LARE LARE Grading and Earthwork 5 — Questions and Answers
Question 1: 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?
- 3.0 ft
- 2.5 ft (Correct answer)
- 0.5 ft
- 1.0 ft
Correct 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.
Question 2: 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:
- Prevent frost heave from damaging the foundation
- Direct surface runoff away from the structure to prevent water infiltration (Correct answer)
- Provide accessible pedestrian clearance at building entrances
- Reduce the visual impact of the building's mass
Correct 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.
Question 3: 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?
- 5 feet
- 10 feet
- 20 feet (Correct answer)
- 50 feet
Correct answer: 20 feet
At 5% maximum grade: horizontal distance = vertical rise ÷ grade = 1 ft ÷ 0.05 = 20 feet minimum between each 1-foot contour.
Question 4: Which soil type is MOST susceptible to liquefaction during seismic activity, posing grading and foundation stability concerns?
- Dense, well-graded gravel
- Saturated, loose fine sand (Correct answer)
- Stiff, overconsolidated clay
- Fractured bedrock
Correct 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.
Question 5: 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?
- 5,625 CY
- 4,050 CY (Correct answer)
- 3,600 CY
- 5,000 CY
Correct 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.
Question 6: 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?
- 2:1 (H:V) — 50%
- 3:1 (H:V) — 33% (Correct answer)
- 4:1 (H:V) — 25%
- 6:1 (H:V) — 17%
Correct 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.
Question 7: 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:
- An error — contours should not cross drainage channels
- A culvert or pipe carrying flow under a road or path (Correct answer)
- A ford where vehicles can cross the stream at grade
- A low-water crossing with riprap protection
Correct 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.
LARE LARE Grading and Earthwork 5
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?