Excavation and trenching - Michigan

Michigan operates an OSHA-approved State Plan covering most private sector workers and all state and local government workers.

MIOSHA’s excavation rules govern the digging of excavations and trenches which an employee is required to enter, and the supporting systems used in construction operations.

MIOSHA incorporates the federal OSHA standards governing excavations by reference, and these federal rules have the same force and effect as any rule promulgated by the state of Michigan.

MIOSHA’s excavation rules provide the following additional information and requirements:

• Definitions. Michigan excavation regulations define certain terms that are not defined in the federal excavation regulations. These terms include:
  • Braces or struts
  • Kickout
  • Qualified person
  • Sheet piling
  • Slope
  • Soil (including clay, soft clay, medium clay, firm soil, stiff clay, fill, granular soil, organic soil, and running soil)
  • Stringers
  • Toe of slope
  • Trench jack
  • Trench shield
• Public utility lines. Employers must:
  • Exercise reasonable care, including hand digging when public utility lines are exposed or likely to be exposed;
  • Provide all reasonable support to protect public utilities in and near the construction area;
  • Notify the public utility immediately if there is contact or damage to any pipe, cable, or its protective coating, or any other underground facility of the utility; and
  • If an energized electrical cable is severed, an energized conductor is exposed, or dangerous fluids or gases escape from a broken utility line, the employer must evacuate the employees from the immediate area while awaiting the arrival of the public utility personnel.
• Soil types. If different textured soils are encountered in the side of an excavation, each soil type of the excavation must be cut to the proper angle of repose, except that the slope must not steepen between the toe of the slope and the ground level where soft clay or running soil is encountered in the lower cut.
• Forms, walls, and similar structures. When installed forms, walls, or similar structures create a trench between the form, wall, or structure and the side of the excavation, an employer must comply with the angle of repose, support systems, benching, and sloping provisions of R 408.40941 to R 408.40944.
• Egress methods:
  • Ladder: An employee in an excavation 48 or more inches in depth must be provided with either a ladder extending not less than 3 feet above the top as a means of access or with a ramp.
  • Earth ramp: An earth ramp may be used in place of a ladder if:
    • The ramp material is stable;
    • The sides of the excavation above the ramp are maintained to the angle of repose or sheeted or shored along the means of egress;
    • The angle of the ramp is not more than 45 degrees; and
    • The vertical height between the floor of the trench and the toe of the ramp is no more than 30 inches.
• Angle of repose (slope). The side of an excavation more than 5 feet deep must be sloped as required by R 408.40941, Table 1, unless otherwise properly supported. An excavation less than 5 feet in depth must be effectively protected when examination of the ground indicates an expectation of hazardous earth movement.
• Supporting systems:
  • Design and angle of repose factors. The angle of repose and the design of the supporting system for a side of an excavation must be based on the evaluation of:
    • Depth of cut and type of soil;
    • Possible variation in the water content of the material while the excavation is open;
    • Anticipated changes in the material due to exposure to air, sun, water, or freezing temperatures;
    • Load imposed by structures, equipment, overlying material, or stored material; and
    • Vibration from traffic, equipment, or blasting.
  • Qualified design. A support system must be designed by a qualified person, and the design maintained at the jobsite. Changes from the design must be approved by a qualified person.
  • Tie rods and tie backs. Tie rods and other forms of tie backs used to restrain the top of sheeting must be anchored a minimum of 10 feet. The measurement to the anchor point starts at the intersection of an angle of repose with the surface of the soil retained. The tie back and anchor must be capable of restraining any pressure exerted on the system.
  • Sheeting or sheet piling. When sheeting or sheet piling is used, pressures due to existing ground water conditions must be considered in the design. Sheet piling must be driven to the predetermined depth set forth in the required design. Changes from the design must be approved by the designer of the support system.
  • Materials. Support materials must be in good serviceable condition, and when timbers are used, they must be sound and free of large or loose knots.
  • Adjacent excavations. A supporting system must have additional bracing approved by the designer when the sides of excavations are cut adjacent to a previous known excavation or a known fill, particularly when the separation between the previous excavation and the new excavation is less than the depth of the excavation.
  • Bracing or anchoring. Sheeting shall be braced or anchored at the bottom and along the vertical plane to prevent lateral movement.
  • Excavations 20 feet or more deep. Protective systems for use in excavations more than 20 feet in depth must be designed by a registered professional engineer.
• Additional requirements for trench support systems. In unstable or running soil, the jacks and braces must be removed from above the trench after employees have cleared the trench.
• Benching and sloping:
  • The angle of repose must be flattened when an excavation has water conditions, silty materials, loose boulders, or areas where erosion, deep frost action, or slide planes appear.
  • When benching the side of an excavation, the vertical rise must not be more than five feet, and the step back must extend at least to the angle of repose as required by R 408.40941, Table 1.
  • When benching a side of a trench, the height of the lower bench must not be more than the lesser of 5 feet or width of the trench measured at the bottom.
• Trenching boxes and shields:
  • Portable trench boxes or sliding trench shields may be used for the protection of personnel in place of a shoring system or sloping, if they are used, designed, constructed, and maintained in a manner that provides protection equal to or greater than the sheeting or shoring required for the trench.
  • The use of benching in conjunction with a portable trench box is permitted when the toe of the trench box is not more than 2 feet above the trench bottom, but only if the trench box is designed to resist the forces calculated for the full depth of the trench and if there are no indications, while the trench is open, of a possible cave-in below the bottom of the trench box.
  • Shield systems must not be subjected to loads exceeding those which the system was designed to withstand.
  • Employees must be protected from the hazard of cave-ins when entering or exiting the areas protected by shields.
• Walkways, runways, ramps, or bridges. If an employee or equipment is required or permitted to cross a trench or ditch, a walkway, runway, ramp, or bridge must be provided and must have a designed capacity of not less than 3 times the imposed load. A compliant guardrail must be provided.
• Adjacent structures:
  • Protection. A structure that is adjacent to an excavation or trench below the level of the base or footing of any foundation or retaining wall must be protected against settlement, lateral movement, undermining, or washout.
  • Design. The design of the protection must be set forth by a qualified person who is knowledgeable in the subject area.
  • Shoring, bracing, and underpinning. Must be inspected daily or more often, as conditions warrant, by a competent person.
• Appendix. An Appendix to the Michigan excavation rules contains 13 examples of good engineering practices for excavation and trench protection. They are not mandatory requirements.