KDOT Geotechnical & Earthwork Inspection 5 — Questions and Answers
Question 1: What is the primary purpose of performing a proofroll of the prepared subgrade with a loaded tandem-axle dump truck?
- To pre-consolidate the subgrade before paving
- To visually identify weak or soft zones that deflect or pump under load (Correct answer)
- To measure the bearing capacity in pounds per square foot
- To compact the top 6 inches of subgrade to specification
Correct answer: To visually identify weak or soft zones that deflect or pump under load
Proofrolling uses a heavy loaded truck to stress the subgrade and reveal soft or yielding zones through visible deflection or pumping.
Question 2: A borrow pit soil has a natural moisture content of 12% and an OMC of 16%. What action is needed before placing this material as fill?
- The material can be placed as-is since it is below OMC
- Water must be added to bring moisture content up to near OMC before or during placement (Correct answer)
- The material must be dried to 8% before placement
- The plasticity index must be tested before any moisture adjustment
Correct answer: Water must be added to bring moisture content up to near OMC before or during placement
Material below OMC must have water added during placement or at the borrow pit to bring it within the specified moisture window for compaction.
Question 3: What is the maximum allowable depth of ruts left in the subgrade surface by construction traffic before grading and recompaction are required?
- 0.5 inch
- 1 inch (Correct answer)
- 2 inches
- 3 inches
Correct answer: 1 inch
KDOT typically requires grading and recompaction when ruts exceed 1 inch in depth, as deeper rutting indicates subgrade disturbance.
Question 4: During earthwork inspection, an inspector encounters material that smells organic and has fibrous texture. Under KDOT specifications, this material should be:
- Tested for compaction before making a determination
- Rejected and removed from the fill area (Correct answer)
- Placed only in the upper 2 feet of embankment
- Mixed with aggregate to dilute the organic content
Correct answer: Rejected and removed from the fill area
Organic material is unsuitable for embankment fill as it compresses over time causing settlement and has low shear strength; it must be removed from the fill zone.
Question 5: When a KDOT inspector observes cracking on the slope face of a newly constructed embankment, what is the most critical first action?
- Apply a thin soil cover to seal the cracks cosmetically
- Notify the project engineer immediately and document the location and extent of cracking (Correct answer)
- Increase watering of the slope to reduce drying shrinkage cracks
- Resume compaction on the slope face to close the cracks
Correct answer: Notify the project engineer immediately and document the location and extent of cracking
Slope cracking may indicate internal shear failure or settlement; the engineer must be notified immediately and the condition documented before any remedial action is taken.
Question 6: What frequency of in-place density testing is typically required per KDOT standard practice for general embankment fill?
- One test per every 500 cubic yards placed
- One test per lift per lane or as specified in project documents (Correct answer)
- One test per day regardless of quantity placed
- Testing is only required for the final lift of embankment
Correct answer: One test per lift per lane or as specified in project documents
KDOT specifications generally require density testing per lift per lane or at intervals defined in the project special provisions to ensure consistent compaction throughout.
Question 7: During subgrade stabilization inspection, what does a 'pozzolanic reaction' refer to in the context of lime-treated soils?
- The physical blending of lime particles with soil grains
- The long-term chemical reaction between lime, silica, and alumina producing cementitious compounds (Correct answer)
- The immediate pH increase caused by adding lime to soil
- The drying effect of quicklime absorbing soil moisture
Correct answer: The long-term chemical reaction between lime, silica, and alumina producing cementitious compounds
The pozzolanic reaction is the long-term chemical bonding between calcium from lime and silica/alumina from clay minerals, forming cementitious compounds that permanently strengthen the soil.
KDOT Geotechnical & Earthwork Inspection 5
What is the primary purpose of performing a proofroll of the prepared subgrade with a loaded tandem-axle dump truck?