Chapter 15, Problem 15.1P

(a)

To determine

Whether the statement “A key is provided at the base of a cantilever retaining wall to improve the stability with respect to overturning” is true or false.

Answer to Problem 15.1P

The given statement is $\underset{\_}{\text{False}}$.

Explanation of Solution

Actually a key is provided to increase the passive resistance at the toe which will increase the factor of safety against sliding. Hence, the base key will improve the stability of wall with respect to sliding.

Therefore, the given statement is $\underset{\_}{\text{False}}$.

(b)

To determine

Whether the statement “The earth pressure distribution beneath the base of the retaining wall is uniform” is true or false.

Answer to Problem 15.1P

The given statement is $\underset{\_}{\text{False}}$.

Explanation of Solution

The distribution of earth pressure below the base slab is not uniform because,

• Different earth pressure exerts on the base slab.
• The base slab is not a homogeneous one (concrete has homogeneous property).
• The friction between soil and base slab can distribute the earth pressure that is non-uniform in nature.

Therefore, the given statement is $\underset{\_}{\text{False}}$.

(c)

To determine

Whether the statement “The lateral earth pressures in active state are greater in loose sands than in dense sands” is true or false.

Answer to Problem 15.1P

The given statement is $\underset{\_}{\text{True}}$.

Explanation of Solution

• Active lateral earth pressure is the tilting of wall away from the position.
• The chance of tilting is more in loose sands compared to dense sands. Hence, the lateral earth pressures in active state are greater in loose sands than in dense sands.

Therefore, the given statement is $\underset{\_}{\text{True}}$.

(d)

To determine

Whether the statement “A base heave problem is more serious in soft clays than in stiff clays” is true or false.

Answer to Problem 15.1P

The given statement is $\underset{\_}{\text{True}}$.

Explanation of Solution

• Braced cuts in clay may become unstable due to the formation of heaving at the bottom of the excavation.
• Heave is the upward movement of the ground due to the expansion of clay, which swells when wet.
• More expansion will lead to heave. The expansion of soft clay is more compared to stiff clay. Hence, the base heave problem is more serious in soft clays than in stiff clays.

Therefore, the given statement is $\underset{\_}{\text{True}}$.

(e)

To determine

Whether the statement “Cantilever sheet piles have to be driven deeper in loose sands than in dense sands” is true or false.

Answer to Problem 15.1P

The given statement is $\underset{\_}{\text{True}}$.

Explanation of Solution

• The reason to drive sheet piles at a certain depth below the bottom excavation is to reduce the lateral yielding of wall during the last stages of excavation.
• The lateral yielding in the loose sands is greater than the dense sands. Hence, the cantilever sheet piles have to be driven deeper in loose sands than in dense sands. The deeper piles will reduce the lateral yielding.

Therefore, the given statement is $\underset{\_}{\text{True}}$.