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

1.22

Answer

1.84

Answer

0.94

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

It equals the current effective overburden stress for all soils

Answer

It defines the maximum shear stress the soil can resist

Answer

It is the stress at which soil permeability becomes zero

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

80 kPa

Answer

160 kPa

Answer

20 kPa

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

40.5%

Answer

73.2%

Answer

26.8%

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

Liquid limit value alone

Answer

Grain size D50 value

Answer

Specific gravity of solids

Question 6

In a sieve analysis, what percentage of soil passes the No. 200 sieve if the retained amounts are: No. 4 = 15 g, No. 10 = 25 g, No. 40 = 35 g, No. 200 = 45 g, and pan = 30 g from a total dry mass of 150 g?

Accepted Answer

20%

Answer

30%

Answer

50%

Answer

80%

Question 7

A compaction curve shows optimum moisture content (OMC) at 15%. A contractor compacts soil at 12% moisture. Compared to the dry side of optimum, what is the most significant engineering implication?

Accepted Answer

Higher strength and stiffness but more brittle and susceptible to collapse upon wetting

Answer

Lower permeability and higher swell potential

Answer

Higher plasticity index and more uniform structure

Answer

Lower dry density and lower friction angle