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All questions of Earth Pressure & Retaining Walls for Civil Engineering (CE) Exam

The earth pressure distribution due to surcharge load q per unit area is
  • a)
    Triangular
  • b)
    Rectangular
  • c)
    Parabolic
  • d)
    Circular
Correct answer is option 'B'. Can you explain this answer?

Rithika Reddy answered
The earth pressure distribution due to the surcharge load is = q, Ka and is uniform throughout the length of the retaining wall.

Passive pressure in soil is associated with
  • a)
    Lateral expansion of the soil 
  • b)
    Lateral compression of the soil 
  • c)
    Zero lateral strain
  • d)
    None of these
Correct answer is option 'B'. Can you explain this answer?

Rajdeep Gupta answered
Passive pressure compresses soil horizontally. It occurs when the retaining wall moves towards the backfill. Active pressure stretches soil horizontally and exerts tensile force in soil layer. It occurs when the retaining wall moves away from the backfill.

The value of K0(coefficient of earth pressure at rest) for loose sand is __________
  • a)
    0.6
  • b)
    0.5
  • c)
    0.4
  • d)
    0.8
Correct answer is option 'C'. Can you explain this answer?

Sravya Rane answered
Co-efficient of Earth Pressure at Rest (K0) for Loose Sand

Co-efficient of Earth Pressure at Rest (K0) is the ratio of the lateral stress to the vertical stress exerted on the soil mass when it is in a state of rest. It is a dimensionless quantity that depends upon the physical properties of the soil, such as the unit weight, friction angle, and the angle of internal friction of the soil.

Loose sand is a type of soil that is characterized by its low density and high porosity. The value of K0 for loose sand is determined by the following factors:

1. Porosity

The porosity of the soil is the ratio of the volume of voids to the total volume of the soil. Loose sand has a high porosity, which means that it contains a large number of voids. This results in a low value of K0.

2. Angle of Internal Friction

The angle of internal friction is a measure of the resistance of the soil to shearing stresses. Loose sand has a low angle of internal friction, which means that it offers little resistance to shearing stresses. This results in a low value of K0.

3. Cohesion

Cohesion is the property of the soil that allows it to resist shearing stresses even in the absence of friction. Loose sand has a very low cohesion, which means that it offers very little resistance to shearing stresses. This results in a low value of K0.

Conclusion

The value of K0 for loose sand is 0.4, which is lower than that for other types of soils. This is because loose sand has a high porosity, a low angle of internal friction, and a low cohesion.

The pore water pressure in the capillary zone is
  • a)
    Zero
  • b)
    Positive
  • c)
    Negative
  • d)
    Very low
Correct answer is option 'C'. Can you explain this answer?

Niharika Yadav answered
Pore Water Pressure in the Capillary Zone

Pore water pressure is the pressure exerted by the water present in the soil pores. In the capillary zone, the pore water pressure is negative. Let's understand why.

Capillary Zone

The capillary zone is the region in the soil where the pore size is small enough to create capillary forces. Capillary forces are the forces that cause water to rise in a small-diameter tube due to the adhesive forces between the water and the tube's surface.

Negative Pore Water Pressure

In the capillary zone, the pore size is small enough to create capillary forces that cause the pore water pressure to be negative. The negative pore water pressure occurs due to the following reasons:

- Adhesion: The water molecules adhere to the soil particles due to which the water level in the soil is lower than the water level in the free surface.
- Surface Tension: The surface tension of water causes it to stick to the soil particles and reduce the pore water pressure.
- Attraction: The soil particles attract the water molecules, causing the water level to be lower than the free surface.

Conclusion

In conclusion, the pore water pressure in the capillary zone is negative due to the capillary forces, adhesion, surface tension, and attraction between the soil particles and water molecules.

What will be the coefficient of earth pressure at rest for a rigid retaining wall, If the backfill consists of cohesion less soil having φ = 26°?
  • a)
    0.1295
  • b)
    0.6552
  • c)
    0.5616
  • d)
    0.7383
Correct answer is option 'C'. Can you explain this answer?

The coefficient of earth pressure at rest for a rigid retaining wall, if the backfill consists of cohesion less soil having no surcharge, is typically assumed to be 0.5. However, the actual value may vary depending on the specific characteristics of the soil and the retaining wall design. It is important to conduct a thorough analysis and consider factors such as soil properties, wall geometry, and loading conditions when determining the coefficient of earth pressure at rest for a particular project.

Based on the assumptions of Rankine’s theory, the soil mass is __________
  • a)
    Stratified
  • b)
    Submerged
  • c)
    Homogeneous
  • d)
    All of the mentioned
Correct answer is option 'C'. Can you explain this answer?

Diya Ahuja answered

Assumptions of Rankine’s Theory:

Rankine's theory is based on certain assumptions about the soil mass being analyzed. One of the key assumptions is that the soil mass is homogeneous.

Explanation:

Homogeneous Soil Mass:
- In Rankine's theory, it is assumed that the soil mass is uniform and does not have variations in its composition or properties.
- This assumption allows for simplified calculations and analysis of soil behavior under different loading conditions.
- A homogeneous soil mass is easier to model and analyze compared to a stratified or layered soil mass.

Importance of Homogeneity:
- The assumption of homogeneity is crucial in simplifying the analysis of soil mechanics problems.
- It helps in predicting the behavior of the soil mass accurately and making informed engineering decisions.
- By assuming homogeneity, engineers can focus on the overall behavior of the soil mass without having to account for complex variations within the mass.

Therefore, based on the assumptions of Rankine's theory, the soil mass is considered to be homogeneous. This assumption simplifies the analysis and allows for a better understanding of soil behavior under different conditions.

Originally, Rankine’s theory of lateral earth pressure can be applied to only _______
  • a)
    Cohesion less soil
  • b)
    Cohesive soil
  • c)
    Fine grained soil
  • d)
    Coarse grained soil
Correct answer is option 'A'. Can you explain this answer?

Rankine is a unit of measurement used in engineering and fluid dynamics to quantify pressure or temperature. It is named after the Scottish engineer and physicist William John Macquorn Rankine, who developed the Rankine scale for temperature measurement. The Rankine scale is based on the Fahrenheit scale, with absolute zero defined as 0 Rankine. The Rankine unit for temperature is equal to one degree Fahrenheit. In addition to the temperature scale, Rankine is also used as a unit of pressure in the British engineering system, where 1 Rankine is equal to 0.000192 psi (pounds per square inch).

The following refer to the stability analysis of an earth dam under different conditions:
1. Stability of D/S slope during steady seepage.
2. Stability of D/S slope during sudden drawdown.
3. Stability of U/S and D/S slopes during construction.
Which of these statements are correct?
  • a)
    1 and 2
  • b)
    1 and 3
  • c)
    2 and 3
  • d)
    1, 2 and 3
Correct answer is option 'B'. Can you explain this answer?

Swati Dasgupta answered
For earth dam during steady seepage, the critical condition occurs for D/S slope. For rapid drawdown case U/S slope represents critical condition. In both cases the pore water pressure is determined from flow net.
During construction, the excess pore pressure is likely to develop and stability of U/S and D/S slopes during or immediately after construction should be considered. 

Why are weep holes provided at the back of retaining walls?
  • a)
    To reduce the active earth pressure on the walls.
  • b)
    To reduce the build-up of hydrostatic pressure.
  • c)
    To provide better compaction.
  • d)
    To increase the passive earth pressure.
Correct answer is option 'B'. Can you explain this answer?

Rajeev Menon answered
The correct answer is b) To reduce the build-up of hydrostatic pressure.
Weep holes are small openings that are provided in retaining walls to allow water to drain from behind the wall. They are typically located near the base of the wall, and their purpose is to reduce the build-up of hydrostatic pressure that can occur when water collects behind the wall.

If water is allowed to accumulate behind a retaining wall, it can exert a significant amount of pressure on the wall, which can lead to structural damage or failure. By providing weep holes, the water can drain away from the wall, reducing the hydrostatic pressure and helping to prevent damage to the wall. Weep holes can be especially important in areas where the wall is likely to be subjected to heavy rain or other sources of water infiltration.

A cantilever sheet pile derives its stability from
  • a)
    Lateral resistance of soil
  • b)
    Self weight
  • c)
    The deadman
  • d)
    The anchor rod
Correct answer is option 'A'. Can you explain this answer?

Divya Mehta answered
Introduction:
A cantilever sheet pile is a type of retaining wall structure that is used to provide lateral support and prevent soil erosion. It is commonly used in various construction projects, such as deep excavations, waterfront structures, and underground structures. The stability of a cantilever sheet pile is primarily derived from the lateral resistance of the soil.

Lateral Resistance of Soil:
The primary mechanism that provides stability to a cantilever sheet pile is the lateral resistance of the soil. When the sheet pile is driven into the ground, it displaces the soil laterally, creating a zone of pressure behind the wall. This pressure generates a resistance force that acts in the opposite direction of the applied lateral load.

Passive Earth Pressure:
The lateral resistance of the soil is commonly referred to as passive earth pressure. It is the result of the soil's ability to resist movement and deformation when subjected to external forces. The magnitude of the passive earth pressure depends on several factors, including the soil properties, the angle of internal friction, the wall's depth, and the wall's embedment length.

Key Points:
- The lateral resistance provided by the soil prevents the cantilever sheet pile from overturning or sliding.
- The passive earth pressure acting on the sheet pile increases with the depth of the wall and the angle of internal friction of the soil.
- The cantilever sheet pile relies on this lateral resistance to counteract the applied lateral load, thereby maintaining its stability.

Other Factors:
While the lateral resistance of the soil is the primary source of stability for a cantilever sheet pile, other factors also contribute to its overall stability. These factors include:

1. Self-weight: The weight of the sheet pile itself adds to its stability by providing an additional downward force that counteracts the lateral load.

2. The Deadman: A deadman is a large mass of soil or concrete that is placed at the anchor point of the sheet pile. It helps to anchor the sheet pile and provides additional resistance against lateral movement.

3. The Anchor Rod: In some cases, an anchor rod or tieback may be used to provide additional stability to the sheet pile. The anchor rod is typically attached to the sheet pile and anchored into the ground, creating tension that helps resist lateral movement.

Conclusion:
In conclusion, the stability of a cantilever sheet pile is primarily derived from the lateral resistance of the soil. The passive earth pressure generated by the soil provides the necessary resistance to counteract the applied lateral load. While other factors such as self-weight, the deadman, and anchor rods contribute to the overall stability, the lateral resistance of the soil remains the key mechanism for ensuring the stability of a cantilever sheet pile.

Rankine’s theory of lateral pressure was extended to other soil by __________
  • a)
    Resal and Bell
  • b)
    Mohr
  • c)
    None of the mentioned
  • d)
    All of the mentioned
Correct answer is option 'A'. Can you explain this answer?

Charvi Kaur answered
Rankine is a unit of temperature in the Imperial system, commonly used in engineering and thermodynamics. It is denoted by the symbol "°R" and is equal to one degree Fahrenheit above absolute zero. The Rankine scale starts at absolute zero (0°R) and is based on the Fahrenheit scale, where the freezing point of water is 491.67°R and the boiling point is 671.67°R.

Rankine's theory of earth pressure assumes that the back of the wall is
  • a)
    Plane and smooth
  • b)
    Plane and rough
  • c)
    Vertical and smooth
  • d)
    Vertical and rough
Correct answer is option 'C'. Can you explain this answer?

Muskaan Sen answered
Rankine's earth pressure theory assumes that the retaining wall is smooth and vertical and the ground surface is piane which may be inclined or horizontal.

The factor that is responsible for inclination of resultant pressure to the retaining wall is __________
  • a)
    Frictional force
  • b)
    Surcharge
  • c)
    Earth pressure
  • d)
    Weight of the wall
Correct answer is option 'A'. Can you explain this answer?

Lavanya Menon answered
The retaining walls are constructed of masonry or concrete, due to this the frictional force develops. The existence of the friction makes the resultant pressure inclined to the wall at an angle that approaches the frictional angle between the soil and the wall.

Coulomb’s theory of earth pressure is based on
  • a)
    the theory of plasticity
  • b)
    the theory of elasticity
  • c)
    empirical rules
  • d)
    wedge theory
Correct answer is option 'D'. Can you explain this answer?

Meghana Desai answered
Coulomb is the SI unit of electric charge, symbolized as C. It is named after the French physicist Charles-Augustin de Coulomb, who made pioneering contributions to the study of electromagnetism in the 18th century. One Coulomb of electric charge is defined as the amount of charge that passes through a conductor in one second, when a current of one ampere flows through it. It is a fundamental unit of measurement in electricity and magnetism, and is used to express the magnitude of electric force and electric field strength.

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