LARE Grading and Earthwork Flashcards

A landscape architect is designing a bio-retention basin (rain garden) with a bottom elevation of 95.0 ft. The overflow inlet is set at 97.5 ft and the basin perimeter berm top is at 98.0 ft. What is the maximum design ponding depth?

Answer: 2.5 ft

Maximum ponding depth = overflow inlet elevation − bottom elevation = 97.5 − 95.0 = 2.5 feet; water exits via overflow before reaching berm top.

When establishing grades around a building, a landscape architect designs a minimum 2% slope within 10 feet of the foundation. This is primarily intended to:

Answer: Direct surface runoff away from the structure to prevent water infiltration

Grading away from foundations at minimum 2% ensures surface water drains away from the building, preventing moisture infiltration into basements and crawl spaces.

On a LARE grading problem, you are given a 50-foot contour interval map (1-foot contours). A road must maintain a maximum 5% grade. What is the minimum horizontal distance between successive 1-foot contours along the road alignment?

Answer: 20 feet

At 5% maximum grade: horizontal distance = vertical rise ÷ grade = 1 ft ÷ 0.05 = 20 feet minimum between each 1-foot contour.

Which soil type is MOST susceptible to liquefaction during seismic activity, posing grading and foundation stability concerns?

Answer: Saturated, loose fine sand

Saturated loose fine sands are most susceptible to liquefaction because seismic shaking causes pore water pressure to exceed confining stress, causing the soil to behave like a liquid.

A landscape architect needs to calculate the earthwork balance for a site. Cut volume = 4,500 CY (bank measure), swell factor = 1.25, shrinkage factor = 0.90. How many cubic yards of compacted fill can this cut material produce?

Answer: 4,050 CY

Compacted fill = bank volume × shrinkage factor = 4,500 × 0.90 = 4,050 CY; the swell factor applies to loose (hauled) volume, not the final compacted fill calculation.

A designer must select the most appropriate slope ratio for a mowed grass maintenance area. Which slope is at the upper limit for safe mower operation on a turf slope?

Answer: 3:1 (H:V) — 33%

A 3:1 (H:V) slope at 33% is the generally accepted maximum for riding mower safety; steeper slopes require unmowed ground covers or other treatments.

A grading plan shows proposed contours that bend upstream (into the flow direction) when crossing a drainage channel. This indicates the designer intends to show:

Answer: A culvert or pipe carrying flow under a road or path

When proposed contours cross a drainage channel and bend upstream (instead of downstream as natural contours do), it conventionally indicates a culverted crossing where the channel is piped underground.