How to Dig a Bell Hole for a Pipeline

This measure is taken to prevent a cave-in -- a result of sliding, toppling, tension cracked or bulging material -- from burying laborers. The United States Occupational Safety and Health Administration, or OSHA, provides strict guidelines for the proper excavation of bell holes. Though a bell hole requires more time to dig than the rest of the trench, excavating one is simple.

1. Expand the bottom width of the trench threefold. The purpose of a bell hole is space in addition to safety. If the excavation of a bell hole is for the purpose of installing a valve, for example, a hole three times as wide as the trench gives laborers space for tools and supplies, and room to work around one another.

2. Calculate the depth of the trench with a tape measure or a grade rod. The depth of the trench determines the number of benches the bell hole requires or the starting point of the shore. OSHA requires one bench every 4 feet. As a result, a 16-foot deep trench requires a bell hole with three benches: one bench 4 feet from the bottom of the hole, another 8 feet from the bottom and another 12 feet above the bottom.

3. Excavate down the sides of the hole, 1 1/2 bucket widths wide, removing material from the walls. Stop removing material from the walls 4 feet above the bottom of the hole. The step created by this process, from the bottom of the hole to the surrounding walls, is the first bench.

4. Repeat the process; excavate down the sides of the hole -- again, 1 1/2 bucket widths wide -- removing material from the wall. Stop 4 feet above the first bench, or 8 feet from the bottom of the hole, for the second bench. Continue benching the hole until the final bench is 4 feet or less from ground level. Clean each bench. Remove any material that may have fallen as you excavated from above.