LARE LARE Soils and Site Conditions 1 — Questions and Answers
Question 1: According to USDA soil texture classification, which soil type has the highest percentage of sand particles?
- Loam
- Silt loam
- Sandy loam (Correct answer)
- Clay loam
Correct answer: Sandy loam
Sandy loam contains a high proportion of sand (typically 70–85% sand) with smaller amounts of silt and clay, resulting in fast drainage and low water retention.
Question 2: What does soil 'percolation rate' measure, and why is it important for landscape design?
- The rate at which organic matter decomposes in the soil profile
- The speed at which water moves through the soil, affecting drainage and irrigation design (Correct answer)
- The rate at which soil compacts under foot traffic loading
- The nutrient release rate from slow-release fertilizers
Correct answer: The speed at which water moves through the soil, affecting drainage and irrigation design
Percolation rate measures how quickly water moves through the soil, which is critical for sizing bioretention facilities, septic systems, and determining irrigation schedules.
Question 3: Which USDA natural resources document is the primary reference landscape architects use to obtain detailed soil survey data for a project site in the US?
- FEMA Flood Insurance Rate Map
- Web Soil Survey (WSS) published by NRCS (Correct answer)
- USGS National Land Cover Database
- EPA EnviroMapper Site Report
Correct answer: Web Soil Survey (WSS) published by NRCS
The USDA-NRCS Web Soil Survey provides county-level soil maps, series descriptions, limitations, and engineering properties for all US project sites.
Question 4: What does the term 'soil horizon' refer to in site analysis?
- The maximum depth of a site's seasonal high water table
- A distinct layer of soil with different physical and chemical properties from adjacent layers (Correct answer)
- The horizontal extent of a soil type across a site
- The depth at which bedrock is encountered during boring
Correct answer: A distinct layer of soil with different physical and chemical properties from adjacent layers
Soil horizons are distinct horizontal layers within the soil profile (O, A, B, C) that differ in color, texture, structure, and composition.
Question 5: On a LARE site section, which layer is typically shown as 'fill' and why must it be identified?
- The organic topsoil layer placed after grading is complete
- Previously placed non-native material that may be unstable or contaminated (Correct answer)
- Bedrock material excavated and recompacted on-site
- Imported loam used for planting bed preparation
Correct answer: Previously placed non-native material that may be unstable or contaminated
Fill is previously deposited non-native material that may be poorly compacted, contain debris or contaminants, and have unpredictable bearing capacity, requiring special design consideration.
Question 6: What soil property does a 'standard Proctor compaction test' measure, and how is it used in landscape construction?
- Soil pH and buffering capacity for plant nutrient availability
- Maximum dry density and optimum moisture content for compaction specifications (Correct answer)
- Soil permeability at various saturation levels
- Bearing capacity of undisturbed native soils
Correct answer: Maximum dry density and optimum moisture content for compaction specifications
The Proctor test determines the maximum dry density and optimum moisture content of a soil, which becomes the baseline for compaction specifications in construction documents.
LARE LARE Soils and Site Conditions 1
According to USDA soil texture classification, which soil type has the highest percentage of sand particles?