Environmental, Health and Safety Services

Excavation Definitions

Accepted Engineering Practices means the standards of practice required by a registered professional engineer.

Adjacent Structure Stability refers to the stability of the foundation of adjacent structures whose location may create surcharges, changes in soil conditions, or other disruptions that have the potential to extend into the failure zone of the excavation.

Aluminum Hydraulic Shoring means a manufactured shoring system consisting of aluminum hydraulic cylinders (cross braces) used with vertical rails (uprights) or horizontal rails (wales). Such system is designed to support the sidewalls of an excavation and prevent cave-ins. Picture

Bell-bottom Pier Hole means a type of shaft or footing excavation, the bottom of which is made larger than the cross section above to form a belled shape.

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

Cave-in means the movement of soil or rock into an excavation, or the loss of soil from under a trench shield or support system, in amounts large enough to trap, bury, or injure and immobilize a person.

Cemented soil means a soil in which the particles are held together by a chemical agent, such as calcium carbonate, such that a hand-size sample cannot be crushed into powder or individual soil particles by finger pressure.

Class "A" soil means cohesive soils with an unconfined, compressive strength of 1.5 ton per square foot (tsf) (144 kPa) or greater. Examples of cohesive soils are: clay, silty clay, sandy clay, clay loam and, in some cases, silty clay loam and sandy clay loam. Cemented soils such as caliche and hardpan are also considered Type A. However, no soil is Type A if:

  • The soil is fissured; or
  • The soil is subject to vibration from heavy traffic, pile driving, or similar effects; or
  • The soil has been previously disturbed; or
  • The soil is part of a sloped, layered system where the layers dip into the excavation on a slope of four horizontal to one vertical (4H:1V) or greater; or
  • The material is subject to other factors that would require it to be classified as a less stable material.

Class "B" soil means:

  • Cohesive soil with an unconfined compressive strength greater than 0.5 tsf (48 kPa) but less than 1.5 tsf (144 kPa); or
  • Granular cohesionless soils including: angular gravel (similar to crushed rock), silt, silt loam, sandy loam and, in some cases, silty clay loam and sandy clay loam.
  • Previously disturbed soils except those which would otherwise be classified as Type C soil.
  • Soil that meets the unconfined compressive strength or cementation requirements for Type A, but is fissured or subject to vibration; or
  • Dry rock that is not stable; or
  • Material that is part of a sloped, layered system where the layers dip into the excavation on a slope less steep than four horizontal to one vertical (4H:1V), but only if the material would otherwise be classified as Type B.

Class "C" soil means:

  • Cohesive soil with an unconfined compressive strength of 0.5 tsf (48 kPa) or less; or
  • Granular soils including gravel, sand, and loamy sand; or
  • Submerged soil or soil from which water is freely seeping; or
  • Submerged rock that is not stable, or
  • Material in a sloped, layered system where the layers dip into the excavation or a slope of four horizontal to one vertical (4H:1V) or steeper.

Competent Person means one who has been trained to identify hazards in the workplace, or working conditions that are unsafe for employees, and who has the authority to have these hazards eliminated or controlled.

Cross Braces mean the horizontal members of a shoring system installed from side to side of the excavation. The cross braces bear against either uprights or wales. Picture

Department means a department at the university that conducts work in excavations.

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

Faces or Sides mean the vertical or inclined earth surfaces formed as a result of excavation work.

Failure means the movement or damage of a structural member or connection that makes it unable to support loads.

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

Ingress and Egress mean "entry" and "exit" respectively, and refer to the safe means for employees to enter or exit.

Kickout means the accidental movement or failure of a cross brace.

Protective System means a method of protecting employees from cave-ins, from material that could fall or roll from an excavation face 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 the necessary protection.

Ramp means an inclined walking or working surface that is used to gain access to one point from another. A ramp may be constructed from earth or from structural materials such as steel or wood.

Registered Professional Engineer means a person who is registered as a professional engineer in Virginia.

Safety Coordinator means the individual at Environmental, Health and Safety Services (EHSS) responsible for developing and implementing this program, conducting unannounced work site inspections, and ensuring that the departments comply with the program requirements.

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

Shield or Shield System means a structure used in an excavation to withstand cave-ins and which will protect employees working within the shield system. Shields can be permanent structures or portable units moved along as work progresses. Picture

Shoring or Shoring System means a structure that is built or put in place to support the sides of an excavation to prevent cave-ins.

Sides See "Faces"

Sloping or Sloping System means sloping the sides of the excavation away from the excavation to protect employees from cave-ins. The required slope will vary with soil type, weather, and surface or near surface loads that may affect the soil in the area of the trench (such as adjacent buildings, vehicles near the edge of the trench and so forth).

Soil classification terminology - click here.

Stable Rock means natural solid mineral material that can be excavated with vertical sides that will remain intact while exposed.

Structural Ramp means a ramp built of steel or wood, 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 an adjacent structure, underground installation, or the sides of an excavation.

Surface Encumbrances include utilities, foundations, streams, water tables, transformer vaults, walkways, bridges, roads, and geologic anomalies.

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

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

Trench means a narrow excavation (in relation to its length) made below the surface of the ground. Picture

Trench Box or Shield See "Shield".

Unconfined Compressive Strength is the load per unit area at which soil will fail in compression.

Underground Installations include, but are not limited to, utilities, tunnels, shafts, vaults, foundations, and other underground fixtures or equipment that may be encountered during excavation work. Picture

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 are horizontal members of a shoring system placed in the direction of the excavation face whose sides bear against the vertical members of the shoring system or earth (the uprights or sheeting). Picture