233)

• For the retaining wall considered in Example 8.1,
  what is the Rankine passive force per unit length
  of the wall?

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Solution
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Solution
5m
588.75lN/m
1.67m
235.5kN/m2
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Example 8.3 (page 234)

• If the retaining wall shown in Figure 8.14a is
  restrained from moving, what will be the lateral
  force per unit length of the wall?

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Solution
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Solution
5m
98.1lN/m
1.67m
39.25kN/m2
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Example 8.4

• For retaining wall shown in Figure 8.17a,
  determine the active force per unit length of the
  wall for Rankine state. Also find the location of
  the resultant.

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Example 8.4
? 16 kN/m3 F 30º c 0
3m
GWT
?sat 18 kN/m3 F 30º c 0
3m
z
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Solution
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Solution
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Solution
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Solution
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Solution
3m
16

3m
13.0
29.43
19.67
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Solution
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Solution
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Solution
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Pa 117.15kM/m
1.78m
13.0
36.1
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Example 8.5

• A retaining wall, having a soft, saturated clay
  backfill, is shown in Figure 8.18a. For undrained
  condition (f0) of the backfill, determine
• a. the maximum depth of the tensile crack.
• b. Pa before the tensile crack occurs.
• c. Pa after the tensile crack occurs.

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Solution
Soft saturated clay ?15.72kN/m2 F0 cu16.77kN/m2
6m
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Solution
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Solution
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Solution
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Solution
33.54kN/m2
2.13m
3.87m
60.87kN/m2
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Cohesive Soil with Horizontal Backfill

• For frictionless retaining wall with cohesive
  soil backfill (ACTIVE!!!!).

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Cohesive Soil with Horizontal Backfill
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Cohesive Soil with Horizontal Backfill
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Cohesive Soil with Horizontal Backfill

• For frictionless retaining wall with cohesive
  soil backfill (PASSIVE!!!!).

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Cohesive Soil with Horizontal Backfill
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Example 8.6

• A frictionless retaining wall is shown in Figure
  8.19a. Find the passive resistance (Pp) on the
  backfill, and the location of the resultant
  passive force.

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Example 8.6
q10kN/m2
?15kN/m3 F26º c8kN/m2
4m
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Solution
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Solution
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Solution
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Solution
512kN/m
1m
153.6kN/m2
51.2kN/m2