Measuring manhole inverts accurately

Tue, 11 Mar 2025 17:59:55 GMT

What tools do y'all use to accurately measure sanitary sewer inverts especially offset manholes.

Taso

Sat, 29 Mar 2025 17:46:28 GMT

Taso, I have explored this subject myself, and here is what I have come up with: It depends on the job.
I like using a Leica Disto. It is a handheld laser measurer. The higher-end models have a function called Smart Horizontal Mode, which reduces the distance to a vertical distance instead of a slope.
Another way is to just set up next to the manhole with a total station and shoot the pipe directly in reflectorless mode. Another option is to use a tilt enabled poles or GPS sensors and shoot it directly. A more expensive option is to set a terrestrial LiDAR scanner above the manhole, invert the sensor, and scan the whole thing. And my last option is to use a tape measure, measure the slope distance, measure the offset, and then solve the triangle.
Good luck out there.

Sun, 30 Mar 2025 20:39:48 GMT

I do not recall ever working at a company that did not have issues with inverts (measure downs). The best method that I have seen involves a level rod, a string line (plumb bob gammon reel), a clinometer and conscientiousness. Put the level rod in the invert. Put the string line across the center of the manhole (where you took the shot). Lean the level rod to the string line and note the measure down at the string line (side “c” of the right triangle in the back of your field book). Then, with the level rod held in position where you took the measure down at the string line, use the clinometer to get the angle of the lean (angle “A” of the right triangle in the back of your field book). Then multiply side “c” by the cosine of angle “A” to get the vertical measure down (side “b” of the right triangle in the back of your field book). The conscientiousness part will be self-explanatory. The Suunto Tandem is a good clinometer/compass combo that I have used. I think there are also clinometer apps for your phone.
Hope that helps,
David