KDOT Geotechnical & Earthwork Inspection 2 — Questions and Answers
Question 1: When inspecting embankment fill placement, what is the maximum allowable loose lift thickness for cohesive soils compacted with standard equipment per KDOT specifications?
- 6 inches
- 8 inches
- 12 inches (Correct answer)
- 18 inches
Correct answer: 12 inches
KDOT specifications typically allow a maximum loose lift thickness of 12 inches for cohesive soils before compaction.
Question 2: During a proctor test, the optimum moisture content is defined as the moisture at which:
- The soil reaches 100% saturation
- The maximum dry density is achieved (Correct answer)
- The soil becomes plastic
- Compaction effort is minimized
Correct answer: The maximum dry density is achieved
Optimum moisture content is the water content at which a soil achieves its maximum dry density under a specified compaction effort.
Question 3: A soil sample has a liquid limit of 45 and a plastic limit of 20. What is the plasticity index?
- 65
- 45
- 25 (Correct answer)
- 20
Correct answer: 25
Plasticity Index (PI) = Liquid Limit minus Plastic Limit, so PI = 45 - 20 = 25.
Question 4: Which type of soil classification would a KDOT inspector most likely require additional stabilization for before using as embankment fill?
- GW (Well-graded gravel)
- SP (Poorly graded sand)
- CH (High plasticity clay) (Correct answer)
- SM (Silty sand)
Correct answer: CH (High plasticity clay)
CH soils (high plasticity clays) are expansive, unstable when wet, and typically require lime or cement stabilization before use as embankment fill.
Question 5: What is the primary purpose of moisture conditioning soil prior to compaction?
- To increase the soil's bearing capacity permanently
- To bring the soil moisture within the specified range for achieving density requirements (Correct answer)
- To reduce the need for compaction equipment passes
- To eliminate the requirement for proctor testing
Correct answer: To bring the soil moisture within the specified range for achieving density requirements
Moisture conditioning adjusts soil water content to within the specified window near optimum so proper density can be achieved during compaction.
Question 6: During earthwork inspection, a KDOT inspector observes pumping of subgrade material under compaction equipment. This most likely indicates:
- The soil has achieved maximum density
- The subgrade moisture content is too high (Correct answer)
- The compaction roller is too heavy
- The lift thickness is insufficient
Correct answer: The subgrade moisture content is too high
Pumping or rutting of subgrade under compaction equipment is a classic sign of excessive moisture content making the soil unstable.
Question 7: When must an inspector document a failing nuclear density gauge test result?
- Only when the area will be covered by pavement
- Immediately and notify the project engineer before allowing additional fill placement (Correct answer)
- After completing the entire lift and averaging all test results
- Only if three consecutive tests fail
Correct answer: Immediately and notify the project engineer before allowing additional fill placement
Failing density tests must be documented immediately and the engineer notified before additional fill is placed over the deficient area.
KDOT Geotechnical & Earthwork Inspection 2
When inspecting embankment fill placement, what is the maximum allowable loose lift thickness for cohesive soils compacted with standard equipment per KDOT specifications?