CLARB Soils and Geology 2 — Questions and Answers
Question 1: Which ASTM standard governs the Standard Proctor compaction test used to determine optimal moisture content for maximum dry density?
- ASTM D698 (Correct answer)
- ASTM D1557
- ASTM D2216
- ASTM D4318
Correct answer: ASTM D698
ASTM D698 defines the Standard Proctor test using standard compaction energy; ASTM D1557 is the Modified Proctor test with higher compaction energy.
Question 2: Which soil condition presents the greatest risk for building foundations and hardscape due to volumetric changes with moisture fluctuations?
- Sandy soils
- Gravelly soils
- Expansive clay soils (Correct answer)
- Organic peat soils
Correct answer: Expansive clay soils
Expansive clays (high in montmorillonite) swell significantly when wet and shrink when dry, causing differential movement that damages foundations and pavements.
Question 3: The angle of repose is a critical soil engineering property that most directly influences which landscape design consideration?
- Irrigation system design
- Slope stability and cut/fill grading design (Correct answer)
- Plant species selection
- Drainage pipe sizing
Correct answer: Slope stability and cut/fill grading design
The angle of repose defines the steepest angle at which loose soil remains stable; it directly dictates maximum allowable slope gradients for cut and fill sections.
Question 4: What does soil bearing capacity describe in the context of landscape construction?
- The soil's ability to retain water between irrigation cycles
- The maximum load per unit area soil can support without failure or excessive settlement (Correct answer)
- The amount of organic amendments soil can incorporate
- The soil's resistance to erosion from surface runoff
Correct answer: The maximum load per unit area soil can support without failure or excessive settlement
Bearing capacity defines the maximum stress the soil can withstand before shearing or settling excessively, which is critical when designing structures, walls, and pavements.
Question 5: Liquefaction — where saturated soil temporarily loses strength and behaves like a liquid — is most commonly triggered by which event?
- Heavy sustained rainfall
- Seismic (earthquake) activity (Correct answer)
- Prolonged drought followed by irrigation
- Repeated freeze-thaw cycles
Correct answer: Seismic (earthquake) activity
Earthquakes generate rapid cyclic loading that increases pore water pressure in saturated, loose granular soils until effective stress drops to zero, causing liquefaction.
Question 6: What is the primary purpose of conducting a soil percolation test on a landscape site?
- Determining soil pH and fertility levels
- Measuring the rate at which soil absorbs water for drainage or infiltration system design (Correct answer)
- Assessing the structural bearing capacity of native soils
- Evaluating soil compaction using penetration resistance
Correct answer: Measuring the rate at which soil absorbs water for drainage or infiltration system design
Percolation tests measure how quickly water drains through soil, which is essential for sizing septic drain fields, rain gardens, bioretention cells, and other infiltration-based stormwater features.
Question 7: Which phenomenon occurs when soil consolidates vertically under the weight of overlying fill or structures over time?
- Liquefaction
- Compaction
- Settlement/consolidation (Correct answer)
- Frost heave
Correct answer: Settlement/consolidation
Consolidation is the time-dependent compression of fine-grained saturated soils as pore water is slowly squeezed out under sustained load, causing gradual vertical settlement.
CLARB Soils and Geology 2
Which ASTM standard governs the Standard Proctor compaction test used to determine optimal moisture content for maximum dry density?