Things You'll Need
Sonotubes are thick cardboard tubes that you place in the ground. They are forms used to create concrete pillars for foundations. Depending on the length of the tube and how deep you need to install it, you will likely have some amount of tube sticking out of the ground. You must cut the sonotubes before you fill them with concrete. Since you fill sonotubes to the top with concrete, it is important that all of the sonotubes used in the foundation remain level. This adds to the difficulty level of cutting sonotubes.
Place a wooden stake next to each sonotube and drive it into the ground with a mallet. The stake must stick out of the ground at a level higher than you want to cut your sonotubes.
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Tie a string to each stake and then place a line level onto the string between each sonotube.
Raise or lower the string on each stake until the line levels all indicate level and each string is at the same height.
Cut around the sonotube with a keyhole saw. A keyhole saw has a pointy tip that you can press into the cardboard. This eliminates the need to drill a pilot hole for the saw. Keep the cut around the tube level with the strings.