18 Questions
What is the value of the coefficient of earth pressure at rest (Ko) for normally consolidated clays?
Ko is typically in the range of 0.4 - 0.6
What condition is required for a soil element to be in the Ko state?
The soil element must not undergo any lateral strains
What is the expression for the coefficient of earth pressure at rest (Ko) when the soil mass is treated as a linear elastic continuum?
Ko = $\nu / (1 + \nu)$
What is the typical range of the coefficient of earth pressure at rest (Ko) for overconsolidated soils?
Ko can be larger than 1.0
Which theory is used to determine the lateral earth pressure at rest?
Earth pressure at rest theory
In the example problem, what is the overconsolidation ratio (OCR) of the soil?
OCR = 1.0
According to the figure, which of the following statements is true about the lateral earth pressure variation with wall movement?
The wall movement required to mobilize the active state is less than that required to mobilize the passive state.
Which of the following is NOT one of the three special cases of lateral earth pressures discussed in this chapter?
Rankine earth pressure
In a homogeneous soil mass with a horizontal ground level, what is the ratio of effective horizontal stress ($\sigma_h$) to effective vertical stress ($\sigma_v$) called?
At-rest earth pressure coefficient
What is the assumption made about the reader's prior knowledge in this chapter?
The reader has studied lateral earth pressure in the past.
Which of the following structures is NOT shown as an example of an earth retaining structure in Figure 2.3?
Sheet pile wall
What are the two extreme loadings where the soil is at failure?
Active earth pressure and passive earth pressure
According to the lateral earth pressure theory, what is the primary factor influencing the magnitude of active earth pressure?
The angle of internal friction of the soil
What is the key difference between Rankine's and Coulomb's theories for active earth pressure?
Rankine's theory neglects wall friction, while Coulomb's accounts for it
For a normally consolidated clay, what is the typical range of the coefficient of earth pressure at rest ($K_o$)?
$0.6 < K_o < 0.8$
Which of the following equations is used to calculate the active earth pressure coefficient ($K_a$) according to Coulomb's theory?
$K_a = \cos(\phi) / (\cos^2\beta \sqrt{\cos^2\alpha \cos^2(\phi + \beta)})$
If the soil friction angle ($\phi$) is $30^\circ$, the wall friction angle ($\delta$) is $20^\circ$, and the wall is vertical ($\beta = 0^\circ$), what is the value of the active earth pressure coefficient ($K_a$) according to Coulomb's theory?
0.333
What is the primary assumption in the Rankine theory for active earth pressure?
The soil is cohesionless
Study Notes
Lateral Earth Pressure Theory
- The chapter focuses on three special cases of lateral earth pressures: at-rest earth pressure, active earth pressure, and passive earth pressure.
- Active and passive pressures are the two extreme loadings where the soil is at failure.
At-Rest Earth Pressure
- The soil is known to be “at rest” and the constant is called the coefficient of earth pressure at rest, denoted by Ko.
- When the soil is at rest, there is no lateral strain within the soil.
- A clay element subjected to one-dimensional consolidation does not undergo any lateral strains and hence is in the Ko state (at rest).
- Ko of a normally consolidated soil is typically in the range of 0.4– 0.6, and when soil is overconsolidated it can be larger and sometimes even exceed 1.0.
Coefficient of Earth Pressure at Rest (Ko)
- Ko can be expressed as (2.7a) when the soil mass is treated as a linear elastic continuum, where μ is the Poisson’s ratio of the elastic medium.
Lateral Earth Pressure
- The nature of variation of the lateral pressure (σ’h) at a certain depth of the wall with the magnitude of wall movement is shown in Figure 2.2.
- The wall movement required to mobilize the active state is less than that required to mobilize the passive state.
Lateral Earth Pressure on a Retaining Wall
- Figure 2.1 shows the nature of lateral earth pressure on a retaining wall.
- Example 2.1 involves determining the lateral earth force at rest per unit length of the wall and the location of the resultant force.
Rankine’s Active Pressure and Coulomb’s Active Pressure
- Figures 2.4 and 2.6 show Rankine’s active pressure and Coulomb’s active pressure, respectively.
Tables and Equations
- Tables 2.2, 2.3, and 2.4 show the values of Ka for different β, α, δ, and φ values.
- Equations (2.5a) and (2.6a) are used to calculate Ko for normally consolidated clays.
Earth Retaining Structures
- Figure 2.3 shows examples of earth retaining structures, including retaining walls, crib walls, and basement walls.
Learn about the concept of lateral earth pressure at rest and the coefficient of earth pressure at rest, symbolized by Ko. Understand the behavior of clay elements under one-dimensional consolidation and the implications for lateral strains in soils.
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