CESSWI CESSWI Soil Properties and Site Characterization 1 — Questions and Answers
Question 1: Which USDA soil texture class is generally considered the most erodible by water?
- Clay
- Silt loam (Correct answer)
- Gravel
- Sandy clay
Correct answer: Silt loam
Silt loam soils are highly erodible because silt particles detach easily under raindrop impact and are readily transported by sheet flow.
Question 2: What does the letter 'D' represent in NRCS Hydrologic Soil Group (HSG) classification?
- Very high infiltration rate
- High infiltration rate
- Slow infiltration rate
- Very slow infiltration rate — highest runoff potential (Correct answer)
Correct answer: Very slow infiltration rate — highest runoff potential
HSG D soils have very slow infiltration rates (typically clay-rich or shallow over impervious layers) and generate the highest surface runoff.
Question 3: The Universal Soil Loss Equation (USLE) factor 'K' represents what soil property?
- Slope steepness
- Soil erodibility (Correct answer)
- Crop management
- Conservation practice
Correct answer: Soil erodibility
The K factor in USLE quantifies a soil's susceptibility to detachment and transport by rainfall and runoff, based on texture, organic matter, and permeability.
Question 4: A soil with a Unified Soil Classification of 'CH' is best described as:
- Well-graded gravel
- Poorly graded sand
- Fat clay with high plasticity (Correct answer)
- Silty sand
Correct answer: Fat clay with high plasticity
In the Unified Soil Classification System, CH denotes fat (high-plasticity) clay, which swells when wet and shrinks when dry, posing stability and erosion challenges.
Question 5: Which field test is commonly used on a construction site to estimate soil permeability in the field?
- Atterberg limits test
- Proctor compaction test
- Double-ring infiltrometer test (Correct answer)
- Hydrometer analysis
Correct answer: Double-ring infiltrometer test
The double-ring infiltrometer measures the rate at which water infiltrates the soil surface, giving a field estimate of saturated hydraulic conductivity.
Question 6: On a construction site soil report, a 'dispersion' problem refers to which condition?
- Soil particles that resist compaction
- Soil that collapses suddenly when wetted
- Soil particles that deflocculate in water, making it highly erodible (Correct answer)
- Soil with high organic matter content
Correct answer: Soil particles that deflocculate in water, making it highly erodible
Dispersive soils have clay particles that repel each other in water, causing the soil to erode internally (piping) or on the surface at very low shear stresses.
CESSWI CESSWI Soil Properties and Site Characterization 1
Which USDA soil texture class is generally considered the most erodible by water?