Key Terms

Aluminum hydraulic shoring means a pre-engineered shoring system made of aluminum hydraulic cylinders (crossbraces) used in conjunction with vertical rails (uprights) or horizontal rails (walers). It is designed to support the sidewalls of an excavation and prevent cave-ins.

Benching (benching system) is a method of protecting employees from cave-ins by excavating the sides of an excavation to form one or a series of horizontal levels or steps, usually with vertical or near-vertical surfaces between levels.

Cave-in refers to the separation of soil or rock material from the side of an excavation, or the loss of soil from under a trench shield or support system, and its sudden movement into the excavation, either by falling or sliding, in sufficient quantity as to entrap, bury, or otherwise injure and immobilize a person.

Competent person is a person capable of identifying existing and predictable worksite hazards that are unsanitary, hazardous, or dangerous to employees, and who has authorization to take prompt corrective measures to eliminate them.

Crossbraces are the horizontal members of a shoring system installed perpendicular to the sides of the excavation, the ends of which bear against either uprights or wales.

Excavation means any human-made cut, cavity, trench, or depression in an earth surface formed by earth removal.

Faces or sides are the vertical or inclined earth surfaces formed as a result of excavation work.

Failure means the breakage, displacement, or permanent deformation of a structural member or connection, which reduces its structural integrity and its supportive capabilities.

Hazardous atmosphere is an atmosphere that may cause death, illness, or injury by reason of being explosive, flammable, poisonous, corrosive, oxidizing, irritating, oxygen deficient, toxic, or otherwise harmful.

Kickout means the accidental release or failure of a crossbrace.

Maximum allowable slope is the steepest incline of an excavation face that is acceptable for the most favorable site conditions as protection against cave-ins, and is expressed as the ratio of horizontal distance to vertical rise (H:V).

Protective system refers to a method of protecting employees from cave-ins, from material that could fall or roll from an excavation face or into an excavation, or from the collapse of adjacent structures. Protective systems include support systems, sloping and benching systems, shield systems, and other systems that provide necessary protection.

Ramp refers to an inclined walking or working surface used to gain access to one point from another and is constructed from earth or from structural materials such as steel or wood.

Registered professional engineer refers to a person who is registered as a professional engineer in the state where the work is to be performed.

Sheeting refers to the members of a shoring system that retain the earth in position and in turn are supported by other members of the shoring system.

Shield (shield system) refers to a structure able to withstand the forces imposed on it by a cave-in and thereby protect employees within the structure. Shields can be either permanent structures or designed to be portable and moved along as work progresses. Additionally, shields can be either premanufactured or job-built (in accordance with 29 CFR §1926.652). Shields used in trenches are usually referred to as "trench boxes" or "trench shields."

Shoring (shoring system) refers to a structure such as a metal hydraulic, mechanical, or timber shoring system that supports the sides of an excavation and is designed to prevent cave-ins.

Sloping (sloping system) means a method of forming sides of an excavation that are inclined away from the excavation so as to prevent cave-ins. The angle of incline required to prevent a cave-in varies with differences in soil type, environmental conditions of exposure, and application of surcharge loads.

Spoil is the term used for the soil, dirt, and rubble that results from an excavation.

Stable rock means natural solid mineral material that can be excavated with vertical sides and will remain intact while exposed. Unstable rock is considered to be stable when the rock material on the sides of the excavation is secured against caving-in or movement by rock bolts or by another protective system designed by a registered professional engineer.

Structural ramp means a ramp built of steel or wood that is usually used for vehicle access. Ramps made of soil or rock are not considered structural ramps.

Support system means a structure such as underpinning, bracing, or shoring, which provides support to a nearby structure, underground installation, or the sides of an excavation.

Surcharge means an excessive vertical load or weight caused by spoil, overburden, vehicles, equipment, or activities that may affect trench stability.

Tabulated data means tables and charts approved by a registered professional engineer and used to design and construct a protective system.

Trench (trench excavation) means a narrow excavation (in relation to its length) made below the surface of the ground. In general, the depth is greater than the width, but the width of a trench (measured at the bottom) is not greater than 15 feet (4.6 m). An excavation is also considered to be a trench if forms or other structures are installed or constructed in the excavation to reduce the dimension measured from the forms or structure to the side of the excavation to 15 feet (4.6 m) or less (measured at the bottom of the excavation).

Uprights mean the vertical members of a trench shoring system placed in contact with the earth and usually positioned so that individual members do not contact each other. Uprights placed so that individual members are closely spaced, in contact with or interconnected to each other, are often called "sheeting."

Wales means horizontal members of a shoring system placed parallel to the excavation face whose sides bear against the vertical members of the shoring system or earth.

To learn more about Trenching and Excavation visit our Trenching and Excavation Safety Online Training web page.