NETTCP Soils and Aggregates 3 — Questions and Answers
Question 1: The California Bearing Ratio (CBR) test measures:
- Soil permeability under load
- Resistance of subgrade to penetration relative to a standard crushed stone (Correct answer)
- Maximum aggregate particle size in subgrade
- Settlement rate under static load
Correct answer: Resistance of subgrade to penetration relative to a standard crushed stone
CBR compares the load required to penetrate a soil specimen to the load required to penetrate a standard high-quality crushed limestone.
Question 2: What is the purpose of the sand equivalent (SE) test for fine aggregate?
- Determine gradation of sand particles
- Measure the proportion of clay-like fines relative to sand-size particles (Correct answer)
- Establish optimum moisture for compaction
- Assess freeze-thaw resistance
Correct answer: Measure the proportion of clay-like fines relative to sand-size particles
The sand equivalent test quantifies the relative amount of fine dust or clay-like material in fine aggregate using a flocculation procedure.
Question 3: When field moisture content is above optimum during compaction, the likely result is:
- Higher dry density than maximum
- Pumping and rutting of the subgrade (Correct answer)
- Reduced plasticity index
- Improved CBR value
Correct answer: Pumping and rutting of the subgrade
Compacting soil wetter than optimum moisture results in a weak, unstable subgrade that can pump and rut under roller or traffic loads.
Question 4: A soil classified as A-7-6 under AASHTO is best described as:
- Excellent granular material for base course
- Highly plastic clay, generally poor subgrade (Correct answer)
- Well-graded sand with low plasticity
- Silty sand with good drainage
Correct answer: Highly plastic clay, generally poor subgrade
A-7-6 soils are highly plastic clays with high volume change potential, considered the poorest subgrade materials under AASHTO classification.
Question 5: Which aggregate property is tested using the sodium sulfate soundness test?
- Hardness under abrasion
- Resistance to weathering and freeze-thaw degradation (Correct answer)
- Gradation and particle size distribution
- Specific gravity and absorption
Correct answer: Resistance to weathering and freeze-thaw degradation
The sodium sulfate soundness test simulates freeze-thaw action to evaluate aggregate durability against weathering deterioration.
Question 6: In USCS classification, the symbol 'ML' refers to:
- Well-graded sandy gravel
- Inorganic silt of low to medium plasticity (Correct answer)
- Organic clay of high plasticity
- Poorly graded clean sand
Correct answer: Inorganic silt of low to medium plasticity
ML in the Unified Soil Classification System designates inorganic silt or very fine sand with low to medium plasticity.
Question 7: What effect does excessive clay content have on aggregate base course performance?
- Increases load-bearing capacity
- Reduces moisture sensitivity
- Causes strength loss when wet and frost heave potential (Correct answer)
- Improves compaction characteristics
Correct answer: Causes strength loss when wet and frost heave potential
Clay in aggregate base courses absorbs water, weakens under wet conditions, and increases frost susceptibility leading to heave and failure.
NETTCP Soils and Aggregates 3
The California Bearing Ratio (CBR) test measures: