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Trenching and Excavation

Learning Objectives

  • Recognize the key terms associated with excavation work.
  • Identify principles and practices used in designing excavations.
  • Recognize the principles and practices associated with constructing an excavation.
  • Identify the dangers and safe practices to follow when working in or near an excavation.

Available in English

30 minutes

Trenching and excavation hazards during construction activities resulted in 488 deaths between 1992 and 2000—an average of 54 fatalities each year.

U.S. Bureau of Labor Statistics (BLS)

For excavation work, the Occupational Safety & Health Administration’s (OSHA) excavation standard requires a "competent person" to make several key determinations. How do you determine who qualifies as a “competent person”?

  • They must be capable of identifying existing, regular hazards in excavation work.
  • They must have been trained in and be knowledgeable about: soils analysis, the use of protective systems, and other requirements of OSHA’s 1926 (P) standard.
  • They must have the authority to take prompt measures to reduce any hazards.

Before any digging starts, a qualified person needs to create an excavation design that meets specific safety standards, established to prevent potentially deadly cave-ins. These standards include getting safely in and out; sloping and benching systems, and supports, shields, and other protective systems. Someone on a work team has to think through the situation.

These safety standards are designed to prevent potentially deadly cave-ins and other potential hazards such as contacting buried or overhead utilities. They identify getting safely in and out of the excavation or trench, sloping and benching systems, and supports, shields, and other protective systems.

Rules for Using Ramps

Ramps used instead of steps must be treated to prevent slipping.

Cleats or other means used to connect runway structural members must be attached to the bottom of the runway to prevent tripping.

A stairway, ladder, ramp, or other safe means of leaving trench excavations shall be used at depths of 4 feet (1.22 m) or more.
Where ladders are used they shall extend at least 3 feet above grade and require no more than 25 feet (7.62 m) of lateral travel to the access point.

Sloping and benching systems are intended for worker safety. To properly slope or bench an excavation requires that soil conditions be examined and classified by a competent person.  Soil classification determines its cohesiveness or ability to hold together and not collapse. Common components of soil include sand, silt, clay, and organic matter.

Two means of soil classification must be performed by the competent person whenever the soil type or conditions change:

Physical Test

  • The competent person handles the soil to feel its cohesiveness or how well it sticks together.
  • Can be done by performing the ribbon test—rolling soil in the palm of the hand to form a ribbon.

Mechanical Test

  • Penetrometer—a device that determines the compressive nature of the soil

Additional Considerations

  • For excavations in solid rock, sheer walls are allowed as long as the formation is stable.
  • Frozen soil is not considered solid rock.
  • All previously excavated soils, such as in utility trenches, are considered type C soils.

Materials and equipment used for protective systems must be free from damage or defects and maintained in accordance with the recommendations of the manufacturer.

When they are damaged, a competent person must examine the material or equipment and evaluate its suitability for continued use. Any material not approved must be removed from service, and evaluated and approved by a registered professional engineer before being returned to service.

Before digging—and throughout the excavation—precautions must be taken to avoid causing any problems around and below the proposed digging site. You have to plan around existing underground lines and installations, and consider how the excavation might affect them and any adjacent buildings. Undermining a footing of a wall of a building might cause structural damage or collapse.

Workers also need to know the rules for installing and removing support systems for the excavation. The use of shoring or supports should be reviewed and approved by an engineer to ensure adequate safety.

Before Digging

  • Determine the estimated location of utilities like sewer, telephone, natural gas, fiber optic, electric, water lines, etc. by contacting your local or state utility “one-call” provider.
  • Plan at least 48 hours in advance of excavation activities to ensure all utilities are marked—if you are digging, it is your responsibility to ensure that all utilities have been accounted for. 
  • Advise utility owners of the proposed work and ask them to mark locations of underground installations.
  • Markings are approximations of a utility location with the actual location lying within 2-3 feet of either side of the mark.
  • Utilities on private properties may require the property owner to indicate where the utilities are located.
  • Use detection equipment when utilities or owners can’t respond within 24 hours, or can’t establish exact locations.

During Digging

  • When within 1.5 feet of the outer edges of an installation, use hand digging for positive location.
  • When excavation is open, protect, support or remove the underground installations.

Do not excavate below the base of any foundation unless:

  • A support system is provided;
  • The excavation is in stable rock;
  • A registered professional engineer confirms that any structures, including sidewalks and pavements, will be unaffected;
  • A registered professional engineer has confirmed the excavation work will not pose a hazard to workers.
Course Outline
  • Introduction
  • Key Terms
  • Designing an Excavation
  • Constructing an Excavation
  • Working In and Around Excavations
  • 29 CFR 1926 Subpart P