ASCE Geotechnical and Foundation Engineering 3

Question 1

The water table is at the ground surface in a soil with saturated unit weight 20 kN/m³. Using γw = 9.81 kN/m³, what is the vertical effective stress at 5 m depth?

Accepted Answer

about 51 kPa

Answer

σ' = 5 × (20 - 9.81) ≈ 51 kPa.

Question 2

For a cohesionless backfill with φ' = 30° behind a smooth vertical wall with a horizontal surface, the Rankine active earth pressure coefficient Ka is:

Accepted Answer

0.33

Answer

Ka = tan²(45° - φ/2) = tan²(30°) = 1/3.

Question 3

For the same backfill with φ' = 30°, the Rankine passive earth pressure coefficient Kp is:

Accepted Answer

3.00

Answer

Kp = tan²(45° + φ/2) = tan²(60°) = 3.0.

Question 4

An unconsolidated-undrained (UU) triaxial test on a saturated clay typically yields a failure envelope with:

Accepted Answer

φ = 0 and strength equal to the undrained shear strength cu

Answer

Saturated UU tests give equal deviator stresses regardless of confining pressure, producing a horizontal φ = 0 envelope.

Question 5

A sand has Gs = 2.65 and void ratio e = 0.65. What is the critical hydraulic gradient that would cause a quick condition?

Accepted Answer

1.00

Answer

ic = (Gs - 1)/(1 + e) = 1.65/1.65 = 1.00.

ASCE - American Society of Civil Engineers Certification Practice Test

ASCE - American Society of Civil Engineers Certification Practice Test

ASCE Geotechnical and Foundation Engineering 3