CPG Geotechnical Engineering & Risk Assessment 2

Question 1

A saturated soil element has a total vertical stress of 200 kPa and a pore water pressure of 80 kPa. What is the vertical effective stress?

Accepted Answer

120 kPa

Answer

Terzaghi's effective stress principle gives σ' = σ − u = 200 − 80 = 120 kPa.

Question 2

Which deposit is MOST susceptible to earthquake-induced liquefaction?

Accepted Answer

Loose, saturated, clean fine sand

Answer

Loose, saturated, cohesionless soils build excess pore pressure under cyclic loading and lose strength.

Question 3

In an unconsolidated-undrained (UU) triaxial test on saturated clay, the Mohr failure envelope is typically:

Accepted Answer

Horizontal, giving φu = 0 and strength equal to su

Answer

Saturated clay tested undrained shows the same deviator stress regardless of confining pressure, so φu = 0 and strength equals su.

Question 4

A clay has a preconsolidation pressure of 300 kPa and a current vertical effective stress of 100 kPa. Its overconsolidation ratio (OCR) and state are:

Accepted Answer

3.0, overconsolidated

Answer

OCR = σ'p / σ'v0 = 300/100 = 3, indicating an overconsolidated clay.

Question 5

If the drainage path length of a clay layer is doubled, the time to reach the same degree of primary consolidation will:

Accepted Answer

Increase about fourfold

Answer

Since t = Tv·Hdr²/cv, time scales with the square of the drainage path.

CPG - Certified Professional Geologist Practice Test

CPG - Certified Professional Geologist Practice Test

CPG Geotechnical Engineering & Risk Assessment 2