LARE Soils and Site Conditions Flashcards

Which soil pH range is considered optimal for most landscape plants in the US?

Answer: 5.5–7.0 (slightly acidic to neutral)

A pH of 5.5–7.0 allows maximum nutrient availability and supports the widest range of landscape plant species in US conditions.

What is 'hydric soil,' and why is its presence significant on a project site?

Answer: Soil that forms under saturated conditions, indicating potential wetland jurisdiction

Hydric soils form in anaerobic, saturated conditions and are one of three indicators used to delineate wetlands under federal jurisdiction, triggering permitting requirements.

In slope stability analysis, which factor MOST increases the risk of soil failure on a cut slope?

Answer: Seepage of water parallel to the slope face through a permeable layer

Subsurface water seeping parallel to a slope reduces effective stress and pore water pressure equilibrium, dramatically increasing the risk of shallow translational landslides.

What does 'shrink-swell potential' refer to in expansive clay soils, and how does it affect site design?

Answer: Volume changes in clay soil as moisture content changes, causing foundation and pavement movement

Expansive clays (high shrink-swell potential) expand when wet and shrink when dry, causing significant heaving and cracking of pavements, foundations, and retaining structures.

Which test method is commonly used on-site to quickly estimate soil drainage for bioretention basin design?

Answer: In-situ percolation test (falling head permeability)

An in-situ falling-head percolation test measures how quickly water infiltrates the native soil, providing the infiltration rate needed to size bioretention cells and rain gardens.

What is 'topsoil stripping and stockpiling,' and why is it specified in landscape grading documents?

Answer: Removing the organic-rich A horizon before grading and replacing it after rough grading is complete

Stripping and stockpiling topsoil before mass grading preserves the biologically active organic layer so it can be redistributed over finished grades to support plant establishment.