Lateral Earth Pressure Quiz and Flashcards for Geotechnical Engineering

Study Notes

Lateral Earth Pressure

Lateral earth pressure is the force exerted on a vertical or sloping structure, such as a retaining wall or a trench, due to the weight and the friction of the soil. It is one of the main loading conditions that must be considered when designing these structures. Lateral earth pressure is influenced by several factors, including the soil properties, the wall height, and the angle of the backfill with respect to the horizontal.

Factors Influencing Lateral Earth Pressure

Height of the Pressure Surface: The height of the pressure surface on the wall (h) is a critical factor in determining the magnitude of the lateral earth pressure. The pressure surface is the point on the wall where the lateral earth pressure is acting.
Soil Properties: The unit weight of the soil (γ), the friction angle between the backfill material and the face of the wall (δ), and the angle from the backfill surface to the horizontal (β) all contribute to the lateral earth pressure. The effective friction angle of the soil (ø) is also a crucial factor, as it determines the resistance of the soil to sliding.
Wall Interface Friction Angle: The friction angle between the backfill material and the face of the wall (δ) is a critical factor in determining the lateral earth pressure. Higher friction angles result in higher lateral earth pressures.
Angle of the Failure Plane: The angle between the failure plane and the horizontal (α) is another factor that affects the lateral earth pressure. The failure plane is the point where the soil begins to slide or fail.
Coefficient of Active Lateral Earth Pressure (Ka): Ka is a coefficient that represents the ratio of the active earth pressure to the total active earth pressure. For active earth pressure, the lateral earth pressure acts against the wall and can cause it to tilt away from the soil.
Coefficient of Passive Lateral Earth Pressure (Kp): Kp is a coefficient that represents the ratio of the passive earth pressure to the total passive earth pressure. For passive earth pressure, the lateral earth pressure acts in the opposite direction, pushing the wall into the soil.

Lateral Earth Pressure Variation with Depth

Lateral earth pressure varies linearly with depth. The resultant earth pressure acts at a distance equal to one-third of the wall height from the base. The direction of the lateral earth pressure acts parallel to the slope of the backfill. The magnitude of the active earth pressure can be determined using Coulomb's active wedge theory, while the magnitude of the passive earth pressure can be determined using Coulomb's passive wedge theory.

Active and Passive Earth Pressure

There are two types of lateral earth pressure: active and passive. Active earth pressure occurs when the wall tends to move away from the soil, while passive earth pressure occurs when the wall tends to move into the soil. The state of the active and passive earth pressure depends on the expansion or compression transformation of the backfill from the elastic state to the state of plastic equilibrium.

In the case of a retaining wall, the lateral earth pressure distribution is calculated using the Rankine, Coulomb, Log Spiral, and Trial Wedge methods. The resultant earth pressure is the force that causes bending, sliding, and overturning in the wall.

Estimating Lateral Earth Pressure

To estimate the lateral earth pressure on a retaining wall, the coefficient of at-rest pressure (Ko), the coefficient of active pressure (Ka), and the coefficient of passive pressure (Kp) are used. The coefficient of at-rest pressure (Ko) is used when the wall is completely restrained from moving. The coefficient of active pressure (Ka) is used when the wall may tilt away from the soil, and the coefficient of passive pressure (Kp) is used when the wall may be pushed into the soil.

In summary, lateral earth pressure is a crucial factor in the design of structures such as retaining walls and trenches. It is influenced by various factors, including soil properties, wall interface friction angle, and wall movement. Proper estimation of lateral earth pressure is essential for ensuring the stability and safety of these structures.

Description

This quiz covers the fundamental concepts of lateral earth pressure, including the factors that influence it, its variation with depth, and the differences between active and passive earth pressure. It's essential for designing retaining walls and trenches, ensuring their stability and safety.