Chapter 19, Problem 19.1P

(a)

To determine

State whether the statement “drilled shafts also include large diameter driven piles” is true or false.

Answer to Problem 19.1P

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

Explanation of Solution

The drilled shafts are cylindrical and deep; cast-in-place concrete foundations are poured in these shafts and by drilling process; whereas driven piles are commonly driven into the ground in situ.

Hence, the drilled shafts do not include large diameter of driven piles.

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

(b)

To determine

State whether the statement “drilled shafts can be 500 mm in diameter” is true or false.

Answer to Problem 19.1P

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

Explanation of Solution

The drilled shaft diameter can range from 2 ft (609.6 mm) to 30 feet (9,144 mm). Thus, the drilled shafts cannot be in diameter of 500 mm.

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

(c)

To determine

State whether the statement “adhesion factor $\alpha \ast$ in the unit skin friction in clays is larger for soft clays than stiff clays” is true or false.

Answer to Problem 19.1P

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

Explanation of Solution

The adhesion factor for stiff clays can range from 0.3 to 0.45, and the larger value of adhesion factor is used for soft clay due to its more unit skin friction.

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

(d)

To determine

State whether “drilled shafts in sands derive most of their load carrying capacity from the point resistance than the skin friction” is true or false.

Answer to Problem 19.1P

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

Explanation of Solution

The drilled shafts’ capacity is developed from the combination of end bearing and side shear. The side shear is correlated to the soil shear strength and in sands, the friction is less.

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

(e)

To determine

State whether the statement “when the settlement is 1% of the drilled shaft diameter, greater fraction of skin friction is mobilized than the point load in sands and clays” is true or false.

Answer to Problem 19.1P

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

Explanation of Solution

The arrangement of sands and clays was done during the initial drilling process rather than the end point. When 1% of settlement is achieved, the soil which is around the shaft gets mobilized much earlier than the end point.

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