A pipe laser target (receiver) is placed in the bell end of the pipe during installation. When the laser beam from the upstream manhole hits the target at its center, the pipe is at design grade and horizontal alignment. Upper LED means the pipe is too high (beam below center); lower LED means the pipe is too low (beam above center). The target must be at the pipe invert — not resting on bedding material or a joint gap.
Pipe Laser Setup: Key Steps
- Set the grade on the laser. Enter the design grade % on the pipe laser control panel (Topcon TP-L6GV, Spectra DG813, Leica Piper 200G). Verify the display matches the plan grade.
- Calculate mounting height. Height = (design invert elevation − manhole bottom elevation) + pipe radius. This centers the laser beam on the pipe invert centerline.
- Mount and align the laser. Install the manhole bracket at the calculated height. Mount the laser, confirm it is level in the grade direction, and align the beam horizontally to the pipe centerline using a plumb bob or the laser’s alignment sight.
- Verify beam elevation at the instrument. Hold a target at the laser mounting location and confirm the beam hits at the expected mounting height.
Reading the Target During Installation
As each pipe section is placed and bedded:
- Set the pipe laser receiver in the bell end of the pipe at the pipe centerline elevation
- Look at the target LED display from the instrument end: center green = on grade, upper = pipe too high, lower = pipe too low
- Adjust the pipe by lifting or lowering the bell end until the target shows on-grade
- Verify horizontal alignment at the same time by looking down the beam and confirming the pipe runs true to the laser direction
Common Target Reading Issues
| Symptom | Cause | Fix |
|---|---|---|
| Target consistently reads high (pipe always low) | Laser mounting height too high; design grade entered wrong | Re-verify mounting height; check laser grade setting |
| Target reads fine at near joints, off at far end | Horizontal misalignment; laser beam walk over distance | Re-align laser; take midpoint level-and-rod check |
| Target unstable or flickering | Loose target mount; vibration from compaction nearby | Secure target; move compaction equipment away |
| Cannot see target signal from instrument end | Dirt or mud on target face; laser beam obstruction | Clean target; remove obstructions in beam path |
Intermediate Grade Checks on Long Runs
For runs over 150 ft, supplement the laser target with a level-and-rod grade check at the midpoint. The pipe laser beam spreads slightly over distance, and accumulated settling in the manhole bracket can cause the beam to drift. An independent check catches errors before the entire run is installed.
See also: Gravity Sewer Installation: Grade and Alignment Control and Pipe Grade Calculator.