A trench is defined as a narrow channel, deeper than it is wide and made below the surface of the ground. A trench can be up to 15 feet wide. An excavation is any man-made hole or trench that is made by removing earth. Trenching is recognized as one of the most hazardous construction activities. The greatest risk is a cave-in.
Each year trenching cave-ins result in more than 5,000 serious injuries and 100 deaths in the United States. Trenches are needed for the installation and repair of utility lines, water and sewer lines, television cable, building roads, and many other uses. Anyone whose work requires them to work in or around a trench should be aware of the hazards so that they neither cause nor become involved in an accident.
The Occupational Safety and Health Administration (OSHA) requires a competent person to inspect trenches on a daily basis for possible cave-ins, failures of protective systems and equipment, hazardous atmospheres, or other hazardous conditions.
Soil, or any material removed from the ground to form a trench or hole, can weigh more than 100 pounds per cubic foot. Most soil is thought of in terms of cubic yards. One cubic yard of soil may weigh more than 2700 pounds.
Cave-ins can be caused by:
Vibration of nearby construction equipment or vehicle traffic;
Weight of equipment that is too close to the edge of the trench;
Soils that do not hold tightly together;
Soil that has been dug in before that is not as stable as undisturbed earth; and
- Water weakening the strength of the trench sides.