Design Requirements For Sloping And Shoring, The Use Of Data, And Trench Boxes
Appropriate Protective System Designs
Designing a protective system can be complex. You must consider many factors, including:
- soil classification
- depth of cut
- water content of soil
- changes due to weather and climate
- other operations in the vicinity
Once you have selected an approach, however, the system must meet the required OSHA performance criteria.
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 1½:1. (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.
Method 2: Design Using Data
Use tabulated data such as tables and charts approved by a registered professional engineer to design excavation. This data must be in writing and must include enough explanatory information, including the criteria for making a selection and the limits on the use of the data, for the user to make a selection.
At least one copy of the data, including the identity of the registered professional engineer who approved it, must be kept at the worksite during the construction of the protective system.
After the system is completed, the data can then be stored away from the jobsite. However, a copy must be provided upon request to the Assistant Secretary of Labor for OSHA.
Method 3: Trench Box or Shield
In this method, you would use a trench box or shield designed or approved by a registered professional engineer. Timber, aluminum, or other suitable material may also be used in the construction. OSHA standards permit the use of a trench shield if it provides the same level of protection as the appropriate shoring system.
Employers can choose the most practical method for the particular circumstance, but that system must meet the required performance criteria. The standard doesn’t require a protective system when an excavation is made entirely in stable rock or is less than five feet deep.
However, in this case, a competent person must examine the ground and find no indication of a potential cave-in.
