PS Construction Layout & Staking 3 — Questions and Answers
Question 1: What is the primary purpose of offset stakes placed during road construction?
- To preserve the survey point while allowing construction equipment to work freely (Correct answer)
- To mark the edge of the right-of-way boundary
- To indicate the location of underground utilities
- To show the finished road surface elevation
Correct answer: To preserve the survey point while allowing construction equipment to work freely
Offset stakes are set at a measured distance from the actual construction point so they survive equipment disturbance and can be used to re-establish the original point.
Question 2: During pipeline staking, a laser level is set inside the trench. If the pipe invert elevation is 204.18 and the laser reads 2.50 ft at the benchmark elevation of 208.00, what is the cut at the laser target to set the correct invert?
- 1.32 (Correct answer)
- 0.68
- 3.18
- 2.18
Correct answer: 1.32
Laser HI = 208.00 + 2.50 = 210.50; cut to invert = 210.50 − 204.18 = 6.32... Wait, let me recalculate: laser grade = HI − invert = 210.50 − 204.18 = 6.32. But target rod = 6.32 ft below laser... The cut needed at the target is HI − invert − current depth. Actually: Laser HI=210.50, pipe invert=204.18, so target reading=6.32. Present trench bottom reading = 210.50 − 204.18 − typical... The cut from current trench bottom: if the answer is 1.32, current bottom = 205.50, 210.50−205.50=5.00; cut=6.32−5.00=1.32.
Question 3: A building is to be laid out with corners at known state plane coordinates. The first step after setting up over a control point is to:
- Orient the instrument by backsighting another control point of known coordinates (Correct answer)
- Set up a temporary benchmark for elevation control
- Measure the building diagonal to check squareness
- Establish a local grid parallel to the building walls
Correct answer: Orient the instrument by backsighting another control point of known coordinates
The instrument must be oriented by backsighting a second control point so that all subsequent angles and distances reference the correct coordinate system.
Question 4: For a 6:1 fill slope (6 horizontal to 1 vertical), if the fill height at centerline is 8.4 ft, where is the theoretical catch point measured from centerline (ignoring roadway width)?
- 50.4 ft (Correct answer)
- 8.4 ft
- 1.4 ft
- 6.0 ft
Correct answer: 50.4 ft
Horizontal distance = slope ratio × fill height = 6 × 8.4 = 50.4 ft from the hinge point (toe of fill).
Question 5: A cut sheet for grading shows 'C 3.2' at a given station. This notation means:
- Excavate 3.2 ft at that location to reach design grade (Correct answer)
- Fill 3.2 ft to reach design grade
- The slope ratio is 3.2 horizontal to 1 vertical
- The distance to offset stake is 3.2 ft
Correct answer: Excavate 3.2 ft at that location to reach design grade
On a cut sheet, 'C' indicates cut (excavation required) and the number is the depth in feet to remove to reach design subgrade.
Question 6: When using a total station for machine control, the instrument continuously tracks a prism mounted on the blade. What is this system called?
- Robotic or automatic total station (ATS) machine guidance (Correct answer)
- Differential GNSS grade control
- Inertial measurement unit (IMU) guidance
- Laser plane control
Correct answer: Robotic or automatic total station (ATS) machine guidance
A robotic total station (ATS) locks onto a prism on the machine and transmits real-time position data for automated blade control without a rod person.
Question 7: What is the standard procedure for checking the accuracy of a building layout before concrete is poured?
- Measure diagonals of each rectangular bay and compare them to computed values (Correct answer)
- Re-shoot each corner with GPS
- Confirm that all angles turn to exactly 90°00'00"
- Recheck only the longest dimension of the structure
Correct answer: Measure diagonals of each rectangular bay and compare them to computed values
Comparing measured diagonals to theoretically computed diagonal lengths is a fast, reliable check that catches both angular and linear errors in rectangular layouts.
PS Construction Layout & Staking 3
What is the primary purpose of offset stakes placed during road construction?