ASCE Geotechnical and Foundation Engineering 5

Question 1

In the alpha (α) method for driven piles in clay, unit skin friction is calculated as:

Accepted Answer

fs = α × cu

Answer

The α method is a total stress approach where fs = α·cu, with α decreasing as cu increases.

Question 2

Negative skin friction (downdrag) on a pile is most likely to develop when:

Accepted Answer

Recently placed fill causes the surrounding soft clay to consolidate and settle more than the pile

Answer

Downdrag occurs when surrounding soil settles relative to the pile, dragging it downward.

Question 3

For an infinite slope of dry cohesionless soil with friction angle φ inclined at angle β, the factor of safety is:

Accepted Answer

tan φ / tan β

Answer

For dry cohesionless infinite slopes, FS = tan φ / tan β, independent of depth.

Question 4

A field SPT blow count N = 20 was recorded with a hammer having 75% energy efficiency. What is N60?

Accepted Answer

25

Answer

N60 = N × ER/60 = 20 × 75/60 = 25.

Question 5

A 60-in rock core run recovers pieces of 6, 3, 8, 2, 5, and 12 in. What is the Rock Quality Designation (RQD)?

Accepted Answer

52%

Answer

Only pieces ≥ 4 in count: (6 + 8 + 5 + 12)/60 = 31/60 ≈ 52%.

ASCE - American Society of Civil Engineers Certification Practice Test