LARE LARE Grading and Earthwork 4 — Questions and Answers
Question 1: A designer specifies a 4:1 (H:V) slope for a graded embankment in a residential project. What percentage grade does this represent?
- 4%
- 25% (Correct answer)
- 40%
- 14%
Correct answer: 25%
Grade % = (vertical rise ÷ horizontal run) × 100 = (1 ÷ 4) × 100 = 25%.
Question 2: Which of the following correctly describes the prismatoid formula for earthwork volume calculation, and when is it preferred over the average end area method?
- It averages three cross-sections and is preferred when end areas are nearly equal
- It uses the middle cross-section area and is more accurate when end areas differ significantly (Correct answer)
- It calculates volume using only the largest end area and is faster to compute
- It is used exclusively for rock excavation calculations
Correct answer: It uses the middle cross-section area and is more accurate when end areas differ significantly
The prismatoid formula incorporates the middle cross-section area (V = L/6 × (A1 + 4Am + A2)) and is more accurate than average end area when end areas differ significantly.
Question 3: A landscape architect needs to establish finish floor elevation (FFE) for a building pad. The 100-year flood elevation is 215.5 feet. Per best practice, the FFE should be set at a minimum of:
- 215.5 ft (at the flood elevation)
- 216.5 ft (1 foot above base flood elevation) (Correct answer)
- 217.5 ft (2 feet above base flood elevation)
- 214.5 ft (1 foot below to allow drainage)
Correct answer: 216.5 ft (1 foot above base flood elevation)
FEMA and most local floodplain regulations require the FFE to be set at a minimum of 1 foot above the base flood elevation (BFE) for freeboard.
Question 4: During construction observation, you notice that fill is being placed in lifts that are 18 inches thick before compaction. The specification requires 8-inch maximum compacted lifts for structural fill. The correct course of action is:
- Allow it if the contractor achieves the specified compaction density
- Stop work and require the contractor to comply with the lift thickness specification (Correct answer)
- Increase the required compaction percentage to compensate
- Notify the owner but allow construction to proceed
Correct answer: Stop work and require the contractor to comply with the lift thickness specification
Lift thickness directly affects the ability of compaction equipment to achieve uniform density throughout the layer; exceeding the specified lift thickness requires stopping and correcting the work.
Question 5: Two contour lines on a grading plan are spaced very close together. This indicates:
- A gentle, gradually sloping terrain
- A steep slope or abrupt grade change (Correct answer)
- A flat area that needs drainage improvement
- An error in the contour interpolation
Correct answer: A steep slope or abrupt grade change
Closely spaced contour lines indicate a steep slope because the same vertical interval is covered over a short horizontal distance.
Question 6: A grade break occurs where a 4% slope meets a 1% slope on a paved driveway. To provide a smooth transition for vehicles, a designer should:
- Use a vertical curve to blend the grade change over a minimum distance (Correct answer)
- Insert a level landing 10 feet wide at the grade break
- Steepen the 1% slope to match the 4% slope
- Place a speed bump at the grade break location
Correct answer: Use a vertical curve to blend the grade change over a minimum distance
Vertical curves smooth the transition between different slopes, preventing abrupt grade breaks that can scrape low-clearance vehicles.
Question 7: What is the primary purpose of a subdrain (French drain) installed in a graded fill slope?
- To prevent surface erosion by intercepting sheet flow
- To intercept and remove subsurface water from the fill mass, preventing hydrostatic pressure buildup (Correct answer)
- To carry stormwater from roof downspouts to a discharge point
- To aerate compacted fill and improve root growth
Correct answer: To intercept and remove subsurface water from the fill mass, preventing hydrostatic pressure buildup
Subdrains intercept groundwater moving through the fill, relieving hydrostatic pressure that could cause slope failure or wall movement.
LARE LARE Grading and Earthwork 4
A designer specifies a 4:1 (H:V) slope for a graded embankment in a residential project.
What percentage grade does this represent?