Civil Engineering PE Soil Mechanics and Lab Testing Questions and Answers

Question 1

A geotechnical engineer is reviewing lab results for a fine-grained soil sample.
The results are: Liquid Limit (LL) = 65%, Plastic Limit (PL) = 25%.
What is the Plasticity Index (PI) of the soil, and how would it be classified based on this value?

Accepted Answer

PI = 40%, Highly plastic

Answer

PI = 90%, Low plasticity

Answer

PI = 40%, Non-plastic

Answer

PI = 65%, Medium plastic

Question 2

During a Standard Proctor compaction test (ASTM D698), a soil sample is compacted in a standard mold. Which of the following sets of parameters is consistent with the standard procedure?

Accepted Answer

5.5 lb rammer, 12-inch drop, 3 layers, 25 blows per layer

Answer

10.0 lb rammer, 18-inch drop, 5 layers, 25 blows per layer

Answer

5.5 lb rammer, 18-inch drop, 3 layers, 56 blows per layer

Answer

10.0 lb rammer, 12-inch drop, 5 layers, 56 blows per layer

Question 3

An unconfined compression test is performed on a cylindrical specimen of cohesive soil. The test is most suitable for determining the short-term shear strength of which of the following soil types?

Accepted Answer

Saturated, intact clay

Answer

Dry, fissured clay

Answer

Clean, uniform sand

Answer

Well-graded gravel with some fines

Question 4

In a one-dimensional consolidation (oedometer) test, a saturated clay sample is subjected to incremental loading. What is the primary parameter determined from the time-settlement data for each load increment?

Accepted Answer

Coefficient of consolidation (Cv)

Answer

Preconsolidation pressure (σ'c)

Answer

Compression index (Cc)

Answer

Overconsolidation ratio (OCR)

Question 5

A key advantage of the triaxial shear test over the direct shear test is that the triaxial test allows for:

Accepted Answer

Control of drainage conditions and measurement of pore water pressure

Answer

Testing of cohesionless soils only

Answer

A more rapid and less expensive testing procedure

Answer

The failure plane to be forced along a predetermined horizontal surface

Question 6

Which of the following factors would most likely lead to a DECREASE in the coefficient of permeability (k) of a sandy soil?

Accepted Answer

A decrease in the average particle size (D10)

Answer

An increase in the void ratio

Answer

An increase in the degree of saturation from 85% to 100%

Answer

An increase in the temperature of the permeating water