Aluminum rail design for trench shoring

May 5, 1992

Mr. Bill Barnhart
Director of Engineering
BIL-JAX Inc.
[Recipient address omitted]
Dear Mr. Barnhart:

Your January 15 letter to Mr. Arnis Andersons, Area Director, Occupational Safety and Health Administration (OSHA), requesting an interpretation of OSHA's excavation standards has been referred to the Office of Construction and Maritime Compliance Assistance for a response. We apologize for the delay in responding to your concerns.

We have coordinated the response as follows:

1. In your drawing, the proposed aluminum rail is oriented vertically with a 2-foot 8-inch span. In Table D-1.4 of the OSHA standards, the aluminum rail is oriented horizontally as a wale, with a 6-foot to 10-foot span, as shown in Figure No. 4 of Appendix D to Subpart P, 29 CFR 1926. Thus, there is no direct correlation between these two cases. The required value for the section modules of an aluminum rail certainly can be calculated by your registered professional engineer (RPE). However, to cover all different conditions of Type C soil, we recommend that a rectangular distribution of the lateral pressure with an intensity of PA+80H=72 psf, be used, where "H" is the depth of the trench. This pressure intensity is illustrated in Tables C-1.3 and C-2.3 of Appendix C to Subpart P, 29 CFR 1926.

2. Since the shoring system you proposed is different from the OSHA suggested shoring system, the size and thickness of the proposed aluminum liner must be independently designed by proper procedures, such as those specified for aluminum structures by the Aluminum Association, Inc. Again, we recommend the lateral pressure intensity listed in Item 1 be used in your design.

3. The subsection 29 CFR 1926.652(c)(2) Option (2) - Design Using Manufacturer's Tabulated Data is applicable in your case. A new table similar to Table D-1.4 of the OSHA standards could be developed, and would be very helpful to both the employer and the OSHA Compliance Officers.

4. In your drawing, the note on the use of plywood is not applicable. Any use of plywood as a material for primary structural members, must be per generally accepted recommendations, such as those contained in the Plywood Design Specification, by the American Plywood Association.

If we can be of any additional assistance, please contact Mr. Scott Jin in the Office of Construction and Engineering at (202) 523-8244 or Mr. Roy F. Gurnham or Mr. Dale R. Cavanaugh of my staff in the Office of Construction and Maritime Compliance Assistance at (202) 523-8136.

Sincerely,
Patricia K. Clark, Director
Directorate of Compliance Programs