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157 Excavation Safety: Basic
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Protective System Designs

Designing a protective system can be complex. You must consider many factors, including:

  1. soil classification
  2. depth of cut
  3. water content of soil
  4. changes due to weather and climate
  5. other operations in the vicinity

Once you have selected an approach, however, the system must meet the required OSHA performance criteria.

For every 1 foot of height, excavate the trench back 1.5 feet. Click to see an example.

The OSHA standard describes methods and approaches for designing protective equipment. Let's discuss the different methods to designing protective equipment.

Method 1: Sloping

Slope the sides to an angle that isn't steeper than 1.5:1 (34 degrees measured from the horizontal).

For example, for every foot of depth, the trench must be excavated back 1½ feet. All simple slope excavations 20 feet or less deep should have a maximum allowable slope of 1½:1. These slopes must be excavated to form configurations similar to those for Type C soil. A slope of this gradation or less is safe for any type of soil.

Knowledge Check Choose the best answer for the question.

2-5. To achieve a slope of 34 degrees, for every one foot in depth, excavate the sides back _____.