Civil Engineering PE Soil Mechanics and Lab Testing 5

Question 1

A soil has a shrinkage limit (SL) of 12%, plastic limit (PL) of 22%, and liquid limit (LL) of 48%. What is the shrinkage ratio if the soil volume at the shrinkage limit is 24.5 cm³ and dry mass is 36 g, using γw = 1 g/cm³?

Accepted Answer

1.47

Answer

Shrinkage ratio SR = Ms/(Vs × γw) = 36/(24.5 × 1.0) = 1.47 g/cm³.

Question 2

In geotechnical engineering, what is the significance of the preconsolidation pressure (σ'c) determined from a consolidation test?

Accepted Answer

It marks the stress boundary between recompression and virgin compression behavior

Answer

Preconsolidation pressure separates the lightly (elastic) recompression range from the normally consolidated (plastic) compression range on the e-log p curve.

Question 3

A saturated soil specimen in an unconsolidated-undrained (UU) triaxial test shows zero friction angle (φ = 0). If the unconfined compressive strength (qu) is 80 kPa, what is the undrained shear strength (su)?

Accepted Answer

40 kPa

Answer

For φu = 0, su = cu = qu/2 = 80/2 = 40 kPa; the Mohr circle radius equals the shear strength.

Question 4

A sand has a maximum void ratio of 0.82 and minimum void ratio of 0.45. A field sample has a void ratio of 0.60. What is the relative density (Dr)?

Accepted Answer

59.5%

Answer

Dr = (emax − e)/(emax − emin) × 100 = (0.82 − 0.60)/(0.82 − 0.45) × 100 = 0.22/0.37 × 100 ≈ 59.5%.

Question 5

Which index property best distinguishes between a silty soil (ML or MH) and a clayey soil (CL or CH) in the USCS classification system?

Accepted Answer

Position relative to the A-line on the plasticity chart

Answer

The A-line (U = 0.73(LL − 20)) on the Casagrande plasticity chart separates clays (above) from silts and organic soils (below).

Civil Engineering PE Practice Test

Civil Engineering PE Practice Test

Civil Engineering PE Soil Mechanics and Lab Testing 5