Common Soil Problems That Create Hazards In Excavations
Common Soil Problems
The terms soil and earth are commonly referred to in the excavation process to describe the naturally occurring materials uncovered on a project. Soil conditions vary from one site to the next. Soil may be loose or partially cemented, organic or inorganic. However, most soils can be referred to as a mixture or an accumulation of mineral grains that are not cemented together. An exception is hard rock, which remains firm after exposure to the elements.
Soil failure is defined as the collapse of part or all of an excavation wall. The most common soil failure is typically described as an unexpected settlement, or cave-in, of an excavation. Soil sliding is the most common factor leading to soil failure.
Proper planning and supervision can avoid the unsafe working conditions caused by soil sliding. Unless such safety precautions have been implemented, sliding soil failure can occur in all types of excavations (including sloped trenches and excavations with braced trench boxes).
How Cave-ins Occur
Undisturbed soil stays in place because opposing horizontal and vertical forces are evenly balanced. When you create an excavation, you remove the soil that provides horizontal support. Soil will eventually move downward into the excavation. The longer the face (a side of the excavation) remains unsupported, the more likely it is to cave in.
What means of access and egress must employers provide?
OSHA requires employers to provide ladders, steps, ramps, or other safe means of egress for workers working in trench excavations 4 feet (1.22 meters) or deeper. The means of egress must be located so as not to require workers to travel more than 25 feet (7.62 meters) laterally within the trench. Any structural ramps used solely for worker access or egress must be designed by a competent person. Structural ramps used for access or egress of equipment must be designed by a competent person qualified in structural design. Also, structural members used for ramps or runways must be uniform in thickness and joined in a manner to prevent tripping or displacement.
What protective equipment are employers required to provide to workers in pier holes and confined footing excavations?
Employers must ensure that any worker who enters a bellbottom pier hole or similar deep and confined footing excavation wears a harness with a lifeline. The lifeline must be attached securely to the harness and must be separate from any line used to handle materials. Also, the lifeline must be individually attended by an observer at all times when the worker wearing the lifeline is in the excavation.