Shoring sewer trench
Shoring sewer trench
(OP)
I recently had a client ask me if I would approve using timber shoring in place of metal cage to lay sewer 10 feet deep in type C soil. I told my client that this was not an area of my expertise and that I would need to consult a geotechnical engineer for an alternative design. While browsing OSHA site I found a table which described the dimension of cross braces, etc., however, many disclaimers regarding soil and construction conditions were sited. My question is should I recommend a design be made by geotech or is this usually more expensive then continuing to use metal cage. The job is small (<2acres) the line is relatively short (300 lf).
By the way, the client was suggesting 2" x 4" braces and 1-1/4" plywood, which to me sounds way under designed. I would not get in the trench with less than at least 6" x 6" braces.
By the way, the client was suggesting 2" x 4" braces and 1-1/4" plywood, which to me sounds way under designed. I would not get in the trench with less than at least 6" x 6" braces.





RE: Shoring sewer trench
RE: Shoring sewer trench
Timber shoring, when designed and installed properly, protects the workers in the trench and adjacent minor structures. A metal cage (I assume you are refering to a trench box or shield) protects the workers in the trench but does not protect or support adjacent structures very well. This is due to the large amount of open excavation required to initially set the cage and to advance the cage as the pipe is installed and backfilled.
Designing and installing timber trench sheeting is a dying art. The old timers really haven't passed down enough of their tricks or methods. The OSHA manual probably has as much information on the subject as you will find anywhere.
Years ago, many sewer contractors just built the timber shoring without engineered designs. They knew what worked (or thought they did). However, today, what they did years ago does not work anymore - on PAPER, that is. Nowadays, everyone wants a design submission for approval and what worked for many years no longer meets newer criteria, codes, specs, etc.
RE: Shoring sewer trench
RE: Shoring sewer trench
Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See FAQ158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"
RE: Shoring sewer trench
RE: Shoring sewer trench
RE: Shoring sewer trench